Carbon-free method and apparatus for producing iron and steel
A low-temperature sodium-based process for producing iron and steel from iron ore and red bauxite addresses emissions and waste issues by converting iron oxides with liquid sodium, producing valuable co-products and reducing environmental impact.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- CAVALIER MARCUS
- Filing Date
- 2025-11-20
- Publication Date
- 2026-05-28
AI Technical Summary
Traditional methods of producing iron and steel contribute significantly to greenhouse gas emissions, and hydrogen-based direct reduction (DRI) faces challenges with hydrogen leakage and inefficient production, while existing alumina extraction processes generate environmental hazards like red mud.
A method using liquid sodium to react with iron ore at low temperatures, avoiding carbon usage and producing iron and steel without emissions, and simultaneously extracting alumina, utilizing renewable energy for electrolysis and capturing by-products like sodium oxide and chlorine gas.
This method reduces greenhouse gas emissions, eliminates the need for carbon and hydrogen, and recycles by-products into valuable industrial products, while avoiding the environmental impacts of red mud production.
Smart Images
Figure GB2025052538_28052026_PF_FP_ABST
Abstract
Description
[0001] Carbon-Free Method and Apparatus for Producing Iron and Steel
[0002] Field of the Invention
[0003] The present invention concerns a method and apparatus for producing iron from an iron ore and / or from a source of waste iron oxide, and the onward conversion of that iron into steel.
[0004] Background of the Invention
[0005] Iron may be present in an iron ore as at least one of the mineral and mineraloid forms of iron oxide and iron oxyhydroxide, including hematite and maghemite ( / '. e., polymorphs of Fe2C>3), magnetite ( / '. e., FesC ), goethite and lepidocrocite ( / '.e., polymorphs of FeO(OH)) and limonite ( / '.e., FeO(OH) ■ n(H2O)). However, iron is also present in red bauxite, which is an aluminium ore also comprising a significant proportion of iron. Iron ores, wherein the iron is present as at least one of the mineral and mineraloid forms of iron oxide and iron oxyhydroxide, occur in deposits which have either been weathered over geological time or not. In both cases, quartz ( / '.e., silica, SiC>2) is the most common gangue mineral found in the ore as well. In weathered iron ore deposits, clays, like halloysite (2SiO2‘ AI2O3 4H2O), kaolinite ^SiCh'A Os^^O) and gibbsite (AI(0H)3), are also common gangue species, whereas in unweathered iron ore deposits, iron silicates, like minnesotaite (Fe2+3Si4Ow(OH)2) and stilpnomelane, are often found as gangue species instead. The chemical formula of stilpnomelane is highly variable, depending on its composition, but may typically be represented by K(Fe2+,Mg,Fe3+)8 (Si,AI)i2(O,OH)27 ■ n(H2O). Magnesium is the most common cation substituent for iron in iron silicates because it has an ionic radius similar to an Fe2+ion and the same electrical charge.
[0006] Traditionally, iron has been extracted from iron ore by heating the iron ore in a blast furnace to temperatures above about 1200 “Celsius, with coke or a similar source of carbon used as a reducing agent to produce elemental iron. Initially, the carbon is partially oxidized into carbon monoxide, which reduces iron oxides in the iron ore according to the sequence:
[0007] Fe20s — > FesO4 — > FeO — > Fe [Eqn. 1]
[0008] Complete oxidation of the carbon monoxide as the iron oxides are reduced results in the production of carbon dioxide gas. Calcium carbonate ( / '.e., limestone) introduced into the blast furnace along with the iron ore and carbon is thermally decomposed by the high temperatures into calcium oxide ( / '.e., lime). This reacts with the silica and other gangue species in the ore to form a slag, the main constituent of which is calcium metasilicate ( / '.e., wollastonite). The thermal decomposition of the lime results in the production of more carbon dioxide. However, the present climate crisis demands that all the carbon dioxide thus produced, as well as any remaining carbon monoxide, should be captured and stored or otherwise mitigated, because the production of iron and steel contributes about 7-8% of total global greenhouse gas emissions. It is therefore widely recognised that the traditional method for producing iron in a blast furnace cannot be continued in its present form.
[0009] A currently popular proposal for mitigating the production of such greenhouse gases during the production of iron is to use hydrogen as a reducing agent instead of carbon. This is commonly known as direct reduction of iron by hydrogen, or hydrogen-DRI. In hydrogen-DRI, iron ore is prepared for reduction by being sintered and pelletised, before the iron ore is introduced into a direct reduction shaft furnace operated at or around atmospheric pressure and a temperature of about 800 to 900 “Celsius. Whereas carbon is above iron in the reactivity series, hydrogen is below iron in the reactivity series. Hydrogen must therefore be preheated to about 800 to 900 “Celsius before being injected into the shaft furnace. Reduction of iron oxides in the iron ore by the hydrogen is also endothermic, with an enthalpy of reaction at 800 “Celsius of about +31 kJ per mol of iron produced, requiring heat to be injected as well to maintain the reaction. In contrast, the traditional reduction of iron ore by carbon monoxide in a blast furnace is exothermic, with an enthalpy of reaction at 800 “Celsius of about -19 kJ per mol of iron produced, allowing the heat thus generated to be extracted and recycled.
[0010] Reduction of the iron oxides in the iron ore by hydrogen results in the production of water vapour instead of carbon dioxide, thus avoiding the production of this greenhouse gas. In principle, therefore, this water vapour could just be released into the environment. However, since water vapour is itself also a significant greenhouse gas, this would be undesirable if hydrogen-DRI were to be conducted at scale. Moreover, the gases emitted by the shaft furnace actually comprise a mixture of water vapour and hydrogen because not all of the hydrogen injected into the shaft furnace is oxidised into water vapour when the iron oxides from the ore are reduced. This mixture of gases is therefore usually captured to allow the hydrogen and water vapour to be separated from each other, so that the unoxidized hydrogen can be recycled to the shaft furnace and the water vapour can be condensed to produce hydrogen again by electrolysis. However, because diatomic hydrogen is the smallest molecule with the lowest molecular mass and a low viscosity, processing the hydrogen in this way presents a significant risk of hydrogen leakage. Although hydrogen is not itself a greenhouse gas, if released, it interferes detrimentally with atmospheric chemistry, thereby increasing the production of other greenhouse gases like methane.
[0011] In order to use hydrogen-DRI to produce iron from iron ore, therefore, the hydrogen must itself first be produced, for example by electrolysing water into hydrogen and oxygen. If the electricity for this comes from a source of renewable energy, such as wind or solar, or from nuclear power, this does not generate any greenhouse gases. However, the production of hydrogen by electrolysis using such zero-carbon electricity (commonly called "green” hydrogen) currently only accounts for about 4% of all hydrogen production. At present, therefore, about 96% of all hydrogen produced is still derived from fossil fuels (commonly called "blue” hydrogen). This breaks down into about 48% produced by steam-methane reforming (SMR), 18% from the gasification of coal, and 30% from the partial oxidation of hydrocarbons by other means. All of these processes also produce carbon dioxide, possibly along with other greenhouse gases like carbon monoxide, which must therefore be captured and stored if they are not to be released into the environment. Hydrogen-DRI therefore just pushes the problem with producing carbon dioxide and other greenhouse gases in ironmaking one step up the supply chain to hydrogen. Moreover, whatever the source of the hydrogen, technological problems with storing and transporting the hydrogen remain. Thus hydrogen-DRI cannot be seen as a complete solution for replacing traditional ironmaking in a blast furnace. The present invention addresses this problem.
[0012] By way of further background, several alkali and alkaline earth metals are produced industrially by fusing and electrolysing a chloride salt of the metal in question. These metals include sodium. Application of an electrical current to sodium chloride in solid phase fuses ( / '.e., melts) the sodium chloride by ohmic heating. Subsequent electrolysis of the sodium chloride produces metallic sodium in liquid phase, with chlorine gas produced as a coproduct. In order to lower the temperature at which the electrolysis takes place, the sodium chloride may be mixed with one or more other salts to form a eutectic mixture. Electrolysis of sodium chloride to produce elemental sodium typically occurs at a temperature of about 600 to 625 “Celsius. The high-temperature chlorine gas produced as a co-product is usually cooled, condensed and bottled. The liquid sodium produced in this way generally has a high purity of better than 99% and may therefore subsequently be used in other industrial processes. Moreover, the properties, behaviour and handling of liquid sodium are well known and understood from many decades of its use as a heat transfer fluid in the nuclear power industry.
[0013] As further background, aluminium is produced on an industrial scale by the electrolysis of alumina ( / '. e., aluminium oxide). The alumina for this is extracted from an aluminium ore, most usually bauxite. This is a sedimentary rock containing different mineral forms of aluminium hydroxide, as well as several other minerals. Chief amongst these other minerals are aluminosilicates, such as clays, and iron oxides and hydroxides, such as hematite and goethite. If the other minerals are predominantly silica-bearing, the bauxite has a whitish colour, and is therefore known as white bauxite. If, however, the other minerals are chiefly iron oxides and / or oxyhydroxides, these give the bauxite a reddish colour, which is therefore known as red bauxite. Which technique is used to extract alumina from bauxite depends on the relative proportions of these other minerals present, apart from the aluminium hydroxides. In the case of red bauxite, the main technique which is used is the Bayer process. Since red bauxite is by far the most commonly mined aluminium ore, the Bayer process currently accounts for about 95% of all alumina produced globally. In the Bayer process, iron-containing minerals are separated from aluminium hydroxide minerals and end up in a waste product called "red mud” because of the colour it takes from the iron it contains. As a result of the Bayer process, however, red mud is highly caustic. Traditionally, it has been stored in large, open-air ponds, which therefore present a significant environmental hazard. More recently, it has also been thickened and dried into a solid residue as well. Whereas several proposals have been made to remediate and / or exploit existing deposits of red mud, ongoing use of the Bayer process still creates more red mud every day. This therefore continues to present an environmental hazard. In addition, a major source of often high-grade iron ore, which could otherwise be used for ironmaking, is wasted by the extraction of alumina from red bauxite via the Bayer process. Object of the Invention
[0014] It is therefore an object of the invention to provide a method and apparatus for producing iron from an iron ore, wherein the iron is present as at least one of the mineral and mineraloid forms of iron oxide and iron oxyhydroxide, without using any carbon, and with an option for the onward conversion of that iron into steel. Preferably, the same method and apparatus may also be used to produce iron from red bauxite, as well as from sources of waste iron oxide, such as mill scale.
[0015] Description of the Invention
[0016] Accordingly, in one aspect, the present invention provides a method of producing iron from an iron ore in which the iron is present as at least one of the mineral and mineraloid forms of iron oxide and iron oxyhydroxide. The method comprises comminuting the iron ore into fines, dehydrating the iron ore and dehydroxylating hydroxylated compounds contained in the ore. The ore thus treated is then reacted in an inert atmosphere and at a temperature of less than 450 “Celsius with an amount of liquid sodium in excess of the stoichiometric amount thereof required for a redox reaction between the liquid sodium and iron oxide from the ore. This precipitates out from the liquid sodium both iron and other insoluble products at least comprising sodium oxide. The method then comprises separating the iron from the other insoluble products, and separating the iron and the other insoluble products as a solid phase from the liquid sodium. Separating the iron from the other insoluble products and this phase separation may be carried out in any order. Before being subjected to the above method, the iron ore may undergo one or more processes of beneficiation, which may possibly comprise known processes, to increase the proportion of iron oxide and / or oxyhydroxide in the ore relative to gangue.
[0017] The method of the invention has at least the following advantages.
[0018] Unlike the traditional extraction of iron from iron ore in a blast furnace and unlike hydrogen-DRI, which are both solid-gas phase reactions, the reaction between the iron ore and the liquid sodium is a solid-liquid phase reaction. The iron ore therefore does not have to be prepared by being sintered and pelletised, which uses less energy and removes the need to use other raw materials.
[0019] Gangue species remaining in the ore after its dehydration and dehydroxylation either dissolve in the liquid sodium or can be removed from the iron produced by the redox reaction with the liquid sodium during one or both of the subsequent separation of the iron from the other insoluble products and the phase separation. Unlike traditional processes for extracting iron from iron ore, therefore, the method of the invention does not require the use of lime to react with and capture silica and other gangue species in order to form a slag. The thermal decomposition of limestone to produce this lime, with the accompanying release of carbon dioxide from the limestone, is thereby avoided entirely.
[0020] Since no carbon is used in the method of the invention, the carbon content of the iron produced can be controlled to a very low level. Furthermore, in comparison both to reducing iron ore with carbon in a blast furnace and to hydrogen-DRI, the greater reactivity of sodium than both carbon and hydrogen means that reducing iron ore with liquid sodium takes place at a much lower temperature and is also significantly more exothermic, which therefore reduces the total quantity of heat required.
[0021] The liquid sodium may be produced by electrolysis, for example from sodium chloride, with the co-production of chlorine gas. Electricity for the electrolysis may be provided by a source of renewable energy, such as wind or solar, or come from nuclear power, and therefore need not generate any greenhouse gas emissions. Unlike the most common methods of producing hydrogen for hydrogen-DRI, the production of liquid sodium in this way does not involve any fossil fuels. The method of the invention therefore need not produce any greenhouse gases at all.
[0022] At least some of the liquid sodium and chlorine gas may be produced together, for example, by fusing and electrolysing solid sodium chloride. This may be performed using a known technique, like the Downs process. Alternatively or additionally, at least some of the liquid sodium and chlorine gas may be produced separately from each other by firstly electrolysing an aqueous solution of sodium chloride ( / '.e., brine) using the chlor-alkali process to produce an aqueous solution of sodium hydroxide and the chlorine gas. In some embodiments, the brine may be brine concentrate produced as a waste product by a desalination plant, in which case, the electrolysis may advantageously be conducted near the desalination plant and this waste can then be eliminated. If at least some of the brine is electrolysed in a standard type of membrane cell, then hydrogen gas may be produced as well. Alternatively or additionally, at least some of the brine may be electrolysed without co-production of hydrogen, using a technique such as that described in US patent appln. no. 2005 / 0026005 A1 . Subsequently drying at least some of the aqueous solution of sodium hydroxide to produce solid sodium hydroxide then allows the solid sodium hydroxide to be fused and electrolysed to produce the liquid sodium, as well as hydrogen gas and oxygen gas. Fusing and electrolysing the solid sodium hydroxide may be performed using a known technique, like the Castner process. Whereas the Castner process is generally regarded as obsolete, fusing and electrolysing the solid sodium hydroxide via the Castner process after having produced the sodium hydroxide for this via the chlor-alkali process has the advantage that the two processes can be viewed as a combined electrolysis of equimolar amounts of sodium chloride and water. This is because the back-reaction of water in the Castner cell with the liquid sodium thus produced also produces hydrogen gas, as follows:
[0023] Chlor-alkali process: 2 NaCI <aq) + 2 H2O — > 2 NaOH <aq) + CI2 + H2 [Eqn. 2a]
[0024] I Dry
[0025] Overall: 2 NaCI + 2 H2O 2 Na + CI2+ 2 H2+ O2[Eqn. 2d] The hydrogen gas thus produced may then be used, for example, as a fuel and / or to replace the use of SMR in the production of ammonia (such as in the Haber-Bosch process). The oxygen gas is a useful co-product which may be used, for example, in a steelmaking process by injecting it into molten iron.
[0026] Moreover, unlike the water vapour produced by hydrogen-DRI as a by-product, which has little or no commercial value, the method of the invention also produces sodium oxide as a co-product, which is a useful industrial product in its own right, and electrolysing sodium chloride to produce liquid sodium produces chlorine gas as well. For example, the sodium oxide may be hydrated to produce sodium hydroxide, and the chlorine may be used to produce hydrochloric acid and / or one or more chlorinated organic compounds. The electrical energy required to produce the liquid sodium is therefore shared between the production of several useful industrial products, and is not just consumed by the production of iron.
[0027] Whereas the method of the invention can be used to extract iron from traditional iron ores like banded iron formations, it has the additional advantage that it can also be used to extract iron from red bauxite, whilst still permitting alumina to be extracted from the red bauxite as well, as described further below. The production of red mud by the Bayer process can therefore be avoided entirely.
[0028] The method of the invention will now be described in greater detail.
[0029] Comminution
[0030] Firstly, the iron ore is comminuted into fines to increase its surface area and to help separate mineral species in the ore from each other. Fines are generally considered to be less than about 6 or 7 mm across. Comminuting the ore may comprise a mechanical process, such as one or more of agitation, crushing, grinding, hammering, milling and rolling, as well as other similar processes. Alternatively or additionally, comminuting the ore may comprise a chemical process, such as one in which the ore is at least partially dissolved and / or iron-bearing particles are precipitated out from solution.
[0031] Comminution produces fine ore particles with a range of different sizes. Smaller particles are more desirable because they have a greater surface area. This helps to accelerate dehydration and dehydroxylation of the ore particles, as well as their reaction with liquid sodium, described below. However, creating smaller particles with a greater surface area also requires more energy to be expended on comminuting the ore than would otherwise be expended on creating larger particles. The optimum size of particles will therefore be partly determined in any particular case by the most economic energy balance overall between comminuting the ore on the one hand and the next two stages in the method of the invention on the other. This energy balance will in turn depend in any particular case on the specific energy requirements of the comminution device or devices which are used, the prior chemical composition of the iron ore itself, and on the outcome of any beneficiation which the ore has undergone before comminution. If beneficiation has already resulted in finely comminuted ore particles (for example, having an average size of less than about 1 or 2 mm), then any further comminution will be unnecessary. Apart from increasing its surface area, comminuting the iron ore into fines can also change one or more of the physicochemical properties of the ore in a desirable manner. For example, it may help to detach particles of iron oxide and / or oxyhydroxide from particles of gangue species also present in the ore. Comminution may also be effective not only in releasing water which is trapped in the ore, thereby helping to dehydrate it, but may also contribute to dehydroxylating hydroxylated compounds, such as iron oxyhydroxides and clays, which the ore may contain. The preferred range of particle sizes at the end of comminution can therefore be determined in any particular case from the best combination of overall energy expenditure with the desirable physicochemical properties of the resultant ore particles.
[0032] Comminution may further comprise sieving, separating and recycling larger particles for further comminution into smaller particles.
[0033] The method of the invention has the significant advantage that after comminution, the resulting fines do not need to undergo any agglomeration to prepare them for further processing. This is unlike ironmaking in a conventional blast furnace and unlike hydrogen-DRI, which both require iron ore fines to be agglomerated, for example by being briquetting with the addition of a binder, nodulized with carbon, or sintered with other ingredients and pelletized into a particular range of sizes (typically about 10 to 20 mm) before the resulting pellets are introduced into a furnace. Since sintering and pelletizing typically involve heating the ore fines to 1200 “Celsius or more, the method of the invention saves a considerable amount of energy, has no need to use any other raw materials, and generates no polluting combustion products, in comparison to the agglomeration techniques required for traditional ironmaking in a blast furnace and in hydrogen-DRI.
[0034] Dehydration and Dehydroxylation
[0035] During and / or after its comminution into fines, the iron ore is dehydrated, and hydroxylated compounds contained therein are dehydroxylated, preferably completely, and at least to a high degree. This converts iron oxyhydroxides, if any are present in the ore, into iron oxides and avoids such other hydroxylated compounds as may also be present in the ore from reacting with the liquid sodium in the subsequent reaction of the ore with the liquid sodium. It therefore minimises the production of gaseous hydrogen during this subsequent reaction, which might otherwise present an explosion risk.
[0036] If the ore contains magnetite and dehydration and dehydroxylation are conducted in atmospheric air, such dehydration and dehydroxylation may also result in at least partial oxidation of the magnetite into hematite by the opposite sequence to that of Eqn. 1. In some embodiments, therefore, if the ore initially contains a significant proportion, for example at least about 5% by weight and in some cases, more than about 10% by weight, of magnetite, dehydrating and dehydroxylating the ore may be conducted in an atmosphere which is at least partially deoxygenated in comparison to atmospheric air, to inhibit further oxidation of the magnetite into hematite. This has the advantage that the iron oxide is then in a lower oxidation state for its subsequent reduction by the liquid sodium. On the other hand, if the ore comprises red bauxite, it may initially contain a significant admixture of organic matter, such as tree roots and humus. This is because red bauxite is typically found in near-surface deposits which are extracted by open-cast mining. Preferably, therefore, if the ore comprises red bauxite, dehydrating and dehydroxylating the ore are carried out in an oxygenated atmosphere, such as in atmospheric air, and the ore is heated to at least about 250 “Celsius, more preferably at least about 280 “Celsius, and most preferably at least about 300 “Celsius, which is above the auto-ignition temperature of any wood present. Any organic matter mixed in with the ore therefore combusts to produce carbon dioxide gas and water vapour, leaving ash. Comminution of the ore and therefore of any associated organic matter ensures that large pieces of organic matter are broken up, encouraging their complete combustion and preventing the formation of localised hotspots. Combustion reduces the mass of ash remaining to between only about 0.5% and 2% of the mass of organic matter originally present. Therefore, if, for example, the ore initially contained an admixture of 10% organic matter, this is reduced to only 0.05% to 0.2% ash remaining after combustion. The main components of the ash are calcium carbonate (typically about 25% to 45% of the ash), potassium carbonate (typically up to about 10%), alumina, silica and iron oxide, with trace amounts of other metal oxides. These are therefore incorporated into the other inorganic gangue species already present in the ore. In such a case, dehydration and dehydroxylation are preferably also carried out by enclosing the comminuted ore as it is heated so that it is contained in its own atmosphere and is not exposed to its surrounding environment. This has the advantages that the carbon dioxide thus produced, as well as any fly ash, are not released into the surrounding environment, and that the carbon dioxide may be captured, for example by reacting it with the sodium oxide produced by the subsequent reaction of the ore with the liquid sodium, as described further below.
[0037] Regardless of the initial chemical composition of the ore, dehydration and dehydroxylation may be carried out by supplying the ore with heat from at least one of several different sources. Preferably, however, heat is transferred to the ore by one or more of:
[0038] (I) cooling the liquid sodium before reacting the iron ore with the liquid sodium;
[0039] (ii) cooling the iron ore after it has been dehydrated and dehydroxylated, and before reacting the iron ore with the liquid sodium;
[0040] (ii) cooling the liquid sodium from which the iron and the other insoluble products have been separated as a solid phase; and
[0041] (iv) cooling at least a component of the solid phase separated from the liquid sodium.
[0042] The component of the solid phase from which heat is extracted may be any one or more of iron, sodium oxide and a gangue species, for example. All of these methods of dehydrating and dehydroxylating the iron ore have the advantage that they re-use heat from other parts of the method of the invention which would otherwise have been lost to the environment, and that therefore none of them requires any more energy to be consumed than is already used to produce the liquid sodium for the subsequent reaction with the iron ore. The total quantity of heat required for dehydration and dehydroxylation, and therefore the temperature to which the ore particles should be heated, the dwell time of the particles at any given temperature, and the rate of heating them from their initial temperature, will all depend in any particular case on the original chemical composition of the iron ore (after any beneficiation), and on the effects of comminution on the ore, including its degree of comminution and the temperature of the ore particles after comminution. For example, if the ore contained less water initially and / or has been more finely comminuted, it will require less heat to dry. Moreover, comminuting the iron ore also tends to raise its temperature by converting mechanical energy into heat through friction.
[0043] Nonetheless, it is preferable that after its comminution into fines, the iron ore should be heated to above the boiling point of water. This has at least three advantages, as follows. Firstly, water in the ore is driven off as steam. Secondly, as the water vaporizes, if the water is trapped in pores within the ore, this can cause decrepitation ( / '. e., fracturing) of the ore as the water expands into steam, thereby further increasing the surface area of the ore particles. Thirdly, since at atmospheric pressure, the boiling point of water is above the melting point of sodium, if the temperature of the ore is maintained above the melting point of sodium after dehydration and dehydroxylation, this also avoids the risk that the ore will quench the reaction of iron oxide from the ore with the liquid sodium by rapidly cooling the liquid sodium when the ore particles subsequently come into contact with the liquid sodium. Because the ore particles have a large surface area-to-volume ratio after comminution, they tend to heat up and cool down relatively quickly to any given temperature.
[0044] If the iron ore contains any clay-like minerals as gangue, dehydroxylation of the ore decomposes these minerals into their constituent oxides, silica (SiO2) and / or alumina (AI2O3), and / or compounds thereof, releasing their water of crystallization, which escapes as water vapour. For example, halloysite and kaolinite decompose into metakaolinite (2SiO2‘ AI2O3). Gibbsite decomposes firstly into boehmite (AIOOH) and then into alumina (AI2O3). Iron oxyhydroxides also decompose into their respective oxides, releasing water vapour. For example, goethite (Fe(OH)3 or FeO(OH)' H2O) decomposes into ferric oxide (Fe2C>3). Iron silicates, however, if any are present as gangue, tend to dehydrogenate before they dehydroxylate because dehydrogenation consumes OH groups which would otherwise be available for dehydroxylation. For example, in atmospheric air, minnesotaite dehydrogenates over a temperature range of about 300 to 700 “Celsius. The evolved hydrogen reacts immediately with atmospheric oxygen to produce water vapour and leave an oxidised intermediate product called "oxy- minnesotaite”, which retains the minnesotaite structure. Subsequent dehydroxylation of oxy-minnesotaite is complete by about 850 “Celsius in atmospheric air and decomposes it into iron oxides and silica.
[0045] In these examples, the respective decomposition temperatures are dependent not only on the initial chemical composition of the ore and the crystal structure of each mineral component thereof, but also on the effects of comminuting the ore into fines. In other words, dehydration and dehydroxylation of the ore is a result of a combination of mechanical action (milling, etc.) and heating. This is because the enthalpy of dehydroxylation decreases with decreasing particle size. Therefore, it may not be necessary to heat the comminuted ore particles to a particularly high temperature, in order to achieve a high degree of or even complete dehydroxylation, if the particles have already been finely comminuted. For example, under laboratory conditions, clay-like minerals decompose into their constituent oxides over a temperature range of about 400 to 600 “Celsius. However, dehydroxylation of kaolinite commences after just 2 hours of concentric disk milling at an ambient temperature of only 25 “Celsius and is completed under the same conditions after 10 hours of such milling. Even without such extensive comminution, heating to a temperature of from 100 “Celsius to about 500 “Celsius is therefore usually sufficient to achieve nearly complete, or complete, dehydration and dehydroxylation. With more extensive comminution, a lower peak temperature during dehydration and dehydroxylation of only about 300 or 400 “Celsius may suffice.
[0046] Moreover, heating the iron ore can also contribute to its comminution. For example, if the ore contains quartz (as is commonly the case) and the ore is heated to above the quartz inversion temperature of 573 “Celsius, a small percentage increase in volume which accompanies the phase transition from a to p quartz at this temperature can help to split the iron ore apart. Comminution, dehydration and dehydroxylation therefore interact synergistically with each other.
[0047] Without any prior comminution into fines, dehydroxylation of any clay-like minerals present in the ore would occur over a range of about 400 to 600 “Celsius, as already mentioned. Goethite also decomposes into ferric oxide over a range of about 210 to 340 “Celsius. The decomposition of gibbsite firstly into boehmite, and then into alumina, exhibits enthalpy transitions firstly at 246 and 312 “Celsius, and then at 542 “Celsius. The decomposition of diaspore exhibits an enthalpy transition at 532 “Celsius. Thus, even without any prior comminution, in any event, a maximum temperature of about 600 “Celsius is sufficient for their complete dehydration and dehydroxylation. Since this maximum temperature is several hundred degrees lower than the temperature which would otherwise be required to sinter and pelletize iron ore fines ready for ironmaking in a traditional blast furnace or for hydrogen- DRI, considerable energy is therefore saved. Furthermore, heating the iron ore to too high a temperature risks undesirably encouraging the comminuted ore particles to sinter, as well as risking undesirable and uncontrolled side reactions involving gangue mineral species, such as the thermal decomposition of any carbonates present. It is therefore preferable that the iron ore should not be heated to above about 650 “Celsius (which is the Tammann temperature of Fe2O3), more preferably about 600 “Celsius, and most preferably about 550 “Celsius. This also has the advantage that such temperatures are about the same as or below the temperature of liquid sodium produced by fusing and electrolysing solid sodium chloride, and may easily be reached by electrical heating alone, which therefore avoids the need to burn any fuel, including any fossil fuel.
[0048] Heating is also effective to decompose any iron pyrite (FeS2) in the iron ore into iron sulphide (FeS) and elemental sulphur. The sulphur can then be oxidized by atmospheric oxygen to form sulphur dioxide gas (SO2), which is driven off. The iron sulphide produced by this decomposition, as well as any other iron sulphide which may already be present in the ore, can then also be oxidized further into ferric oxide (Fe2O3) by controlling the atmospheric conditions surrounding the ore, as described below. Ideally, for the subsequent reaction of the treated ore with the liquid sodium, the ore would be completely dehydrated and dehydroxylated, since any water or hydroxylated compounds contained therein may otherwise react with the liquid sodium to produce a variety of different contaminants. However, complete dehydration and dehydroxylation requires more heat to be transferred to the ore than just a high degree of dehydration and dehydroxylation. The degree of dehydration and dehydroxylation to achieve can therefore be determined in any particular case from the overall balance between the quantity of heat required for dehydration and dehydroxylation on the one hand and the desired purities and percentage yields of the products from the subsequent reaction of the ore particles with liquid sodium on the other. The latter will in turn depend on the prior chemical composition of the ore itself, as well as on the outcome of dehydration and dehydroxylation. Thus a high degree of dehydration and dehydroxylation, rather than complete dehydration and dehydroxylation, may suffice in most cases.
[0049] The degree of dehydration and dehydroxylation of the comminuted ore particles may be measured by repeatedly weighing the ore at least during heating, and possibly also during comminution, because the comminuted ore particles lose weight as they dry and as water vapour is driven off. A relatively rapid decrease in weight is therefore indicative of ongoing dehydration and dehydroxylation, whereas when the rate of weight-loss diminishes with ongoing comminution and / or heating, this indicates that dehydration and dehydroxylation are nearly complete. The best conditions for dehydrating and dehydroxylating any particular batch of iron ore may be determined by sampling the ore particles before drying, and performing a loss-on-ignition (LOI) test on each sample thus collected. Alternatively or additionally, the degree of dehydration and dehydroxylation achieved may be measured by sampling the ore particles during and / or after drying, and performing a similar LOI test on each sample thus collected.
[0050] The rate of dehydration and dehydroxylation may be increased and the thermal efficiency of dehydration and dehydroxylation may be improved by passing sodium oxide (Na20), which is produced by the subsequent reaction of iron oxides from the dried ore with the liquid sodium, or sodium hydroxide derived from hydrating at least some of this sodium oxide, through an atmosphere to which the iron ore is exposed as it is dehydrated and dehydroxylated. Sodium oxide is powerfully hygroscopic and therefore will absorb water vapour from this atmosphere to produce (solid-phase) sodium hydroxide. At atmospheric pressure and at temperatures above about 65 “Celsius, this sodium hydroxide is anhydrous, which itself is also strongly hygroscopic. This reduces the partial pressure of water vapour within the atmosphere to which the iron ore is exposed, thereby increasing the rate of vaporization of water from the ore particles.
[0051] Moreover, recirculating at least some of the sodium oxide produced by the subsequent reaction of the dried and comminuted iron ore with the liquid sodium also has the beneficial effect of recovering and recycling heat from this subsequent reaction, because the sodium oxide typically carries away about 30% of the heat produced by the reaction of iron oxides from the ore with the liquid sodium. For example, suppose that the iron ore has a temperature of 323 K (= 50 “Celsius) after its comminution into fines, the sodium oxide has a temperature of 673 K (= 400 “Celsius), and that 3 mol of sodium oxide are circulated through the atmosphere containing the ore for every 1 mol of iron oxide present in the ore. Table 1 below gives the molar heat capacities at constant pressure, Cp, of all the main species present in the subsequent reaction of the ore particles with the liquid sodium, as well as, for comparison, that of superheated water:
[0052] (s.t.p. denotes standard temperature and pressure)
[0053] Table 1
[0054] As Table 1 shows, sodium oxide at 673 K has a molar heat capacity greater than that of water superheated to 393 K at a pressure of 5 atm. For the iron oxide to reach thermal equilibrium with the sodium oxide, and to a first-order approximation which assumes that the molar heat capacities of Table 1 are constant over the stated temperature differences, AT, the quantity of heat, Qout, lost by the sodium oxide as it heats the iron ore is equal to the quantity of heat, Qin, gained by the iron oxide, when both reach an equilibrium temperature, Teq. Therefore, where n denotes the number of mol of each component:
[0055] Qout = n(Na2O) Cp(Na20) AT(Na20) = 3 x 88 x (673 - Teq) [Eqn. 3a]
[0056] & Qin = n(Fe2O3) CP(Fe2O3) AT(Fe2O3) = 1 x 103.9 x (Teq- 323) [Eqn. 3b]
[0057] But at Teq, Qin = Qout [Eqn. 3c]
[0058] => 3 x 88 x (673 - Teq) = 1 x 103.9 x (Teq- 323) [Eqn. 3d]
[0059] => Teq = 574 K = 301 °C [Eqn. 3e]
[0060] This example also assumes that the additional presence of gangue species in both the iron ore and in the sodium oxide can effectively be ignored. However, if, as is to be expected, the ore and the sodium oxide each contain about the same amount of gangue, which also have similar heat capacities to each other, their nett effect on the equilibrium temperature will tend to be slight, making this assumption valid.
[0061] As the above example shows, even assuming that this heat transfer is only partially efficient, to account for any heat lost to the surroundings, and that the iron ore may not have sufficient time to reach thermal equilibrium with the sodium oxide, the temperature of the ore can easily be raised to over 250 “Celsius, just by passing hot sodium oxide through an atmosphere to which the iron ore is exposed and without the need to apply any additional heating from another source. The efficiency of this heat transfer process may be improved by ensuring that the atmosphere containing the ore is properly thermally insulated from the surrounding environment. Moreover, since heating of the ore by the sodium oxide is likely to occur mostly by convection and radiation, rather than by conduction, in order to encourage the iron ore to approach thermal equilibrium with the sodium oxide more quickly, the rate of circulation of the atmosphere to which the iron ore is exposed may also be increased, for example, by being fan- driven, in order to increase the rate of convective heat transfer. The rate of radiative heat transfer may similarly be improved, for example, by at least partially enclosing this atmosphere within a reflective lining.
[0062] The reaction of the sodium oxide with the water vapour driven off from the comminuted ore particles to produce sodium hydroxide is also strongly exothermic, which contributes to heating the ore particles further. Finally, both the sodium oxide and the sodium hydroxide thus produced are also effective in capturing any carbon dioxide and sulphur dioxide which are driven off from the ore by the combustion of organic matter or by the decomposition of iron pyrite, respectively, during heating. This therefore also reduces the partial pressure of sulphur dioxide gas within the atmosphere containing the ore, which encourages any remaining iron sulphide (FeS) to oxidize further into Fe2C>3, thereby effectively desulphurizing the iron ore as well. The sulphur dioxide gas captured by the sodium oxide and by the sodium hydroxide in both cases produces a small admixture in them of anhydrous sodium sulphite (Na2SC>3), which can be processed as described below. Carbon dioxide from the combustion of any organic matter mixed in with the ore reacts with the sodium oxide to produce sodium carbonate, according to the equation:
[0063] C02<g) + Na20 (S) — > Na2CO3<S) [Eqn . 4a]
[0064] The carbon dioxide also reacts with the sodium hydroxide. At temperatures of from about 310 to about 400 “Celsius, inclusive, this reaction produces anhydrous sodium carbonate as the only solid-phase product, a reduced amount of carbon dioxide gas and water vapour, according to the equation:
[0065] 2 NaOH (S) + 2 CO2 (g> — > Na2CO3 <S) + CO2 (g> + H2O <g) [Eqn. 4b]
[0066] Recycling the reduced amount of carbon dioxide gas and the water vapour produced by the reaction of Eqn. 4b in an atmosphere closed off from the surrounding environment allows all the carbon dioxide created by the combustion of organic matter to be captured and converted into sodium carbonate by the reactions of Eqns. 4a and 4b.
[0067] Whereas sodium oxide and any gangue species mixed therein have high melting points, which are well above the maximum temperature for dehydrating and dehydroxylating the iron ore, the anhydrous sodium hydroxide thus produced melts at 323 “Celsius and any anhydrous sodium sulphite produced as well melts at about 500 “Celsius. Depending on the temperature the sodium oxide reaches during dehydration and dehydroxylation of the ore, it may therefore be necessary when transporting the sodium oxide through the atmosphere containing the iron ore, to accommodate a phase change from solid to liquid of at least a component part thereof. This can be achieved by suitable ducting of the sodium oxide.
[0068] If heating the iron ore comprises cooling the liquid sodium to a temperature of less than 450 “Celsius before reacting the iron ore with the liquid sodium, liquid sodium produced in an electrolytic cell may be circulated as a heat transfer fluid (HTF) through and / or around a dryer containing the ore before reacting the iron ore with the liquid sodium. If heating the iron ore comprises cooling excess liquid sodium remaining from the reaction between the iron ore and the liquid sodium, which in other words is the liquid sodium from which the iron and the other insoluble products of the reaction have been separated, the excess liquid sodium may similarly be circulated as an HTF through and / or around a dryer containing the ore before the iron ore reacts with the liquid sodium.
[0069] Comminution on the one hand and dehydration and dehydroxylation on the other may be at least partially combined, to discourage sintering of the ore particles as they are heated. In other words, some or all of the comminution of the iron ore may be carried at the same time as when the ore is being dehydrated and dehydroxylated. For example, a dryer of the ore may comprise one or more comminution devices, such as moving parts for separating the ore particles as they are dried. On the other hand, some or all of the comminution does not have to be carried out near to or in the same location as dehydration and dehydroxylation. For example, prior beneficiation of the iron ore in one location may already result in finely comminuted ore particles, which may then be delivered to a different location for dehydration and dehydroxylation, before being reacted with liquid sodium.
[0070] Depending on the temperature to which the ore is heated during dehydration and dehydroxylation, the ore particles may also require cooling before they are introduced into the liquid sodium. The temperature to which the ore should be cooled after dehydration and dehydroxylation can be determined from the process conditions for the reaction of the ore particles with the liquid sodium, which are described below. The time taken to cool the ore particles down will be determined not only by their temperature immediately after dehydration and dehydroxylation, but also by the temperature gradient to which they are exposed in order to reach the target temperature for the ore particles before they are introduced to the liquid sodium. Because of the large surface area-to-volume ratio of the ore particles after comminution, the ore particles can be cooled relatively quickly to this desired temperature, just by being exposed to the ambient temperature of the environment. This may be achieved without exposing the dried ore particles to the surrounding environment itself by including a counterflow system within a dryer of the ore, whereby dried ore particles leaving the dryer are brought into thermal, but not physical, contact with ore particles entering the dryer at or near to ambient temperature, such that heat is exchanged from the dehydrated and dehydroxylated ore to the iron ore entering the dryer. An example of such a counterflow system is given below.
[0071] Any of the above techniques for heating the iron ore in order to dehydrate and dehydroxylate it may optionally be combined with one or more other known heating techniques.
[0072] Reaction with Liquid Sodium
[0073] After its comminution into fines, dehydration and dehydroxylation, the iron ore thus treated is reacted with an excess of liquid sodium. This may be done, for example, by introducing the comminuted and dried ore particles into a bath of liquid sodium. The iron oxide(s) in the ore are reduced by the liquid sodium to produce elemental iron and sodium oxide (Na20). In the case of hematite, this reaction proceeds according to the equation:
[0074] 6 Na + Fe20s <s) — * 3 Na20 (Sj + 2 Fe (Sj - 438 kJ [Eqn. 5] Reduction of the hematite may occur by the same sequence as in Eqn. 1 , above. In the case of other iron oxides, the starting point in Eqn. 1 may be different, but the reaction products are still the same as in the righthand side of Eqn. 5. In other words, the initial oxidation state of the iron oxide(s) in the ore is immaterial to the eventual outcome of this reaction.
[0075] Since the solubility of iron in liquid sodium is only about 3 to 8 ppm by weight of iron, the iron produced by the reaction of Eqn. 5 is insoluble in the liquid sodium and precipitates out. The solubility of sodium oxide in liquid sodium is low but increases with temperature. At temperatures below about 400 “Celsius, however, the solubility of sodium oxide in liquid sodium is less than about 0.1 % by weight of oxygen. Virtually all the sodium oxide produced by this reaction therefore precipitates out as well, leaving only a trace amount dissolved in the excess liquid sodium. (The exact amount remaining depends on the temperature at which the reaction of Eqn. 5 is carried out and on how much liquid sodium is present.) Precipitation of both of the reaction products of Eqn. 5 ensures that the reaction is one-way.
[0076] To ensure that all the iron oxide(s) from the ore are consumed, the amount of liquid sodium present should be in excess of the stoichiometric amount thereof required for this redox reaction between the liquid sodium and the iron oxide. This excess amount of liquid sodium also absorbs some of the heat generated by the reaction of Eqn. 5. The excess amount of liquid sodium to use can therefore be determined from the desired temperature profile of the reaction, described below. As may be seen from Eqn. 5, the reduction of iron oxides by liquid sodium is exothermic, but not violently so. For example, if all the iron oxide is present as hematite and is therefore in its most oxidized state (Fe2C>3), this reaction produces about -73 kJ of heat per mol of liquid sodium consumed. For comparison, the reaction of elemental sodium with oxygen in atmospheric air produces about -208 kJ of heat per mol of sodium consumed. The reduction of iron oxides by liquid sodium is therefore at most about 2.85 times less exothermic than the reaction of sodium with atmospheric oxygen.
[0077] The reaction of Eqn. 5 can be carried out at any temperature of from about 390 K up to about 720 K. Below about 390 K, the liquid sodium risks freezing at the melting point of sodium, which at atmospheric pressure, is 98 “Celsius (= 371 K). Above about 720 K, reacting the liquid sodium with iron oxides from the iron ore risks producing ternary oxides like Na4FeO3, as the Na - Na2O - Fe system transitions to a Na - Na4FeO3 - Fe system. Such ternary oxides are generally soluble in liquid sodium, which both contaminates the liquid sodium and reduces the yield of elemental iron. The temperature of the reaction should therefore preferably be controlled to remain below about 705 K, more preferably below about 690 K, and most preferably below about 675 K.
[0078] As a result of the prior dehydration and dehydroxylation of the iron ore, gangue species still present in the ore may comprise any one or more of silica (SIO2), alumina (AI2O3), dehydrated aluminosilicates like metakaolinite, and iron silicates such as stilpnomelane and minnesotaite, which may also have been thermally altered into species like oxy-minnesotaite, depending on the temperature reached during the prior dehydration and dehydroxylation. The direct reduction by liquid sodium of either silica to produce elemental silicon or alumina to produce elemental aluminium in a manner similar to the reaction of Eqn. 5 is not thermodynamically favoured, since the Gibbs free energy of both such reactions, AG > 0 across the range of available operating temperatures for the reaction of Eqn. 5. A disproportionation reaction between liquid sodium and silica to produce sodium metasilicate (Na2SIO3) and elemental silicon according to the equation:
[0079] 4 Na <4 + 3 SiC>2 <S) — 2 Na2SiC>3 + Si [Eqn. 6a] has a Gibbs free energy, AG < 0 across the range of available operating temperatures for the reaction of Eqn. 5. However, the activation energy for this reaction is high and the reaction kinetics are correspondingly slow. The reaction of Eqn. 6a therefore has an onset temperature only above about 520 “Celsius, outside the range of available operating temperatures for the reaction of Eqn. 5. A similar disproportionation reaction between liquid sodium and alumina to produce sodium aluminate (NaAI02) and elemental aluminium according to the equation:
[0080] 3 Na <4 + 2 AI2O3 (S) — > 3 NaAI02 + Al [Eqn. 6b] has a Gibbs free energy, AG, which is only slightly negative across the range of available operating temperatures for the reaction of Eqn. 5 and has even slower reaction kinetics. Any effects of the reaction of Eqn. 6b may therefore effectively be ignored as negligible. Any elemental aluminium which is able to form by this or any other mechanism could in principle dissolve in the liquid sodium, but is likely to be oxidized back to insoluble AI2O3 by the reduction of Fe2O3, SIO2 or Na20. Similarly, any elemental silicon which is able to form will also contribute to the reduction of Fe2O3 and therefore tend to be oxidized back to SIO2.
[0081] However, sodium oxide produced by the reaction of Eqn. 5 can also react in a Lux-Flood acid-base neutralization reaction with either silica or alumina since these reactions have Gibbs free energies, AG < 0 across the range of available operating temperatures for the reaction of Eqn. 5. In the case of silica, the sodium oxide can react with the silica to produce sodium metasilicate (Na2SIO3) and / or sodium orthosilicate (Na4SIO4) according to the two equations:
[0082] Na20 (S) + SIO2(S) — > Na2SIO3 [Eqn. 7a]
[0083] 2 Na20 (S) + Si O2 (S) — > Na4SIO4 [Eqn. 7b] which are both exothermic reactions. Sodium orthosilicate is produced as the only product of these two reactions if the molar ratio of Na20 to SIO2 exceeds 2:1 , whereas a mixture of sodium meta- and orthosilicates are produced at lower mol ratios than this. In the case of alumina, whereas sodium oxide can react with alumina to produce sodium aluminate according to the equation:
[0084] Na20 (S) + AI2O3 (S) — > 2 NaAI02 [Eqn. 7c] the kinetics of this reaction are again very slow, similarly to the reaction of Eqn. 6b, so that its effects may again be considered negligible. On the other hand, the reactions of Eqns. 7a and 7b have sufficiently fast rates for these reactions to have an onset temperature above about 300 “Celsius, which lies in the middle of the range of available operating temperatures for the reaction of Eqn. 5. A reaction of sodium oxide produced by the reaction of Eqn. 5 with any silica present in gangue species surviving after dehydration and dehydroxylation can therefore be initiated and go to completion over a range of temperatures of from about 320 to about 350 “Celsius. If so, sodium orthosilicate, as well as any possible sodium metasilicate, produced by the reactions of Eqns. 7a and 7b readily dissolves in the liquid sodium.
[0085] If any dehydrated aluminosilicates like metakaolinite remain after dehydration and dehydroxylation, these are similarly attacked at temperatures above about 300 “Celsius by sodium oxide produced by the reaction of Eqn. 5 to produce alumina, sodium orthosilicate, as well as possibly also sodium metasilicate. For any iron silicates which remain, such as oxy-minnesotaite and / or stilpnomelane, the liquid sodium attacks the crystal structure of these less thermodynamically stable minerals, which are reduced to produce elemental iron, sodium oxide and silica. At temperatures above about 300 “Celsius, sodium oxide further reacts with this silica to produce sodium silicate(s) as described above. In either case, cations of group I and II metals like potassium and magnesium, released, for example, by the reduction of stilpnomelane, behave as follows. The potassium cations are reduced by the liquid sodium to elemental potassium because the equilibrium oxide in the sodium-potassium system is sodium oxide (Na2O). The potassium metal thus produced is completely miscible with liquid sodium, so no potassium oxide is produced as a solid phase and the elemental potassium instead remains in solution with the liquid sodium as sodium-potassium alloy (NaK). In contrast, magnesium cations scavenge oxygen anions from the sodium oxide to produce magnesia (MgO), which, like sodium oxide, has very low solubility in liquid sodium, so remains in solid phase.
[0086] In some embodiments, therefore, wherein the dehydrated and dehydroxylated iron ore comprises a silicate mineral (including, possibly, quartz), the method may comprise conducting the redox reaction of Eqn. 5 at a temperature of at least about 320 “Celsius, more preferably at least about 340 “Celsius, and most preferably at least about 360 “Celsius, in order to induce a reaction between the sodium oxide and silica derived from the silicate mineral to produce at least sodium orthosilicate. In alternative embodiments, wherein the dehydrated and dehydroxylated iron ore comprises a silicate mineral, the method may instead comprise conducting the redox reaction of Eqn. 5 at a temperature of less than about 300 “Celsius, more preferably less than about 290 “Celsius, and most preferably less than about 280 “Celsius, to inhibit a reaction between the sodium oxide and silica derived from the silicate mineral. In this way, it is possible to select whether the silicate mineral remains in the other insoluble products precipitated out from the liquid sodium or whether silica is removed from the other insoluble products as sodium orthosilicate, as well as possibly also sodium metasilicate, produced by the reactions of Eqns. 7a and 7b. In the former case, any aluminosilicate gangue species present precipitate out along with the iron and undissolved sodium oxide produced by the redox reaction of Eqn. 5, whereas in the latter case, iron and / or alumina derived from silicate gangue species precipitate out, but the silica component of such silicate gangue species dissolves in the liquid sodium as sodium orthosilicate, as well as possibly also sodium metasilicate.
[0087] Nonetheless, in both of these two possible alternatives and subject to the respective temperature constraints they impose, the reaction of Eqn. 5 is preferably also conducted at or above the middle of the respective range of available operating temperatures in each case, to increase the rate of reaction for Eqn. 5, whilst also leaving a sufficient margin below the top of each such range at which other undesired reactions may occur. In each case, the rate of reaction may also be increased by stirring or otherwise mixing the comminuted ore particles into the liquid sodium. Stirring and / or mixing of the reaction mixture may comprise applying a magnetic field to it and passing an electric current through the liquid sodium to create a magnetohydrodynamic force acting on the liquid sodium, causing it to move. However, as the reaction of Eqn. 5 is exothermic, as are the reactions of Eqns. 7a and 7b, the temperature of the reaction mixture will rise from its initial temperature when the comminuted and dried ore particles are introduced into the liquid sodium. The temperature of the reaction should therefore be controlled to remain within the desired range of operating temperatures by appropriate cooling, not just of the reagents before they are introduced to each other, but also of the reaction mixture itself, as will now be described.
[0088] As mentioned above, the liquid sodium may be produced by fusing and electrolysing solid sodium chloride in a Downs-type electrolytic cell. Since such an electrolytic cell operates at a temperature of about 600 to 625 “Celsius, the liquid sodium thus produced typically leaves the cell at a similar temperature. Therefore, if the liquid sodium for reaction with the iron ore is produced close to the reaction of Eqn. 5, the liquid sodium must firstly be cooled before it meets the iron ore, to prevent the reaction of Eqn. 5 from overheating. Preferably, the liquid sodium is cooled to a temperature of less than about 250 “Celsius, and more preferably, less than about 200 “Celsius. From Table 1 above, it can be seen that liquid sodium has a molar heat capacity of 31.5 J K1mol1at 400 K, and from Eqn. 5, that 6 mol of liquid sodium are required to reduce 1 mol of Fe2O3 to produce 2 mol of iron. For example, therefore, to cool 6 mol of liquid sodium from about 600 “Celsius to about 175 “Celsius, to a first-order approximation which assumes that the molar heat capacity of liquid sodium is constant over the stated temperature difference, AT, the quantity of heat, Q, which must be extracted from the liquid sodium is given by:
[0089] Q = n(Naw) Cp(Naw) AT = 6 x 31 .5 x (175 - 600) = - 80.3 kJ [Eqn. 8] where n denotes the number of mol of liquid sodium. However, as Eqns. 3d and 3e above show, only 26 kJ of heat is sufficient to heat 1 mol of Fe2O3 from 50 “Celsius to 301 “Celsius. At least some of the excess heat extracted from the liquid sodium may therefore also be used to heat or power other processes, such as the production of the inert atmosphere in which the reaction of Eqn. 5 is carried out, as described below.
[0090] The iron ore may be heated or cooled to fall within the desired range of operating temperatures before it is introduced to the liquid sodium by using any one or more of the techniques described above.
[0091] The subsequent reaction of the iron ore with the liquid sodium may, for example, be cooled by conducting the reaction in a reaction vessel surrounded by a heat exchanger in which a heat transfer fluid (HTF) circulates to extract heat from the reaction. Preferably, however, the reaction is cooled by maintaining a continuous flow of the excess liquid sodium through the reaction mixture, which can itself therefore be used as an HTF for extracting heat from the reaction. More preferably still, the excess liquid sodium circulates through the reaction mixture in a loop. In such a case, the liquid sodium from which the iron and the other insoluble products of the reaction have been separated is cooled before being returned to the reaction, and the degree of cooling and / or the rate at which the liquid sodium is returned to the reaction mixture may be adjusted to keep the temperature of the reaction within its desired range of operating temperatures. Furthermore, cooling of the liquid sodium from which the iron and the other insoluble products of the reaction have been separated may be combined with purifying the liquid sodium in a cold trap to remove dissolved contaminants remaining in the liquid sodium after removing undissolved contaminants. In some embodiments, the excess sodium may be pumped through the reaction mixture to encourage mixing of the iron ore with the liquid sodium before the reaction products precipitate out. At least some of the heat extracted from the liquid sodium may, for example, then be transferred to the iron ore before it enters the reaction mixture, in order to help dehydrate and dehydroxylate it.
[0092] Carrying out the reaction of Eqn. 5 in an inert atmosphere has the advantages of preventing the liquid sodium from reacting with atmospheric oxygen, and of inhibiting the formation of ternary oxides such as Na4FeO3. For example, the inert atmosphere may consist of at least one of nitrogen and argon. Either nitrogen or argon, or both, may be produced on site by pressure swing adsorption (PSA) of atmospheric air. An on-site PSA generator of such inert gases may be powered, for example, using waste heat derived from cooling at least one of the iron ore, fresh liquid sodium before it is introduced into the reaction of Eqn. 5 and the liquid sodium from which the iron and the other insoluble products of the reaction have been separated, as described above.
[0093] The inert atmosphere may be maintained at around atmospheric pressure or just above. A small positive pressurization of the inert atmosphere in which the reaction is carried out to above atmospheric pressure, for example by about 10 to 25%, is desirable to prevent ingress of air from the environment by leakage. The vapour pressure, p, in pascal of liquid sodium as a function of temperature, T, in kelvin from its melting point up to 700 “Celsius is given by the following equation: logic P = 9.71 - (5377 1 T) [Eqn. 9]
[0094] Table 2 below gives some representative examples of the values of this vapour pressure across the range of operating temperatures for the reaction of Eqn. 5:
[0095] Table 2
[0096] As Table 2 shows, the vapour pressure of liquid sodium over the range of operating temperatures for the reaction of Eqn. 5 is always less than about 190 Pa, or less than about 0.19% of standard atmospheric pressure. Thus if the reaction of Eqn. 5 is carried out at around atmospheric pressure or just above, the loss of liquid sodium from the reaction mixture by vaporization is negligible and the effect of any such vaporization on the pressure of the inert atmosphere in which the reaction is carried out is negligible as well.
[0097] If the ore contains a small admixture of calcium carbonate and / or potassium carbonate as a result of the combustion of organic matter during dehydration and dehydroxylation of the ore, these gangue species fail to react with the liquid sodium and also precipitate out. It has been experimentally determined that no reaction occurs in the case of potassium carbonate within the desired range of operating temperatures for the reaction of Eqn. 5. In the case of calcium carbonate, the onset temperature for a reaction between liquid sodium and powdered calcium carbonate is 717 K, at the very top end of the desired range of operating temperatures for Eqn. 5.
[0098] If any small amount of residual water (for example, water of crystallization) remains in the iron ore after dehydration and dehydroxylation, this residual water is reduced by the liquid sodium to produce sodium hydroxide (NaOH), sodium oxide (Na20) and hydrogen, according to a family of reactions including the following two equations:
[0099] 2 H20 + 2 Naw2 NaOH(s)+ H2 (g)[Eqn. 10a]
[0100] H2O + 2 Na^j — > Na20 (S> + H2<g) [Eqn. 10b]
[0101] Eqn. 10a is thought to predominate at temperatures below the melting point of sodium hydroxide, whereas only sodium oxide is produced above the melting point of sodium hydroxide. The sodium oxide precipitates out as described above. Some dissolution of any sodium hydroxide produced in the liquid sodium may occur at a low level, depending on the temperature of the reaction mixture and the concentration of the sodium hydroxide. This reacts with the liquid sodium according to the reversible reaction:
[0102] 2 NaOH + 2 Na^j <-> 2 Na2O (S> + H2<g) [Eqn. 10c]
[0103] However, this is unproblematic since dissolved sodium hydroxide can be removed by subsequent purification of the liquid sodium, as described below. The solubility of hydrogen in liquid sodium increases over the operating temperature range, but remains very low even at the top of the range, where it is less than about 100 ppm by weight of hydrogen. At temperatures above about 350 “Celsius, any dissolved hydrogen also reacts with the liquid sodium to produce sodium hydride, which dissociates in the liquid sodium as Na+and H~ ions. (Any subsequent hydration of this sodium hydride would ultimately lead to the formation of sodium hydroxide as well.) Hydrogen gas which is released into the inert atmosphere above the liquid sodium will therefore reach an equilibrium with the hydrogen thus dissolved in the liquid sodium, according to the temperature of the reaction mixture and the corresponding partial pressure of the hydrogen gas above the liquid sodium. Thus hydrogen released by the reactions of Eqns. 10a, 10b and 10c may cause a slight increase in the pressure of the inert atmosphere. For safety and in order to maintain the pressure of the inert atmosphere similar to or slightly more than that of the surrounding environment, the pressure of the inert atmosphere should preferably be monitored, for example by means of a pressure gauge. To prevent any undesirable build-up of pressure, any reaction vessel in which the reaction of Eqn. 5 is carried out may be fitted with a pressure-relief valve, through which pressurised gas may be vented from the inert atmosphere to the surroundings. If so, the vented gases should preferably be cooled to below the dew point of sodium vapour before being released, to recover any sodium and to ensure that the remaining gases are harmless. On the other hand, if the pressure of the inert atmosphere above the reaction mixture needs to be increased for any reason, extra inert gas can instead be introduced into the reaction vessel along with the iron ore. After reacting the iron ore with the liquid sodium, the iron produced by the reaction of Eqn. 5 is separated from the other insoluble products, and both the iron and the other insoluble products are separated as a solid phase from the liquid sodium. However, it does not matter in which order these two operations are carried out. In alternative possible embodiments, either a "wet” separation of the different solid species may be carried out first, in which the iron is separated from the other insoluble products whilst both are still suspended or entrained in liquid sodium, followed by separation of the iron as a solid phase from the liquid sodium and separation of the other insoluble products as a solid phase from the liquid sodium in two different process streams, or separation of both the iron and the other insoluble products as a solid phase from the liquid sodium in a single process stream may be carried out first, followed by a "dry” separation of the iron from the other insoluble products. Separation of the different solid species and the phase separation may even be combined, as described below. In the following, therefore, although separating the iron from the other insoluble products is described before the solid-liquid sodium phase separation, this does not imply that they should be carried out in that order.
[0104] Separation of Iron from Other Insoluble Products
[0105] Table 3 below gives the molar magnetic susceptibilities, Xmoicgs, of all the main species present in the reaction of the iron ore with the liquid sodium, as well as, for comparison, that of water:
[0106] (* at s.t.p., unless otherwise stated)
[0107] Table 3
[0108] 260 K is the Morin transition temperature of Fe20s. 950 K is the Neel temperature of Fe20s and 1043 K is the Curie temperature of iron, both of which temperatures are well above the top of the range of operating temperatures for the reaction of Eqn. 5. As Table 3 shows, all of the reaction products are diamagnetic, except for iron, which is strongly (and famously) ferromagnetic at temperatures below its Curie temperature. Since iron is strongly ferromagnetic, it is powerfully attracted to regions of high magnetic field. In contrast, since the other insoluble products, including the sodium oxide, are all diamagnetic, they are weakly repelled by regions of high magnetic field. The iron may therefore easily be separated from the other insoluble products in the precipitate by bringing them into proximity with a region of high magnetic field, even if the precipitate is still hot from the reaction of Eqn. 5 because the maximum operating temperature for the reaction of Eqn. 5 is significantly below the Curie temperature of iron. Moreover, since the magnetic susceptibility of iron is many orders of magnitude greater than that of the different iron oxides, the degree of separation which is achieved is also very much greater than can typically be obtained when magnetically separating an iron oxide from gangue during the beneficiation of iron ore. Nonetheless, any residual amount of unreacted iron oxide surviving from the reaction of Eqn. 5, since it is weakly ferromagnetic at temperatures above the Morin transition temperature and below its Neel temperature, will also be attracted to regions of high magnetic field and is therefore likely to be separated out with the iron.
[0109] On the other hand, liquid sodium is only slightly paramagnetic. It is therefore very weakly attracted to regions of high magnetic field and can easily flow through them without any appreciable magnetic deflection. For example, therefore, in a "wet” magnetic separation of the type described above, wherein the iron and the other insoluble products are all initially present in liquid sodium, the precipitate from the reaction of Eqn. 5 may easily be separated into a stream of liquid sodium with entrained iron and a stream of liquid sodium with the other insoluble products entrained therein. Equally, in a "dry” magnetic separation of the type described above, wherein the precipitate from the reaction of Eqn. 5 is first separated as a solid phase from the liquid sodium, the iron may also be separated from the other insoluble products by bringing them both into proximity with a region of high magnetic field.
[0110] In some embodiments, magnetically separating the iron from the other insoluble products may comprise applying a magnetic field gradient to the liquid sodium with the iron and the other insoluble products suspended or entrained therein. This has the advantage of inhibiting the production of other species from side reactions between the iron and the other insoluble products, by commencing separation of the iron and the other insoluble products from each other as soon as they are produced.
[0111] Iron is also considerably denser than all the other main species present in the reaction of the iron ore with the liquid sodium, and is nearly 3.5 times denser than sodium oxide. As well as or instead of the magnetic separation just described, therefore, separating the iron from the other insoluble products may comprise separating them based on their different densities. For example, in a "wet” density-based separation, a stream of liquid sodium with the iron and the other insoluble products suspended or entrained therein may be supplied to an inlet of a device functioning like a hydrocyclone (but which may instead be called a "natrocyclone”), in which the denser iron particles are directed to an underflow outlet thereof and particles of less dense other species are directed to an overflow outlet thereof. The construction and functioning of such a device are described in detail in the present applicant's UK patent application no. 2517311.3 ("Apparatus and Method for Separating Different Chemical Species”; applicant's ref: NE-P-GB 010), the entire contents of which is incorporated herein by reference. Alternatively, in a "dry” density-based separation, a stream of dry gas acting as a transport medium in which the iron and the other insoluble products are suspended or entrained, which may also be inert to avoid reoxidizing the iron, may be supplied to an inlet of a cyclonic separator which functions in a similar manner to separate these different species from each other.
[0112] Moreover, magnetic and density-based separation of the iron from the other insoluble products may also be combined. For example, if "wet” magnetic separation of the iron from other species comprises applying a magnetic field gradient to the liquid sodium with the iron and the other insoluble products suspended or entrained therein, the magnetic field gradient may have a non-zero component which increases in a direction antiparallel to a gravitational potential gradient, in other words in a vertical direction, such that the strength of the magnetic field increases downwardly. Thus the less dense, diamagnetic particles of sodium oxide will be repelled by the region of higher magnetic field and the denser, ferromagnetic iron particles will be attracted to the region of higher magnetic field, whereby the magnetic and density-based separation of the iron from the other insoluble products work together to enhance the speed and efficiency of their separation. In another example, if density-based separation of the iron from the other insoluble products comprises their "wet” or "dry” cyclonic separation, a magnetic field gradient having a non-zero component which increases in a direction parallel to a centrifugal force, in other words in a radial direction, such that the strength of the magnetic field increases outwardly, may be applied to at least a part of the circumference of the "natrocyclone” or cyclonic separator, respectively, to attract iron particles outwardly and repel diamagnetic species inwardly towards the eye of the cyclone.
[0113] Regardless of whether the precipitated products from the reaction of Eqn. 5 are subject to "wet” or "dry” magnetic and / or density-based separation, this solid-species separation of the same process stream may be repeated, in order to increase the degree of separation finally achieved.
[0114] Solid Phase Separation from Liquid Sodium
[0115] Separating the iron and the other insoluble products as a solid phase from the liquid sodium may, for example, comprise at least one of settlement under gravity, filtration ( / '.e., trapping) and centrifugation. For example, the present applicant's UK patent application no. 2417052.4 ("Apparatus and Method for Separating a Contaminant from Liquid Metal”; applicant's ref: NE-P-GB 002), the entire contents of which is incorporated herein by reference, shows and describes an apparatus and method for separating undissolved contaminants, for example in the form of suspended or entrained particulates, from liquid metal, such as liquid sodium. In another example, a liquid sodium centrifuge is shown and described on pp. 29 to 33 of Summary of the APDA Sodium Technology Program by J.E. Meyers published under United States Atomic Energy Commission Contract No. AT (11-1)-865, Project Agreement No. 11 (June 1970), the entire contents of which is also incorporated herein by reference.
[0116] If the phase separation comprises filtration, a filter substrate may be used which comprises, for example, a ceramic foam made, for example, of a titania- or zirconia-based ceramic, and / or a wire mesh or wool, made, for example, of one of the same materials as the inner surface of the first reaction vessel, such as grade 316 LN or 316 FR stainless steel or a titanium alloy having the composition described below. If the separated precipitate still contains iron, in order to remove any residual liquid sodium contained therein, the degree of phase separation may be improved by flushing the separated precipitate with an inert gas which is hot enough for the liquid sodium to remain in liquid phase. Using such an inert gas prevents reoxidation of the hot iron and avoids the formation of more sodium oxide. If, on the other hand, the iron has already been separated from the phase-separated precipitate, the remaining, iron-depleted precipitate may simply be flushed with dry air, which just converts any residual liquid sodium into sodium oxide.
[0117] In some embodiments, separating the iron from the other insoluble products may be combined with the phase separation of both from the liquid sodium by carrying out the phase separation in proximity to a region of high magnetic field. For example, if the phase separation comprises filtration, a magnetized filter substrate may be used to attract iron particles to the substrate whilst repelling the other insoluble products from the substrate.
[0118] Regardless of how the phase separation is carried out, phase separation of the same process stream may be repeated, in order to increase the degree of separation finally achieved.
[0119] Liquid sodium recovered from the phase separation is preferably purified of dissolved contaminants, such as residual sodium oxide, sodium hydride and / or sodium hydroxide dissolved therein, as well as other dissolved species, which may have been produced by reactions with gangue, or carbon derived from stainless steel pipework used to transport the liquid sodium. The purification may be carried out using one or more know techniques, such as gettering, and hot and cold trapping. For example, gettering and / or trapping with zirconium, titanium and tantalum can be used to remove impurities. The recovered liquid sodium is then preferably recycled for reuse in the reaction of Eqn. 5, thereby maintaining the amount of excess liquid sodium used therein.
[0120] If the reaction of the dehydrated and dehydroxylated ore with the liquid sodium was conducted at a temperature above the onset temperature for the reactions of Eqns. 7a and 7b, then the liquid sodium may have at least sodium orthosilicate dissolved therein, as described above. If so, the liquid sodium with the sodium silicate(s) dissolved therein may be processed as described in the present applicant's UK patent application no. 2417073.0 ("Method and Apparatus for Producing an Alkaline Mixture comprising Sodium Silicate”; applicant's ref: NE-P-GB 009), the entire contents of which is incorporated herein by reference.
[0121] Optional Conversion into Steel
[0122] After the iron has been separated from the other insoluble products and from the liquid sodium, the iron may then be used in a steelmaking process. For example, the iron may be melted by at least one of ohmic heating, as in an arc furnace, and induction heating, as in an induction furnace, and alloyed with carbon and possibly also with other elements as desired to produce steel of an intended composition. If the electricity required to melt the iron comes from a source of renewable energy, such as wind or solar, or from nuclear power, then no greenhouse gases are produced by this process.
[0123] However, iron produced by the present invention is in the form of a finely divided particulate, similar to a product which is sometimes known as zero-valent iron. It is therefore particularly suited for use in powder metallurgical (PM) techniques, such as hot isostatic pressing ("hipping”), cold pressing followed by sintering, and so on. Accordingly, iron produced by the present invention may be mixed with finely divided carbon, such as with powdered graphite and / or carbon black, and possibly also with other alloying elements as desired, and the resulting powdered mixture may be subjected to a PM process to produce steel of an intended composition. If so, the iron may firstly be washed in deionized water and dried to dissolve and thus remove any residual sodium oxide. This is preferably conducted in an inert atmosphere to avoid reoxidizing the finely divided iron. As is well known, finished steel products having a desired shape (gears, for example) may be produced directly by using PM techniques. Alternatively or additionally, steel made from iron produced by the present invention may be fashioned using PM techniques into generic shapes like plates and / or ingots.
[0124] In comparison to steel made by melting iron, all PM processes have the advantage that the powdered mixture does not have to be melted to make steel and only has to be heated to above the Tammann temperature of the major alloying elements in the mixture to sinter the powdered mixture into a bulk mass. Wastage from PM steelmaking techniques is considerably lower as well. However, all PM processes for making steel still require a source of powdered iron, which is made in the prior art from molten iron. Therefore, by combining iron produced by the present invention with a PM process to make steel, melting the iron can be avoided entirely. The enthalpy ef fusion of the iron is thereby also saved, in addition to the quantity of heat which is saved by heating the powdered mixture only to above the Tammann temperature instead of to the melting point of iron. Steel made by the present invention is therefore energetically significantly cheaper than steel made using prior art techniques, even including those which already comprise a PM process. The present invention therefore provides a way of turning iron ore into steel, including into a finished steel product, which is considerably more energy efficient than prior art steelmaking techniques.
[0125] Other Insoluble Products
[0126] At this stage, the iron has been extracted from the iron ore and has possibly also been used to make steel. However, it would be wrong to view the other insoluble products remaining after the solid-species and phase separations as an undesirable by-product, not least because these other insoluble products comprise a high proportion of sodium oxide from the reaction of Eqn. 5 and therefore have several useful applications. They should therefore properly be viewed as a co-product of the present invention, apart from the iron, so will be referred to hereinafter as "the basic co-product” (or BCP). For example, at least some of the BCP may be used as a reagent in one or more other chemical reactions because of its high overall pH and / or high sodium content, without requiring any or substantial further processing. In some embodiments, such uses may comprise as a CO2 sorbent and / or as a neutralizing agent, as described in the present applicant's UK patent application no. 2417079.7 ("Method and Apparatus for Producing Oxides of Calcium, Magnesium and Iron from Carbonate Mineral Ores without Burning Carbonaceous Fuels”; applicant's ref: NE-P-GB 005), the entire contents of which is incorporated herein by reference. Alternatively or additionally, at least some of the BCP may be used and / or processed as described below. The BCP will generally be of one of four different types, as shown in Table 4 below. As Table 4 shows, the chief constituents of the BCP depend on the type of iron ore used and the temperature at which the liquid sodium reaction has been carried out. If the iron ore chiefly comprises a traditional iron ore, such as from a banded iron formation, the BCP will have a relatively lower alumina content, whereas if the iron ore chiefly comprises red bauxite, the BCP will have a relatively higher alumina content. Moreover, if the liquid sodium reaction has been carried out at a temperature below the onset temperature for the reactions of Eqns. 7a and 7b, silica may also be present in the BCP, whereas if the liquid sodium reaction has been carried out above that temperature, the BCP may be substantially silica-free.
[0127] Temperature of liquid sodium reaction
[0128] Table 4
[0129] These four different types of BCP may therefore be used as follows. In some embodiments, the BCP in the toplefthand cell of Table 4 may be used to produce an alkaline activator for an alkaline activated or geopolymer cement by adding liquid water to the BCP to achieve a desired concentration of sodium silicate and sodium hydroxide therein, as described further below. If instead the ore chiefly comprises red bauxite, the BCP may be treated as an aluminium ore from which the iron has already been removed. It is therefore desirable both from an economic and from an environmental point of view to process this BCP to extract as much alumina from it as possible, as well as any other useful products (such as titanium) which can also be recovered from other gangue species originally present in the red bauxite. In principle, therefore, the BCP in the bottom-lefthand cell of Table 4 could be used as a feedstock for the Bayer process. Preferably, however, if the ore chiefly comprises red bauxite, the liquid sodium reaction is carried out at a temperature above the onset temperature for the reactions of Eqns. 7a and 7b, and the BCP in the bottom-righthand cell of Table 4 is instead processed to extract alumina from it as described further below. In principle, the same technique could also be used to extract alumina from the BCP in the top-righthand cell of Table 4, but this is unlikely to be economic because of its lower alumina content. Finally, in some embodiments, the BCP in any of the cells of Table 4 may be processed as follows to recover the sodium oxide therefrom.
[0130] Recovery of Sodium Oxide
[0131] The sodium oxide may be recovered from the BCP by progressively adding the BCP to liquid water. Since the BCP is at an elevated temperature because of the exothermic nature of the reaction of Eqn. 5 (and possibly also of Eqns. 7a and 7b), it may first need to be cooled closer to ambient temperature, for example to less than about 100 “Celsius. The sodium oxide in the BCP readily dissolves in the water, whereas gangue species like silica, alumina and magnesia also present in the BCP do not. The sodium oxide hydrates to produce an aqueous solution of sodium hydroxide, according to the equation:
[0132] Na20 (S) + H2O t) — > 2NaOH <aq) [Eqn . 11]
[0133] The amount of water to which the BCP is added should be enough to create an aqueous solution, in which the final concentration of sodium hydroxide after the BCP has been added to it is less than about 2.5 M ( / '. e., less than about 100 g dm3), more preferably less than about 2 M. If the final concentration of sodium hydroxide is kept below about this level and if the temperature of the aqueous solution is kept down as well, the sodium hydroxide will not react with other, gangue species like silica and alumina in the BCP to any appreciable extent. Adding the BCP to water, rather than the other way round, also ensures that the final concentration of the aqueous solution is approached from below. However, the reaction of Eqn. 11 is significantly exothermic, with an enthalpy of reaction, AHreaction = - 239 kJ at s.t.p. Therefore, this reaction should be controlled, for example by appropriate cooling, to keep the temperature of the aqueous solution substantially below its boiling point, for example at less than about 85 “Celsius, more preferably at less than about 75 “Celsius, and most preferably at less than about 65 “Celsius if the solution is at atmospheric pressure. At least some of the heat extracted from firstly cooling the BCP and / or from cooling the reaction of Eqn. 11 may then be used to contribute to drying and dehydroxylating the ore initially. Once the BCP has been added to the water, any undissolved silica and alumina, along with any other undissolved solids, such as magnesia, may be phase-separated from the aqueous solution, for example by settlement under gravity, filtration and / or centrifugation, to leave just the aqueous solution of sodium hydroxide. Preferably, this phase separation is carried out soon after the reaction of Eqn. 11, so that the silica and / or alumina do not have time to start reacting with the sodium hydroxide.
[0134] Whereas this technique for recovering sodium oxide from the BCP has been described above for ease of explanation as being conducted after separating the iron from the BCP, the same technique may instead be carried out before separating the iron from the BCP after both have been phase-separated from the liquid sodium. This is because any iron which remains mixed in with the BCP will not react with such a dilute aqueous solution of sodium hydroxide either to any appreciable extent, under the stated conditions.
[0135] The aqueous solution of sodium hydroxide thus produced has many different possible uses. For example, at least some of it may be dried to produce solid sodium hydroxide, which may then be used to produce more liquid sodium for use in the reaction of Eqn. 5, so that the sodium is recycled in a closed loop. If so, the liquid sodium may be produced from the solid sodium hydroxide either by fusing and electrolysing it using the Castner process or by thermochemically decomposing it into its constituent elements, as described in the present applicant's UK patent application no. 2517327.9 ("Method and Apparatus for Producing Liquid Sodium”; applicant's ref: NE-P-GB 011), the entire contents of which is incorporated herein by reference, or by a combination of both techniques. Moreover, the sodium oxide in the BCP has a high affinity for carbon dioxide. At least some of this sodium oxide, whether separated as just described or left unseparated, may therefore be used in a carbonation reaction with carbon dioxide gas to produce at least sodium carbonate. For example, the carbon dioxide may be captured from atmospheric air and / or from one or more other industrial processes, in order to mitigate greenhouse gas emissions. If so, the present invention can have a significantly negative carbon footprint overall.
[0136] If the sodium oxide in the BCP is used in such a reaction with carbon dioxide gas, this carbonation reaction is also significantly exothermic. Heat may therefore also be extracted from this reaction and used to contribute to dehydrating and dehydroxylating the iron ore. Furthermore, at least some of the heat carried by sodium carbonate produced by this reaction may similarly be used to contribute to dehydrating and dehydroxylating the iron ore. This has the advantage that the heat which the sodium carbonate carries immediately after it has been produced, as well as the heat generated during the carbonation reaction, are not wasted, but are re-used, making the invention more energy efficient overall. It also has the advantage of reducing the temperature of the sodium carbonate towards ambient temperature.
[0137] Once sodium oxide has been recovered from the BCP as described above, the undissolved solids remaining after the phase separation comprise the respective contents of each of the cells in Table 4, minus the Na20 in each cell. In the case of either of the righthand cells in Table 4, therefore, the undissolved solids essentially consist just of alumina. In principle, therefore, this alumina could be used as a feedstock for extracting aluminium therefrom by fusing and electrolysing the undissolved solids with little further processing. (For example, the undissolved solids may be rinsed with a weak solution of hydrochloric acid to remove any residual sodium hydroxide and neutralize them, then washed in deionised water and dried, before being subjected to electrolysis.) In practice, however, the undissolved solids are likely to contain one or more contaminants in addition to the alumina. In the case of the bottom-righthand cell of Table 4, this may well include titania (TI02), for example. Preferably, therefore, these contaminants are firstly removed by the process for extracting alumina from the BCP described hereinafter, before aluminium is extracted from the decontaminated alumina by electrolysis.
[0138] Processing of Basic Co-product to Produce an Alkaline Activator
[0139] As mentioned above, the BCP in the top-lefthand cell of Table 4 may be used to produce an alkaline activator for an alkaline activated or geopolymer cement. A technique for doing so will therefore now be described. Firstly, if the dehydrated and dehydroxylated iron ore comprises a silicate mineral, the redox reaction should be conducted at a temperature of less than about 300 “Celsius, so that silica derived from the silicate mineral does not dissolve in the liquid sodium and instead remains in the other insoluble products. The method then comprises adding liquid water to at least some of the other insoluble products, thereby hydrating the sodium oxide therein, to produce a hot, concentrated aqueous solution of sodium hydroxide. Since the BCP is already at an elevated temperature as a result of the reaction of Eqn. 5, it may need to be cooled before the water is added to it. However, the water may be heated by the BCP, as well as by the exothermic nature of the reaction of Eqn. 11 . Since the silica in the other insoluble products is in the form of a finely divided particulate, it readily reacts with the hot, concentrated solution of sodium hydroxide thus formed to dissolve at least some of the silica therein and produce an aqueous solution of sodium silicate. "Hot” in this context means that the final temperature of the aqueous solution of sodium hydroxide after its hydration should be at least about 15 “Celsius and preferably more than about 25 “Celsius above ambient temperature, in order to increase the rate at which the silica dissolves therein. The final temperature of the aqueous solution of sodium hydroxide is also preferably above about 50 “Celsius, more preferably above about 60 “Celsius and most preferably above about 70 “Celsius. "Concentrated” in this context means that the final concentration of the aqueous solution of sodium hydroxide after its hydration should be at least about 2.5 M because at lower concentrations than this, the rate of dissolution of the silica in the aqueous solution of sodium hydroxide may become unacceptably low. Preferably, the final concentration of the aqueous solution of sodium hydroxide should be at least about 3.5 M, more preferably, at least about 4.5 M, and most preferably, at least about 5.5 M. This has the advantage that it reduces the amount of water present as a solvent in the resulting aqueous solution of sodium silicate, which water is subsequently to be removed. Since water has a high specific heat capacity, this in turn reduces the quantity of heat required to remove this water of solution. The method then comprises drying the aqueous solution of sodium silicate to produce a solid phase comprising the sodium silicate. The excess water may be removed by evaporation and / or by boiling it off. Heat produced by the exothermic hydration reaction of Eqn. 1 1 may be used to help this drying process. Thereafter, at least some of the resulting solid phase may be used as an alkaline activator for an alkaline activated or geopolymer cement by rehydrating it.
[0140] Processing of Basic Co-product to Extract Alumina
[0141] A technique for processing the basic co-product to extract alumina therefrom will now be described. Whereas this technique can in principle be applied to the BCP in either of the cells in the righthand column of Table 4, it is most applicable to extracting alumina from bauxitic ore. Furthermore, whereas this technique is modelled on the Bayer process, it is distinguished therefrom in three major respects, as follows. Firstly, organic matter mixed in with the bauxitic ore has already been combusted when drying and dehydroxylating the ore, as described above. Secondly, iron has already been removed from the bauxitic ore by the redox reaction with the liquid sodium. Thirdly, silica is also absent from the BCP because in this case, the redox reaction with the liquid sodium is conducted at a temperature of at least about 320 “Celsius, preferably above about 340 “Celsius, and more preferably above about 360 “Celsius, to induce a reaction between the sodium oxide produced by the redox reaction and silica derived from the silicate mineral in the ore, to produce at least sodium orthosilicate, which dissolves in the liquid sodium as described above. Thus, according to this new technique, no desilication product (DSP) is formed, unlike in the Bayer process. Since this DSP in the Bayer process is a waste product, which removes sodium hydroxide from the Bayer mixture, both the consumption of sodium hydroxide and the generation of waste by this new technique are reduced in comparison to the Bayer process, making it both more economic and more environmentally friendly than the Bayer process. On the other hand, since silica is also absent from the BCP, there is no risk of silica contaminating the alumina which is eventually extracted by this new technique, even though no DSP is formed.
[0142] In red bauxite, n(Fe2O3) « n(SiO2) present as gangue, where n denotes the number of mol of each respective component thereof. However, the stoichiometry of Eqn. 5 implies that 3 mol of Na2O are produced by this redox reaction for every mol of Fe20a consumed. Typically, therefore, the molar ratio of Na20: SIC>2 in red bauxite comfortably exceeds the minimum 2:1 ratio for all the sodium silicate produced by the reactions of Eqns. 7a and / or 7b to be in the form of sodium orthosilicate, which leaves approximately 1 mol of unreacted Na20 remaining in the other insoluble products per mol of Fe20a consumed, assuming that enough excess liquid sodium is also used to dissolve all the sodium silicate thus formed at the temperature of the liquid sodium. However, this remaining amount of Na20 may not be sufficient to react with and dissolve the alumina in the BCP, if this Na20 is hydrated as described below. Accordingly, in some embodiments, the molar ratio of Fe20a: AI2O3 may be increased by adding one or more iron oxide(s), for example in the form of mill scale, and / or another non-bauxitic iron ore, such as from a banded iron formation, to the red bauxite before the comminuted, dehydrated and dehydroxylated ore is reacted with the liquid sodium. Thus the relative proportion of unreacted sodium oxide in the BCP is increased. Alternatively or additionally, BCP from the top-righthand cell of Table 4 produced from a non-bauxitic iron ore may be added to the BCP from the bottom-righthand cell of Table 4, to increase the ratio of sodium oxide to alumina therein.
[0143] Thereafter, the new technique proceeds as follows. Firstly, water in liquid or vapour phase is added sparingly to the BCP. The water hydrates the sodium oxide in the BCP to produce sodium hydroxide according to the reaction of Eqn. 11. In this case, however, the amount of water added should only be enough to create a concentrated aqueous solution of sodium hydroxide, in which the final concentration of sodium hydroxide after the water has been added is preferably from about 100 g dm3to about 300 g dm3, inclusive ( / . e., from about 2.5 M to about 7.5 M, inclusive), more preferably from about 150 g dm3to about 275 g dm3, inclusive, and most preferably from about 200 g dm3to about 250 g dm3, inclusive. Since the BCP is already at an elevated temperature as a result of the reaction of Eqn. 5, it may need to be cooled before the water is added to it. Since the reaction of Eqn. 11 is exothermic, the temperature of this reaction should also be controlled by appropriate cooling to remain within a range of temperatures of from about 210 to about 280 “Celsius, more preferably from about 220 to about 270 “Celsius, and most preferably from about 230 to about 260 “Celsius. As this range of temperatures is well above the boiling point of the concentrated aqueous solution of sodium hydroxide at atmospheric pressure, this reaction should be conducted in a pressure vessel to prevent the aqueous solution from boiling. At least some of the heat extracted from cooling the reaction of Eqn. 11 may again be used to contribute to dehydrating and dehydroxylating the ore initially.
[0144] In this case, the superheated aqueous solution of sodium hydroxide starts to react with and dissolve the alumina in the BCP to produce sodium aluminate (NaAIO2 = I^O'A Os) according to the equation:
[0145] 2 NaOH (aq) + AI2O3 (S) — 2 NaAIO2 <aq) + H2O [Eqn. 12]
[0146] As mentioned, any silica originally present in the ore as gangue has already been substantially removed during the reaction of the dehydrated and dehydroxylated ore with the liquid sodium. And after subsequently separating the iron from the other insoluble products of this reaction, any iron originally present in the ore has been removed as well. The chief constituent of the BCP, apart from sodium oxide, is therefore just alumina. If the ore comprises red bauxite, any organic matter originally mixed in with the ore has also been reduced to only a small admixture of ash as a result of the prior dehydration and dehydroxylation of the ore. The main constituent of this ash is calcium carbonate, which is insoluble in aqueous solution at high pH and high temperature and therefore precipitates out, whereas the sodium aluminate remains in solution at the concentrations of sodium hydroxide and temperatures just specified. The precipitated calcium carbonate, along with any other undissolved solids, may then be separated as a solid phase from the solution of sodium aluminate. This phase separation may be carried out, for example, by settlement, filtration and / or centrifugation. The remaining solution of sodium aluminate, from which the undissolved solids have been removed, may then be processed as described below.
[0147] In some embodiments, however, before separating the undissolved solids as just described, calcium oxide ( / '.e., lime) may be added to the aqueous solution of sodium aluminate to help remove other dissolved contaminants. This calcium oxide may be obtained by a technique as described in the present applicant's UK patent application no. 2417079.7 ("Method and Apparatus for Producing Oxides of Calcium, Magnesium and Iron from Carbonate Mineral Ores without Burning Carbonaceous Fuels”; applicant's ref: NE-P-GB 005). The amount of calcium oxide to add may be determined by the respective amounts of any dissolved contaminants present and the stoichiometry of their reactions with the calcium oxide. For example, if a small residual amount of silica still remains in the BCP and this silica has dissolved in the superheated sodium hydroxide as sodium orthosilicate, the calcium oxide reacts with this dissolved sodium orthosilicate to produce calcium orthosilicate (Ca2SIO4), as follows:
[0148] 2 CaO (s) + Na4SIO4 <aq) + 2 H2O (4) — > Ca2SIO4 (Sj + 4 NaOH (aq) [Eqn. 13]
[0149] This calcium orthosilicate then precipitates out. If the BCP has already been used to absorb some sulphur dioxide gas, the reaction of this sulphur dioxide with the sodium oxide in the BCP, or with solid-phase sodium hydroxide derived therefrom, will have formed a small proportion of sodium sulphite (Na2SO3) in the BCP. The addition of the calcium oxide to the aqueous solution converts this into both calcium sulphite (CaSOs) and calcium sulphate (CaSO4) according to the following two equations:
[0150] CaO (S) + Na2SO3 (aq) + H2O — > CaSOs <S) + 2 NaOH (aqj [Eqn. 14a]
[0151] CaO (S) + Na2SO3 <aq) + 2 H2O — > CaSO4 <S) + 2 NaOH (aqj + H2 (g> [Eqn. 14b]
[0152] Whereas calcium sulphate is slightly more soluble than insoluble calcium sulphite at ambient temperature and pressure, co-precipitation of calcium sulphite and calcium sulphate from the aqueous solution can now occur because calcium sulphate has inverse or retrograde solubility, which decreases with increasing temperature. The relative proportions of sulphate and sulphite precipitated out will depend on the initial concentrations of sodium sulphite and hydroxide, on the reaction temperature and pressure, and on the pH of the solution.
[0153] If the BCP has already been used to absorb some carbon dioxide gas, the other insoluble products will contain a small proportion of sodium carbonate as a result of the reactions of Eqns. 4a and 4b. The addition of the calcium oxide to the aqueous solution converts this into calcium carbonate as follows:
[0154] CaO (S) + Na2CO3 <aq) + H2O — > CaCOs <S) + 2 NaOH (aqj [Eqn. 15] This calcium carbonate precipitates out, along with any other calcium carbonate already present, for example as a result of the prior combustion of organic matter mixed in with the ore.
[0155] As mentioned above, the most preferred total amount of lime to add is determined by the stoichiometry of the reactions of Eqns. 13 to 15 and the quantities of any gangue species present in the BCP. Thus, for example, if silica were the only gangue species present, then twice the molar amount of calcium oxide to the number of mols of dissolved sodium orthosilicate should be added to the superheated aqueous solution of sodium hydroxide because of the stoichiometry of the reaction of Eqn. 13. Addition of calcium oxide in excess of this stoichiometric amount would tend to reduce the yield of sodium hydroxide. The bauxitic ore may initially also have contained a significant proportion of titanium dioxide (TIO2) as an impurity. However, since titanium dioxide is unreactive either with liquid sodium under the reaction conditions specified above or with the aqueous solution of sodium hydroxide, it remains undissolved and precipitates out independently of the addition of any calcium oxide.
[0156] The result of adding lime to the superheated aqueous solution of sodium hydroxide is therefore both a precipitate and a solution, with the sodium aluminate remaining in solution. The precipitate may comprise any one or more of calcium orthosilicate ( / .e., larnite), calcium sulphate ( / '.e., gypsum), calcium sulphite, calcium carbonate and titanium dioxide, depending on the original chemical composition of the ore and the treatment of the BCP after the reaction of the ore with the liquid sodium. This precipitate is then separated out from the solution as described. One or more flocculants may be used to aid their separation. After its separation, the wet precipitate or slurry may be washed with water to reduce the amount of any sodium hydroxide remaining therein, which may be returned to the remaining solution. The wet precipitate or slurry may then be bubbled thoroughly with carbon dioxide gas, which may, for example, be captured from atmospheric air and / or from one or more other industrial processes. In particular, the carbon dioxide may have been captured from the combustion of organic matter mixed in with the ore originally. The carbon dioxide converts any hydroxide ions remaining in the slurry into carbonate ions according to the equation:
[0157] 2 OH- <aq) + 002 [Eqn. 16]
[0158] This has several advantages as follows. Firstly, it neutralizes the pH of the slurry. Secondly, it consumes carbon dioxide, thereby helping to mitigate greenhouse gas emissions. Thirdly, since the reaction of Eqn. 16 is exothermic, it also helps to heat and dry the slurry. Any calcium sulphite present in the slurry may be oxidized to calcium sulphate using manganese as a catalyst, as described, for example, in "Catalytic Oxidation of Calcium Sulfite in Solution / Aqueous Slurry” by X-Q Wu et a / ., J. Environ. Sci. (China), vol. 16, no. 6, pp. 973-977 (2004), the entire contents of which is incorporated herein by reference. This leaves a largely inert solid-phase end-product, which may be dried and compacted, for use, for example, as drywall insulation. Alternatively or additionally, if the precipitate comprises a significant proportion of titanium dioxide, at least some of the precipitate may be used as a feedstock for the production of titanium dioxide, which may be extracted from it using known techniques.
[0159] In order to recover alumina from the remaining solution, the latter is cooled to between about 85 and about 55 “Celsius and depressurized back to atmospheric pressure, for example by being flash-cooled in a series of flash tanks of successively reduced pressure. High-temperature steam from the flash tanks may be recycled back to hydrate the sodium oxide initially. The cooled and depressurized solution may then be diluted with more water and seeded with crystals of AI(OH)s to act as nucleation sites for the precipitation of aluminium hydroxide from the sodium aluminate remaining in solution, according to the equation:
[0160] NaAICh <aq) + 2 H2O t) — > AI(0H)3 <S) + NaOH <aq) [Eqn. 17]
[0161] This precipitation may be carried out using established techniques from the Bayer process. As in the Bayer process, the aluminium hydroxide precipitated out is phase-separated from the remaining solution, then washed with water and dried, after which it may be thermally decomposed to obtain alumina. Thus alumina may be recovered from the bauxitic ore, the production of red mud is avoided completely, carbon dioxide may be mineralized, and a useful solid-phase end-product, consisting, for example, of a mixture of larnite and / or gypsum and / or calcium carbonate, can be produced instead.
[0162] Precipitation of aluminium hydroxide typically results in a reduction in the concentration of sodium aluminate remaining in the solution by about two-thirds. The remaining solution of sodium aluminate from which the precipitated aluminium hydroxide has been phase-separated may be recycled back to the start of the alumina extraction process, as in the Bayer process. However, this would tend to cause an accumulation of sodium ions.
[0163] In some embodiments, therefore, hydrochloric acid may be added to at least some of this remaining solution of sodium aluminate to precipitate out additional aluminium hydroxide and leave an aqueous solution of sodium chloride. This therefore increases the yield of alumina. The additional aluminium hydroxide may be precipitated out as pseudoboehmite or bayerite, for example. Further details concerning such a process may be found in "Preparation of Aluminium Hydroxide by Reacting Sodium Aluminate Solutions with Mineral Acid” by Taichi Sato, Journal of Chemical Technology and Biotechnology, vol. 31 , issue 1 , pp. 670-675 (1981), the entire contents of which is incorporated herein by reference. In such embodiments, after the additional aluminium hydroxide has been phase-separated from the remaining aqueous solution of sodium chloride, the latter may be used to produce liquid sodium and gaseous chlorine by electrolysis. The electrolysis may comprise the Downs process and / or a combination of the chlor-alkali and Castner processes, for example, as described above. The liquid sodium may then be used in the redox reaction with the comminuted, dehydrated and dehydroxylated ore, and the gaseous chlorine may used to produce the hydrochloric acid.
[0164] Alternatively or additionally, in some embodiments, at least some of the remaining solution of sodium aluminate has several useful applications similar to those already described above for the BCP before it was processed to extract alumina therefrom. These include its use in a reaction with carbon dioxide gas to produce at least sodium carbonate, thereby mitigating greenhouse gas emissions, and / or as a reagent in one or more other chemical reactions because of its high pH and / or high sodium content. Further details concerning the possibility of using at least some of the remaining solution of sodium aluminate to capture carbon dioxide may be found in "CO2 Capture and Crystallization of ATH Using Sodium Aluminate Solution in a Bubble Column Scrubber” by Pao-Chi Chen et al., Energies, vol. 15, no. 3, pp. 1031-1052 (2022). If the remaining aqueous solution of sodium aluminate is used in such a carbonation reaction, this reaction also precipitates out additional aluminium hydroxide from the remaining solution of sodium aluminate, thereby increasing the yield of alumina as well, and leaves the sodium ions in solution as sodium carbonate, which itself is a useful industrial product in its own right. As before, if at least some of the remaining solution of sodium aluminate is used in a reaction with carbon dioxide, this carbonation reaction is significantly exothermic, and heat may therefore be extracted from it and used to contribute to dehydrating and dehydroxylating the iron ore.
[0165] Any potassium cations which were present in the BCP, for example as a result of the prior combustion of organic matter mixed in with the ore, follow the same reaction pathway as the sodium and therefore remain in solution with the sodium hydroxide. The sodium and potassium cations may subsequently be separated from each other using a known technique, such as by evaporative crystallization based on the different solubilities of the two hydroxides in aqueous solution at different temperatures, as described, for example, in US patent no. 1 ,562,805, and / or by another technique, such as that described in "Ion-Exchange Separation of Sodium and Potassium Ions on Dihydrogen Tetratitanate Hydrate Fibers at Various Temperatures” by Y. Komatsu et al., Solvent Extraction and Ion Exchange, vol. 11 , issue 1 , pp. 159-169 (1993).
[0166] Any of the methods described herein may be carried out as a continuous, semi-batch or batch process. However, they are preferably carried out as a continuous process for reasons of economy and efficiency.
[0167] Apparatus
[0168] In a second aspect, the present invention also provides an apparatus for producing iron from an iron ore in which the iron is present as at least one of the mineral and mineraloid forms of iron oxide and oxyhydroxide. The apparatus comprises an ore preparation subassembly comprising a comminution device and a dryer, a gas-tight first reaction vessel, and a separation subassembly comprising a solid-species separator and a solid-liquid sodium phase separator. The comminution device is for comminuting the iron ore into fines. The dryer is for dehydrating the iron ore and dehydroxylating hydroxylated compounds contained therein. The ore preparation subassembly therefore comprises an inlet for the iron ore and an outlet for the ore thus treated. The first reaction vessel is for reacting the iron ore thus treated in an inert atmosphere and at a temperature of less than 450 “Celsius with an amount of liquid sodium in excess of the stoichiometric amount thereof required for a redox reaction between the liquid sodium and iron oxide from the iron ore. The first reaction vessel comprises a first inlet for receiving the comminuted, dehydrated and dehydroxylated iron ore from the outlet of the ore preparation subassembly, a second inlet for the liquid sodium, and an outlet for the liquid sodium with iron and other insoluble products comprising sodium oxide entrained therein. The solid-species separator is for separating the iron from the other insoluble products, and the solid-liquid sodium phase separator is for separating the iron and the other insoluble products from the liquid sodium. The separation subassembly therefore comprises an inlet for receiving the liquid sodium with the iron and the other insoluble products entrained therein from the outlet of the first reaction vessel, and respective outlets for each one of the liquid sodium, the iron and the other insoluble products. The comminution device may comprise one or more known types of comminution device, such as a rock crusher, grinder, hammer mill, ball, disc and / or rod mill, autogenous mill, roller mill, vibrator, and / or the like.
[0169] The dryer may, for example, comprise a continuous tunnel dryer through which the comminuted ore is transferred, for example on a moving conveyor. Such a dryer may be compared and contrasted with a Dwight-Lloyd sintering machine, as follows. Like a Dwight-Lloyd sintering machine, the ore fines can be advanced through a hot zone of the dryer in order to dehydrate and dehydroxylate them, and the rate of advance may be similar to that in a Dwight- Lloyd sintering machine. However, unlike a Dwight-Lloyd sintering machine, the iron ore is not mixed with any other ingredients and is not fired or exposed to a flame front, and is only heated instead.
[0170] The dryer may have an interior which is closed off from the surrounding environment, for example by means of one or more doors or curtains, so that the ore fines can be enclosed within the dryer as they are heated, are not exposed to the surrounding environment and may instead be contained in their own atmosphere. Enclosing the ore fines as they are heated so that they are contained in their own atmosphere allows this atmosphere to be controlled, and also helps to prevent gases like carbon dioxide and sulphur dioxide which may be released from the ore as it is heated from escaping into the surrounding environment. Enclosing the ore in this way also helps to maintain the thermal efficiency of its dehydration and dehydroxylation by reducing the loss of heat to the environment.
[0171] In some embodiments, the dryer may contain an atmosphere to which the iron ore is exposed during dehydration and dehydroxylation, and the dryer may comprise means for reducing a pressure of this atmosphere to less than that of atmospheric air outside the dryer. Thus when ore enters or leaves the dryer, this pressure differential causes atmospheric air from outside the dryer to enter the dryer along with the ore, thereby hindering or preventing the escape of gases like carbon dioxide and sulphur dioxide into the surrounding environment.
[0172] In some embodiments, the apparatus may comprise a heat transfer pathway for transferring heat to the iron ore within the dryer from at least one of:
[0173] (I) the liquid sodium before it enters the first reaction vessel;
[0174] (ii) the iron ore after it has been dehydrated and dehydroxylated, but before it enters the first reaction vessel;
[0175] (ill) the first reaction vessel; and
[0176] (iv) at least one of the liquid sodium, the iron and the other insoluble products after they have left the first reaction vessel.
[0177] This has the advantage that heat used to dehydrate and dehydroxylate the ore need not come from an external source. If so, the heat transfer pathway may contain the liquid sodium as a heat transfer fluid. For example, liquid sodium from the first reaction vessel may be circulated in pipework passing through and / or around the dryer before being returned to the first reaction vessel.
[0178] The first reaction vessel may be made, for example, of steel of a type already used for containing and transporting liquid sodium, such as grades 316 LN or 316 FR stainless steel. In such a case, the inner surface of the reaction vessel may be provided with a sacrificial layer having the same chemical composition, for gradual corrosion by the highly reactive sodium oxide. Thus depending on the desired composition of other, minor elements mixed in with the iron eventually produced, the chemical constituents of the sacrificial layer will either be the same as those already present in the products of the reaction between the iron ore and the liquid sodium ( / '.e., iron) or may be entirely acceptable as minor constituents of the reaction products ( / '.e., Cr, Ni, Mo). Alternatively, the reaction may be carried out in a reaction vessel made from or lined with titanium or a titanium alloy, such as one having a composition by weight of 98.8% Ti, 0.8% Ni and 0.4% Mo. Titanium and titanium alloy are found to be highly resistant to corrosion by sodium oxide across the entire range of operating temperatures for the reaction between the iron ore and the liquid sodium, by forming a stable surface passivation layer of titanium dioxide.
[0179] The first reaction vessel may, for example, be a stirred tank reactor. If the first reaction vessel is made of an austenitic steel, titanium or a titanium alloy as just described, a magnetic field may then be applied from outside the vessel into its interior because these materials all have low magnetic susceptibility. This would allow magnetohydrodynamic stirring and / or mixing of the vessel's contents as described previously, by also passing an electrical current through the liquid sodium contained therein, causing it to move. In some embodiments, the first inlet of the first reaction vessel may comprise an airlock to prevent atmospheric oxygen from being introduced into the first reaction vessel whenever the vessel is fed with iron ore. If so, the airlock may have an interior for holding iron ore and may also comprise first and second gas-tight doors, an inlet to the interior of the airlock for inert gas, and an outlet from the interior of the airlock for atmospheric air. The first gas-tight door connects the interior of the airlock with a surrounding environment of the first reaction vessel, and the second gas-tight door connects the interior of the airlock with an inside of the first reaction vessel. The inlet for inert gas and the outlet for atmospheric air each comprises a respective valve for opening and closing a respective one of the inlet and the outlet. Thus a charge of iron ore may be introduced into the interior of the airlock via the first door, and atmospheric air may be purged from within the interior of the airlock by opening and closing the valves to replace the air inside the airlock with inert gas, before the iron ore is released into the first reaction vessel via the second door.
[0180] If the first inlet of the first reaction vessel does comprise such an airlock, the apparatus may further comprise a heat exchanger for transferring heat from the first reaction vessel to the inert gas upstream of the inlet to the airlock. Thus the inert gas can be heated to a temperature similar to that inside the first reaction vessel before it enters the first reaction vessel, which helps to prevent a build-up of pressure within the first reaction vessel, and to purge atmospheric air from within the airlock.
[0181] In some embodiments of the apparatus, the solid-species separator may be a "dry” solid-species separator, wherein the solid-liquid sodium phase separator comprises an inlet for receiving the liquid sodium with the iron and the other insoluble products entrained therein from the outlet of the first reaction vessel, a first outlet for liquid sodium, and a second outlet for the iron and the other insoluble products, and the solid-species separator comprises an inlet for receiving the iron and the other insoluble products from the second outlet of the solid-liquid sodium phase separator, a first outlet for the iron, and a second outlet for the other insoluble products. In other embodiments of the apparatus, the solid-species separator may instead be a "wet” solid-species separator, wherein the solid-species separator comprises an inlet for receiving the liquid sodium with the iron and the other insoluble products entrained therein from the outlet of the first reaction vessel, a first outlet for liquid sodium with iron entrained therein, and a second outlet for liquid sodium with the other insoluble products entrained therein. If so, the solid-liquid sodium phase separator comprises a first phase separating device and a second phase separating device, wherein the first phase separating device comprises an inlet for receiving the liquid sodium with iron entrained therein from the first outlet of the solid-species separator, a first outlet for the liquid sodium, and a second outlet for the iron, and the second phase separating device comprises an inlet for receiving the liquid sodium with the other insoluble products entrained therein from the second outlet of the solid-species separator, a first outlet for the liquid sodium, and a second outlet for the other insoluble products.
[0182] In either the "wet” or "dry” case, however, both the solid-species separator and those parts of the solid-liquid sodium phase separator which come into contact with the other insoluble products are preferably made of a material like the first reaction vessel, which is adapted to accommodate or withstand corrosion by sodium oxide, as described above.
[0183] In some embodiments of the apparatus, at least one of the first outlets for liquid sodium of the solid-liquid sodium phase separator may be connected upstream of the second inlet of the first reaction vessel, so that the separated liquid sodium can be recycled back to the reaction with the iron ore.
[0184] In both the "wet” and "dry” cases, the apparatus may comprise a conduit for transporting at least some of the other insoluble products from the second outlet for the other insoluble products through an atmosphere to which the iron ore is exposed in at least one of the comminution device and the dryer. Thus the other insoluble products can be used to transfer heat from the first reaction vessel to the iron ore as it is comminuted, dehydrated and dehydroxylated, and sodium oxide within the other insoluble products, or solid sodium hydroxide derived therefrom, can also be used to absorb water vapour, and other gases like sulphur dioxide, from the iron ore, or if the ore comprises red bauxite, carbon dioxide produced by combustion of organic matter mixed in with the ore.
[0185] In some embodiments, the apparatus may comprise a hydration vessel for reacting at least some of the sodium oxide from the first reaction vessel with water to produce an aqueous solution of sodium hydroxide. In such cases, the hydration vessel comprises a first inlet for receiving the other insoluble products from the second outlet for the other insoluble products, a second inlet for the water, and at least a first outlet for the aqueous solution of sodium hydroxide and undissolved solids. If so, the apparatus also comprises a solid-aqueous phase separator for separating the undissolved solids from the aqueous solution of sodium hydroxide. The solid-aqueous phase separator comprises an inlet downstream of the first outlet of the hydration vessel, a first outlet for the aqueous solution of sodium hydroxide, and a second outlet for the undissolved solids. Such an apparatus may be used to recover the sodium oxide produced by the reaction of the iron ore with the liquid sodium, separated from other gangue species like silica and alumina. If the apparatus comprises a hydration vessel as just described, in some embodiments, the apparatus may also comprise a heat transfer pathway for transferring heat from the hydration vessel to the iron ore within the dryer. Thus heat from the exothermic hydration reaction can be used to help dehydrate and dehydroxylate the ore.
[0186] In some embodiments, the hydration vessel may further comprise a third inlet for calcium oxide and a second outlet for gases, and all of the inlets and outlets of the hydration vessel may each comprise a respective valve for opening and closing a respective one of the inlets and outlets, whereby the aqueous solution of sodium hydroxide can be held under pressure in a superheated condition within the hydration vessel by closing said valves. In such cases, the solid-aqueous phase separator may comprise a plurality of settlement tanks connected in series. If so, the apparatus also comprises a precipitation vessel and a second solid-aqueous phase separator. The precipitation vessel, which may also comprise a plurality of precipitation tanks connected in series, comprises a first inlet downstream of the first outlet of the solid-aqueous phase separator, a second inlet for liquid water, a third inlet for aluminium hydroxide crystals, and an outlet. The second solid-aqueous phase separator comprises an inlet connected via a valve to the outlet of the precipitation vessel, a first outlet for a solid phase and a second outlet for an aqueous phase. Such an apparatus may be used to extract alumina from the other insoluble products of the reaction of the iron ore with the liquid sodium.
[0187] In some embodiments, the apparatus may comprise a carbonation vessel and a heat transfer pathway for transferring heat from the carbonation vessel to the iron ore within the dryer. The carbonation vessel is for reacting at least some of the sodium oxide from the first reaction vessel, or sodium hydroxide derived from hydrating at least some of this sodium oxide, with carbon dioxide gas to produce at least sodium carbonate. The carbonation vessel comprises a first inlet for receiving the sodium oxide or sodium hydroxide, a second inlet for the carbon dioxide gas, and an outlet for at least the sodium carbonate. Thus if sodium oxide produced by the reaction of the iron ore with the liquid sodium, or sodium hydroxide derived from hydrating at least some of this sodium oxide, is used to mineralize carbon dioxide gas, heat from this exothermic carbonation reaction and / or from the sodium carbonate produced thereby can be used to help dehydrate and dehydroxylate the ore.
[0188] Brief Description of the Drawings
[0189] Further features and advantages of the present invention will become apparent from the following detailed description, which is given by way of example and in association with the accompanying drawings, in which:
[0190] Fig. 1 is a flow diagram of a first embodiment of a method of producing iron from an iron ore, in which the iron is present as at least one of the mineral and mineraloid forms of iron oxide and oxyhydroxide;
[0191] Fig. 2 is a flow diagram of a second embodiment of such a method;
[0192] Fig. 3 is a flow diagram of a third embodiment of such a method;
[0193] Fig. 4 is a flow diagram of a fourth embodiment of such a method;
[0194] Fig. 5 is a flow diagram of a fifth embodiment of such a method;
[0195] Fig. 6 is a flow diagram of a sixth embodiment of such a method; Fig. 7 is a flow diagram of a seventh embodiment of such a method;
[0196] Fig. 8 is a flow diagram of an eighth embodiment of such a method;
[0197] Fig. 9 is a flow diagram of a ninth embodiment of such a method;
[0198] Figs. 10A and 10B together are a flow diagram of a tenth embodiment of such a method;
[0199] Fig. 11 is a flow diagram of an eleventh embodiment of such a method;
[0200] Fig. 12A is a flow diagram of a twelfth embodiment of such a method;
[0201] Fig. 12B is a flow diagram of a thirteenth embodiment of such a method;
[0202] Fig. 13 is a schematic diagram of a first embodiment of an apparatus for producing iron from an iron ore, in which the iron is present as at least one of the mineral and mineraloid forms of iron oxide and oxyhydroxide;
[0203] Fig. 14 is a schematic diagram of an embodiment of an airlock;
[0204] Fig. 15 is a schematic diagram of a second embodiment of an apparatus for producing iron from an iron ore, in which the iron is present as at least one of the mineral and mineraloid forms of iron oxide and oxyhydroxide;
[0205] Fig. 16 is a schematic diagram of a third embodiment of such an apparatus;
[0206] Fig. 17 is a schematic diagram of a fourth embodiment of such an apparatus;
[0207] Fig. 18 is a schematic longitudinal section through an embodiment of a dryer;
[0208] Fig. 19 is a schematic diagram of a fifth embodiment of an apparatus for producing iron from an iron ore, in which the iron is present as at least one of the mineral and mineraloid forms of iron oxide and oxyhydroxide;
[0209] Fig. 20 is a schematic diagram of a sixth embodiment of such an apparatus;
[0210] Fig. 21 is a schematic diagram of a seventh embodiment of such an apparatus;
[0211] Fig. 22 is a schematic diagram of an embodiment of an apparatus for extracting aluminium from the other insoluble products when the iron ore comprises red bauxite;
[0212] Fig. 23A is a schematic diagram of first and second embodiments of a heat transfer pathway; and Fig. 23B is a schematic diagram of third and fourth embodiments of a heat transfer pathway.
[0213] Detailed Description
[0214] Fig. 1 shows a first embodiment of a method 300a of producing iron from an iron ore, in which the iron is present as at least one of the mineral and mineraloid forms of iron oxide and oxyhydroxide. The method 300a comprises comminuting 301 the iron ore into fines, and drying 302 the iron ore to dehydrate it and so that hydroxylated compounds contained in the ore are dehydroxylated. Comminution 301 of the ore and its dehydration and dehydroxylation 302 interact with each other as described above. The comminuted, dehydrated and dehydroxylated ore particles are then reacted 303 in an inert atmosphere and at a temperature of less than 450 “Celsius with an amount of liquid sodium in excess of the stoichiometric amount thereof required for a redox reaction between the liquid sodium and iron oxide from the iron ore. This reaction precipitates out from the liquid sodium both iron and other insoluble products comprising sodium oxide. In this embodiment, the iron and the other insoluble products are firstly separated 305 as a solid phase from the liquid sodium before the iron and the other insoluble products are then separated 304a from each other in a "dry” solid-species separation. Fig. 2 shows a second embodiment of a method 300b of producing iron from such an iron ore. As in the method 300a, the ore is comminuted 301 , and dehydrated and dehydroxylated 302, before being introduced to react 303 with the liquid sodium. In this embodiment, the liquid sodium is produced by firstly fusing and electrolysing 101 b solid sodium chloride, for example in a Downs cell, which also produces chlorine gas as a co-product. Since this electrolysis gives the liquid sodium a temperature of about 600 “Celsius, the sodium is then cooled 309a before being introduced to react 303 with the ore by circulating it through pipework of a heat exchanger surrounding and / or contained within a dryer of the ore. This heats 308 the ore in the dryer, thereby helping to dehydrate and dehydroxylate it, as well as cooling 309a the liquid sodium to a temperature which is below the top of the range of available operating temperatures for reacting 303 it with the ore. As in the method 300a, the iron and the other insoluble products from this reaction are then separated 305 as a solid phase from the liquid sodium before the iron and the other insoluble products are separated 304a from each other in a "dry” solid-species separation.
[0215] Fig. 3 shows a third embodiment of a method 300c of producing iron from an iron ore when the ore comprises at least 5% by weight of magnetite. As in the methods 300a, 300b, the ore is comminuted 301 into fines, and dehydrated and dehydroxylated 302, before being introduced to react 303 with the liquid sodium. However, to inhibit further oxidation of the magnetite, dehydration and dehydroxylation 302 of the ore are conducted 302a in a deoxygenated atmosphere in comparison to atmospheric air by enclosing the ore within a dryer having a controlled atmosphere. In this embodiment, at least some of the heat required to dehydrate and dehydroxylate the ore is provided by a counterflow system within the dryer, whereby dehydrated and dehydroxylated hot ore leaving the dryer is cooled 309b by transferring 308 heat to ore which enters the dryer at closer to ambient temperature. After the subsequent reaction 303 of the ore with the liquid sodium, in this embodiment, the iron is separated 304b from the other insoluble products in a "wet” solid-species separation, whilst both are still suspended or entrained in the liquid sodium. The iron is then phase separated 305a from the liquid sodium, and the other insoluble products are phase separated 305b from the liquid sodium, in two separate process streams.
[0216] Fig. 4 shows a fourth embodiment of a method 300d of producing iron from an iron ore when the ore comprises red bauxite. The method 300d comprises comminuting 301 the bauxitic ore into fines and drying and dehydroxylating 302 the ore, wherein dehydration and dehydroxylation 302 of the ore comprise heating 302b the ore to at least 250 “Celsius in an oxygenated atmosphere. This causes organic matter mixed in with the ore to auto-ignite and combust 307. However, the oxygenated atmosphere is closed off from the surrounding environment, so that carbon dioxide gas produced by this combustion is captured 306 and is not released into the environment. As in the method 300a, the ore particles are then reacted 303 with liquid sodium, and the iron and the other insoluble products precipitated out from this reaction are firstly separated 305 as a solid phase from the liquid sodium, before the iron and the other insoluble products are separated 304a from each other. The other insoluble products are then passed 311 through the atmosphere of the dryer, to which the ore is exposed. The hot sodium oxide in the other insoluble products reacts 312 with the captured carbon dioxide gas to produce at least sodium carbonate. Fig. 5 shows a fifth embodiment of a method 300e of producing iron from an iron ore, in which the iron is present as at least one of the mineral and mineraloid forms of iron oxide and oxyhydroxide. As before, the method 300e comprises comminuting 301 and drying and dehydroxylating 302 the ore, before reacting 303 the ore with liquid sodium in an inert atmosphere. In this embodiment, comminuting 301 the ore does not change the chemical composition of the ore very much, so drying and dehydroxylating 302 the iron ore comprises heating 302c the ore to a temperature of between 100 and 600 “Celsius, inclusive. The temperature of the reaction 303 is also controlled 313 by cooling 309c the liquid sodium from which the iron and the other insoluble products have been separated 305 following this reaction, and then returning 314 at least some of the cooled liquid sodium to the reaction in a loop or circuit. Before returning it to the reaction 303, the liquid sodium is cooled 309c by being circulated through pipework of a heat exchanger surrounding and / or contained within a dryer of the ore. Heat from the liquid sodium is used to heat 308 the ore in the dryer to the desired temperature. Adjusting 315 a flow rate of the liquid sodium in this cooling circuit also allows the temperature of the reaction 303 to be controlled 313 to remain below 450 “Celsius. The flow rate of the liquid sodium may be adjusted 315 by such things as an initial choice of how much liquid sodium in excess of the stoichiometric amount thereof required for the reaction 303 is used and / or an initial choice of the diameter of the pipework. Alternatively or additionally, a pumping rate for the liquid sodium around the cooling circuit may be varied. Following separation 305 of the iron and the other insoluble products as a solid phase from the liquid sodium, the iron and the other insoluble products are then separated 304a from each other, as before.
[0217] Fig. 6 shows a sixth embodiment of a method 300f of producing iron from such an iron ore. In this embodiment, after comminution 301 , dehydration and dehydroxylation 302, and reaction 303 of the ore with the liquid sodium, separating 304b the iron from the other insoluble products comprises applying 316 a magnetic field gradient to the liquid sodium with the iron and the other insoluble products suspended or entrained therein. In this embodiment, the magnetic field gradient has a non-zero component in a vertical direction, such that the strength of the magnetic field increases downwardly. Thus a difference in buoyancy in the liquid sodium between the iron (density, p(Fe) = 7.87 g cm3) and the less dense other insoluble products from the reaction 303 (p(Na2O) = 2.27 g cm3; p(SiC>2) = 2.65 g cm3; p(Al2O3) = 3.99 g cm3) is enhanced by the magnetic field gradient. Magnetic separation 304b of the iron from the other insoluble products therefore commences as soon as the reaction products are created. Following their magnetic separation 304b, the iron is separated 305a as a solid phase from the liquid sodium, and the other insoluble products are also separated 305b as a solid phase from the liquid sodium, in two separate process streams. Whereas in the present embodiment the magnetic field gradient is applied with a non-zero component in a vertical direction, such that the strength of the magnetic field increases downwardly, in other possible embodiments, the magnetic field gradient may be applied in other directions. For example, if separating 304b the iron from the other insoluble products comprises a centrifugal separation process, their degree of separation may be enhanced by applying a magnetic field gradient to the liquid sodium with the reaction products suspended or entrained therein in a radial direction, with the strength of the magnetic field increasing outwardly, so that the strength of the magnetic field increases in a direction parallel to a centrifugal force applied to the reaction products.
[0218] Fig. 7 shows a seventh embodiment of a method 300g of producing iron from such an iron ore, wherein at least some of the iron is then used to make steel. As before, the ore is comminuted 301 , and dehydrated and dehydroxylated 302, before reacting 303 with liquid sodium. In this embodiment, the iron and the other insoluble products are firstly separated 305 as a solid phase from the liquid sodium before the iron and the other insoluble products are then separated 304a from each other in a "dry” solid-species separation. In other possible embodiments, however, the iron could instead be separated from the other insoluble products in a "wet” solidspecies separation, whilst both are still suspended or entrained in the liquid sodium, after which the iron could then be phase separated from the liquid sodium. In any case, thereafter, a proportionately small amount of powdered carbon is added 337 to the iron which has been separated from the other insoluble products and from the liquid sodium. The amount of carbon added 337 to the iron is determined by the desired properties of the steel to be produced. If desired, one or more other alloying elements may be added to the iron at this stage as well. This small admixture of carbon, as well as of any possible other alloying elements, are then thoroughly mixed 338 together with the iron to result in a powdered mixture. The resulting powdered mixture is then subjected 339 to a powder metallurgical process to produce steel. For example, the powder metallurgical process may comprise cold pressing the resulting powdered mixture to produce a "green” article, which is then heated to above the Tammann temperature of the iron to sinter the powdered mixture and create a finished steel product.
[0219] Fig. 8 shows an eighth embodiment of a method 300h of producing iron from such an iron ore. In this embodiment, the ore is comminuted 301 , and dehydrated and dehydroxylated 302, before reacting 303 with liquid sodium, as before. The iron is separated 304b from the other insoluble products using a "wet” separation technique, and then the iron and the other insoluble products are each phase-separated 305a, 305b from the liquid sodium, in two separate process streams. The hot other insoluble products, which comprise sodium oxide, are then cooled 309d significantly closer to ambient temperature, for example using a heat transfer fluid, and at least some of the heat extracted from the other insoluble products is used 308 to help dehydrate and dehydroxylate 302 the ore. The method 300h further comprises adding 317 at least some of the other insoluble products to liquid water, thereby hydrating the sodium oxide in the other insoluble products, to produce an aqueous solution of sodium hydroxide having a final concentration of less than 2.5 M. Helped by the prior cooling of the other insoluble products, the temperature of this solution can be controlled to remain below 85 “Celsius, for example by using a technique as described below in relation to Fig. 12A. The method 300h then comprises separating 318 undissolved solids, such as silica and alumina, as a solid phase from the aqueous solution of sodium hydroxide, which is dried 319 to produce solid sodium hydroxide. At least some of the solid sodium hydroxide is then used 320 to produce liquid sodium, whilst also producing gaseous hydrogen and oxygen as co-products. This may be done, for example, by fusing and electrolysing it using the Castner process and / or by thermochemically decomposing it into its constituent elements, as described in UK patent application no. 2517327.9 ("Method and Apparatus for Producing Liquid Sodium”; applicant's ref: NE-P-GB 011) mentioned previously. Since this electrolysis gives the liquid sodium a temperature of about 330 “Celsius, at least some of the liquid sodium is then recycled 321 back to react 303 with more iron ore again, without needing any further heating or cooling.
[0220] Fig. 8 also shows a possible variant of the eighth embodiment, which is represented in Fig. 8 by reference numerals in parentheses and elements shown in dashed lines. In this variant, the iron ore is a bauxitic ore, dehydration and dehydroxylation 302 of the bauxitic ore is conducted by heating 302b the ore to at least 250 “Celsius in an oxygenated atmosphere closed off from its surrounding environment to combust 307 organic matter mixed in with the ore, and the redox reaction 303 is conducted 303a at a temperature of at least 320 “Celsius. According to this variant embodiment, the method 300h further comprises fusing and electrolysing 340 at least some of the undissolved solids separated 318 from the aqueous solution of sodium hydroxide to extract aluminium from them. Whereas this variant of the eighth embodiment also comprises capturing 306 carbon dioxide gas produced by combusting 307 organic matter mixed in with the bauxitic ore, these additional features of this possible variant have only been omitted from Fig. 8 for improved clarity and ease of illustration.
[0221] Fig. 9 shows a ninth embodiment of a method 300I of producing iron from an iron ore in which the iron is present as at least one of the mineral and mineraloid forms of iron oxide and oxyhydroxide, and the ore comprises a silicate mineral, which remains in the ore added to the liquid sodium after the ore has been comminuted, dehydrated and dehydroxylated. The method 300I initially comprises the same processes 301 , 302, 303, 304b, 305a, 305b and 309d as the method 300h of Fig. 8, except that the redox reaction 303b of the comminuted, dehydrated and dehydroxylated ore with the liquid sodium is conducted at a temperature of less than about 300 “Celsius. This ensures that silica derived from the silicate mineral in the ore remains in the other insoluble products of the redox reaction 303b and is not dissolved in the liquid sodium as sodium orthosilicate, for example. Following cooling 309d of the other insoluble products, the method 300I then comprises adding 341 liquid water to at least some of the other insoluble products, thereby hydrating the sodium oxide therein, to produce a hot aqueous solution of sodium hydroxide having a final concentration of at least 2.5 M. This aqueous solution of sodium hydroxide reacts 342 with the silica in the other insoluble products to dissolve at least some of the silica therein and produce an aqueous solution of sodium silicate. Next, the aqueous solution of sodium silicate is dried 343 to produce a solid phase comprising the sodium silicate. In this embodiment, at least some of this solid phase is subsequently used 344 as an alkaline activator for an alkaline activated or geopolymer cement. For example, this may be done by adding water to the solid phase at the time of its use in the presence of an activated clay, in order to rehydrate the sodium silicate in the solid phase. However, such use 344 does not have to follow immediately after the solid phase has been produced, and may be preceded by an intervening storage period and / or transport of the solid phase to another location, such as a building site, for example.
[0222] Figs. 10A and 10B together show a tenth embodiment of a method 300j of producing iron from an iron ore when the ore comprises red bauxite including a silicate mineral. In the method 300j, comminution 301 of the ore, its dehydration and dehydroxylation 302b, reaction of the ore with liquid sodium, and the subsequent phase separation 305 and solid-species separation 304a of the reaction products and excess sodium, all proceed as in the method 300d of the fourth embodiment, except that in the method 300j, the reaction 303a of the ore with the liquid sodium is conducted at more than about 350 “Celsius, to induce a reaction between sodium oxide produced by the redox reaction 303a and silica derived from the silicate mineral in the ore, to produce at least sodium orthosilicate, which dissolves in the liquid sodium. In addition, the method 300j comprises adding water 322 as pressurized steam to at least some of the other insoluble products, which hydrates the sodium oxide they contain. Enough steam is added to produce an aqueous solution of sodium hydroxide having a final concentration of from 2.5 M to 7.5 M, inclusive, which is kept in liquid phase under pressure at a temperature between 210 and 280 “Celsius, inclusive. The aqueous solution of sodium hydroxide is allowed to react 323 with alumina in the other insoluble products to dissolve at least some of it in the sodium hydroxide as sodium aluminate. To remove contaminants also dissolved in the sodium hydroxide, calcium oxide is then added 324 to the aqueous solution to precipitate these contaminants out from the aqueous solution as insoluble calcium compounds. The method 300j then comprises separating 325 at least some of the aqueous solution from undissolved solids to produce a remaining solution and a slurry at least comprising these insoluble calcium compounds. The remaining solution is then cooled 326 to between 85 and 55 “Celsius and depressurized back to atmospheric pressure, diluted 327 with water and seeded with crystals of AI(OH)3 to precipitate out aluminium hydroxide. This aluminium hydroxide is washed 328 with water and dried, before being thermally decomposed 329 into alumina and water vapour. The remaining solution from which the precipitated aluminium hydroxide has been removed is used 330 as a chemical reagent in another process, such as that described in the present applicant's UK patent application no. 2417079.7 ("Method and Apparatus for Producing Oxides of Calcium, Magnesium and Iron from Carbonate Mineral Ores without Burning Carbonaceous Fuels”; applicant's ref: NE-P-GB 005). Meanwhile, the pH of the slurry is neutralized 331 by injecting the slurry with carbon dioxide gas, and any calcium sulphite present in the slurry is oxidized 332 to calcium sulphate using manganese as a catalyst. The slurry is then dried and compacted 333 to produce a solid-phase end-product.
[0223] Fig. 11 shows an eleventh embodiment of a method 300k of producing iron from an iron ore when the ore again comprises red bauxite and the ore also comprises a significant proportion of a silicate mineral. The method 300k therefore differs from the method 300j of Figs. 10A and 10B in the following respects. Firstly, after comminution 301 of the iron ore (not shown in Fig. 11 for the sake of conciseness) and its dehydration and dehydroxylation 302b at sufficiently high temperature to combust any organic matter mixed therein, iron oxide, in the form of mill scale, is added 345 to the redox reaction 303a with the liquid sodium, along with the comminuted, dehydrated and dehydroxylated ore. This therefore increases the proportion of iron oxide in the reaction mixture than that provided just by the ore, which in turn increases the proportion of sodium oxide produced by the redox reaction 303a. The redox reaction 303a is conducted at more than about 350 “Celsius to induce a reaction between this sodium oxide and silica derived from the silicate mineral, to produce at least sodium orthosilicate, which dissolves in the liquid sodium. Phase separation 305 and separating 304a the iron from the other insoluble products then proceed as in the method 300j to extract the elemental iron from the excess liquid sodium and other reaction products. The excess liquid sodium with sodium silicate(s) dissolved therein may be processed as described in the present applicant's UK patent application no. 2417073.0 ("Method and Apparatus for Producing an Alkaline Mixture comprising Sodium Silicate”; applicant's ref: NE-P-GB 009), mentioned previously.
[0224] The silica content of the ore has already been removed from the other insoluble products remaining after the solidspecies and phase separations 304a, 305 by conducting 303a the redox reaction at more than about 350 “Celsius. The BCP therefore substantially consists of only sodium oxide produced by the redox reaction, alumina and any other unreactive gangue species present in the ore originally, such as titania (TIO2). This BCP is processed by the method 300k without adding any lime to the BCP in aqueous solution, unlike the method 300j of Figs. 10A and 10B. The method 300k therefore next comprises adding water 322 as pressurized steam to the BCP. This hydrates the sodium oxide in the BCP to produce an aqueous solution of sodium hydroxide having a final concentration of from 2.5 M to 7.5 M, inclusive, which is kept in liquid phase under pressure at a temperature between 210 and 280 “Celsius, inclusive. This sodium hydroxide is then allowed to react 323 with the alumina in the BCP to dissolve at least some of it therein as sodium aluminate. The method 300k then comprises phase separating 325 at least some of this aqueous solution from the other unreactive gangue species like titania, to produce a remaining solution of sodium hydroxide with alumina dissolved therein as sodium aluminate, and a solid phase comprising the titania. The remaining solution is then subjected to the same processes 326, 327, 328, 329 as described above in relation to Figs. 10A and 10B (not shown in Fig. 11 for conciseness) to extract the alumina therefrom. The solid phase comprising the titania may be used as a feedstock for the production of titanium, which may be extracted from it using known techniques, or as a feedstock for the production of titanium aluminide, for example.
[0225] In Fig. 11 , the proportion of alumina in the bauxitic ore (at 34 mol %) is much higher than that of iron oxide (only 8.8 mol %). Thus reduction of this iron oxide by the liquid sodium in the redox reaction 303a cannot create sufficient sodium oxide both to dissolve the silica from the ore (at 8.5 mol %) as sodium silicate(s) in the liquid sodium and leave enough sodium oxide to produce an aqueous solution of sodium hydroxide having sufficient concentration to dissolve 323 the alumina therein as sodium aluminate. However, this problem is solved in the method 300k by adding 345 mill scale to the redox reaction 303a. This increases the proportion of iron oxide in the reaction mixture, which therefore also increases the amount of sodium oxide produced. Thus after the silica from the ore has dissolved in the liquid sodium as sodium silicate(s), enough sodium oxide still remains to produce an aqueous solution of sodium hydroxide of sufficient concentration to dissolve 323 all the alumina therein. Moreover, the yield of iron produced by the redox reaction 303a in also increased at the same time. This same problem may be solved in one of several ways, as follows. For example, as well as or instead of mixing the bauxitic ore with one or more iron oxide(s) from another source, such as with mill scale, another iron ore having a higher ratio of iron oxide(s) to alumina, such as ore from a BIF, may be mixed with the bauxitic ore to achieve a higher overall ratio of iron oxide(s) to alumina, before these mixed ores are then introduced to the redox reaction 303a together. Alternatively or additionally, the BCP produced by reduction of the iron oxide in the bauxitic ore during the redox reaction 303a, which therefore has a composition as in the bottom-righthand cell of Table 4, may be mixed with BCP from the top- righthand cell of Table 4, to give a higher overall ratio of sodium oxide to alumina, before the mixed BCPs are hydrated 322 together.
[0226] Fig. 12A shows a twelfth embodiment of a method 300m of producing iron from an iron ore, in which the iron is present as at least one of the mineral and mineraloid forms of iron oxide and oxyhydroxide. The method 300m comprises all the same processes as either the method 300j of Figs. 10A and 10B or the method 300k of Fig. 11. In addition, however, the method 300m further comprises cooling 334 the hydration reaction 322 to keep the temperature of the resulting aqueous solution of sodium hydroxide in the desired temperature range of from 210 to 280 “Celsius, inclusive. At least some of the heat extracted from this hydration reaction 322 is then used 308 to help dehydrate and dehydroxylate 302 the iron ore. In another possible embodiment, a similar technique may be used to extract heat from the hydration reaction 317 in the method 300h of Fig. 8 to keep the temperature of the resulting aqueous solution of sodium hydroxide below 85 “Celsius.
[0227] Fig. 12B shows a thirteenth embodiment of a method 300n of producing iron from such an iron ore. The method 300n firstly comprises capturing 306 carbon dioxide gas. The carbon dioxide may be captured from atmospheric air and / or from an industrial process, such as from the combustion of organic matter mixed in with the iron ore itself, as described above. The method 300n then comprises reacting 312 the captured carbon dioxide with at least some of the sodium oxide in the other insoluble products from the reaction 303 between the iron ore and the liquid sodium, to produce at least sodium carbonate. In the present embodiment, this sodium oxide is not separated from other gangue species which may also be present in the other insoluble products, before the carbon dioxide reacts 312 with the sodium oxide. Thus after this carbonation reaction 312, the sodium carbonate is mixed with other gangue species like silica and alumina, making it suitable for use 336 as an ingredient in the manufacture of soda-lime glass, if combined in desired proportions with other ingredients like sand and lime. In other possible embodiments, however, if a purer form of sodium carbonate is required for another application, the carbon dioxide may instead be reacted with the sodium oxide after the latter has been separated from other gangue species in the other insoluble products, or with sodium hydroxide derived from hydrating at least some of this sodium oxide, using a technique such as those described above in relation to Fig. 8, Figs. 10A and 10B or Fig. 11. In any case, since the carbonation reaction 312 is strongly exothermic, the method 300n further comprises cooling 335 this carbonation reaction 312, and using 308 at least some of the heat extracted from it to help dehydrate and dehydroxylate 302 the iron ore.
[0228] Fig. 13 schematically shows a first embodiment of an apparatus 3a for producing iron from an iron ore, in which the iron is present as at least one of the mineral and mineraloid forms of iron oxide and oxyhydroxide. The apparatus 3a comprises a comminution device 2, a dryer 4, a gas-tight first reaction vessel 130, a solid-species separator 180a, and first and second phase separating devices 190a, 190b. The comminution device 2 is for comminuting the iron ore into fines and the dryer 4 is for dehydrating the ore and dehydroxylating hydroxylated compounds contained therein. The iron ore is fed firstly to the comminution device 2 and from there to the dryer 4. Water vapour and other gases like sulphur dioxide are liberated from the ore in the dryer 4. The sulphur dioxide may be captured using a known technique for scrubbing flue gases.
[0229] The first reaction vessel 130 comprises a first inlet 131 for receiving the comminuted, dehydrated and dehydroxylated ore and a second inlet 132 for liquid sodium. The first reaction vessel 130 is for reacting the ore in an inert atmosphere and at a temperature of less than 450 “Celsius with an amount of liquid sodium which is in excess of the stoichiometric amount thereof required for a redox reaction between the liquid sodium and iron oxide from the iron ore. For example, the first reaction vessel 130 may contain a bath of liquid sodium to which the ore is added. Liquid sodium consumed in the reaction is replenished by fresh liquid sodium introduced via the second inlet 132, in order to maintain the level of liquid sodium in the first reaction vessel 130 roughly constant. The first reaction vessel 130 also comprises an outlet 134 for the liquid sodium with iron and other insoluble products comprising sodium oxide produced by the reaction entrained therein.
[0230] By way of example, the first reaction vessel 130 may have a generally cylindrical shape and an internal capacity of about 1 .5 to 2 m3, designed to hold a bath of liquid sodium of about 1 .25 m3(« 50 kmol) in volume, for receiving enough iron ore fines to contain about 160 kg (« 1 kmol) of Fe2Oa and 6 kmol of fresh liquid sodium at the same rate as that at which the Fe2Oa and liquid sodium are consumed by the reaction of Eqn. 5, therefore generating 438 MJ of heat at the same rate. In such a case, the bath of liquid sodium provides enough thermal inertia to absorb and distribute the heat thus generated, whereby the temperature of the reaction may be maintained within its desired range of operating temperatures using one of the techniques for circulating the liquid sodium described below in relation to Figs. 16 and 17, for example. The dimensions of the reaction vessel 130 and of any associated pipework may be scaled up or down using this particular example as a guide.
[0231] The first reaction vessel 130 is sealed in a gas-tight manner from its surrounding environment to prevent the liquid sodium it contains from reacting with oxygen from atmospheric air. A head space in the reaction vessel 130 above the bath of liquid sodium is filled with an atmosphere consisting of one or more inert gases, such as nitrogen and / or argon. Either nitrogen or argon, or both, may be produced on site by pressure swing adsorption (PSA) of atmospheric air. An on-site PSA generator of inert gas may be powered using waste heat from the first reaction vessel 130 itself or from another source.
[0232] To prevent atmospheric oxygen from being introduced into the first reaction vessel 130 whenever the vessel is fed with iron ore, in this embodiment, the first inlet 131 comprises an airlock 20, which is schematically shown in Fig. 14. The airlock 20 comprises two gas-tight doors 21 , 22. The first such door 21 connects an interior 25 of the airlock 20 with the surrounding environment E, whereas the second such door 22 connects the interior 25 of the airlock 20 with an inside 135 of the first reaction vessel 130. The airlock 20 also comprises an inlet 23 to the interior 25 of the airlock 20 for inert gas and an outlet 24 from the interior 25 of the airlock 20 for atmospheric air. The inlet 23 and the outlet 24 each comprises a respective valve 23V, 24V for opening and closing a respective one of the inlet 23 and the outlet 24. To introduce a fresh charge of ore via the airlock 20 into the first reaction vessel 130, the first gas-tight door 21 is opened and the ore particles are introduced into the interior 25 of the airlock 20, whilst the second gas-tight door 22 is kept closed. The first door 21 is then closed again and the interior 25 of the airlock 20 is flushed with inert gas by opening the valve 23V, and then also opening the valve 24V to purge atmospheric air from the airlock 20 via outlet 24. Both valves 23V, 24V are then closed again, before the second door 22 is opened to introduce the ore into the first reaction vessel 130, whilst the first gas-tight door 21 is kept closed. The second gas-tight door 22 is then closed again, and the airlock 20 is ready to be used again, to introduce another charge of iron ore into the reaction vessel 130.
[0233] To prevent the first reaction vessel 130 from being pressurized by inert gas which enters the reaction vessel 130 from the interior 25 of the airlock 20 together with the ore, by reason of the inert gas expanding as it heats up from the temperature of the surrounding environment E to the temperature inside 135 the first reaction vessel 130, the inert gas may be preheated before it is injected via inlet 23 into the airlock 20 to the same temperature as the temperature of the atmosphere of inert gas inside 135 the reaction vessel 130. This may be done using waste heat from the first reaction vessel 130 itself or from another source. For example, as shown in Fig. 14, the inert gas may be heated by liquid sodium from the first reaction vessel 130, via a heat exchanger HE6. Preheating the inert gas also has the advantage that it pressurizes the inert gas before it is injected into the airlock 20, thereby avoiding the need for the inert gas to be pumped into the airlock 20 and helping to purge the atmospheric air from the interior 25 of the airlock 20.
[0234] The first reaction vessel 130, which is a stirred tank reactor, is made of steel of a type normally used for containing and transporting liquid sodium. An interior surface of the first reaction vessel 130 comprises a sacrificial layer to accommodate corrosion caused by sodium oxide produced by the reaction. Liquid sodium introduced into the reaction vessel 130 establishes a gradient of concentration of dissolved species in the sodium bath, from the purest liquid sodium at the second inlet 132 to the highest concentration of dissolved species at the outlet 134. For safety, the first reaction vessel 130 may also comprise an overflow outlet for liquid sodium, as well as a pressure relief valve. This is preferably located at or near the top of the head space in the reaction vessel 130, not only to relieve excess pressure, but also to vent any light gases, such as hydrogen, which would tend to collect there.
[0235] In the embodiment of Fig. 13, the undissolved reaction products are then subjected to a "wet” separation technique, in which the iron is separated from the other insoluble products whilst both are still suspended in liquid sodium, before phase separation of the iron from the liquid sodium and phase separation of the other insoluble products from the liquid sodium is conducted in two different process streams. Thus the solid-species separator 180a for carrying out this "wet” separation comprises an inlet 181 connected to the outlet 134 of the first reaction vessel 130 and two outlets 184, 185, respectively for liquid sodium with entrained iron, and for liquid sodium with entrained sodium oxide and gangue. The solid-species separator 180a may be of a type normally used to separate iron from a flow of entrained particles, such as a wet drum magnetic separator, except that the components of the separator should be made of materials suitable for containing and transporting liquid sodium. A series of such separators may be used to increase the separation efficiency. The outlet 184 of the solid-species separator 180a is connected to an inlet 191 a of the first phase separating device 190a, and the outlet 185 is connected to an inlet 191 b of the second phase separating device 190b. The first phase separating device 190a, for separating the iron from the liquid sodium, therefore comprises a first outlet 194a for liquid sodium and a second outlet 195a for iron, whereas the second phase separating device 190b, for separating the other insoluble products from the liquid sodium, comprises a first outlet 194b for liquid sodium and a second outlet 195b for sodium oxide and gangue. The present applicant's UK patent application no. 2417052.4, ("Apparatus and Method for Separating a Contaminant from Liquid Metal”; applicant's ref: NE-P-GB 002) mentioned above, shows and describes suitable phase separating devices 190a, 190b. In this embodiment, the liquid sodium from the outlets 194a, 194b is then combined into a single stream, which is cooled, before being recycled to join fresh liquid sodium entering the first reaction vessel 130 via its second inlet 132.
[0236] Fig. 15 schematically shows a second embodiment of an apparatus 3b for producing iron from such an iron ore. The apparatus 3b comprises a comminution device 2, a dryer 4, a gas-tight first reaction vessel 130, a solid-species separator 180b and a solid-liquid sodium phase separator 190. The comminution device 2, dryer 4 and first reaction vessel 130 are arranged and function as described above in relation to Fig. 13. In this embodiment, however, the phase separator 190 comprises an inlet 191 connected to the outlet 134 of the first reaction vessel 130, a first outlet 194 for liquid sodium and a second outlet 195 for the undissolved reaction products. The phase separator 190 is therefore arranged to receive the undissolved reaction products from the first reaction vessel 130 and to separate them as a solid phase from the liquid sodium in a single process stream. A suitable solid-liquid sodium phase separator 190 is again shown and described in UK patent application no. 2417052.4 ("Apparatus and Method for Separating a Contaminant from Liquid Metal”; applicant's ref: NE-P-GB 002), mentioned previously. The liquid sodium from the first outlet 194 is cooled and recycled to join fresh liquid sodium entering the first reaction vessel 130 via its second inlet 132. The iron and the other insoluble products from the second outlet 195 are then separated from each other by the solid-species separator 180b in a "dry” magnetic separation.
[0237] The solid-species separator 180b comprises an inlet 181 connected to the second outlet 195 of the solid-liquid sodium phase separator 190, a first outlet 186 for iron and a second outlet 187 for the other insoluble products. The solid-species separator 180b receives the iron and the other insoluble products mixed together, using inert gas as a transport medium. This avoids oxidation of the iron, which is likely to be finely divided and therefore to have a high surface area, and may also still be very hot, making it susceptible to reoxidation if brought into contact with atmospheric air before it has had an opportunity to cool down. The solid-species separator 180b may, for example, be a cyclonic separator comprising an underflow outlet, which provides the first outlet 186 for iron, and an overflow outlet, which provides the second outlet 187 for the other insoluble products. In the solid-species separator 180b, the flow of material from the solid-liquid sodium phase separator 190 also passes through a magnetic field to enhance the separation of the iron from the other insoluble products. A series of such separators may be used to increase the separation efficiency still further. In this embodiment, the apparatus 3b further comprises a first valve V1 , a second reaction vessel 140 and a carbonation vessel 160. The second reaction vessel 140 comprises first, second and third inlets 141 , 142, 143, respectively, and first and second outlets 144 and 145, respectively. The carbonation vessel 160 comprises first and second inlets 162 and 163, respectively, and an outlet 166. The second outlet 145 of the second reaction vessel 140 is connected via a second valve V2 to the first inlet 162 of the carbonation vessel 160. The second outlet 187 of the solid-species separator 180b is connected to the first valve V1 , which divides the other insoluble products into a first portion and a second portion. The first valve V1 passes the first portion to the third inlet 143 of the second reaction vessel 140 and the second portion to the second inlet 163 of the carbonation vessel 160.
[0238] By way of example, the second reaction vessel 140 contains a series of chemical reactions which consume the sodium oxide in the first portion, along with other reagents R1 , R2 introduced into the second reaction vessel 140 via the first and second inlets 141 , 142 thereof. These reactions produce an aqueous solution, which is retained in the second reaction vessel 140, a precipitate Ppt, and carbon dioxide gas. The precipitate Ppt leaves the second reaction vessel 140 via the first outlet 144 thereof, mixed with gangue species like silica and alumina from the first portion. The carbon dioxide is released from the second outlet 145 of the second reaction vessel 140 by opening the second valve V2 into the carbonation vessel 160. For example, the carbonation vessel 160 may comprise a fluidized bed reactor containing the second portion, into which the carbon dioxide gas is introduced. In the carbonation vessel 160, the carbon dioxide reacts with the hot sodium oxide in the second portion to produce at least sodium carbonate, which leaves the carbonation vessel 160 via the outlet 166 thereof. Thus carbon dioxide produced by the series of chemical reactions in the second reaction vessel 140 is captured and mineralized as sodium carbonate in the carbonation vessel 160. The sodium carbonate thus produced, since it is mixed with gangue species like silica and alumina from the second portion, is suitable for use as an ingredient in the manufacture of soda-lime glass, if combined in desired proportions with other ingredients like sand and lime.
[0239] Fig. 16 schematically shows a third embodiment of an apparatus 3c for producing iron from such an iron ore. The apparatus 3c comprises a comminution device 2, a dryer 4, a gas-tight first reaction vessel 130, a solid-species separator 180b and a solid-liquid sodium phase separator 190, all of which are arranged and function as described above in relation to Fig. 15, except as follows. In this embodiment, fresh liquid sodium is produced by fusing and electrolysing solid sodium chloride, for example in a Downs cell. This liquid sodium therefore has a temperature immediately after it is produced of about 600 “Celsius. In order to cool the liquid sodium to a temperature within the range of operating temperatures for the reaction of Eqn. 5, the apparatus 3c further comprises pipework 5, which circulates the liquid sodium around the dryer 4 before it enters the first reaction vessel 130 via the second inlet 132 thereof. In addition, liquid sodium from the first outlet 194 of the solid-liquid sodium phase separator 190, which may therefore have a temperature of about 400 “Celsius, is routed to combine and mix with the fresh liquid sodium at about 600 “Celsius to reach an intermediate temperature dependent on their relative proportions, before the combined liquid sodium passes through the pipework 5. Thus the liquid sodium can be cooled from this intermediate temperature to a temperature within the range of operating temperatures for the reaction of Eqn. 5 and the iron ore within the dryer 4 can simultaneously be heated by the pipework 5 to a sufficient temperature to dehydrate and dehydroxylate it. For example, if the iron ore enters the dryer 4 at an initial temperature after comminution of about 50 “Celsius, the ore and the liquid sodium may reach thermal equilibrium within the dryer 4 at a temperature of about 275 “Celsius, which each therefore carries with them into the first reaction vessel 130, before meeting in the exothermic reaction of Eqn. 5.
[0240] Fig. 17 schematically shows a fourth embodiment of an apparatus 3d for producing iron from such an iron ore. The apparatus 3d comprises a comminution device 2, a dryer 4, a gas-tight first reaction vessel 130, a solid-species separator 180b and a solid-liquid sodium phase separator 190, all of which are arranged and function as described above in relation to Fig. 15, except as follows. In this embodiment, fresh liquid sodium is produced by fusing and electrolysing solid sodium hydroxide, for example in a Castner cell. This liquid sodium therefore has a temperature immediately after it is produced of about 330 “Celsius, which is already within the range of operating temperatures for the reaction of Eqn. 5, so does not need cooling significantly before it is introduced into the first reaction vessel 130. However, the apparatus 3d further comprises pipework 5, which circulates liquid sodium from the first outlet 194 of the phase separator 190, and which therefore has a temperature of about 400 “Celsius, around the dryer 4, before this liquid sodium is routed to combine with the fresh liquid sodium. For example, if the iron ore enters the dryer 4 at a temperature after comminution of about 50 “Celsius, the ore and the liquid sodium from the phase separator 190 may reach thermal equilibrium within the dryer 4 at about 200 “Celsius. This liquid sodium then combines and mixes with the fresh liquid sodium at about 330 “Celsius to reach an intermediate temperature dependent on their relative proportions, before the combined liquid sodium enters the first reaction vessel 130 via the second inlet 132 thereof. Thus the liquid sodium enters the first reaction vessel 130 at a temperature within the range of operating temperatures for the reaction of Eqn. 5 and the iron ore can simultaneously be heated by the pipework 5 to a sufficient temperature to dehydrate and dehydroxylate it before it also enters the first reaction vessel 130 via the first inlet 131 thereof.
[0241] Whereas the apparatuses 3c and 3d in the embodiments of Figs. 16 and 17 both use a "dry” separation technique to separate the iron from the other insoluble products, as in the embodiment of Fig. 15, the same alternative possibilities for cooling the liquid sodium and heating the iron ore within the dryer 4 via pipework 5 may equally well be applied to an apparatus which uses a "wet” separation technique instead, as in the embodiment of Fig. 13. Thus the temperature of the reaction of Eqn. 5 may be controlled to remain within its desired range of operating temperatures by varying at least one of the flow rate of liquid sodium through the pipework 5, the cross-sectional area of the pipework 5 and the amount of liquid sodium in excess of the stoichiometric amount thereof required for the reaction of Eqn. 5.
[0242] Fig. 18 schematically shows an embodiment of a dryer 4 suitable for use in an apparatus of the invention. The dryer 4 comprises an entry 6 and an exit 7 located in proximity to each other at one end of the dryer 4. The entry 6 and exit 7 may each be provided with spring-loaded doors and / or curtains to help maintain and control an atmosphere within the dryer 4. The atmosphere within the dryer 4 may also be held at a pressure below that of atmospheric air outside the dryer 4, to draw air in through the entry 6 and / or exit 7 and thereby hinder or prevent the release of gases from within the dryer 4 via the entry 6 and / or exit 7. Iron ore 1 at or close to ambient temperature enters the dryer 4 via the entry 6 on a first conveyor 8a and travels towards a hot zone 9 located at an opposite end of the dryer 4 from the entry 6 and exit 7. The hot zone 9 comprises means for heating the ore 1 , such as pipework 5 described above. This establishes a temperature gradient from the entry 6 and exit 7, increasing along the dryer 4 towards the hot zone 9 at the opposite end thereof. A fan 10 mounted in a duct 11 extracts water vapour and other gases, such as sulphur dioxide, driven off from the heated iron ore through a vent 12 also located in the hot zone 9. This reduces the partial pressure of these gases within the dryer 4, which promotes dehydration, dehydroxylation and desulphurization of the ore 1. The fan 10 can also be used to maintain the total pressure within the dryer 4 below that of the air outside the dryer 4 by overcompensating for the increased pressure of the atmosphere within the dryer 4 caused by its expansion on heating. The dryer 4 also comprises an inlet 13, whereby, for example, dry air or inert gas may be introduced into the dryer 4, in order to adjust the level of oxygen within the dryer 4. Thus, for example, if the iron ore 1 comprises at least 5% by weight of magnetite, inert gas may be introduced into the dryer 4 via the inlet 13 to reduce the level of oxygen within the dryer 4. In another example, if the iron ore 1 comprises red bauxite having organic matter mixed in with the ore, dry air may be introduced into the dryer 4 via the inlet 13 to replace oxygen consumed by combustion of the organic matter within the hot zone 9.
[0243] When the iron ore 1 reaches the hot zone 9, it falls under gravity onto a second conveyor 8b contained within the dryer 4 and is transported by this in the opposite direction back towards the exit 7. As the iron ore travels from the hot zone 9 back towards the exit 7, it radiates heat towards the iron ore entering the dryer 4 on the first conveyor 8a. The dryer 4 may have a reflective lining to increase a rate of this radiative heat transfer. The radiative heat transfer may also be enhanced by convective heat transfer, by circulating the atmosphere within the dryer 4 from the second conveyor 8b towards the first conveyor 8a using appropriate ducting and / or one or more additional fans. Thus heat is transferred from the dehydrated and dehydroxylated ore leaving the dryer to fresh ore entering the dryer in a counterflow system within the dryer 4. When the ore 1 reaches the end of the second conveyor 8b, it falls under gravity through the exit 7 onto a third conveyor 8c and is transported by this towards the first inlet 131 of the first reaction vessel 130.
[0244] Whereas in Fig. 18, the dryer 4 is schematically represented as being only about twice as long as it is high, this is for illustrative and explanatory purposes only. In practice, the dryer 4 may be several tens of metres long in comparison to a height of only about one or two metres, so that the entry 6 and exit 7 are remotely located from the hot zone 9, and a significant temperature gradient can be established and maintained between the entry 6 and exit 7 at one end of the dryer 4 and the hot zone 9 at the other end. If the means for heating the ore in the hot zone 9 comprises pipework 5 which contains liquid sodium intended for the first reaction vessel 130, the counterflow system described above will increase the temperature at which the ore arriving in the hot zone 9 reaches thermal equilibrium with the liquid sodium, but will also decrease the temperature at which the ore leaves the dryer 4. Thus liquid sodium leaving the pipework 5 will enter the first reaction vessel 130 at a higher temperature, but the ore leaving the dryer 4 will enter the first reaction vessel 130 at a lower temperature, than if no such counterflow system were present. However, the total quantity of heat transferred to the first reaction vessel 130 by the liquid sodium and the iron ore together remains the same as if no such counterflow system were present. If on the other hand, the means for heating the iron ore in the hot zone 9 supplies heat to the ore from another source, the total quantity of heat transferred to the first reaction vessel 130 will be different.
[0245] Fig. 19 schematically shows a fifth embodiment of an apparatus 3e for producing iron from such an iron ore. The apparatus 3e comprises a comminution device 2, a dryer 4, a gas-tight first reaction vessel 130, a solid-species separator 180b and a solid-liquid sodium phase separator 190, all of which are arranged and function as described above in relation to Fig. 19, except as follows. In this embodiment, the apparatus 3e comprises a conduit 137 for transporting at least some of the other insoluble products from the second outlet 187 of the solid-species separator 180b through an atmosphere within the dryer 4. These other insoluble products may be transported along the conduit 137 for example mechanically (e.g., using a screw conveyor) and / or at least partially under gravity, for example. Since the other insoluble products are hot from the reaction of Eqn. 5, heat radiated by the other insoluble products heats the iron ore. Moreover, since they are in the form of a finely divided particulate, sodium oxide in the other insoluble products readily absorbs water vapour driven off from the heated iron ore to produce at least sodium hydroxide, as well as possibly also absorbing other gases like sulphur dioxide to produce sodium sulphite. Since hydrating the sodium oxide in this manner is exothermic, this increases the temperature of the other insoluble products, which in turn helps to heat the iron ore in the dryer 4 further. After leaving the dryer 4, the other insoluble products may then be routed to one or more other reaction vessels, as described above in relation to Fig. 15, for example.
[0246] Fig. 20 schematically shows a sixth embodiment of an apparatus 3f for producing iron from an iron ore comprising red bauxite. The apparatus 3f comprises a comminution device 2, a dryer 4, a gas-tight first reaction vessel 130, a solid-species separator 180a, and first and second phase separating devices 190a, 190b, all of which are arranged and function as described above in relation to Fig. 13, except as follows. In this embodiment, the apparatus 3f comprises a conduit 137 for transporting at least some of the other insoluble products from the second outlet 195b of the second phase separating device 190b through an atmosphere within the dryer 4. Once again, these other insoluble products may be transported along the conduit 137 for example mechanically (e.g., using a screw conveyor) and / or at least partially under gravity, for example. Since the other insoluble products are hot from the reaction of Eqn. 5, heat radiated by the other insoluble products heats the red bauxite to above about 250 “Celsius. Organic matter mixed in with the ore therefore auto-ignites and combusts to produce carbon dioxide gas and water vapour, leaving ash. As it is in the form of a finely divided particulate, sodium oxide in the other insoluble products readily absorbs this carbon dioxide gas and water vapour, as well as water vapour driven off from the red bauxite, to produce at least sodium hydroxide and sodium carbonate. The sodium oxide may also absorb lesser quantities of other gases like sulphur dioxide liberated from the red bauxite and / or from the organic matter to produce sodium sulphite. Since carbonating and hydrating the sodium oxide to produce sodium hydroxide and sodium carbonate are both exothermic reactions, these increase the temperature of the other insoluble products, which in turn helps to heat the red bauxite in the dryer 4 further. After leaving the dryer 4, the other insoluble products may be routed to one or more other reaction vessels, as described below in relation to Fig. 22, for example.
[0247] Whereas the apparatus 3e of Fig. 19 uses a "dry” separation technique as in the embodiment of Fig. 15 to separate the iron from the other insoluble products, and the apparatus 3f of Fig. 20 instead uses a "wet” separation technique as in the embodiment of Fig. 13, in other possible embodiments, these different separation techniques could be interchanged. In other words, the type of separation technique used to separate the iron from the other insoluble products does not depend on whether or not the iron ore comprises red bauxite.
[0248] Fig. 21 schematically shows a seventh embodiment of an apparatus 3g for producing iron from an iron ore, in which the iron is present as at least one of the mineral and mineraloid forms of iron oxide and oxyhydroxide. The apparatus 3g comprises a comminution device 2, a dryer 4, a gas-tight first reaction vessel 130, a solid-species separator 180b and a solid-liquid sodium phase separator 190, all of which are arranged and function as described above in relation to Fig. 15. However, the apparatus 3g also comprises a hydration vessel 170 having a first inlet 171 connected to the second outlet 187 of the solid-species separator 180b for receiving the other insoluble products therefrom. The hydration vessel 170 also comprises a second inlet 172 for liquid water and an outlet 174. The outlet 174 is connected to an inlet 176 of a solid-aqueous phase separator 175, such as a settlement tank, filter and / or centrifuge. The solid-aqueous phase separator 175 also has a first outlet 178 for an aqueous phase and a second outlet 179 for a solid phase.
[0249] During operation of the apparatus 3g, water is firstly introduced into the hydration vessel 170 via the second inlet 172, before the other insoluble products are introduced into it via the first inlet 171. The sodium oxide in the other insoluble products dissolves in the water to produce an aqueous solution of sodium hydroxide. However, the amount of water already present into the hydration vessel 170 is enough to ensure that the final concentration of this aqueous solution is less than 2.5 M, and the temperature of this solution is also kept below 85 “Celsius. An embodiment of a heat transfer pathway for controlling the temperature in this way is described below in relation to Fig. 23A. Thus gangue species like silica and alumina also present in the other insoluble products do not dissolve as well, and are precipitated out. The aqueous solution of sodium hydroxide is then separated from the undissolved gangue species in the solid-aqueous phase separator 175. The aqueous solution of sodium hydroxide, which leaves the solid-aqueous phase separator 175 via the first outlet 178, is therefore substantially free of these gangue species and may be used as desired. For example, it may be dried and then subjected to thermal decomposition into sodium oxide and water vapour, whereby the sodium oxide can be recovered from the other insoluble products. The gangue species leave the solid-aqueous phase separator 175 via the second outlet 179 thereof.
[0250] Fig. 22 schematically shows an embodiment of an apparatus 3h for extracting aluminium from the other insoluble products when the iron ore comprises red bauxite. The apparatus 3h at least comprises a hydration vessel 270, a first solid-aqueous phase separator 250, a precipitation vessel 230, a second solid-aqueous phase separator 240, a carbonation vessel 260 and a third solid-aqueous phase separator 280. The hydration vessel 270 comprises a first inlet 271 for receiving the other insoluble products from the reaction of the red bauxite with the liquid sodium, such as from the apparatus 3f of Fig. 20. The hydration vessel 270 also comprises a second inlet 272 for water in liquid or vapour phase, a third inlet 273 for lime, a first outlet 274 for non-gaseous reaction products, and a second outlet 275 for reaction products in gaseous or vapour phase. Each of the inlets and outlets of the hydration vessel 270 is provided with a respective valve V3, V4, V5, V6, V7 for opening and closing a respective one of the inlets and outlets, so that the hydration vessel 270 can be operated at above atmospheric pressure. The first outlet 274 of the hydration vessel 270 is connected to an inlet 251 of the first solid-aqueous phase separator 250, which also comprises a first outlet 254 for an aqueous phase and a second outlet 255 for a solid phase. In this embodiment, the first solid-aqueous phase separator 250 comprises a plurality of settlement tanks connected in series. The first outlet 254 of the first solid-aqueous phase separator 250 is connected to a first inlet 231 of the precipitation vessel 230, which also comprises a second inlet 232 for liquid water, a third inlet 233 for aluminium hydroxide crystals and an outlet 234. Also in this embodiment, the precipitation vessel 230 comprises a plurality of precipitation tanks connected in series. The outlet 234 is connected via a valve V8 to an inlet 241 of the second solid-aqueous phase separator 240, which also comprises a first outlet 244 for a solid phase and a second outlet 245 for an aqueous phase. The second outlet 245 is connected to a second inlet 263 of the carbonation vessel 260, which also comprises a first inlet 262 for carbon dioxide gas and an outlet 266. The outlet 266 is connected via a valve V9 to an inlet 281 of third solid-aqueous phase separator 280, which also comprises a first outlet 284 for a solid phase and a second outlet 285 for an aqueous phase. The third inlet 233 of the precipitation vessel 230 is connected to the first outlet 244 of the second solid-aqueous phase separator 240, as is the first outlet 284 of the third solid- aqueous phase separator 280.
[0251] During operation of the apparatus 3h, the other insoluble products are firstly introduced into the hydration vessel 270 via the first inlet 271 by opening and then closing valve V3, before water in liquid or vapour phase is introduced into it via the second inlet 272 by opening and then closing valve V4. The sodium oxide in the other insoluble products dissolves in the water to produce an aqueous solution of sodium hydroxide with a final concentration between about 2.5 M and about 7.5 M, inclusive. Since this hydration reaction is exothermic, the temperature of the aqueous solution rises and is allowed to reach a temperature of between about 210 and about 280 “Celsius, above which any excess heat may be removed using a heat transfer pathway such as that described below in relation to Fig. 23A, for example. The aqueous solution of sodium hydroxide is prevented from boiling by keeping all of the valves V3, V4, V5, V6 and V7 closed, so that the alumina in the other insoluble products starts to dissolve in the superheated solution as well. The temperature within the hydration vessel 270 may also be controlled by opening and then closing valve V7 to vent water vapour, as well as any hydrogen which may be formed by a reaction such as that of Eqn. 14b, for example. After the alumina has dissolved in the aqueous solution of sodium hydroxide to form sodium aluminate, calcium oxide ( / '.e., lime) may be progressively added to the aqueous solution via the third inlet 273 by opening and then closing valve V5, in order to precipitate out insoluble calcium compounds from the superheated aqueous solution. The hydration vessel 270 is then flashed down to atmospheric pressure and the heat recovered, which again may be removed using a heat transfer pathway such as that described below in relation to Fig. 23A, for example. Finally, valve V6 is opened and then closed to transfer the aqueous solution and precipitate to the first solid-aqueous phase separator 250.
[0252] In the first solid-aqueous phase separator 250, the aqueous solution of sodium hydroxide and sodium aluminate is separated from the precipitate comprising the insoluble calcium compounds. These leave the first solid-aqueous phase separator 250 via the second outlet 255 thereof and may subsequently be dried and compacted. The aqueous phase leaves the first solid-aqueous phase separator 250 via the first outlet 254 thereof and is transferred to the precipitation vessel 230. Here, the aqueous phase is diluted down with water added via the inlet 323 of the precipitation vessel 230 and seeded with smaller aluminium hydroxide crystals abstracted from the first outlet 244 of the second solid-aqueous phase separator 240. These crystals act as nucleation sites for the precipitation of more aluminium hydroxide in the precipitation vessel 230, until this precipitate and the now diluted aqueous phase are transferred to the second solid-aqueous phase separator 240 by opening and then closing valve V8. In the second solid-aqueous phase separator 240, the aluminium hydroxide is separated from the aqueous phase and leaves via the first outlet 244 thereof. Larger crystals of aluminium hydroxide from the first outlet 244 are taken away for washing, drying and thermal decomposition into alumina, ready for electrolysis.
[0253] Meanwhile, the diluted aqueous phase is transferred from the second outlet 245 of the second solid-aqueous phase separator 240 to the second inlet 263 of the carbonation vessel 260. Here, gaseous carbon dioxide admitted via the first inlet 262 thereof is bubbled through the aqueous phase to form an aqueous solution of sodium carbonate, from which more crystals of aluminium hydroxide precipitate out. The carbon dioxide may be captured from atmospheric air and / or from an industrial process, thereby giving the alumina extraction process a negative carbon footprint overall. Since this carbonation reaction is exothermic, heat generated thereby may be removed using a heat transfer pathway such as that described below in relation to Fig. 23B, for example. The crystals of aluminium hydroxide and aqueous solution of sodium carbonate are then transferred to the third solid-aqueous phase separator 280 by opening and then closing valve V9. Here, the aluminium hydroxide is separated from the aqueous solution of sodium carbonate, before leaving via the first outlet 284 thereof, to be added to the aluminium hydroxide from the first outlet 244 of the second solid-aqueous phase separator 240, thus increasing the overall yield of aluminium hydroxide produced. Meanwhile, the aqueous solution of sodium carbonate leaves the third solid-aqueous phase separator 280 via its second outlet 285 and may subsequently be dried, for example, to produce a solid-phase end-product.
[0254] Fig. 23A schematically shows first and second embodiments of a heat transfer pathway 3j from either of the hydration vessels 170, 270 in the respective apparatuses 3g, 3h of Figs. 21 and 22 to the dryer 4. In both embodiments, the heat transfer pathway 3j comprises a first heat exchanger HE7 in thermal contact with the contents of the respective hydration vessel 170, 270 and pipework 5 which circulates a heat transfer fluid (HTF) in a loop from the first heat exchanger HE7 through and / or around the dryer 4. Thus heat may be extracted from the reaction in the respective hydration vessel 170, 270 and transferred by the HTF to the iron ore in the dryer 4, in order to help dehydrate and dehydroxylate it. Fig. 23B schematically shows third and fourth embodiments of a heat transfer pathway 3k from either of the carbonation vessels 160, 260 in the respective apparatuses 3b, 3h of Figs. 15 and 22 to the dryer 4. In both embodiments, the heat transfer pathway 3k comprises a second heat exchanger HE8 in thermal contact with the contents of the respective carbonation vessel 160, 260 and pipework 5 which circulates a heat transfer fluid HTF in a loop from the second heat exchanger HE8 through and / or around the dryer 4. Thus heat may be extracted from the reaction in the respective carbonation vessel 160, 260 and transferred by the HTF to the iron ore in the dryer 4, in order to help dehydrate and dehydroxylate it.
[0255] In any of the embodiments of Figs. 23A and 23B, when the minimum operating temperature of the heat transfer pathway 3j, 3k is hot enough ( / '.e., greater than about 125 “Celsius), liquid sodium may be used as the HTF. In such a case, the heat transfer pathway 3j, 3k may be integrated with those shown and described above in relation to Figs. 16 and 17. In some embodiments, either of the heat transfer pathways 3j, 3k may comprise a heat pipe, for rapid and effective heat transfer.
[0256] The specific productivity of the apparatus of the invention may be compared to that of a conventional blast furnace as follows. A typical blast furnace has a working capacity of 4 x 103m3and can produce 1 x 104tonnes of iron per day, giving the blast furnace a specific productivity of 2.5 tonnes(Fe) nrr3per day. As described above, a reaction vessel of the invention may, for example, have a working capacity of about 1 .25 m3, equal to the volume of a liquid sodium bath within the reaction vessel, which can produce 110 kg of iron from a single charge of iron ore containing 160 kg (« 1 kmol) of Fe2C>3. Since the iron ore can be fed into the reaction vessel as fast as it is consumed and since the reaction of the Fe2Oa with the liquid sodium is relatively rapid, the rate of production of iron is determined only by the rate at which fresh liquid sodium can be supplied to the reaction vessel. According to Eqn. 5 above, 6 kmol of liquid sodium are consumed in the reaction with this much iron ore, which therefore requires 6 kmol of electrons to produce fresh liquid sodium by electrolysis. These electrons have an electrical charge (given by Faraday's constant) of 6 kmol x 9.6485 x 104C mol1= 5.8 x 108C. US patent appln. no. 2001 / 0045365 A1, for example, describes an electrolytic cell for producing liquid sodium from an electrolyte of 27 wt % NaCI and 73 wt % SrCl2 (= 50 mol % NaCI and 50 mol % SrCh), which is supplied by an electrical current of 55 kA = 5.5 x 104C s-1. Four such cells can therefore supply enough liquid sodium for the reaction of Eqn. 5 in 5.8 x 108 / (4 x 5.5 x 104) = 2632 s ~ 44 minutes. This gives the reaction vessel a specific productivity of 88 kg(Fe) nrr31 2632 s = 2.89 tonnes(Fe) nrr3per day. Thus with a sufficient supply of liquid sodium, the specific productivity of the apparatus of the invention can comfortably exceed that of a conventional blast furnace.
[0257] The net energy consumption of the present invention cannot be directly compared with that of a conventional blast furnace or with that of hydrogen-DRI because, whereas a conventional blast furnace and hydrogen-DRI both produce only a single useful product ( / .e., iron), the present invention produces both iron and sodium oxide as a co-product. Moreover, if the liquid sodium is produced by electrolysing sodium chloride, chlorine may also be produced as a useful co-product, and, if the electrolysis comprises the Castner process, hydrogen may be produced as a useful co-product as well. If the electricity used to produce the liquid sodium is derived from a source of clean energy, the present invention can be a zero-carbon technique of extracting iron from iron ore. Indeed, since sodium oxide has a high affinity for carbon dioxide, if the sodium oxide is also used to mineralize captured carbon dioxide gas by producing sodium carbonate, the present invention can have a negative carbon footprint overall.
[0258] In summary, therefore, the present invention provides a technique using liquid sodium as a chemical reducing agent to produce iron from an iron ore, in which the iron is present as one or more of the mineral and mineraloid forms of iron oxide and oxyhydroxide. The iron ore is prepared for reaction with the liquid sodium by being comminuted into fines, dehydrated and dehydroxylated, and the reaction is carried out in an inert atmosphere and at a temperature in a range below that at which ternary oxides or binary compounds of sodium with elements other than oxygen can form. Unlike previous pyrometallurgical techniques, such as those using a conventional blast furnace or hydrogen-DRI, the invention does not require very high temperatures to extract iron from iron ore. Instead, the iron ore dissolves in the liquid sodium like sugar in a hot cup of tea. The reaction products precipitate out from the liquid sodium, are separated from it as a solid phase, and the iron produced by the reaction is separated from the other reaction products. Thus iron can be extracted from iron ore without producing any greenhouse gases, and sodium oxide, which has a high affinity for carbon dioxide, is produced as a co-product. If the iron ore comprises red bauxite, the reaction products may also be processed to extract alumina from them without creating environmentally hazardous red mud. In some embodiments, the reaction products may be used to produce an alkaline activator for an alkaline activated or geopolymer cement. Of course, whereas the present invention has been described above as being suitable for extracting iron from iron ore, it may also be used to produce elemental iron from other sources of iron oxide(s), such as from mill scale, for example, whereby sources of waste iron oxide may be recycled.
[0259] Whereas the present invention has been described above by reference to particular examples and embodiments, the scope of the invention should not be taken to be limited thereby and is instead defined by the appended claims.
Claims
AMENDED CLAIMS received by the International Bureau on 17 April 2026 (17.04.2026)1. A method (300a - 300k, 300m, 300n) of producing iron from an iron ore in which the iron is present as at least one of the mineral and mineraloid forms of iron oxide and iron oxyhydroxide, the method comprising:5 comminuting (301) the iron ore into fines; dehydrating (302, 302a, 302b, 302c) the iron ore and dehydroxylating hydroxylated compounds contained therein by heating the iron ore to a temperature of from 100 to 600 “Celsius, inclusive; reacting (303, 303a) the iron ore in an inert atmosphere and at a temperature of less than 450 “Celsius with an amount of liquid sodium in excess of the stoichiometric amount thereof required for a redox reaction10 between the liquid sodium and iron oxide from the iron ore, to precipitate out from the liquid sodium both iron and other insoluble products comprising sodium oxide; separating (304a, 304b) the iron from the other insoluble products using at least one of their different magnetic susceptibilities and their different densities; and separating (305, 305a, 305b) the iron and the other insoluble products as a solid phase from the liquid15 sodium using at least one of settlement under gravity, filtration and centrifugation.
2. A method (300d) according to claim 1 , wherein the iron ore comprises at least 5% by weight of magnetite, and dehydrating and dehydroxylating (302) the iron ore is conducted (302a) in an atmosphere which contains less oxygen than atmospheric air.
203. A method (300d) according to claim 1, wherein the iron ore comprises red bauxite, dehydrating and dehydroxylating (302) the iron ore comprises heating (302b) the ore to at least 250 “Celsius in an oxygenated atmosphere closed off from its surrounding environment, and the method further comprises capturing (306) carbon dioxide gas produced by combusting (307) organic matter mixed in with the ore.
254. A method (300b, 300c, 300e, 300h) according to any one of the preceding claims, wherein dehydrating and dehydroxylating (302) the iron ore comprises heating (308) the iron ore using heat extracted from at least one of:(i) cooling (309a) the liquid sodium before reacting (303) the iron ore with the liquid sodium;30 (ii) cooling (309b) the iron ore after it has been dehydrated and dehydroxylated (302), and before reacting (303) the iron ore with the liquid sodium;(ill) cooling (309c) the liquid sodium from which the iron and the other insoluble products have been separated (305, 305a, 305b) as a solid phase; and(iv) cooling (309d) at least a component of the solid phase separated from the liquid sodium.
355. A method (300d) according to any one of the preceding claims, wherein dehydrating and dehydroxylating (302) the iron ore comprises passing (311) at least some of the sodium oxide precipitated out from the liquidsodium, or sodium hydroxide derived from hydrating (317, 322) at least some of this sodium oxide, through an atmosphere to which the iron ore is exposed.
6. A method (300e) according to any one of the preceding claims, comprising controlling (313) the5 temperature of the reaction (303) of the iron ore with the liquid sodium to remain below 450 “Celsius by: cooling (309c) the liquid sodium from which the iron and the other insoluble products have been separated (305, 305a, 305b) as a solid phase; returning (314) at least some of the liquid sodium thus cooled (309c) to the reaction of the iron ore with the liquid sodium; and10 adjusting (315) a rate at which the liquid sodium is returned (314) to the reaction of the iron ore with the liquid sodium.
7. A method (300k) according to any one of the preceding claims, wherein the dehydrated and dehydroxylated iron ore comprises a silicate mineral, and the redox reaction is conducted (303a) at a temperature15 of at least 320 “Celsius to induce a reaction between the sodium oxide and silica derived from the silicate mineral to produce at least sodium orthosilicate.
8. A method (300f) according to any one of the preceding claims, wherein separating (304a, 304b) the iron from the other insoluble products comprises applying (316) a magnetic field gradient to the liquid sodium with the20 iron and the other insoluble products suspended or entrained therein, wherein the magnetic field gradient has a non-zero component which increases in a direction antiparallel to a gravitational potential gradient or parallel to a centrifugal force.
9. A method (300g) according to any one of the preceding claims, further comprising using at least some of25 the iron to make steel by: adding (337) powdered carbon to the iron; mixing (338) the powdered carbon and iron together to produce a resulting mixture; and subjecting (339) the resulting mixture to a powder metallurgical process.30 10. A method (300h) according to any one of the preceding claims, comprising: adding (317) at least some of the other insoluble products to liquid water, thereby hydrating the sodium oxide in the other insoluble products, to produce an aqueous solution of sodium hydroxide having a final concentration of less than 2.5 M and a temperature of less than 85 “Celsius; and separating (318) undissolved solids as a solid phase from the aqueous solution of sodium hydroxide.3511. A method (300h) according to claim 10, further comprising:drying (319) at least some of the aqueous solution of sodium hydroxide from which the undissolved solids have been separated (318) to produce solid sodium hydroxide; at least one of (I) fusing and electrolysing and (II) thermochemically decomposing at least some of the solid sodium hydroxide to produce (320) at least liquid sodium; and5 recycling (321) at least some of the liquid sodium to react with the iron ore.
12. A method (300h) according to claim 10 or claim 11 when dependent on claim 3, wherein: the redox reaction is conducted (303a) at a temperature of at least 320 “Celsius; and the method further comprises fusing and electrolysing (340) at least some of the undissolved solids10 separated (318) from the aqueous solution of sodium hydroxide to extract aluminium therefrom.
13. A method (300I) according to any one of claims 1 to 9, wherein: the comminuted, dehydrated and dehydroxylated iron ore comprises a silicate mineral; the redox reaction is conducted (303b) at a temperature of less than 300 “Celsius; and15 the method further comprises: adding (341) liquid water to at least some of the other insoluble products, thereby hydrating the sodium oxide therein, to produce a hot aqueous solution of sodium hydroxide having a final concentration of at least 2.5 M; reacting (342) this aqueous solution of sodium hydroxide with silica in the other insoluble products derived20 from the silicate mineral to dissolve at least some of the silica in the aqueous solution of sodium hydroxide and produce an aqueous solution of sodium silicate; and drying (343) the aqueous solution of sodium silicate to produce a solid phase comprising the sodium silicate.25 14. A method according to any one of claims 3 to 9, wherein the redox reaction is conducted (303b) at a temperature of less than 300 “Celsius, and the method further comprises using the other insoluble products as a feedstock for the Bayer process.
15. A method (300j) according to any one of claims 3 to 9, wherein:30 the comminuted, dehydrated and dehydroxylated iron ore comprises a silicate mineral; the redox reaction is conducted (303a) at a temperature of at least 320 “Celsius to induce a reaction between the sodium oxide and silica derived from the silicate mineral to produce at least sodium orthosilicate; and the method further comprises: adding (322) water in liquid or vapour phase to at least some of the other insoluble products, thereby35 hydrating the sodium oxide therein, to produce an aqueous solution of sodium hydroxide having a final concentration of from 2.5 M to 7.5 M, inclusive, kept in liquid phase under pressure at a temperature of from 210 to 280 “Celsius, inclusive;reacting (323) the aqueous solution of sodium hydroxide with alumina in the other insoluble products to dissolve at least some of the alumina therein and produce an aqueous solution of sodium aluminate; phase-separating (325) undissolved solids from the aqueous solution of sodium aluminate; cooling (326) the aqueous solution of sodium aluminate to between 85 and 55 “Celsius and5 depressurizing it back to atmospheric pressure; and diluting (327) the aqueous solution of sodium aluminate with water and seeding it with crystals of AI(OH)s to precipitate out aluminium hydroxide.
16. A method (300j) according to claim 15, further comprising, before phase-separating (325) undissolved10 solids from the aqueous solution of sodium aluminate: adding (324) calcium oxide to the aqueous solution of sodium aluminate to precipitate out an insoluble calcium compound, which is phase separated (325) from the aqueous solution of sodium aluminate to produce a slurry; and wherein the method further comprises:15 neutralizing (331) the pH of the slurry by injecting the slurry with carbon dioxide gas; oxidizing (332) any calcium sulphite present in the slurry to calcium sulphate using manganese as a catalyst; and drying and compacting (333) the slurry to produce a solid-phase end-product.20 17. A method (300k) according to claim 15 or claim 16, further comprising at least one of: adding (345) at least one of an iron oxide and a non-bauxitic iron ore to the red bauxite before reacting (303a) the comminuted, dehydrated and dehydroxylated ore with the excess amount of liquid sodium; and after the redox reaction (303a) with the excess amount of liquid sodium and before adding (322) water in liquid or vapour phase to at least some of the other insoluble products, adding to these other insoluble products, a25 second portion of other insoluble products from another redox reaction of a comminuted, dehydrated and dehydroxylated non-bauxitic iron ore with an excess amount of liquid sodium, also conducted at a temperature of at least 320 “Celsius.
18. A method according to any one of claims 15 to 17, further comprising, after diluting (327) the aqueous30 solution of sodium aluminate with water and seeding it with crystals of AI(OH)s to precipitate out aluminium hydroxide: phase-separating the precipitated aluminium hydroxide from the aqueous solution of sodium aluminate; adding hydrochloric acid to the remaining solution of sodium aluminate to precipitate out additional aluminium hydroxide and leave an aqueous solution of sodium chloride;35 phase-separating the additional aluminium hydroxide from the aqueous solution of sodium chloride; using the aqueous solution of sodium chloride to produce liquid sodium and gaseous chlorine by electrolysis; andrecycling (321) at least some of the liquid sodium to react with the iron ore.
19. A method (300m) according to any one of claims 10 to 13 and 15 to 18, wherein dehydrating and dehydroxylating (302) the iron ore comprises heating (308) the iron ore using heat extracted (334) from hydrating5 (317, 322, 341) the sodium oxide.
20. A method (300n) according to any one of the preceding claims, comprising reacting (312) carbon dioxide gas with at least some of the sodium oxide precipitated out from the liquid sodium, or with sodium hydroxide derived from hydrating (317, 322) at least some of this sodium oxide, in a carbonation reaction to produce at least sodium10 carbonate, and wherein dehydrating and dehydroxylating (302) the iron ore comprises heating (308) the iron ore using heat extracted (335) from at least one of the carbonation reaction (312) and the sodium carbonate produced thereby.
21. An apparatus (3a - 3h) for producing iron from an iron ore in which the iron is present as at least one of15 the mineral and mineraloid forms of iron oxide and iron oxyhydroxide, the apparatus comprising: an ore preparation subassembly (2, 4) comprising a comminution device (2) for comminuting the iron ore into fines and a dryer (4) for dehydrating the iron ore and dehydroxylating hydroxylated compounds contained therein, wherein the ore preparation subassembly (2, 4) comprises an inlet for the iron ore and an outlet for the ore thus treated;20 a gas-tight first reaction vessel (130) for reacting the iron ore thus treated in an inert atmosphere and at a temperature of less than 450 “Celsius with an amount of liquid sodium in excess of the stoichiometric amount thereof required for a redox reaction between the liquid sodium and iron oxide from the iron ore, the first reaction vessel (130) comprising a first inlet (131) for receiving the comminuted, dehydrated and dehydroxylated iron ore from the outlet of the ore preparation subassembly (2, 4), a second inlet (132) for the liquid sodium, and an outlet25 (134) for the liquid sodium with iron and other insoluble products comprising sodium oxide entrained therein; and a separation subassembly comprising a solid-species separator (180a, 180b) for separating the iron from the other insoluble products, and a solid-liquid sodium phase separator (190, 190a, 190b) for separating the iron and the other insoluble products from the liquid sodium, wherein the separation subassembly comprises an inlet (181, 191) for receiving the liquid sodium with the iron and the other insoluble products entrained therein from the30 outlet (134) of the first reaction vessel (130), and respective outlets for each one of the liquid sodium (194, 194a, 194b), the iron (186, 195a) and the other insoluble products (187, 195b).
22. An apparatus (3a - 3h) according to claim 21 , wherein the dryer (4) contains an atmosphere to which the iron ore is exposed during dehydration and dehydroxylation, and the dryer (4) comprises means (10, 11 , 12) for35 reducing a pressure of the atmosphere within the dryer (4) to less than that of atmospheric air outside the dryer (4).
23. An apparatus (3c - 3f) according to claim 21 or claim 22, further comprising a heat transfer pathway (5, 8a, 8b) for transferring heat to the iron ore within the dryer (4) from at least one of:(i) the liquid sodium before it enters the first reaction vessel (130);(ii) the iron ore after it has been dehydrated and dehydroxylated, and before it enters the first5 reaction vessel (130);(ill) the first reaction vessel (130); and(iv) at least one of the liquid sodium, the iron and the other insoluble products after they have left the first reaction vessel (130).10 24. An apparatus (3c, 3d) according to claim 23, wherein the heat transfer pathway (5) contains liquid sodium as a heat transfer fluid.
25. An apparatus (3a - 3h) according to any one of claims 21 to 24, wherein the first inlet (131) of the first reaction vessel (130) comprises an airlock (20) having an interior (25), and the airlock (20) comprises:15 a first gas-tight door (21) connecting the interior (25) of the airlock (20) with a surrounding environment (E) of the first reaction vessel (130); a second gas-tight door (22) connecting the interior (25) of the airlock (20) with an inside (135) of the first reaction vessel (130); an inlet (23) to the interior (25) of the airlock (20) for inert gas; and20 an outlet (24) from the interior (25) of the airlock (20) for atmospheric air; wherein the inlet (23) for inert gas and the outlet (24) for atmospheric air each comprises a respective valve (23V, 24V) for opening and closing a respective one of the inlet (23) and the outlet (24).
26. An apparatus (3a - 3h) according to claim 25, further comprising a heat exchanger (HE6) for transferring25 heat from the first reaction vessel (130) to the inert gas upstream of the inlet (23) to the airlock (20).
27. An apparatus (3b, 3c, 3d, 3e, 3g) according to any one of claims 21 to 26, wherein: the solid-liquid sodium phase separator (190) comprises an inlet (191) for receiving the liquid sodium with the iron and the other insoluble products entrained therein from the outlet (134) of the first reaction vessel (130), a30 first outlet (194) for liquid sodium, and a second outlet (195) for the iron and the other insoluble products; and the solid-species separator (180b) comprises an inlet (181) for receiving the iron and the other insoluble products from the second outlet (195) of the solid-liquid sodium phase separator (190), a first outlet (186) for the iron, and a second outlet (187) for the other insoluble products.35 28. An apparatus (3a, 3f) according to any one of claims 21 to 26, wherein: the solid-species separator (180a) comprises an inlet (181) for receiving the liquid sodium with the iron and the other insoluble products entrained therein from the outlet (134) of the first reaction vessel (130), a firstoutlet (184) for liquid sodium with iron entrained therein, and a second outlet (185) for liquid sodium with the other insoluble products entrained therein; and the solid-liquid sodium phase separator (190a, 190b) comprises a first phase separating device (190a) and a second phase separating device (190b), wherein the first phase separating device (190a) comprises an inlet5 (191 a) for receiving the liquid sodium with iron entrained therein from the first outlet (184) of the solid-species separator (180a), a first outlet (194a) for the liquid sodium, and a second outlet (195a) for the iron, and the second phase separating device (190b) comprises an inlet (191 b) for receiving the liquid sodium with the other insoluble products entrained therein from the second outlet (185) of the solid-species separator (180a), a first outlet (194b) for the liquid sodium, and a second outlet (195b) for the other insoluble products.1029. An apparatus (3a - 3g) according to claim 27 or claim 28, wherein at least one of the first outlets (194, 194a, 194b) for liquid sodium of the solid-liquid sodium phase separator (190, 190a, 190b) is connected upstream of the second inlet (132) of the first reaction vessel (130).15 30. An apparatus (3e, 3f) according to any one of claims 27 to 29, further comprising a conduit (137) for transporting at least some of the other insoluble products from the second outlet (187, 195b) for the other insoluble products through an atmosphere to which the iron ore is exposed in at least one of the comminution device (2) and the dryer (4).20 31. An apparatus (3g, 3h) according to any one of claims 21 to 30, comprising: a hydration vessel (170, 270) for reacting at least some of the sodium oxide from the first reaction vessel (130) with water to produce an aqueous solution of sodium hydroxide, wherein the hydration vessel (170, 270) comprises a first inlet (171 , 271) for receiving the other insoluble products from the second outlet (187, 195b) for the other insoluble products, a second inlet (172, 272) for the water, and at least a first outlet (174, 274) for the25 aqueous solution of sodium hydroxide and undissolved solids; and a solid-aqueous phase separator (175, 250) for separating the undissolved solids from the aqueous solution of sodium hydroxide, wherein the solid-aqueous phase separator (175, 250) comprises an inlet (176, 251) downstream of the first outlet (174, 274) of the hydration vessel (170, 270), a first outlet (178, 254) for the aqueous solution of sodium hydroxide, and a second outlet (179, 255) for the undissolved solids.3032. An apparatus (3b, 3h) according to any one of claims 21 to 31 , comprising: a carbonation vessel (160, 260) for reacting at least some of the sodium oxide from the first reaction vessel (130), or sodium hydroxide derived from hydrating at least some of this sodium oxide, with carbon dioxide gas to produce at least sodium carbonate, wherein the carbonation vessel (160, 260) comprises a first inlet (162,35 262) for the carbon dioxide gas, a second inlet (163, 263) for receiving the sodium oxide or sodium hydroxide, and an outlet (166, 266) for at least the sodium carbonate; anda heat transfer pathway (3k) for transferring heat from the carbonation vessel (160, 260) to the iron ore within the dryer (4).
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