Process for the carbothermic smelting of a metalliferous feedstock material using a hot oxidising gas

Abstract

The invention relates to a process for the smelting of a metalliferous feedstock material. More particularly, the invention relates to a process for the smelting of composite agglomerates including metalliferous feedstock material, reductant and fluxes, using hot oxidising gas. According to a first aspect of the present invention, there is provided a process for the carbothermic smelting of a metalliferous feedstock material using oxidising gas including the steps of: (i) feeding composite agglomerates into a reactor to create a packed bed within a reactor, wherein the agglomerates comprise metalliferous feedstock material, reductant and fluxes; (ii) heating and smelting the agglomerates with hot oxidising gas, wherein the hot oxidising gas enters the reactor and is passed through the packed bed to form molten material comprising an intermediate slag constituent and a partially reduced metalliferous constituent; (iii) channelling the molten material into an electrical slag cleaning furnace; (iv) adding additional reductant to the molten material in the electrical slag cleaning furnace to form a liquid metal product, a liquid slag product, and a CO-containing gas; and (v) combusting the CO-containing gas with pre-heated air to form the hot oxidising gas which is oxygen enriched before entering the reactor in step (ii), wherein the temperature of the hot oxidising gas entering the reactor is controlled to be above 1400°C, and wherein the oxygen content of the hot oxidising gas is controlled to be between 0% - 20%.

Description

[0001] PROCESS FOR THE CARBOTHERMIC SMELTING OF A METALLIFEROUS FEEDSTOCK MATERIAL USING A HOT OXIDISING GAS

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a process for the smelting of a metalliferous feedstock material. More particularly, the invention relates to a process for the smelting of composite agglomerates including metalliferous feedstock material, reductant and fluxes, using hot oxidising gas.

[0004] BACKGROUND TO THE INVENTION

[0005] Process routes entailing the pre-reduction of an agglomerated metalliferous feed material prior to carbothermic smelting in an electric furnace are known in the art. The focus on such process routes is due to the proven metallurgical and electrical energy efficiencies during carbothermic smelting of an agglomerated feed material (allowing closer quality control, i.e., mechanical and chemical property control) which has been pre-heated and subjected to pre-reduction prior to carbothermic smelting. This is demonstrated in, for instance, US 457 1259 which discloses a method using an exhausted plasma heated stream for pre-reduction and preheating of the feed material to be introduced into the reactor to produce molten metal.

[0006] In this context and most prominently are such processes wherein the pre-reduction treatment comprises direct or solid-state reduction. In the alternative, WO 2020 / 229994 discloses a process for the smelting of a reductant-containing metalliferous feed material wherein the pre-reduction comprises not only heating and solid-state reduction but melting of the feed material through the use of a hot reducing gas from a gasifier, the products of which are then allowed to flow into an electric furnace for final slag cleaning.

[0007] In further increasing metallurgical and electrical energy efficiencies, it is known to utilise, as feed material to the above-described solid-state reduction, the product agglomerate from a solid-state oxidation process, such as sintering in air.

[0008] However, a fundamental disadvantage remains where solid-state oxidation is utilised in advance of pre-reduction, in that material transfer between the pre-treatment steps and / or a pre-treatment step and the carbothermic smelting step remains viable only in the solid state and as a result, cooling down of the material in transit occurs. This cooling down reduces the specific energy consumption (SEC) of the overall process as any subsequent step would then require re-heating of the feed material, at least to the extent of the heat loss during transfer.

[0009] Accordingly, the known process routes come with disadvantages in SEC, either due to avoidance of the disadvantages associated with solid-state pre-oxidation or through a limitation of pre-oxidation, coupled with increased reductant consumption due to the requirement to utilise pre-reduction to achieve feasible metallurgical and energy efficiencies during electric furnace smelting.

[0010] NL2023109B1 teaches the smelting of a metalliferous feedstock to form liquid metal and slag products, utilising the heat and reducing properties of carbon monoxide (CO) off-gas from a reduction furnace. The invention’s use of CO off-gas is twofold: first, as a reducing agent passing through the agglomerate bed to partially reduce the metalliferous particles in the solid state, and second, as a fuel for combustion in the furnace burner, in combination with oxygen gas, to heat the refractories of the furnace to achieve the high temperatures needed for melting the agglomerates. However, despite this dual use of the CO gas as both a fuel and a reducing gas the invention is still bound by the constraint of solid-state reduction and requires substantial electrical energy input into the furnace to achieve a viable degree of metallisation.

[0011] Further to the above-described disadvantages in the known process steps upstream of carbothermic smelting, it is commonplace that a final off-gas from the electric furnace is flared into the environment to avoid discharging a CO-rich gas. This flaring, by its very nature, introduces a chemical energy inefficiency in the process because of the loss of a high chemical energy product to the non-productive flaring. Furnace off-gas has seen limited application as a recycle into a metallurgical process, and to date, has seen no application beyond for purposes of pre-heating and / or solid-state pre-reduction of the metalliferous feed material.

[0012] A recent exception has been the pre-melting of composite agglomerates making use of combusted furnace gas which is oxidising as exemplified by WO 2020 / 229994. This disclosure excludes the use of reductants, implying that no reduction of the metal oxides can take place. Only pre-melting of the ores is achieved.

[0013] OBJECT OF THE INVENTION

[0014] It is accordingly an object of the present invention to provide a novel process for the carbothermic smelting of a metalliferous feedstock material which overcomes, at least partially, the abovementioned disadvantages and limitations and / or which will provide a useful improvement to existing processes for the carbothermic smelting of metalliferous feedstock material.

[0015] SUMMARY OF THE INVENTION

[0016] For purposes of the present specification, it will be appreciated that the term “partially reduced” refers to the degree of reduction to which metalliferous feedstock material has been reduced where reduction is inadequate to form a viable amount of elemental metal of interest such that further and / or final reduction needs to be performed to achieve a suitable conversion to be utilised in industry or downstream processing.

[0017] It will be appreciated that the term “carbothermic” refers to the reduction of metalliferous feedstock material oxides using carbon (C) as the reducing agent.

[0018] In terms of the present invention, the term “smelt” includes both the melting and reduction of metalliferous feedstock material.

[0019] According to a first aspect of the present invention, there is provided a process for the carbothermic smelting of metalliferous feedstock material using oxidising gas including the steps of: (i) feeding composite agglomerates into a reactor to create a packed bed within a reactor, wherein the agglomerates comprise metalliferous feedstock material, reductant and fluxes;

[0020] (ii) heating and smelting the agglomerates with hot oxidising gas, wherein the hot oxidising gas enters the reactor and is passed through the packed bed to form molten material comprising an intermediate slag constituent and a partially reduced metalliferous constituent;

[0021] (iii) channelling the molten material into an electrical slag cleaning furnace;

[0022] (iv) adding additional reductant to the molten material in the electrical slag cleaning furnace to form a liquid metal product, a liquid slag product, and a CO-containing gas; and

[0023] (v) combusting the CO-containing gas with pre-heated air to form the hot oxidising gas which is oxygen enriched before entering the reactor in step (ii), wherein the temperature of the hot oxidising gas entering the reactor is controlled to be above 1400°C, and wherein the oxygen content of the hot oxidising gas is controlled to be between 0% - 20%.

[0024] In an embodiment of the invention, the metalliferous feedstock material may be any material comprising a metal, metal oxide, metal carbonate of a metal or any combination of metals selected from the group consisting of manganese (Mn), chromium (Cr), vanadium (V), titanium (Ti), nickel (Ni), iron (Fe), and a combination thereof. The metalliferous feedstock material may be fine metalliferous feedstock material, wherein the reference to fine relates to a particle size of less than or equal to 6 mm. Preferably, the particle size of fine metalliferous feedstock material is less than 100 pm at 80% passing sieve size (P80).

[0025] In an embodiment of the invention, the reductant may be selected from the group consisting of anthracite, coke, char, charcoal and a combination thereof. Preferably, the reductant may be anthracite.

[0026] In a preferred embodiment of the invention, the reductant has a stoichiometric carbon content of 105% to 220% in relation to the composite agglomerates.

[0027] In an embodiment of the invention, the flux may be selected from the group consisting of limestone, quartz, dolomite and a combination thereof. Preferably, the flux may be a combination of limestone and quartz.

[0028] In an embodiment of the invention, the feeding of the composite agglomerates may be preceded by the production of the composite agglomerates, wherein the composite agglomerates may be produced at a production facility.

[0029] In an embodiment of the invention, the composite agglomerates may include a binding agent, wherein the binding agent may be selected from the group consisting of bentonite, cement, sodium silicate, molasses and a combination thereof.

[0030] In a preferred embodiment of the invention, the composite agglomerates may be sized to have a diameter of between 15 mm to 40 mm. In an embodiment of the invention, the packed bed may provide a fluid permeable interface locatable at an operatively downstream position relative to a region where the agglomerate is fed to the reactor to permit the hot oxidising gas to be passed therethrough. Preferably, the fluid permeable interface may be situated at an operative base region of the packed bed which is suspended in the reactor.

[0031] In an embodiment of the invention, the packed bed may be suspended at a position of the side walls where the position of the side walls changes.

[0032] In an alternative embodiment of the invention, the packed bed may be suspended in the reactor by an obstruction which may be located at an operatively downstream position relative to the region where the agglomerates are fed to the reactor. The obstruction may be a permeable bed of refractories.

[0033] It is to be appreciated by those skilled in the art that hot oxidizing gas in the present context is to be understood as a gas wherein the mass % of CO2 + O2 in the gas is greater than the mass % of CO + H2 in the gas and which gas has a temperature high enough to heat and smelt the composite agglomerates based on the composition of the composite agglomerates.

[0034] In an embodiment of the invention, as set out above, the hot oxidising gas is the product of combustion of the CO-containing gas, which, in turn, is a product of the reduction reaction which occurs during the formation of the molten material and the liquid metal product in both the reactor and the slag cleaning furnace, respectively.

[0035] In an embodiment of the invention, oxygen enrichment of the hot oxidising gas is performed in the combustion step (v). The composition of the hot oxidising gas is controlled to have an oxygen content of between 0% and 20%, depending on the type of metalliferous feedstock material fed to the reactor.

[0036] In one preferred embodiment of the invention, the oxygen content of the hot oxidising gas may be between 5% and 18%.

[0037] In a preferred embodiment of the invention, the oxygen content of the hot oxidising gas may be between 10% and 15%.

[0038] In an embodiment of the invention, the hot oxidising gas is passed countercurrent to the direction in which the composite agglomerates enter the reactor.

[0039] In terms of the present invention, the temperature of the hot oxidising gas entering the reactor and passing through the packed bed in step (ii) is controlled to be above 1400°C, preferably between 1600°C and 1750°C, when entering the reactor, depending on the type of metalliferous feedstock material fed to the reactor.

[0040] In a preferred embodiment of the invention, the hot oxidising gas entering the reactor is fed at a speed of 1 m / s to 4 m / s.

[0041] In an embodiment of the invention, a combustion chamber may be provided for combusting the CO-containing gas to form the hot oxidising gas.

[0042] It is to be appreciated by those skilled in the art that the slag cleaning step may be performed in a separate slag cleaning furnace in fluid communication with the reactor. In an embodiment of the invention, additional reductant and additional fluxes may be added to the slag cleaning furnace as required to perform additional smelting and conditioning.

[0043] In an embodiment of the invention, the slag cleaning furnace may provide at least one electrode for providing electrical energy to the molten material and addional reductant added thereto in the slag cleaning furnace to allow for the final reduction of the partially reduced metal constituent to form the final liquid metal product and the formation of the liquid slag product.

[0044] In an embodiment of the invention, the mode of operation of the slag cleaning furnace may be selected from the group consisting of open bath, and partially open bath mode.

[0045] In an embodiment of the invention, the additional reductant may be injected into the slag cleaning furnace.

[0046] In an embodiment of the invention, the additional reductant may be selected from the group consisting of anthracite, char, coke, coal and a combination thereof. Preferably, the additional reductant may be anthracite.

[0047] In an embodiment of the invention, additional ores may be added to the slag cleaning furnace as required to perform additional smelting and conditioning.

[0048] In an embodiment of the invention, the temperature of the slag cleaning furnace may be controlled to allow for the selective metallisation of a first target metal in the metalliferous feedstock material so that it reports to the liquid metal product and that non-target metals report to the liquid slag product. It is to be appreciated that the liquid slag product or parts thereof, as referred to above, may constitute the metalliferous feedstock material in a subsequent process, wherein the subsequent process is a process according to the invention, and wherein the operating temperature in the slag cleaning furnace of the subsequent process may be controlled to selectively metallise a second target metal in the metalliferous feedstock material so that the second target metal reports to the liquid metal product of the subsequent process and the remainder to the liquid slag product of the subsequent process.

[0049] In an embodiment of the invention, the liquid slag product may be utilised for further hydrometallurgical and / or pyrometallurgical processing.

[0050] It is to be appreciated by those skilled in the art that the invention departs from the conventional teachings that hot oxidising gas is not suitable for the heating and smelting of composite agglomerates for reasons attributed to the Boudouard reaction depleting the reductant and the high oxidising potential of gases containing O2 and CO2. Based on conventional teachings, knowledge and methods, those skilled in the art have resorted to using reducing gases, such as CO-containing gas, at temperatures below 600°C to allow for solid state and / or direct reduction of agglomerates for purposes of pre-reduction.

[0051] However, and most unexpectantly, the present invention affords the ability to utilise hot oxidising gas, as defined herein, and to operate at temperatures of above 1400°C to smelt composite agglomerates. Such higher temperatures are achieved by the combustion of the CO-containing gas with pre-heated air to form the hot oxidising gas, which is subsequently oxygen enriched as described herein. The combustion of the CO-containing gas, the process off-gas so to speak, allows for the liberation of far more chemical energy which can be utilised for smelting than would otherwise be available had a conventional, low temperature, reducing gas been utilised as known and taught in the art.

[0052] Employing temperatures exceeding 1400°C greatly reduces the downstream energy consumption of the slag cleaning furnace since the chemical energy made available by combusting the CO-containing gas, the process off-gas, to produce a hot oxidising gas which is subsequently oxygen enriched is far greater than that of a traditional reducing gas (approximately three times greater chemical energy). In doing so, the shortcomings associated with solid state and / or direct reduction for pre-reduction are overcome since the temperatures are of an order which is capable of smelting the agglomerates and thereby allowing pre-reduction of the agglomerates to take place in a molten state.

[0053] When the hot oxidising gas is passed through the packed bed in step (ii), a protective molten layer is formed around the end regions of the agglomerates. The protective molten layer allows for pre-reduction of the metalliferous feedstock to occur on the inside of the protective molten layer of the agglomerates which is also melted and reduced. In doing so, despite minimal oxidation of the reductant inside the agglomerates, the higher temperature of the hot oxidising gas allows heating, melting, and a greater degree of reduction of the metalliferous feedstock material as opposed to the pre-reduction taking place in the solid state. It is well known for the Boudouard reaction to consume the reductant contained in the agglomerates when melting the agglomerates at a slow pace as is currently taught and practised in the art. However, in terms of the present invention, given the high temperature of the hot oxidising gas and the protective molten layer referred to above, the agglomerates are smelted at a fast pace which mitigates the impact of the Boudouard rection and preserves the reductant within the agglomerates.

[0054] It is to be appreciated that in the context of the present invention, the effect of the Boudouard reaction is mitigated and not eliminated. The partial oxidation of the reductant in the agglomerates is a welcomed trade-off when compared to the substantial amount of chemical energy made available by using the hot oxidising gas as opposed to using a reducing gas at a far lower temperature and the associated hurdles therewith.

[0055] In this way, the present invention allows for the reduction of the metalliferous feedstock material to occur in a molten state using the hot oxidising gas, as opposed to solid state and / or direct reduction using a reduction gas, which not only lowers the energy consumption of the slag cleaning furnace but also affords a greater degree of reduction of the metalliferous feedstock material in a molten state.

[0056] The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrates, by way of example, the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS:

[0057] The invention will now further be described, by way of example only, with reference to the accompanying drawings wherein:

[0058] Figure 1 is a schematic diagram of a process for carbothermic smelting of a metalliferous feedstock material using hot oxidising gas in accordance with the present invention;

[0059] Figure 2 is a cross-sectional side view of a reactor and slag cleaning furnace as illustrated in Figure 1 ; and

[0060] Figure 3 is a side cross-sectional view of a reactor showcasing the preservation of reductant and the flow of hot oxidising gas, which is oxygen enriched, in accordance with Figure 1 of the process in accordance with the present invention.

[0061] The presently disclosed subject matter will now be described more fully hereinafter with reference to the accompanying description of the preferred embodiment of the present invention, in which representative embodiments are shown. The presently disclosed subject matter can, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the embodiments to those skilled in the art. DETAILED DESCRIPTION OF THE INVENTION

[0062] A non-limiting example of a preferred embodiment of the invention is described in more detail below, with reference to Figures 1 to Figures 3.

[0063] A process for the carbothermic smelting of a metalliferous feedstock material using oxidising gas according to the present invention is generally designated by reference numeral 10 in the accompanying drawings.

[0064] Figure 1 shows a schematic representation of the process 10 flow. Agglomerates comprising metalliferous feedstock material, reductant and fluxes, prepared at a preparation facility 100 are fed A into reactors 12.1 (shown in greater detail in Figure 2) through 12.n where it forms part of a fluid permeable packed bed of agglomerates 14 (shown in Figure 2 with reference to reactor 12.1 ) in each respective reactor 12.1 through 12. n.

[0065] It will be appreciated that it may be well elected to include a binder or binding agent, and the use or disuse of binder or binding agent would depend on the metalliferous feedstock material being processed, the size of the agglomerates used in the process 10 and / or the height at which the packed bed 14 of agglomerates is required to be stacked in the reactor 12.1 to 12.n.

[0066] By means of being suspended by the obstruction 20, the agglomerates in the packed bed 14 are then smelted by means of passing a hot oxidising gas counter current through the packed bed 14. In an embodiment of the invention, the hot oxidising gas is produced in combustion chamber(s) 32.1 through 32. n, whereafter, it is oxygen enriched, so that the composition thereof is between 0% and 20%, depending on the type of metalliferous feedstock material fed to the reactor.

[0067] The hot oxidising gas is fed B operatively downstream position 24 of the packed bed 14 and enters the reactor 12.1 to 12.n counter current to the direction in which agglomerates are fed to the reactor 12.1 , thereby permeating through the packed bed 14 at a temperature sufficient to smelt the agglomerates. The temperature of the hot oxidising gas entering reactor 12.1 to 12.n is controlled to be above 1400°C, preferably above 1600°C, depending on the type of metalliferous feedstock material used. In this fashion, the pressure-drop of the hot oxidising gas across the permeable fluid interface 16 and packed bed 14 is minimised and typically in the order of 5 to 10 kPa. The temperature of the hot oxidising gas, after having passed through the packed bed 14 of agglomerates, is typically less than 800°C.

[0068] The smelting of the agglomerates in the reactor 12.1 to 12.n result in the formation of molten material comprising an intermediate slag constituent and a partially reduced metalliferous constituent.

[0069] With reference to Figure 3, passing the hot oxidising gas through the packed bed 14 allows for the formation of a protective molten layer around the end regions of the agglomerates. The protective molten layer oxidising allows for pre-reduction of the metalliferous feedstock material inside of the protective molten layer. Minimal oxidation of the reductant in the agglomerate does occur during the formation of the protective molten layer. However, the high temperature of the hot oxidising gas entering the reactor 12.1 to 12.n allows for fast smelting of the agglomerates which mitigates the effects of the Boudouard reaction. Therefore, the partial oxidation of the reductant inside the agglomerates serves as an advantage by preserving the reductant in the agglomerates.

[0070] Accordingly, the fluid permeable interface 16, formed at an operatively lower region 22 of the packed bed 14 allows:

[0071] (i) the hot oxidising gas to pass therethrough and into the packed bed 14; and

[0072] (ii) the molten material to flow out of and away from the packed bed 14.

[0073] By controlling the viscosity of the liquid intermediate slag constituent, whether by the addition of fluxes in the agglomerates and / or self-fluxing of the metalliferous feedstock material, the molten material can be channelled C and flows into the electrical slag cleaning furnace 26 (shown as a closed submerged arc AC furnace in Figure 1 ) where additional reductant, fluxes or ore are added D to the molten material contained in the furnace 26.

[0074] As shown in Figure 2, the furnace 26 is provided in fluid flow communication with the reactor 12.1 , thereby minimising heat loss during the transfer of the fluid material. The additional reductant, as particulate anthracite, in combination with electrical energy added to the molten material utilising submerged electrodes 28 of the furnace 26 advances and allows for the formation of a liquid metal product, a liquid slag product, and a CO-containing gas. The liquid metal product and liquid slag product, when contained in the furnace 26, would necessarily be in liquid form, but it will be appreciated by those skilled in the art that solid particles may however also still be present. The liquid metal product and the liquid slag product, in an embodiment of the invention, are formed in the furnace 26 via open bath smelting as a result of an electrochemical reaction between the additional reductant and the partially reduced metalliferous feedstock material in the molten material. The reduction of the partially reduced metalliferous feedstock material in this manner, as part of the molten material, allows for the metallisation thereof to proceed to much higher levels compared to conventional smelting as known in the art.

[0075] The liquid metal product and / or the liquid slag product can then be tapped G from the furnace 26 as known in the art. The liquid metal product and / or the liquid slag product may then be processed further, as required.

[0076] Importantly, the CO-containing gas is captured E from the furnace 26 and passed to a quencher 30 where after the quenched gas is fed F to the combustion chambers 32.1 through 32. n wherein it is combusted with pre-heated air to form the hot oxidising gas, wherein the hot oxidising gas is subsequently oxygen enriched and subsequently channelled into the process 10, where it enters reactor 12.1 to 12.n and is passed through the packed bed, as herein before described.

[0077] A fundamental advantage of the process of the present invention 10 is that it allows for: i) the exploitation of high SEC efficiencies by utilizing hot oxidising gas to presmelt and partially reduce the metalliferous feedstock material within the agglomerates in reactor 12.1 to 12.n prior to smelting in the furnace 26; ii) the mitigation of energy losses by allowing transfer of molten material from reactor 12.1 to 12.n to furnace 26; and iii) channeling the CO-containing gas into the process 10 through combustion of the CO-containing gas to produce the hot oxidising gas suitable for smelting of the agglomerates in the reactor 12.1 to 12.n, while allowing a very high degree of process control to achieve high metallurgical and energy (both electrical and chemical) efficiencies.

[0078] By example, the melting of the agglomerates and viscosity of the resultant molten material is controlled by a number of physical and chemical characteristics of the constituents of the agglomerates, when subjected to the hot oxidising gas. The melting temperature of gangue materials and the viscosity of the resultant liquid phase, and thereby of the molten material, may be decreased by adding suitable fluxes to the agglomerates.

[0079] Where the process 10 includes a preparation facility 100, the process 10 allows for controlling the composition of the agglomerates such that melting the agglomerates is controlled as well as the viscosity of the resultant molten material. Such a change in the melting and resultant fluid material viscosity can in turn impact the rate of melting of constituents of the agglomerates, the degree of reduction of the metalliferous feedstock material in the reactor 12.1 to 12.n and the ease at which the molten material flows to the furnace 26.

[0080] T o illustrate, and if desired, by lowering the melting temperature of gangue materials in the agglomerates and decreasing the viscosity of the molten material through the addition of fluxes, such as limestone or dolomite and quarts, the rate of melting of gangue materials in the agglomerates may be increased at a hot oxidising gas temperature above 1400°C and therefore the molten material will permeate through the packed bed 14 at a higher rate. This, in turn, will result in a decreased residence time of agglomerates in the packed bed 14, which in turn decreases the degree of oxidation of the metalliferous feedstock material in the reactor 12.1 to 12.n.

[0081] Importantly, the process 10 further allows for controlling: i) the addition D of the additional reductant to the furnace 26 itself; and ii) the extent of the combustion of the CO-containing gas in the combustion chambers 32.1 through 32. n, such that the hot oxidising gas has a CO2 + O2 content greater than its CO + H2 content sufficient to produce the partially reduced metalliferous constituent from the agglomerates (by example, O2 between 0% - 20%) and at a temperature sufficient to heat and smelt the agglomerate, whilst preserving the reductant in the agglomerates to allow for reduction to occur within the protective molten layer.

[0082] Simultaneously, the process 10 allows for control of the addition of: i) additional reductant, fluxes and ores to the molten material in the furnace 26 itself; and ii) electrical energy to the molten material in the furnace 26; to: i) ensure a target CO-content of the CO-containing gas and the desired degree of metallisation of the liquid metal product; ii) establish an operating temperature in the furnace 26 to form the liquid metal product and the liquid slag product suitable for tapping G from the furnace 26; and iii) manipulate the constituents of the liquid slag product such that it is compatible with a refractory lining 34 of the furnace 26 and / or a refractory lining of a duct 36 for channelling the molten material from the reactor 12.1 to 12.n to the furnace 26.

[0083] By harnessing the substantially greater amount of chemical energy available from the hot oxidising gas, as elucidated above, as opposed to using a reducing gas, the Applicant has surprisingly and unexpectantly shown that the process of the present invention allows for the agglomerates to be simultaneously melted and partially reduced, to allow for molten material transfer between the furnace before carbothermic smelting occurs. In doing so, metallurgical and energy efficiencies during carbothermic smelting in furnace 26 are improved. Prior hereto, the reduction of metalliferous feedstock material in this way was deemed to be impossible for numerous reasons appreciated by those skilled in the art, including the following.

[0084] The heating of metalliferous feedstock material utilising combusted hot oxidising gases, wherein the metalliferous feedstock material includes a carbonaceous reductant, is limited to 600°C as the carbonaceous reductant is known to be consumed by the Boudouard reaction. Accordingly, since smelting of metal oxides typically requires temperatures of between 1400°C - 1600°C, most of the carbonaceous reductant in the metalliferous feedstock material is expected to be consumed by the CO2 in the combusted hot oxidising gases. The former is best illustrated by WO 2017 / 089651 which discloses a method for preheating and smelting manganese ore sinter wherein the preheating is limited by the Boudouard and Water-gas shift reaction. Therefore, the preheating temperature in the pre-treatment silo can only reach a maximum of 700°C.

[0085] There is an accepted belief by those skilled in the art that smelting of metal oxides (which includes both the melting and reduction of the metal oxides) cannot proceed by using an oxidising gas let alone with one which has a high oxidising potential such as a gas containing oxygen. The known belief is that reduction of metal oxides is only possible, thermodynamically, when the partial pressure of O2 and CO2 are very low, which partial pressures are in orders of magnitude lower than those contained in combusted hot oxidising gases.

[0086] In addition hereto, it will be appreciated by those skilled in the art that reduction of metal oxides of chrome and manganese requires significant amounts of energy as well as the energy to melt them. The generally accepted belief is that there is inadequate energy from hot reducing gases available to smelt ores such as chrome and manganese.

[0087] Furthermore, commercially developed pre-treatment processes are limited to operating in the solid state. The smelted material needs to flow sustainably to a slag cleaning furnace for the final reduction of the metal oxides. The slag produced from the smelting of chrome refractory ore is known to have a high viscosity and would be challenging to flow sustainably. Yet further, it is known that refractory chrome ore smelts above 1700°C, and the accepted belief is that chrome ore can only be smelted using electrical energy, by drawing high temperature arcs.

[0088] By using the following process input for the packed bed 14, as set out in T able 1 below, the Applicant is able to produce the results from the packed bed 14 and the slag cleaning furnace 26, as set out in Table 2, which depicts a high recovery of chromium without drawing high energy electrical arcs as referred to above.

[0089] Table 1 : Process Input Variables Into The Packed Bed 14

[0090] Table 2: Results from the Packed Bed 14 and the Slag Cleaning Furnace 26 based on Table 1

[0091] In view of the above, the Applicant believes that the process of the present invention affords a superior advantage over the currently used technology.

[0092] The description is presented by way of example only in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention and / or the equipment utilised therein in more detail than is necessary for a fundamental understanding of the invention.

Claims

CLAIMS1 . A process for the carbothermic smelting of metalliferous feedstock material using oxidising gas including the steps of:(i) feeding composite agglomerates into a reactor to create a packed bed within a reactor, wherein the agglomerates comprise metalliferous feedstock material, reductant and fluxes;(ii) heating and smelting the agglomerates with hot oxidising gas, wherein the hot oxidising gas enters the reactor and is passed through the packed bed to form molten material comprising an intermediate slag constituent and a partially reduced metalliferous constituent;(iii) channelling the molten material into an electrical slag cleaning furnace;(iv) adding additional reductant to the molten material in the electrical slag cleaning furnace to form a liquid metal product, a liquid slag product, and a CO-containing gas; and(v) combusting the CO-containing gas with pre-heated air to form the hot oxidising gas which is oxygen enriched before entering the reactor in step (ii), wherein the temperature of the hot oxidising gas entering the reactor is controlled to be above 1400°C, and wherein the oxygen content of the hot oxidising gas is controlled to be between 0% - 20%.

2. The process according to claim 1 , wherein the metalliferous feedstock material is any material comprising a metal, metal oxide, metal carbonate of a metal or any combination of metals selected from the group consisting of manganese (Mn), chromium (Cr), vanadium (V), titanium (Ti), nickel (Ni), iron (Fe), and a combination thereof.

3. The process according to claim 1 or claim 2, wherein the metalliferous feedstock material is fine metalliferous feedstock material having a particle size of less than or equal to 6 mm.

4. The process according to claim 3, wherein the particle size of the fine metalliferous feedstock material is less than 100 pm at 80% passing sieve size (P80).

5. The process according to claim 1 , wherein the reductant is selected from the group consisting of anthracite, coke, char, charcoal and a combination thereof.

6. The process according to claim 1 or claim 5, wherein the reductant has a stoichiometric carbon content of 105% to 220% in relation to the composite agglomerates.

7. The process according to claim 1 , wherein the flux is selected from the group consisting of limestone, quartz, dolomite and a combination thereof.

8. The process according to claim 1 , wherein the feeding of the composite agglomerates is preceded by the production of the composite agglomerates, wherein the composite agglomerates are produced at a production facility.

9. The process according to claim 1 or claim 8, wherein the composite agglomerates include a binding agent, wherein the binding agent is selected from the group consisting of bentonite, cement, sodium silicate, molasses and a combination thereof.

10. The process according to any one of claims 1 , 8 or 9, wherein the composite agglomerates are sized to have a diameter of between 15 mm to 40 mm.

11. The process according to claim 1 , wherein the packed bed provides a fluid permeable interface locatable at an operatively downstream position relative to a region where the agglomerate is fed to the reactor to permit the hot oxidising gas to be passed therethrough.

12. The process according to claim 1 , wherein the hot oxidising gas is the product of combustion of the CO-containing gas, which, in turn, is a product of the reduction reaction which occurs during the formation of the molten material and the liquid metal product in both the reactor and the slag cleaning furnace, respectively.

13. The process according to claim 1 or claim 12, wherein the oxygen content of the hot oxidising gas is between 5% and 18%.

14. The process according to claim 1 or claim 13, wherein the oxygen content of the hot oxidising gas is between 10% and 15%.

15. The process according to any one of claims 1 , 12 or 13, wherein the hot oxidising gas is passed countercurrent to the direction in which the composite agglomerates enter the reactor.

16. The process according to any one of claim 1 or claims 12 to 15, wherein the temperature of the hot oxidising gas entering the reactor and passing through the packed bed in step (ii) is controlled to be between 1600°C and 1750°C when entering the reactor, depending on the type of metalliferous feedstock material fed to the reactor.

17. The process according to any one of claim 1 or claims 12 to 16, wherein the hot oxidising gas entering the reactor is fed at a speed of 1 m / s to 4 m / s.

18. The process according to claim 1 , wherein the slag cleaning furnace provides at least one electrode for providing electrical energy to the molten material and additional reductant added thereto in the slag cleaning furnace to allow for the final reduction of the partially reduced metal constituent to form the final liquid metal product and the formation of the liquid slag product.

19. The process according to claim 1 or claim 18, wherein the mode of operation of the slag cleaning furnace is selected from the group consisting of open bath, and partially open bath mode.

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