METHOD FOR TREATING STEELWORKS SLAG

Description

[0001] The invention relates to a method for treating steelworks slag.

[0002] During the production of pig iron and steel, various byproducts are produced. These vary in quality and therefore have diverse uses. Blast furnace slag is produced during the production of pig iron in a blast furnace. In its quenched and ground form, this slag is known as granulated blast furnace slag and is used as an additional main component in cement production. One characteristic of granulated blast furnace slag is its very low iron content of well below 5%. For this reason, the iron content of granulated blast furnace slag is not separated in industrial practice.

[0003] During further processing of the pig iron in the steelworks, the carbon content is reduced and further chemical changes occur. In order to separate out secondary components such as SiO2, manganese or phosphorus, limestone is added again during steel production, as in pig iron production. The limestone consists essentially of CaCO3 and dissociates into CaO and CO2. The carbon dioxide is released and contributes to the CO2 emissions from steel production. Alternatively, the limestone can be processed into quicklime through thermal treatment before being added to the pig iron, and the quicklime can be added to the pig iron instead of the limestone. In this case, the CO2 emissions arise in an upstream process but can be attributed to steel production.The following only considers the case of limestone addition to pig iron, but the presentation includes the use of quicklime instead of limestone after thermal pretreatment of the limestone. The CaO from the addition of limestone and / or quicklime serves to bind the minor components of the pig iron and, together with these and other additives, forms the so-called steelworks slag.

[0004] Steelworks slag can be separated from liquid iron or steel, like blast furnace slag, due to the density difference in the liquid state. Unlike blast furnace slag, steelworks slag contains significant amounts of iron. The iron is present in various oxidation states and compounds. Steelworks slag typically contains metallic iron (Fe), wustite (iron(II) oxide, FeO), hematite (iron(III) oxide, Fe2O3), magnetite (iron(II,III) oxide, Fe3O4), srebrodolskite (Ca2Fe2O5, C2F), tetracalcium aluminate ferrite (brownmillerite, Ca2(Al,Fe)2O5, C4AF) and other iron-containing compounds. Steelworks slags may also contain amorphous, iron-containing components.The compounds mentioned and all other phases described below do not generally occur in chemically pure form, but contain a variety of chemical elements as impurities in varying concentrations. The total iron content of steelworks slag is approximately 30%, if the iron content is expressed as Fe2O3, regardless of the actual oxidation state of the individual components. Separating such high iron contents and returning the iron to the metallurgical process is desirable from an economic perspective and can also improve the quality of a product obtained from steelworks slag. To date, steelworks slag has mostly been landfilled or used for secondary purposes such as road construction.

[0005] It is therefore desirable to be able to recover the iron content from steelworks slag. Ideally, this should be possible both in the still-liquid state and in the cooled and solidified state.

[0006] Steelworks slag also includes converter slag or LD slag, which is produced as slag during the Linz-Donawitz process. Alternatively, it is referred to as BOF slag (basic oxidation furnace). Steelworks slag also includes electric furnace slag, also known as EOS, stainless steel slag, also known as EDS, and secondary metallurgical slag, also known as SEKS. Steelworks slags have an average chemical composition, which varies depending on the steelworks, of approximately: 40% CaO, 30% Fe 2 O 3 , 10% SiO 2 , 5% MgO, 3% Al 2 O 3 , 3% MnO, as well as other elements or oxides in lower concentrations.From a mineralogical point of view, steelworks slags contain approximately: 20 to 30% belite, 15 to 30% srebrodolskite, about 10% wüstite, up to 10% free lime, up to 5% magnetite, up to 5% alite, as well as other crystalline compounds and up to 50% amorphous components.

[0007] The invention is therefore based on Task The aim is to provide a process for treating steelworks slag that enables a large proportion of the iron present to be recovered.

[0008] This object is achieved according to the invention by a method for treating steelworks slag having the features of claim 1.

[0009] Further advantageous embodiments are specified in the dependent claims, the further description and in the embodiment.

[0010] According to claim 1, the method according to the invention involves performing several steps. These steps do not necessarily have to be performed in the order described here.

[0011] The process according to the invention comprises step A) of providing steelworks slag which, when solidified, comprises at least iron(II) oxide (wustite). If solidified rather than still liquid steelworks slag is used, it should be so fine that it has a BET specific surface area of 0.1 m² / g, preferably 0.5 m² / g, in particular 1.0 m² / g or greater. It can be provided in solid form or still molten from a previous process. The iron(II) oxide, like most of the other substances mentioned here, is usually not in chemically pure form but contaminated, for example with foreign ions or grown together with other contents. It can be detected, for example, by means of an XRD analysis.

[0012] In step B), the steelworks slag is treated at a temperature of at least 600°C, preferably at least 800°C, in particular at least 1,000°C, with the addition of oxidizing agents and auxiliary materials. Depending on the condition of the slag after step A), heating may or may not be necessary.

[0013] The oxidizing agents partially or completely oxidize the existing iron(II) oxide to iron(III) oxide and / or iron(II,III) oxide. At the same time, other compounds are also partially or completely oxidized. Furthermore, the auxiliaries form a bond with the calcium present in the steelworks slag. This calcium was previously bound in calcium-iron compounds or other compounds, and during this process, iron(III) oxide and / or iron(II,III) oxide is released. Furthermore, the total amount of calcium silicates (alite, belite, rankinite, wollastonite), particularly belite, present in the treated steelworks slag is increased.

[0014] In a further step C), iron(III) oxide and / or iron(II,III) oxide can be separated from the treated steelworks slag.

[0015] Iron(II) oxide is also known as FeO or wustite and is formed during steelmaking, primarily during the reduction of carbon content. Like many other phases, wustite can contain very high concentrations of foreign oxides. Iron(III) oxide is also known as Fe2O3 and alternatively as hematite, which is the most common natural modification of iron(III) oxide. Iron(III,II) oxide is also known as Fe3O4 and occurs naturally in the form of magnetite.

[0016] Belite is also known as dicalcium silicate and has the chemical formula 2CaO · SiO 2 , the cement chemical abbreviation is C 2 S.

[0017] A basic idea of the invention can be seen in proposing a way to treat iron(II) oxide in steelworks slag, in this case to oxidize it to iron(III) oxide. The underlying reaction equation is as follows: (1) 2 FeO + ½ O 2 → Fe 2 O 3

[0018] Instead of Fe 2 O 3 , Fe 3 O 4 can also be formed, or a mixture of Fe 2 O 3 and Fe 3 O 4 . (2) 3 FeO + ½ O 2 →Fe 3 O 4

[0019] Further oxidation of iron(II, III) oxide also produces iron(III) oxide as a product: (3) 2 Fe 3 O 4 + ½O 2 ↔3 Fe 2 O 3

[0020] Treating, or if necessary heating, the steelworks slag at a temperature of at least 600°C, preferably at least 800°C, and especially at least 1000°C, has proven sufficient. In this state, the steelworks slag is not yet melted, and no unnecessary energy needs to be invested, as the processes described also take place at temperatures as low as 600°C. In the simplest form, oxygen from the air can be used as the oxidizing agent. However, other oxidizing agents such as H2O2 and other peroxides, ozone, or N2O, which are added in addition to the steelworks slag, are also possible.

[0021] According to the invention, additional additives are added to the steelworks slag for a further reaction in order to offer bound calcium from calcium-iron compounds, such as srebrodolskite or other compounds, a reaction partner so that the iron is released. The underlying reaction can be described, for example, as follows (4) 2CaO·Fe 2 O 3 +SiO 2 →2CaO·SiO 2 +Fe 2 O 3 or in cement chemistry shorthand notation C 2 F + S → C 2 S + F

[0022] This produces iron(III) oxide or iron(II,III) oxide and belite, whereby the products can be processed and separated in the further process.

[0023] According to step C) of the process according to the invention, the iron contained in the treated steelworks slag can be separated as iron(III) oxide and / or iron(II,III) oxide, since the iron is no longer bound in calcium-iron compounds or other complex compounds, but is present in the microstructure as an independent phase such as iron(III) oxide and / or iron(II,III) oxide. However, the iron oxide particles are closely intergrown with other phases such as belite.

[0024] The addition of additives, such as SiO2, and oxidizing agents, such as oxygen, can also be carried out in the liquid state, as long as the slag has not yet solidified when it is transferred in liquid form in step A). Iron oxide formation can also be achieved in this way.

[0025] According to the invention, in step A), the steelworks slag is provided in solid form and has a fineness corresponding to a BET specific surface area of 0.1 m² / g, preferably 0.5 m² / g, in particular 1.0 m² / g or greater. The comminution required for this can be carried out, for example, by a suitable grinding unit. It is also possible, however, to granulate still-liquid steelworks slag, for example, during a granulation process, and thus provide it with a sufficient fineness.

[0026] It is further preferred if, in step D), the treated steelworks slag, which has a temperature of at least 600°C, is heated in a reducing atmosphere, in particular by adding reducing agents, so that it is reduced again. In this process, iron(III) oxide is reduced to iron(II,III) oxide. This step is advantageously carried out after step B) and before step C).

[0027] The underlying reaction has already been described previously under (3).

[0028] During the oxidation in step B), depending on the oxidizing agent present and its amount, the iron(II,III) oxide is also oxidized to iron(III) oxide. If magnetic separation of the iron from the treated steelworks slag is desired, it is advisable to reduce the iron(III) oxide completely or almost completely to iron(II,III) oxide, as this can be separated more effectively using magnetic separation. It is preferred if the reduction is carried out without cooling the treated steelworks slag after step B), in order to avoid heating. The reduction can be carried out in a reducing atmosphere, such as CO2-containing air. However, reducing agents such as organic fuels, Fe, or FeO can also be added additionally or alternatively.The thermal treatment can, for example, be carried out in an electrically heated rotary kiln which contains an oxidising atmosphere in the upper part for step B) and a reducing atmosphere in the lower part for step D).

[0029] Step D) can be omitted if in step B) only incomplete oxidation occurred with formation of magnetite instead of hematite or if the formation of magnetite is not desired.

[0030] For further processing, in particular to prepare for step C), it is preferred to cool the warm, treated steelworks slag after the optional step D) or directly after step B), to solidify it, and to comminute it to a fineness corresponding to a BET specific surface area of 0.1 m 2 / g, preferably 0.5 m 2 / g, in particular 1.0 m 2 / g or greater. This can be done, for example, using a mill, in particular a vertical mill.

[0031] In principle, various separation mechanisms can be used to separate the iron(III) oxide and / or iron(II,III) oxide from the treated steelworks slag. Separation can advantageously be carried out using magnetic separation based on magnetic properties, density separation, or flotation. For example, density separation can be performed in conjunction with the previously described comminution of the treated steelworks slag, as processes are known in which density separation can be performed simultaneously with a comminution process.

[0032] For separation, the material to be separated can also be transferred into a suspension, especially with the use of water. Wet magnetic separation can often achieve better and more efficient results than dry magnetic separation.

[0033] Flotation is a physical, chemical separation process for fine-grained solids in which separation can occur based on the different surface wettability of the particles. For example, a suspension in water can be present, into which a gas is blown. Depending on the surface properties of the particles present, added auxiliary substances (collectors) can adsorb to the surface of the particles and temporarily bind the introduced gas bubbles, causing the particles to rise. The adsorption of the auxiliary substances is phase-sensitive, and this is how separation occurs.

[0034] The treated steelworks slag contains belite and other calcium-containing compounds, such as calcium silicates, which are often intergrown with the iron(III) oxide and / or iron(II,III) oxide. These can be broken up by the previously described ultrafine comminution in a mill. As an alternative or additional possibility, in step E), the treatment of the treated steelworks slag with CO2 is proposed in order to fully or partially convert belite (2CaO·SiO2) and, if present, other calcium silicates such as alite, wollastonite and / or rankinite into calcium carbonate (CaCO3) and silicon dioxide (SiO2) or other reaction products, such as dolomite or magnesium carbonate. In this way, the close intergrowth between iron oxide and belite can be largely eliminated, thus facilitating separation.This process step can, for example, be carried out in a suspension, so that the previous step of separation by flotation can be combined with this step. When the treated steelworks slag is mixed with a CO 2 -containing gas, such as air, the following reaction occurs: (5) 2CaO·SiO 2 →2CO 2 →2CaCO 3 +SiO 2 .

[0035] This usually does not produce pure SiO 2 , but rather a SiO 2 -rich residue.

[0036] In detail, step E) can be carried out in an aqueous suspension of the treated, cooled, solidified, and crushed steelworks slag. In this case, a CO2-containing gas can be injected. However, other contact or introduction methods for the CO2 are also possible.

[0037] When the belite is broken up by the chemical reaction according to equation (5), the iron(III) oxides and / or iron(II,III) oxides that are intergrown with it are simultaneously released so that they can be separated.

[0038] As already described, in this context, the CaCO 3 can also be separated, for example in the form of CaCO 3 -rich material with a proportion of at least 70 mass%, preferably at least 80 mass%, even more preferably at least 90 mass% CaCO 3, by means of flotation or other processes subsequent to or simultaneously with the treatment of the treated steelworks slag with CO 2. In principle, the separation of a specific material within the scope of the invention can also be carried out in such a way that other materials are separated by parallel processes, so that only the desired material remains.

[0039] It is preferable if the gas containing CO2 originates from steel production. This occurs as a waste product during steel production, as previously described, and worsens the CO2 balance of steel production. By using it in the process described here, the CO2 can be bound and thus does not escape into the environment. This similarly applies when quicklime is used for steel production, provided quicklime production is incorporated into the overall process. This results in a significantly better environmental balance.

[0040] In this context, the recovered CaCO3-rich material can be fed back into steelmaking or pig iron production for further use. As already described, CaCO3 is used in steelmaking to separate secondary components such as SiO2. By using the recovered CaCO3 in steelmaking, the consumption of limestone, which essentially consists of CaCO3, is significantly reduced, which in turn can reduce the costs of steelmaking. Both the CaCO3-rich residue and the unseparated mixture of CaCO3 and SiO2 can also be fed into cement production as a raw meal component or as an additional main component.

[0041] Similarly, the recovered SiO 2 -rich residue can be reused, for example, with a SiO 2 content of at least 70 mass%, preferably at least 80 mass%, and even more preferably at least 90 mass%. One possible use is as pozzolan in cement production.

[0042] The recovered iron(III) oxide and / or iron(II,III) oxide can also be used for further upstream processes, in this case steel production or blast furnace processes. The same applies to other recovered iron oxides and metallic iron. This, too, is not a pure material. This is particularly suitable because the steelworks slag already originates from these processes and is therefore often located in close proximity.

[0043] When used in the steelworks, the oxygen requirement during refining can also be reduced.

[0044] In a similar way to the SiO 2 -rich residue, the belite-containing material (2CaO·SiO 2 ), for example with a proportion of at least 40 mass% belite, preferably at least 50 mass%, even more preferably at least 60 mass%, can also be fed into cement production. Belite is a component of clinker and must otherwise be produced there through energy-intensive calcination processes. Similarly, a material rich in other calcium silicates such as alite, wollastonite and / or rankinite can also be fed into cement production, wherein the total proportion of calcium silicates is at least 40 mass%, preferably at least 50 mass%, even more preferably at least 60 mass%.

[0045] In principle, metallic iron and / or iron(II,III) oxide, as well as other compounds, can be separated from the steelworks slag prior to step A), for example, using magnetic separation. This significantly reduces the energy required to heat the steelworks slag. This also reduces the effort required for subsequent iron separation.

[0046] The invention is explained in more detail below using an exemplary embodiment and a schematic flow diagram. This drawing shows: Fig. 1 a schematic flow diagram of the method according to the invention

[0047] In Fig. 1 A schematic flow diagram of a possible embodiment of the method according to the invention is shown. This combines possible steps described previously. In principle, it is also possible to omit individual steps.

[0048] In step I, steelworks slag is prepared. In its solidified state, this slag contains various iron-containing compounds, such as metallic iron (Fe), wustite (iron(II) oxide, FeO), hematite (iron(III) oxide, Fe2O3), magnetite (iron(II,III) oxide, Fe3O4), srebrodolskite (Ca2Fe2O5, C2F), and tetracalcium aluminate ferrite (brownmillerite, Ca2(Al,Fe)2O5, C4AF). Converted to iron(III) oxide, the average iron content is approximately 30%.

[0049] The steelworks slag provided in step I is then ground to a sufficient fineness in step II, so that it has, for example, a BET specific surface area of 0.1 m² / g, preferably 0.5 m² / g, in particular 1.0 m² / g or greater. This grinding can be carried out, for example, using a vertical roller mill. Alternatively, the steelworks slag can already be in granular form prior to step I, so that it no longer needs to be further ground and step II can be omitted.

[0050] In one step IIIElemental iron (Fe) and iron(II,III) oxide (Fe 3 O 4 ) can be separated from ground or crushed steelworks slag using magnetic separation. These two components have good ferromagnetic properties, making magnetic separation possible. This is supported by the presence of the described fineness, as the materials are usually no longer intergrown with other phases. This step is also optional.

[0051] The steelworks slag is then heated in step IV. Instead of the process steps described so far, liquid slag from upstream processes can also be used. The treatment, in which solidified slag is also heated, takes place in a normal atmosphere, such as ambient air. Additional ambient air can also be injected. It is essential that an oxidation reaction takes place in the steelworks slag as described in equation (1). (1) 2FeO+½O 2 →Fe 2 O 3

[0052] Alternatively, Fe 3 O 4 can be formed: (2) 3FeO+½O 2 →Fe 3 O 4

[0053] O2 present in the air can serve as an oxidizing agent. Alternatively or additionally, the steelworks slag can also be treated with other oxidizing agents such as H2O2 and other peroxides, ozone, N2O, or pure oxygen.

[0054] In addition, auxiliary materials, for example in the form of SiO 2, are added. This addition can also be made in step II, so that homogenization of solid slag occurs during grinding.

[0055] By adding SiO 2 to the slag, the reaction described in equation (4) takes place: (4) 2CaO·Fe 2 O 3 +SiO 2 →2CaO·SiO 2 +Fe 2 O 3

[0056] Rock flour, for example from sandstone or quartzite, coal fly ash, sand, silica dust, pozzolan and / or fired clay, as well as the SiO 2 -rich residue from this process can be used as SiO 2 sources.

[0057] For separation using a magnetic separator, it is advantageous if the iron(III) oxide is converted into iron(II,III) oxide, as this allows for better separation using a magnetic separator. Therefore, without additional cooling, the heated steelworks slag can be exposed to a reducing atmosphere in step V, resulting in the conversion of the iron(III) oxide to iron(II,III) oxide, as described in equation (3). It should be noted that this reaction, as an oxidation in the reverse direction, already occurred in step IV, and iron(II,III) oxide was oxidized to iron(III) oxide. Accordingly, this step can be omitted if only enough oxidant was added to the slag to produce mainly magnetite and little or no hematite. (3) 2 Fe3O4 +½O2 ↔3Fe2O3

[0058] Subsequently, in step VI, the steelworks slag is cooled again, whereby the existing thermal energy can be recovered.

[0059] In step VIIa, iron(II;III) oxide and, if still present, iron(III) oxide can then be separated from the cooled slag, for example by means of a magnetic separator or density separation. For this purpose, it is advantageous if the cooled slag is ground again so that belite components intergrown with iron(II,III) oxide are separated.

[0060] The remaining slag, which has a high belite content, can then be fed to the cement industry for use as an additional main component or as a raw meal ingredient.

[0061] Alternatively, or additionally, the slag can be further treated in step VIIb by adding water to the slag to create an aqueous suspension. For this purpose, the treated slag can also be finely ground, but this is not absolutely necessary. Air or another CO2-containing gas, such as exhaust air from steel production, can be blown into the suspension, causing the belite and / or other calcium silicates such as alite, wollastonite, and / or rankinite to decompose into calcium carbonate (CaCO3) and silicon dioxide (SiO2) or other reaction products. This separates the belite from intergrown iron oxides, making them easier to separate later. The underlying reaction is described in equation (5). (5) 2CaO·SiO2 +2CO2 →2CaCO3 +SiO2

[0062] The iron oxides that were previously intergrown with other phases can be further separated, for example, by flotation in step VIII. This step can also be carried out simultaneously with step VIIb. This can also involve separating the SiO 2 -rich residue and the calcium carbonate (CaCO 3 ).

[0063] The recovered iron, both in metallic form (Fe) and in the form of iron(III) or iron(II,III) oxides, can subsequently be recycled into steel production. Similarly, calcium carbonate (CaCO3) can also be recycled into steel production, thereby reducing the amount of limestone required.

[0064] As described above, the extracted belite can be fed directly into cement production. The same applies to the SiO 2 -rich residue, which can also be reused in step II. Likewise, the CaCO 3 -rich residue and the unseparated mixture containing SiO 2 and CaCO 3 can be fed into cement production as a raw meal component and / or as an alternative main ingredient.

[0065] The CO 2 required in step VIIb preferably originates from steel production and can thus significantly improve the environmental balance with regard to CO 2 production during steel production, since it can be bound in this process according to the invention.

[0066] The method according to the invention is explained in more detail below using a concrete example.

[0067] For the investigations, a steel mill slag with the following composition, determined by quantitative X-ray diffraction, was used: 17% C2F, 45% β-C2S, 2% γ-C2S, 5% CaO, 3% metallic iron, 4% portlandite, 24% wüstite, and 1% magnetite. The values are given in mass percent and refer to the crystalline components. Amorphous phases are also present, but these were not quantified. This also applies to the analytical results below, which were also determined by quantitative X-ray diffraction.

[0068] The material was ground in a vibrating disc mill and then in a McCrone mill with the addition of water. The ferromagnetic components were then separated using a permanent magnet in an aqueous suspension, and the sample was subsequently dried. The separated amount was 5% of the initial material. The separated product consisted of 6% C2F, 4% β-C2S, 73% metallic iron, 7% magnetite, and 10% wustite. It is therefore an iron-rich material with low levels of CaO, SiO2, and other oxides. Due to its composition, it can be used for the production of pig iron and steel.

[0069] The material remaining after magnetic separation was composed of the following: 15% C2F, 46% β-C2S, 4% γ-C2S, 3% calcite, 1% metallic iron, 4% portlandite, 25% wüstite, and 2% magnetite. This material still contains large amounts of iron, but not in the form of metallic iron. The iron is bound in various mineral phases, primarily as C2F and wüstite. Both phases are non-ferromagnetic and therefore difficult to separate with a magnetic separator.

[0070] To enable the separation of these iron quantities, the material was mixed with an auxiliary material (Sikron SF 6000 SiO2 fine powder) in a ratio of 1:14 (SiO2:modified steelworks slag). The SiO2 fine powder consisted entirely of cristobalite. The two materials were homogenized by grinding them together in a vibrating disc mill for 2 minutes. Subsequently, a portion of the mixture was fired for 4 hours at 1100°C in a muffle furnace. The material was placed in an open crucible and thus had constant contact with the atmosphere and the oxygen it contained.

[0071] During the high-temperature treatment, oxygen uptake and chemical reactions occurred. After cooling, the phase composition was determined by quantitative X-ray diffraction. It was 6% C2F, 48% β-C2S, 4% γ-C2S, 9% C3A, 9% rankinite, 3% wustite, and 22% magnetite. Consequently, the thermal treatment resulted in extensive oxidation of the wustite to magnetite, as the wustite concentration decreased from 23% to 3% and the magnetite concentration increased from 2% to 22%.

[0072] At the same time, the C2F was converted to C2S, consuming cristobalite and releasing iron oxide, which also contributed to an increase in the magnetite concentration in the sample. Thus, the thermal treatment after the addition of the additives resulted in a large portion of the iron being bound in a phase that can be separated by magnetic separation. Apparently, the oxygen supply was not high enough for further oxidation to hematite. Furthermore, the concentration of calcium silicates in the sample increased, as the belite concentration rose from 46% to 52% and the rankinite concentration increased from 0% to 9%.

[0073] After thermal treatment, a large portion of the iron is bound as magnetite and can be separated. To facilitate the separation process, the material was ground again in a McCrone mill with the addition of water for 5 minutes and then treated with CO2. For this purpose, 5 grams of the treated steel mill slag were added to 400 ml of water and continuously stirred while CO2 was simultaneously introduced into the beaker containing the sample. Phase separation was facilitated by the use of ultrasound and the addition of nucleating agents (CaCO3, Merck). After a treatment period of 3 hours, the sample was filtered, dried, and analyzed. After the modified steel mill slag reacted with carbon dioxide, the material no longer contained belite, and the only crystalline compounds detected were C2F, rankinite, magnetite, and calcite. Other reaction products such as amorphous SiO2, magnesium carbonate, and dolomite.

[0074] The magnetite was separated from an aqueous suspension using a permanent magnet. Subsequently, flotation was performed to separate the calcium carbonate and SiO2. Dodecylamine was used as the collector, and starch was used as the pusher, causing the calcium carbonate to rise with the introduced air bubbles and the SiO2 and other phases to sink. This allowed the calcium carbonate to be removed from the top and the SiO2-rich residue to be removed from the bottom. After treatment, these were separated and could be dried.

[0075] The process according to the invention thus allows iron to be separated from steel mill slag in a simple and efficient manner, and even the remaining components can be used to reduce the costs of upstream processes. Furthermore, the process according to the invention enables CO2 capture, thereby significantly improving the environmental impact.

Claims

1. Method for treating steel mill slag having the steps: A) providing steel mill slag, which, when solidified, has iron(II) oxide (FeO) and, if solidified, has a fineness such that the steel mill slag has a specific surface area according to BET of 0.1 m2 / g or more; B) treating the steel mill slag at a temperature of at least 600°C, while adding oxidizing agents and auxiliary agents, wherein the oxidizing agents oxidize at least a part of the iron(II) oxide (FeO) present to iron(III) oxide (Fe2O3) and / or iron(II,III) oxide (Fe3O4) and wherein the auxiliary agents form a bond at least with calcium from calcium-iron compound present and bound in the steel mill slag and thereby release iron(III) oxide (Fe2O3) and / or iron(II,III) oxide (Fe3O4) and further increase the proportion of 2 CaO · SiO2 (belite) and / or other calcium silicates, such as alite, wollastonite and / or rankinite, in the treated steel mill slag, C) separating iron(III) oxide (Fe2O3) and iron(II, III) oxide (Fe3O4) out of the treated steel mill slag.

2. Method according to claim 1, characterized in that the method further includes: D) further treating the steel mill slag treated at a temperature of at least 600°C in a reducing atmosphere by means of adding reducing agents to the heated, treated steel mill slag to reduce iron(III) oxide (Fe2O3) to iron(II, III) oxide (Fe3O4).

3. Method according to claim 2, characterized in that step D) is carried out after step B) and before step C).

4. Method according to any one of claims 1 to 3, characterized in that the warm, treated steel mill slag is cooled, solidified and crushed, in particular ground up, before step C) so that the cooled, solidified and crushed steel mill slag has a specific surface area according to BET of 0.1 m2 / g or more.

5. Method according to any one of claims 1 to 4, characterized in that the separation in step C) is based on magnetic properties, density and / or by means of flotation.

6. Method according to any one of claims 1 to 5, characterized in that the method further includes: E) treating the treated steel mill slag with CO2 to convert 2 CaO · SiO2 (belite) and / or other calcium silicates, such as alite, wollastonite and / or rankinite, into CaCO3 and SiO2 and / or other corresponding reaction products.

7. Method according to claim 6, characterized in that step E) is carried out in an aqueous suspension of cooled, solidified and crushed steel mill slag and in that a gas, which contains CO2, is injected.

8. Method according to claim 6 or 7, characterized in that the method further includes: F) separating CaCO3-rich material after step E), in particular by means of flotation.

9. Method according to any one of claims 6 to 8, characterized in that the gas, which contains CO2, originates from steel production.

10. Method according to claim 8, characterized in that a CaCO3-rich material is separated and / or recovered and fed into the steel or pig iron production process or cement production process for further utilization.

11. Method according to any one of claims 1 to 10, characterized in that an SiO2-rich material is separated and / or recovered and fed into the cement production process for further utilization.

12. Method according to any one of claims 1 to 11, characterized in that the recovered iron(III) oxide (Fe2O3) and / or iron(II, III) oxide (Fe3O4) is fed into the steel production process and / or blast furnace processes for further utilization.

13. Method according to any one of claims 1 to 12, characterized in that a 2 CaO · SiO2 (belite)-rich material and / or a material which is rich in other calcium silicates such as alite, wollastonite and / or rankinite is separated and / or recovered and fed into the cement production process for further utilization.

14. Method according to any one of claims 1 to 13, characterized in that before step A), in a step 0), the steel mill slag is prepared to the desired particle size by means of grinding and / or granulation.

15. Method according to any one of claims 1 to 11, characterized in that in step 0) or after step A) metallic iron (Fe) and / or iron(II, III) oxide (Fe3O4) are separated from the steel mill slag.