Use of particulate material and method for producing material for cement production

Abstract

The present invention relates to the use of a particulate material as an activator for the reduction of chromium (VI) to chromium (III) in the production of cement, concrete, or other similar materials. The particulate material originates from an industrial pyrometallurgical process, preferably a steelmaking process, and contains at least 10% by weight of iron (II) and / or iron (III), calculated as FeO, and preferably no more than 5% by weight, more preferably no more than 3% by weight, of Fe(0), calculated on the dry weight of the particulate material. The present invention also relates to a method for producing a particulate material suitable for use as an activator for the reduction of chromium (VI) to chromium (III) in the production of cement, concrete, or other similar materials.

Description

[Technical Field]

[0001] The present invention relates to the use of particulate material derived from pyrometallurgical processes. The invention also relates to a method for reducing chromium (VI) to chromium (III) in the production of cement, concrete or other similar materials, as well as a method for producing material for cement production according to the subject matter of the appended independent claims. [Background technology]

[0002] Steel slag is one of the major by-products in the production of steel, stainless steel, and carbon steel. It is essential to find uses for all of the various by-products of industrial processes, including steel slag. To date, steel slag has found use as a filler material in various applications, such as coarse aggregate for asphalt, aggregate for concrete production, and in making phosphate slag fertilizer. However, new economical methods for upgrading steel slag into valuable products are needed to utilize the full potential of this industrial by-product.

[0003] Steelmaking, as well as the pyrometallurgical industry in general, produces large amounts of by-products containing calcium, silica, and aluminum oxide. These industrial by-products can be used as raw materials in cement production, replacing limestone. However, these by-products often contain large amounts of iron oxide, which melts in cement kilns and causes problems in kiln operation and subsequent process steps in cement production. For example, unprocessed steel slag can contain up to 35% iron oxide. By-products from pyrometallurgical industries can also contain metal particles that cannot be ground to the required particle size. Therefore, the use of by-products from pyrometallurgical industries for cement clinker production is limited.

[0004] Steelmaking slag and other by-products from pyrometallurgical processes are produced in large quantities today. Therefore, there is a need to develop more viable methods and uses for upgrading steelmaking slag and other by-products into valuable products that are produced in large quantities. Currently, separation of different components of steelmaking slag is a difficult and energy-consuming process. Steelmaking slag has a crystalline mineral composition and contains various amounts of valuable steel and other metal particles. The hard crystalline matrix of the minerals in the slag, combined with the hard metal particles, makes comminution of the slag difficult, and therefore selective separation of components is ineffective, which has limited the feasibility of upgrading from steelmaking slag.

[0005] Typical cement consists of cement clinker and auxiliary cementitious materials. Cement clinker is produced by calcining natural materials containing Ca, Si, Al, and Fe, such as limestone (CaCO3), clay (SiO2 and Al2O3), and sand (SiO2), at high temperatures in a cement kiln. In the cement kiln, limestone calcination (CaCO3 + heat → CaO + CO2) releases large amounts of CO2. This makes the cement industry one of the world's largest CO2 emitters. Growing awareness of climate change requires all industries to critically examine their activities and find new and effective ways to reduce their carbon footprint. The application of pyrometallurgical by-products, such as unprocessed steel slag, as raw materials for clinker would reduce CO2 emissions, but their high chromium and iron content has limited or even prevented their application. The iron oxide content in the cement clinker raw mix is ​​controlled and corrected to a level that achieves a specific amount of liquid phase during the calcination process in the kiln. The final content of Fe2O3 in the clinker is at a maximum level of about 5%.

[0006] Furthermore, the possibility of using by-products from the pyrometallurgical industry in the production of cement clinker is limited by the presence of traces of unwanted heavy metals, particularly chromium. Cement kilns have a highly oxidizing environment, so that chromium fed to the kiln is at least partially oxidized to hexavalent chromium, which is soluble, carcinogenic, mutagenic, and irritating. Hexavalent chromium is formed by the high-temperature oxidation of trivalent chromium in the clinker kiln. Depending on the raw materials, the total chromium content in the cement clinker can be between 10 ppm and 100 ppm, a portion of which is oxidized to Cr(VI). When such cement is mixed with water, the Cr(VI) present dissolves and causes skin irritation.

[0007] Directive 2003 / 53 / EC of the European Parliament and of the Council required member states to ban the use and sale of all cements and cement-containing preparations containing soluble chromium(VI) after hydration, exceeding 2 ppm by dry weight of cement, effective from January 17, 2005. To achieve this limit, Cr(VI) reducing agents can be added to cement to reduce Cr(VI) to insoluble, non-toxic Cr(III). These reducing agents are based on iron sulfate, tin sulfate, or antimony oxide, and Fe(II), Sn(II), or Sb(III) ions precipitate Cr(VI) as a salt. However, these reducing agents are often expensive and not widely available. To minimize the use of reducing agents, the total chromium in the clinker raw mix is ​​typically minimized, and the remaining hexavalent chromium is reduced using available reducing agents or materials.

[0008] Therefore, there is a need in the cement industry to find ways to provide new materials for cement production that reduce the CO2 footprint of the produced cement. Additionally, there is a need for ways to provide effective Cr(VI) reducing agents. Summary of the Invention

[0009] One object of the present invention is to minimize, or perhaps even eliminate, the drawbacks present in the prior art.

[0010] A further object of the present invention is to find new, technologically advantageous uses for particulate materials derived from industrial pyrometallurgical processes.

[0011] Another object of the present invention is to provide a simple and efficient method for producing an activator for the reduction of Cr(VI) to Cr(III) in the production of cement, concrete, or other similar materials.

[0012] These objects are achieved by the invention with the features set out below and in the characterizing parts of the independent claims. Some preferred embodiments of the invention are set out in the dependent claims. The embodiments referred to in this document relate to all aspects of the invention, where applicable, even if not necessarily mentioned separately. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 shows a flow diagram illustrating one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] <Detailed explanation> A typical use of the particulate material according to the invention is as an activator for the reduction of chromium (VI) to chromium (III) in the production of cement, concrete or other similar materials, the particulate material originating from an industrial pyrometallurgical process, preferably a steelmaking process, and comprising at least 10 wt. % iron (II) and / or iron (III), given as Fe2O3, calculated on the dry weight of the particulate material, and preferably no more than 5 wt. %, more preferably no more than 3 wt. %, even more preferably no more than 1 wt. % Fe(0).

[0015] An exemplary process according to the present invention for reducing chromium (VI) to chromium (III) in the production of cement, concrete, or other similar materials comprises: obtaining a particulate material derived from an industrial pyrometallurgical process, preferably a steelmaking process, comprising at least 10% by weight of iron(II) and / or iron(III), calculated as Fe2O3, and preferably not more than 5% by weight, more preferably not more than 3% by weight, even more preferably not more than 1% by weight of Fe(0), calculated on the dry weight of said particulate material; adding said particulate material as an activator to a cement mix, concrete mix, or other similar material to reduce chromium (VI) to chromium (III); Includes.

[0016] An exemplary method according to the present invention for producing a particulate material suitable for use as an activator for the reduction of chromium (VI) to chromium (III) in the production of cement, concrete, or other similar materials comprises: obtaining a starting particulate material comprising iron(II) and / or iron(III) originating from an industrial pyrometallurgical process, preferably from a steelmaking process, and fractionating the starting particulate material into at least a first fraction and a second fraction, wherein the first fraction and the second fraction have different iron(II) and iron(III) contents, the second fraction being a particulate material comprising at least 10% by weight of iron(II) and / or iron(III) calculated on the dry weight of the particulate material, calculated as Fe2O3, and preferably not more than 5% by weight, more preferably not more than 3% by weight, even more preferably not more than 1% by weight of Fe(0); Includes.

[0017] It has now been surprisingly found that particulate material derived from industrial pyrometallurgical processes, when containing at least 10% by weight of iron(II) and / or iron(III), can be used, without further processing, as an activator for reducing chromium(VI) to chromium(III) in the production of cement, concrete, mortar, or other similar materials. The particulate material may be incorporated, i.e., added, to provide a dry cement mix, concrete mix, or other similar material. The use according to the present invention has several advantages, as it provides a valuable use for a by-product that would otherwise be considered waste and deposited as such. Furthermore, the present invention provides a facile and effective method for upgrading material derived from industrial pyrometallurgical processes into particulate material that can be used as an activator for reducing chromium(VI) to chromium(III) in the production of cement, concrete, or other similar materials. Particulate material derived from industrial pyrometallurgical processes, preferably steel slag, contains sufficient iron compounds to effectively reduce chromium(VI) to chromium(III). Furthermore, the resulting reduction effect has been shown to be long-lasting and not diminish significantly over time. The use of particulate materials may also provide additional benefits, such as a strength-enhancing effect on cement, concrete, or other similar materials.

[0018] The particulate material used in the present invention for reducing chromium(VI) to chromium(III) preferably contains iron(II) and / or iron(III) in an amount of at least 15 wt. %, preferably at least 20 wt. %, and more preferably at least 30 wt. % FeO, calculated on the dry weight of the particulate material. The particulate material may contain, for example, 15-90 wt. % or 20-85 wt. % FeO, typically 20-80 wt. % or 25-70 wt. % FeO, more typically 20-60 wt. % or 30-60 wt. % FeO. The high amount of iron(II) and / or iron(III) makes the particulate material an effective activator for reducing chromium(VI) to chromium(III) in the production of cement, concrete, or other similar materials.

[0019] According to one preferred embodiment of the invention, the particulate material is used in a dry state, i.e., it is mixed as a dry mass with the cement mix, concrete mix, or other similar material before or during cement grinding. Alternatively, the particulate material may be added as a dry mass to the finished cement after cement grinding or before cement shipping.

[0020] According to one embodiment, the particulate material may be used as an aqueous slurry, for example when added to cement during the preparation of concrete or mortar.

[0021] According to one preferred embodiment, the particulate material may be used in combination with, i.e., contacted with, a proton-donating chemical activator, preferably in the form of an acid, more preferably an organic acid. The proton-donating chemical activator may be used in liquid or dry form. The proton-donating chemical activator increases the solubility of iron(II) and further reduces iron(III) to iron(II). In this way, when the particulate material is used as an activator in the production of cement, concrete, or other similar materials, an appropriate amount of iron(II) is available to reduce chromium(VI) to chromium(III). According to one embodiment, the proton-donating chemical activator may be an acid, preferably an organic acid such as a carboxylic acid, which is used in combination with, e.g., mixed with, the particulate material to activate Fe(II) solubility.

[0022] The proton-donating chemical activator is preferably an organic acid (more preferably a carboxylic acid) or a salt thereof, more preferably selected from the group including oxalic acid, acetic acid, formic acid, citric acid, tartaric acid, salts thereof, or any combination thereof. Preferably, the organic acid may be a dicarboxylic acid, which is preferably oxalic acid. The proton-donating chemical activator, e.g., an acid, may be in liquid or solid form, preferably in solid form. Treating particulate material with a high iron(II) content with the organic acid increases the rate of dissolution of iron(II).

[0023] According to one embodiment, the particulate material may be used in combination with 0.1 to 50 wt. %, preferably 0.1 to 25 wt. %, more preferably 0.1 to 10 wt. % or 0.5 to 10 wt. % of a proton-donating chemical activator, calculated relative to the total weight of the particulate material. The proton-donating chemical activator is preferably an organic acid, such as a carboxylic acid, its salt, or any mixture thereof, as defined above. For example, the organic acid may be used in an amount of less than 10 wt. % calculated relative to the total weight of the particulate material. The organic acid, e.g., a carboxylic acid, may be used in an amount of 0.25 to 9 wt. % or 0.5 to 7 wt. % calculated relative to the total weight of the particulate material.

[0024] According to one embodiment of the present invention, a proton-donating chemical activator is contacted with the particulate material, which may be before, during, or after the particulate material is added to a cement mix, concrete mix, or other similar material. The particulate material may be first mixed with the proton-donating chemical activator and then added to the cement mix, concrete mix, or other similar material. According to one embodiment, the proton-donating chemical activator may be added to the cement mix, concrete mix, or other similar material separately from the particulate material. For example, the particulate material and the proton-donating chemical activator may be added simultaneously but separately to the cement mix, concrete mix, or other similar material. The particulate material and the proton-donating chemical activator may be added sequentially to the cement mix, concrete mix, or other similar material, one after another.

[0025] According to one embodiment, a proton-donating chemical activator may be mixed with the particulate material to activate Fe(II) solubility before the particulate material is added to a cement mix, concrete mix, or other similar material. Treating the particulate material with a proton-donating chemical activator, such as an acid, preferably an organic acid, in liquid or solid form before use as an activator in cement or concrete production is beneficial for both Cr(VI) reduction and the physical properties of the cement or concrete. The particulate material may be activated by mixing with a proton-donating chemical activator, such as an organic acid, in the presence of moisture, e.g., by mixing naturally moist particulate material with a solid organic acid. In this case, Fe(II) is formed on at least the surface of the particles of the particulate material. This is beneficial because the particulate material is already activated when mixed into a cement mix or concrete mix, and is not dependent on the pH of the cement / water or concrete mix, where Cr(VI) dissolution and reduction to Cr(III) are expected to occur.

[0026] The proton-donating chemical activator may be added dry to a cement mix, concrete mix, or other similar material.

[0027] According to one embodiment of the present invention, a proton-donating chemical activator is combined with, i.e., contacted with, the particulate material, which may occur before, during, or after cement grinding. The proton-donating chemical activator may be used as a liquid, e.g., added to a cement mix before or during cement grinding. The proton-donating chemical activator may also form part of an additive used in grinding, such as a grinding aid. In this case, the particulate material may be combined with the proton-donating chemical activator by adding the particulate material to the cement mix, either before or during cement grinding, or to the finished cement after cement grinding. The activation process between the proton-donating chemical activator and the particulate material occurs when the cement is contacted with water to form mortar or concrete. During the preparation of mortar or concrete, when mixing cement with water, the proton-donating chemical activator may be added in liquid form, either as such or as part of an additive used in mortar and concrete.

[0028] Some particulate materials derived from industrial pyrometallurgical processes have naturally high concentrations or amounts of iron(II) and / or iron(III), i.e., 10% by weight or greater. This high concentration or amount makes such particulate materials suitable for use as activators for the reduction of chromium(VI) to chromium(III). When this is not the case, according to one aspect of the present invention, it is possible to obtain a starting particulate material derived from an industrial pyrometallurgical process and comprising iron(II) and / or iron(III), and to fractionate this starting particulate material to provide a particulate material fraction having a desired iron(II) and / or iron(III) content for use as an activator for the reduction of chromium(VI) to chromium(III).

[0029] The particulate material may be used in varying amounts in the production of cement, concrete, or other similar materials, depending on the concentration of chromium (VI) that must be reduced to chromium (III) and the iron (II) and iron (III) content of the particulate material. However, one advantage of the present invention is that the composition of the particulate material derived from industrial pyrometallurgical processes, such as steel slag, is generally suitable for use in cement, concrete, or other similar materials, and allows for the addition of even large amounts of particulate material, up to 65% by weight. Those skilled in the art can estimate and / or calculate the required amount to be used based on general experience. The particulate material may be used in an amount of, for example, 0.5 to 65% by weight, typically 1 to 40% by weight, and often 1 to 15% by weight or 1.5 to 10% by weight, calculated relative to the total weight of the cement mix, concrete mix, or other similar material.

[0030] In general, the particulate material used in the present invention, either directly or as the starting particulate material, may be any inorganic slag material derived from an industrial pyrometallurgical process and containing iron oxide. In this context, the terms "iron oxide" and "oxide of iron" are used synonymously and are fully interchangeable. Both terms refer to iron(II) and iron(III), which are oxidation states present in the mineral structure of the particulate material and / or slag material derived from the pyrometallurgical process, unless otherwise specified. In this context, "iron oxide" simply refers to the oxidation state of iron, regardless of whether the iron is combined with oxygen or exists as a separate iron compound, when present in the mineral structure of the particulate material.

[0031] The particulate material or starting particulate material derived from a pyrometallurgical process may be selected from ferrous slag, ferroalloy slag, base metal slag, pyrometallurgical tailings, or any combination thereof. The particulate material or starting particulate material may be derived from an industrial pyrometallurgical production process of steel, which may be stainless steel or carbon steel, copper, nickel, or zinc. The particulate material or starting particulate material may be a steelmaking slag selected from basic oxygen furnace slag, electric arc furnace slag, ladle furnace slag, Linz-Donauwitz slag (LD slag), open hearth slag, blast furnace slag, desulfurization slag, or any combination thereof, and is preferably basic oxygen furnace slag, electric arc furnace slag, ladle furnace slag, Linz-Donauwitz slag (LD slag), open hearth slag, or any combination thereof.

[0032] In the present context, the term "steel slag" refers in particular to any solid waste or by-product resulting from the production of steel, stainless steel, or carbon steel. Steel slag may be, but is not limited to, steel slag, stainless steel slag, carbon steel slag, basic oxygen furnace (BOF) slag, electric arc furnace (EAF) slag, or ladle furnace (LF) slag, or any mixture thereof. According to one preferred embodiment, the particulate material or starting particulate material is a steel slag selected from basic oxygen furnace slag, electric arc furnace slag, induction furnace slag, Linz-Donauwitz slag, ladle furnace slag, or any combination thereof, in particular selected from basic oxygen furnace slag, electric arc furnace slag, induction furnace slag, or any combination thereof. These slags have been problematic for industrial use due to their metal particles and / or their chemical composition, e.g., due to their content of heavy metals, in particular chromium, high iron oxide content, and / or calcium oxide content. However, the present invention provides an effective method for converting these slags to be suitable for use as activators for the reduction of chromium (IV) to chromium (III), which, among other uses, can be used in the production of cement clinker or even cement with appropriate grinding and fractionation.

[0033] According to one embodiment, the particulate material or starting particulate material may be a mixture of materials, such as slag or slag material, from different industrial pyrometallurgical processes. Materials from different pyrometallurgical processes carried out at the same production site may be mixed together to form the particulate material or starting particulate material. For example, basic oxygen furnace slag or electric arc furnace slag can be mixed with blast furnace slag.

[0034] The particulate material or starting particulate material used in the present invention and derived from an industrial pyrometallurgical process may be in the form of inorganic mineral particles comprising iron oxide, i.e., iron in the form of oxidation states - iron(II) and iron(III), and preferably containing calcium. Calcium may be present as calcium oxide, calcium silicate, calcium carbonate, or any combination thereof, as indicated above. The particulate material or starting particulate material typically comprises calcined mineral particles containing calcium. The particulate material or starting particulate material typically comprises, for example, brownmillerite (Ca2(Al,Fe)2O5), wustite (FeO), and / or magnetite (FeO * The particulate material used in the present invention therefore contains iron oxides, typically both FeO and FeO, i.e., the particulate material has an initial iron oxide content, expressed as total iron oxide content, before any fractionation. The particulate material derived from an industrial pyrometallurgical process may further contain at least silicon, magnesium, and / or aluminum oxides. When the particulate material is derived from a copper, nickel, or zinc production process, it may contain FeSiO. In particular, slag derived from the production of steel, stainless steel, and carbon steel, also known as steelmaking slag, is a CO2-free material that contains Ca silicate, Ca aluminate, and Ca ferrite and is a source of Fe(II) and Fe(III) ions.

[0035] The particulate material or starting particulate material used in the present invention and derived from an industrial pyrometallurgical process, such as the mineral fraction of steelmaking slag, may have the following main composition (wt%): SiO2 10-50%, e.g. 10-30% Fe2O3 3-35%, e.g. 10-30% Cr2O3 0.1-4%, e.g. 0.1-2.5% MnO 2-5%, e.g., 2.5-4% CaO 15-45%, e.g. 30-45% MgO 1-15%, e.g., 2-10% Al2O3 1-8%, e.g. 1.5-6.5% SO3 0.2-2%, e.g. 0.2-1.5%.

[0036] For example, the iron(II) and iron(III) content in the steelmaking slag used in the present invention may be 1 to 45 wt. %, preferably 3 to 40 wt. %, more preferably 15 to 40 wt. %, or 20 to 40 wt. %, calculated based on the total dry weight of the slag, in terms of Fe2O3. In the present application, when the iron content is given in terms of Fe2O3, it includes both iron(II) compounds and iron(III) compounds, and is calculated assuming that they are in the form of Fe2O3.

[0037] The particulate material or starting particulate material used in the present invention and derived from an industrial pyrometallurgical process may preferably comprise chromium(III) in an amount of 0.05 to 5 wt. %, preferably 0.1 to 4 wt. %, more preferably 0.1 to 1.5 wt. %, calculated on the total dry weight of said particulate material or starting particulate material, calculated on the total dry weight of said particulate material or starting particulate material.

[0038] The iron(II) and iron(III) content of the particulate material can be adjusted by fractionation. In this manner, the iron(II) and iron(III) content of the particulate material can be tailored to suit a particular cement, concrete, or other similar material and its specific application of reducing chromium(VI) to chromium(III). The starting particulate material for fractionation is in the form of mineral particles having variable iron(II) and iron(III) content. The starting particulate material is fractionated into at least a first fraction and a second fraction, wherein the first fraction and the second fraction have different iron(II) and iron(III) contents. The second fraction is in the form of a particulate material containing at least 10% by weight of iron(II) and / or iron(III) calculated as Fe2O3, calculated on the dry weight of the particulate material. This means that iron(II) and / or iron(III) are concentrated in the second fraction, which forms particulate material to be used as an activator for the reduction of chromium(VI) to chromium(III). Fractionation thus provides a means of upgrading various pyrometallurgical specific materials or slags to be suitable for use in the reduction of chromium(VI). After fractionation, the iron(II) and iron(III) content of the second fraction is higher than the initial iron(II) and iron(III) content of the starting particulate material before fractionation. When the starting particulate material is fractionated into a first fraction and a second fraction, the first fraction has a lower iron oxide content than the second fraction, and after fractionation, the iron oxide content of the first fraction is lower than the initial iron oxide content of the starting particulate material before fractionation. The second fraction may have a total iron oxide content of iron(II) and iron(III), calculated on dry weight, that is at least 5% by weight higher, preferably at least 15% by weight higher, more preferably at least 20% by weight higher than the initial total iron oxide content in the starting particulate material.

[0039] The specific number of fractions and the size distribution of particles in the various fractions are not critical to the practice of the present invention. Although first and second fractions are discussed herein as examples, the starting particulate material can be fractionated into first, second, third, and any successive fractions as desired. The number of fractions and the size distribution of particles within the fractions can be designed and planned based on the amount of the starting material, e.g., slag, and the capabilities of the selected separation technique.

[0040] Any suitable fractionation method can be used that allows the particulate material to be fractionated based on its iron oxide content. The fractionation can include one or more fractionation steps, which can be performed using the same or different separation techniques, as described below. According to one embodiment, the separated fractions can be comminuted between fractionation steps. Any of the comminution methods described below in connection with the pretreatment step can be used for comminution between fractionation steps.

[0041] According to one embodiment of the present invention, the starting particulate material may be fractionated into a first fraction and a second fraction by magnetic separation, density separation, size separation, electrostatic separation, flotation separation, eddy current separation, gravity separation, and airflow separation, or any combination thereof, preferably by magnetic separation. For example, the first fraction and the second fraction may be separated by density separation. Generally, iron oxide-rich mineral particles are heavier than mineral particles with a low iron oxide content. Therefore, the first fraction and the second fraction may be separated by conventional density and gravity separators. Alternatively, the first fraction and the second fraction may be separated by size separation. Iron oxide-rich mineral particles are typically harder than mineral particles with a low iron oxide content. Iron oxide-rich mineral particles are typically larger in size after a micronization step, if one is performed, which provides a good basis for size separation or size classification of the first and second fractions.

[0042] Preferably, the fractionation of the starting particulate material is carried out as a dry fractionation. According to one embodiment, the starting particulate material may be fractionated using size separation and / or magnetic separation. Any suitable magnetic separation technique may be applied for magnetic separation.

[0043] According to one preferred embodiment of the present invention, the starting particulate material can be fractionated into a first fraction and a second fraction by using magnetic separation. The iron(II) and iron(III) contents in the first and second fractions can be adjusted by the strength of the magnet used. By appropriately selecting the magnetic field strength, the oxides of Fe(II) and Fe(III) can be concentrated in separate fractions. In this way, the properties of the first fraction can be adjusted to be suitable for producing cement clinker in a cement kiln, and the properties of the second fraction can be adjusted to be suitable for use as an activator for Cr(VI) reduction.

[0044] According to one preferred embodiment, the starting particulate material, e.g., ground slag, may be fractionated using magnetic separation, e.g., weak magnetic separation. For example, the apparatus for separating weakly magnetic particles disclosed in European Patent No. 3283225, incorporated herein by reference, may be used. Magnetic separation provides an effective way to separate particles containing iron oxide from other particles and concentrate them into a second fraction. Because mineral particles have different magnetic properties depending on their iron oxide content, magnetic separation can be used to at least partially separate the first and second fractions. The magnetic field strength used for magnetic separation may be selected depending on the fractionation results required and / or the particulate material used. According to one example, a weak magnet used to separate iron oxide-rich particles has a field strength of 200 to 3000 gauss.

[0045] According to one embodiment of the present invention, the distribution of iron oxide between the first and second fractions can be adjusted by the magnetic field strength used in the magnetic separation. This means that the iron(II) and iron(III) content of the second fraction and the iron(II) and iron(III) content of the first fraction can be adjusted as needed. For example, the magnetic field strength used in the magnetic separation can be adjusted depending on the specific characteristics of the particulate material and / or the desired iron(II) and iron(III) composition of the first and second fractions.

[0046] The magnetic separation step may be performed before or after any of the optional classification steps described below. If a classification and separation step is performed before the magnetic separation step, the fraction(s) resulting from the classification and separation step are each subjected to the magnetic separation as individual fractions - i.e., the resulting fraction(s) having different size distributions are not mixed before the subsequent magnetic separation step.

[0047] In one embodiment of the present invention, magnetic separation is performed in two or more stages. The two stages of magnetic separation can be performed by a first magnetic separation using a weak magnet followed by a second magnetic separation using a strong magnet. A strong magnetic separation can be performed before the weak magnetic separation. A combination of two strong magnetic separations can also be applied. The strong magnetic separation can be performed using a rare earth magnet, an electromagnet, or other types of strong magnet. For example, after the first magnetic separation, one of the recovered fractions can optionally be subjected to a further magnetic separation stage to obtain a fraction containing Fe(II)-bearing particles and a fraction containing Fe(III)-bearing particles that differ in the concentration and state of iron oxide (Fe(II) or Fe(III)). This further magnetic separation stage can be performed using an apparatus and method for separating weakly magnetic particles according to the apparatus and method disclosed in EP 3283225 B1. Since the two mineral fractions cannot be completely separated from each other, the separation is usually partial.

[0048] According to one embodiment, the particulate material may be subjected to a non-magnetic separation step in addition to or instead of the magnetic separation step. The non-magnetic separation may be performed before or after the magnetic separation. The particulate material, e.g., crushed slag, may be subjected to a non-magnetic metal separation step. The non-magnetic separation method may be selected from the list including eddy current separation, gravity separation, and airflow separation to separate non-magnetic heavy metals and non-magnetic light metals. The non-magnetic metal separation step may be performed before or after the classification step, but after the separation and crushing. If classification and separation steps are performed before the non-magnetic separation step, the resulting fraction(s) are subjected to the non-magnetic separation as individual fractions - i.e., fraction(s) with different particle sizes are not mixed before the subsequent non-magnetic separation step.

[0049] After fractionation, the amount of iron(II) and iron(III) in the second fraction in the form of particulate material may be 15% by weight or more, preferably 20% by weight or more, more preferably 30% by weight or more, calculated as Fe2O3, relative to the total dry weight of the particulate material. The total iron oxide content may be, for example, 15-50% by weight, preferably 20-45% by weight, more preferably 30-40% by weight, calculated as Fe2O3, relative to the total dry weight of the particulate material. The iron(II) and iron(III) content in the particulate material will vary depending on the pyrometallurgical process from which the particulate material originates and, optionally, the fractionation method used.

[0050] A high iron(II) content is beneficial for the particulate material when it is used as an activator for reducing chromium(VI) to chromium(III). Fractionation allows for full utilization of the iron(II) oxide in the particulate material. Fractionation can also be used to increase the iron(II) oxide content in the second fraction while reducing the amount of undesired materials, such as free lime and / or periclase (MgO). According to one embodiment of the present invention, the particulate material, e.g., the second fraction after fractionation, may contain at least 5 wt. % iron(II) in terms of FeO, based on the dry weight of the particulate material, preferably 10 wt. % iron(II), more preferably 15 wt. % iron(II), based on the dry weight of the particulate material. The particulate material may contain, for example, 5-10 wt. % iron(II), preferably 10-15 wt. % iron(II), more preferably 15-20 wt. % iron(II), based on the dry weight of the particulate material.

[0051] After fractionation, but prior to optional comminuting, the particulate material can be treated with a proton-donating chemical activator, for example an organic acid in liquid or solid form.

[0052] When used as an activator, the particulate material preferably has a particle size Dv90 of 200 μm or less, preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 30 μm or less. The particulate material may have a particle size Dv90 in the range of 3 to 200 μm, preferably 3 to 100 μm or 3 to 50 μm, more preferably 3 to 30 μm. The particle size Dv90 indicates that 90% of the material, by weight, is below a predetermined size. In this way, the particle size of the particulate material matches the fineness of cement, allowing, for example, the particulate material to be added directly to final cement or concrete. If necessary, the particulate material, e.g., the second fraction after magnetic fractionation, may be subjected to further milling or micronization to obtain fine particles. In one embodiment, the milling or micronization step is performed to ensure that the recovered fine non-magnetic minerals containing calcium, silicates, iron, and alumina are separated from each other. To mill and refine the particular material to the desired particle size Dv90, all milling and refinement methods described below in combination with a pretreatment step can be used.

[0053] The particulate material is added to a cement mix, concrete mix, or other similar material as an activator for reducing chromium (VI) to chromium (III). The particulate material is preferably added as is, i.e., in a dry state. The particulate material may be added to the cement mix before or after the cement mill, meaning that the particulate material is introduced into the cement manufacturing process after the cement kiln. Any chromium that may be present in the particulate material is in the form of Cr(III) because it has not been exposed to an oxidizing environment. Cr(III) is insoluble and safe to use, making the particulate material well suited for use as an auxiliary material in cement production. The particulate material is therefore used as a Cr(VI) reducing agent for the production of cement, concrete, or other similar materials.

[0054] Typically, when excess Cr(VI) is found in clinker, ferrous sulfate, tin sulfate, or antimony oxide is used to compensate for it through precipitation with Fe(II), Sn(II), or Sb(III) ions. When fractionation, e.g., magnetic separation, is used to increase the amount of Fe(II) in the particulate material, the particulate material is particularly suitable for use as an active hexavalent chromium reducing agent for cement, concrete, or other similar materials. When particulate material containing iron(II) oxide is fed to a cement kiln, the iron(II) is oxidized to iron(III) and loses its ability to reduce soluble Cr(VI). This can be avoided in the present invention by concentrating the iron(II) oxide in the particulate material, which bypasses the cement kiln and is fed to a cement mix, concrete mix, or other similar material at a later stage, where it is active as a Cr(VI) reducing agent.

[0055] The particulate material is particularly suitable as an activator for reducing chromium (VI) to chromium (III) in the production of Portland cement, preferably having a general composition of 61-67 wt% CaO, 19-23 wt% SiO2, 2.5-6 wt% Al2O3, 2-5 wt% Fe2O3, and 1.5-4.5 wt% SO3. Prior to the addition of the particulate material, the cement mix for Portland cement may contain 25-60 wt% tricalcium silicate, 20-45 wt% dicalcium silicate, 5-12 wt% tricalcium aluminate, 6-15 wt% tetracalcium aluminoferrite, and 2-10 wt% gypsum. The particulate material may be used to produce general-purpose cements of Type I, II, III, IV, or V.

[0056] According to one embodiment, the particulate material or starting particulate material may be pretreated in one or more pretreatment steps prior to the fractionation step or before the particulate material is used as an activator for chromium(VI) reduction. One pretreatment step may include comminuting the particulate material or starting particulate material derived from an industrial pyrometallurgical process by crushing and / or grinding to liberate any metal particles that may be present from the mineral matrix. The material derived from pyrometallurgical processes typically contains a mineral matrix in which metal particles may be embedded. For example, stainless steel slag may typically contain up to 4-5 wt. % metallic stainless steel, which, while a valuable product, also increases the energy consumption of the comminution step if it remains in the crushed slag.

[0057] Thus, although metal particles, i.e., Fe(0), do not interfere with the reduction of chromium (VI) to chromium (III), their presence in cement can cause processing difficulties and should generally be considered a waste of resources. In this context, the expression "metal particles" generally refers to free metal particles, e.g., Fe(0) particles, and alloy particles, e.g., steel particles. When used as an activator for chromium (VI) reduction, the particulate material preferably contains a low amount of metal particles. The particulate material may contain 5% by weight or less, preferably 3% by weight or less, more preferably 2% by weight or less, even more preferably 1% by weight or less, or 0.5% by weight or less of metal particles, i.e., Fe(0). The particulate material may contain 0 to 5% by weight, typically 0.1 to 3% by weight, and more typically 0.5 to 2% by weight of metal particles, i.e., Fe(0). Sometimes, the particulate material may contain 0.1 to 1% by weight of metal particles, i.e., Fe(0).

[0058] The comminution in the pretreatment step may be carried out using any method suitable for liberating metal particles from the mineral matrix material, including, but not limited to, milling, grinding, the use of a vertical or horizontal shaft impact crusher or a rotor centrifugal crusher, or any combination thereof. Preferably, the comminution is carried out as dry comminution. For example, the comminution may be carried out using an impact crusher, a high-energy impact crusher, a jaw crusher, a cone crusher, a hammer crusher, a roll crusher, a ball mill, a rod mill, or any combination thereof. One preferred comminution method is high-energy impact crushing, in which the material to be crushed is accelerated to a high speed and thrown against a moving counter element, which breaks the material into particles and liberates the metal particles from the mineral matrix. High-energy impact crushing brings the material from the pyrometallurgical process to a state where the mineral particles—i.e., the particulate material—and the metal particles can be further separated from each other.

[0059] For example, steelmaking slag may first be subjected to a pretreatment step of separation and crushing to obtain crushed steelmaking slag, in which metal particles and oxides are at least partially liberated from the hard mineral matrix, and this process allows them to be concentrated, for example, using magnetic separation or other suitable separation. In this disclosure, the term "separation and crushing" refers to a process in which slag is crushed, i.e., to provide smaller particle sizes of solid materials, and the crushing is carried out in a manner that separates the metal particles and minerals in the slag from each other. The separated minerals, i.e., the particulate material or starting particulate material, may contain metals in the form of compounds, such as calcium silicate, calcium ferrite, and brownmillerite. Crushers that can be used include jaw crushers, cone crushers, hammer crushers, impact crushers, and roll crushers, and may also include crushers such as ball mills or rod mills. Physically, separation and crushing refers to any process that can generate a separation force that breaks inclusions (cracks) between metal steel particles and minerals. One example of a separate crushing method is high impact dry crushing according to published patent publication FI128329.

[0060] In one embodiment, the pulverization or separation may be performed using a dry crushing process. In this case, dry crushing means that essentially no water or other liquid is added to the slag before crushing. Traditionally, metal particles, such as stainless steel, are separated from the slag by wet crushing, which requires the addition of water or other liquid to the slag before crushing the metal particles. As a result of wet crushing, the remaining slag becomes a wet slurry, which cannot be recycled. Dry crushing prevents the formation of a wet slurry and allows the mineral fraction to be used as a particulate material or starting particulate material to provide an activator for the production of cement, concrete, or other similar materials. While dry crushing processes, such as high-impact dry crushing, are preferred, the slag may contain a certain amount of moisture depending on the steel and / or stainless steel production and the pretreatment of the slag. In one embodiment, the slag subjected to dry crushing has a moisture content of 2% to 15% by weight, preferably 3% to 8% by weight.

[0061] The refining or separate crushing can be carried out in one stage or in two or more stages. For example, the refining or separate crushing of steel slag can be carried out in two stages, in which a first dry crushing stage produces coarser particles, which are then subjected to a second dry crushing stage, which produces a separated, finer particle size. The refining or separate crushing can also be carried out in three or more stages, in which each subsequent crushing stage produces finer particles compared to the previous crushing stage. Milling can be carried out in two or more stages, each of which can further comprise one or more individual crushing substeps.

[0062] Furthermore, in a pretreatment step, the particulate material or starting particulate material derived from an industrial pyrometallurgical process may be refined to a particle size Dv50 of 10 mm or less, preferably 3 mm or less or 2 mm or less, more preferably 1.5 mm or less. The particle size Dv50 may be in the range of 0.1 to 10 mm, preferably 0.2 to 2 mm, preferably 0.3 to 1.5 mm, and in some cases 0.5 to 1 mm. The particle size Dv50 indicates that 50% of the material by weight is below a predetermined size. As used in this disclosure, particle size is measured according to standards ISO 13320:2020 and ISO 9276-2:2014. The particle size of the particulate material may be adjusted depending on the composition of the material and / or the separation method used for fractionation. When the starting particulate material has a specified particle size, effective separation can be achieved during fractionation. The particulate material may preferably have a particle size of 1.5 mm or less or 1.3 mm or less to avoid damaging cement mill grinding equipment in subsequent process steps, particularly where the material originating from a pyrometallurgical process may contain embedded or trapped metal particles.

[0063] Another pretreatment step for the particulate material or material derived from an industrial pyrometallurgical process to obtain the starting particulate material may further include size classification and / or separation of metal particles. Separation of metal particles may preferably be performed using magnetic separation and / or sieving. The separation and / or size classification pretreatment step may be performed either before or after the above-mentioned fine-graining pretreatment step, or may be performed both before and after the fine-graining pretreatment step. According to one embodiment, after the fine-graining, the pretreatment step comprises separating metal particles from the finely-grained particulate material, preferably using magnetic separation and / or size classification. When the size classification pretreatment is performed before the fine-graining pretreatment, it is possible to obtain a fine fraction having a particle size Dv50 of less than 1 mm and containing up to 50% by weight, typically 10-40% by weight, of total calcium, expressed as equivalent calcium oxide as measured by XRF. In this context, the expression "calcium", unless otherwise specified, refers to the total content of calcium compounds in the form of oxides, hydroxides, silicates, ferrites, aluminates, or trace amounts of carbonates, and includes all chemical compounds of calcium. Thus, total calcium includes all calcium compounds present, including calcium silicates, calcium carbonates, calcium oxides, etc.

[0064] For example, the steel slag crushed in the separation and crushing step is classified based on particle size. Classification of crushed slag particles may be performed using any suitable method for sieving or screening the formed particles. Classification or separation based on particle size can be performed to obtain at least two fractions with different particle sizes. The two fractions can be characterized as a small fraction and a medium fraction. In one embodiment, the large fraction is separated and can be recycled back to the dry crushing step.

[0065] After the pretreatment step, the separated metal particles may be returned or reused in pyrometallurgical processes, such as steelmaking. For example, when material from a basic oxygen furnace or an electric arc furnace, i.e., slag, is refined to a particle size Dv50 of 2 mm or less or 1.5 mm or less, the majority of the metal particles are in the form of large particles having a particle size of 1.5 mm or more, i.e., they can be separated by screening or sieving using a screen or sieve with 1.5 mm openings. Small metal particles that pass through the screen or sieve, e.g., metal particles having a particle size of 1.3 mm or less, are quickly oxidized to iron oxide. Alternatively or additionally, the metal particles can be separated using a known magnetic separator with an appropriate magnetic field.

[0066] After the optional pre-treatment step and before the optional fractionation, the particle size distribution of the particulate material is preferably such that large metal particles having a particle size of 1.5 mm or more are not trapped or embedded within the mineral matrix in the particulate material or starting particulate material.

[0067] The first fraction obtained from the fractionation of the starting particulate material typically has a lower iron(II) and iron(III) content compared to the second fraction, which forms the particulate material used to reduce chromium(VI) to chromium(III). At least a portion of the first fraction can be used to form part of the feed material for producing cement clinker in a cement kiln. This means that the first fraction is used to replace or supplement conventional feed materials for cement clinker production. In this context, the expression "feed material for producing cement clinker" encompasses all materials and combinations or mixtures of materials used to produce cement clinker and introduced into the kiln. The present invention makes it possible to separate and concentrate the first and second fractions from the starting particulate material, with the aim of using them separately in different steps of the cement production process. This way of processing and using certain materials from pyrometallurgical processes makes it possible to benefit from the CO2-neutrality of the materials in addition to their Cr(VI) reduction ability. It has now been surprisingly discovered that by fractionating starting particulate material from an industrial pyrometallurgical process into a first fraction having a relatively low iron oxide content and a second fraction having a relatively high iron oxide content, it is possible to use a larger amount of material from the industrial pyrometallurgical process as feed material for a cement kiln. In this way, problems caused by iron oxide in the cement kiln can be avoided. The present invention allows materials from industrial pyrometallurgical processes, particularly basic oxygen furnaces and electric arc furnaces, to be effectively used in cement production. This is beneficial because it reduces the need for virgin materials from natural sources, such as limestone, that are uncalcined, i.e., emit CO2 in the cement kiln. At the same time, the production volume per ton of kiln feed material can be increased due to reduced CO2 emissions, and the energy consumption of the clinker production process can be reduced due to the partial elimination of the calcination step. Lower NOx emissions can also be achieved due to the lower flame temperatures required in the cement kiln.In particular, when materials from industrial pyrometallurgical processes contain calcium oxide, the total CO2 emissions of cement clinker production can be significantly reduced. In other words, according to one embodiment of the present invention, at least a portion of the first fraction is introduced into the cement clinker production process so that at least a portion of the first fraction participates in the chemical reaction that forms the clinker. The first fraction may be introduced into the kiln as is or in combination with other raw materials. The first fraction may be used as the sole raw material of the feed, or it may be used as part of the feed together with other raw materials. One or more additional raw materials selected from the list including limestone, gypsum, clay, shale, sand, iron ore, bauxite, fly ash, and blast furnace (BF) slag may also be added to the cement kiln feed. Thus, the present invention may even provide a cost-effective and efficient method of producing material for cement clinker production in a cement kiln.

[0068] Fractionation of the starting particulate material may allow adjustment of the iron oxide content between the first and second fractions, i.e., the method may include fractionating the particulate material into a first and a second fraction and adjusting the iron oxide content of the first and second fractions. Preferably, at the same time, the calcium content, such as the calcium silicate, calcium carbonate, and / or calcium oxide content, of the first fraction is increased compared to the initial calcium content of the starting particulate material before fractionation. In this way, it is possible to adjust the iron oxide and / or calcium content of the first and second fractions to suit the desired end use. The first fraction, intended for cement clinker production in a cement kiln, may have a low iron oxide content and a high calcium content, and the second fraction, intended for use as an activator in cement or concrete production, may have a high iron oxide content. According to one embodiment of the invention, the first fraction may have a total iron oxide content, calculated on dry weight, that is at least 5% by weight lower, preferably at least 15% by weight lower, and more preferably at least 20% by weight lower than the initial iron oxide content of the starting particulate material before fractionation. In addition, the first fraction may have a calcium content that is at least 3% by weight higher, preferably at least 5% by weight higher, more preferably at least 7% by weight higher, and in some cases at least 10% by weight higher than the initial calcium content of the starting particulate material before fractionation.

[0069] Thus, the first fraction after fractionation has a lower iron oxide, i.e., iron(II) and iron(III), content than the second fraction. In this way, fractionation preferably produces a first fraction rich in calcium, such as calcium oxide and / or calcium silicate, but low in iron oxide. The first fraction, i.e., the recovered fine non-magnetic particles, contains primarily CaO and SiO, making it an excellent starting material for cement production. The cement raw materials are fed into a rotary cement kiln, which is heated in stages to 1500°C. During this process, the raw materials are converted into typical cement compounds, such as dicalcium silicate (2CaO·SiO2) and tricalcium silicate (3CaO·SiO2), tricalcium aluminate (3CaO·Al2O3), and tetracalcium aluminoferrite (4CaO·Al2O3·Fe2O3). The particulate material preferably contains calcium, such as calcium oxide and / or calcium silicate, and has an initial calcium content. The first fraction may contain, for example, particles of alite, belite, merwinite, gehlenite, periclase, mayenite, dolomite, and / or calcite. The presence of calcium makes the first fraction particularly suitable as a feed material for cement clinker production. The high calcined material content reduces the need to use virgin materials, such as limestone, as feed material for the cement kiln, effectively reducing the total CO2 emissions of the clinker production process. Furthermore, the first fraction contains reduced contents of metals, such as Fe, Cr, and V, due to fractionation, e.g., magnetic separation. This is beneficial because less energy is required for comminution. More importantly, the reduced contents are beneficial because these metals, especially Cr and V, are not desired in the cement kiln.

[0070] The starting particulate material used in the present invention often contains chromium, i.e., the starting particulate material before fractionation has an initial chromium content. It has been observed that the chromium present in the particulate material is usually associated with iron oxide. This means that when the particulate material is fractionated into a first fraction and a second fraction according to the iron oxide content of the particles, at least a portion of the chromium will be transferred to the second fraction along with the iron oxide. This means that the chromium content in the first fraction is reduced, thereby introducing less chromium into the cement kiln during the cement clinker production process, significantly reducing the formation of harmful Cr(VI). According to one embodiment of the present invention, the first fraction may have a chromium content, calculated on a dry weight basis as Cr2O3, that is at least 15% by weight lower, preferably at least 20% by weight lower, and more preferably at least 25% by weight lower, than the initial chromium oxide content of the starting particulate material before fractionation.

[0071] The total chromium content in the first fraction after fractionation may be 0.5 wt. % or less, preferably 0.3 wt. % or less, and more preferably 0.1 wt. % or less, calculated on the dry weight of the first fraction, expressed as Cr2O3. The total chromium content may be, for example, 0.05 to 0.5 wt. % or less, calculated on the dry weight of the first fraction, expressed as Cr2O3. The total chromium content expressed as Cr2O3 includes all oxidation states of chromium. The chromium content varies depending on the starting particulate material used. For example, induction furnaces and electric arc furnaces are often used to produce steel from recycled materials, where at least a portion of the chromium is bound to the steel and iron oxide.

[0072] The first fraction may be refined after the fractionation step to a particle size Dv90 of 200 μm or less, preferably 100 μm or less. The first fraction may preferably be refined to a particle size Dv90 in the range of 0.01 to 200 μm, preferably 0.1 to 100 μm. In this way, the particle size of the first fraction is preferably matched to the other feed materials fed to the cement kiln and used to produce cement clinker.

[0073] The general benefits of the present invention and its various embodiments described above are as follows: use of steelmaking slag in valuable products, reduced energy consumption in the kiln due to the use of calcined slag, reduced stack emissions due to lower CO2 in the slag compared to natural raw materials, and improved safety of the cement due to the reduction of harmful components such as hexavalent chromium. Thus, the present invention may even enable the use of particulate material derived from industrial pyrometallurgical processes as a novel feed material for cement production processes. It is envisaged that the method may offer the possibility of drastically reducing or even completely eliminating the use of natural resources in cement clinker production and may provide a CO2-free production process for cement clinker.

[0074] Some embodiments of the present invention are described in the following numbered paragraphs. 1. A method for producing a material for cement production, said method comprising: obtaining a particulate material containing a content of iron oxide, and preferably calcium, and derived from an industrial pyrometallurgical process; fractionating the particulate material into a first fraction and a second fraction, the first fraction having a lower iron oxide content than the second fraction; Including, at least a portion of said first fraction is used to form part of the feed material for producing cement clinker in a cement kiln; and / or The method wherein at least a portion of the second fraction is used as a supplemental material for cement production.

[0075] 2. The method of paragraph 1, wherein the particulate material is fractionated into the first fraction and the second fraction by using magnetic separation, density separation, size separation, electrostatic separation, flotation, or any combination thereof.

[0076] 3. The method of paragraph 2, wherein the particulate material is fractionated by using magnetic separation.

[0077] 4. The method of any one of paragraphs 1, 2, or 3, wherein the first fraction has an iron oxide content that is at least 5% by weight less, preferably at least 15% by weight less, and more preferably at least 20% by weight less than the iron oxide content in the particulate material before fractionation.

[0078] 5. The method of any one of the preceding paragraphs 1 to 4, wherein the second fraction has an iron oxide content that is at least 5% by weight greater, preferably at least 15% by weight greater, and more preferably at least 20% by weight greater than the iron oxide content in the particulate material before fractionation.

[0079] 6. The method of any one of the preceding paragraphs 1 to 5, wherein the second fraction comprises iron(II) oxide.

[0080] 7. The method of any one of the preceding paragraphs 1 to 6, wherein the particulate material has a particle size Dv50 of less than 10 mm, preferably less than 2 mm, more preferably less than 1.5 mm.

[0081] 8. The method of any one of the preceding paragraphs 1 to 7, characterized in that it comprises, prior to fractionation, a pre-treatment step of reducing the material from the industrial pyrometallurgical process to a particulate material having a particle size Dv50 of 10 mm or less, preferably less than 2 mm, more preferably less than 1.5 mm.

[0082] 9. The method of paragraph 8, wherein the pulverization is carried out using an impact crusher, a high-energy impact crusher, a jaw crusher, a cone crusher, a hammer crusher, a roll crusher, a ball mill, a rod mill, or any combination thereof.

[0083] 10. The method of paragraph 8 or paragraph 9, characterized in that the pre-treatment step comprises separating metal particles from the finely divided particulate material, preferably using magnetic separation and / or size classification to separate metal particles from the finely divided particulate material.

[0084] 11. The method of any one of the preceding paragraphs 1 to 10, wherein the particulate material derived from an industrial pyrometallurgical process is selected from ferrous slag, ferrous alloy slag, base metal slag, pyrometallurgical tailings, or any combination thereof.

[0085] 12. The method of paragraph 11, wherein the particulate material is selected from basic oxygen furnace slag, electric arc furnace slag, ladle furnace slag, Linz-Donauwitz slag (LD slag), open hearth slag, blast furnace slag, desulfurization slag, or any combination thereof.

[0086] 13. The method of any one of the preceding paragraphs 1 to 11, wherein an acid, preferably an organic acid, is mixed with the second fraction.

[0087] 14. The method according to paragraph 12, characterized in that the organic acid is selected from oxalic acid, acetic acid, formic acid, citric acid, tartaric acid, or any combination thereof, preferably oxalic acid.

[0088] 15. The method of any one of the preceding paragraphs 1 to 12, characterized in that the first fraction is, after the fractionation step, micronized to a particle size Dv90 of 200 μm or less, preferably in the range of 0.01 to 200 μm, and / or the second fraction is, after the fractionation step, micronized to a particle size Dv90 of 30 μm or less, preferably in the range of 3 to 30 μm.

[0089] An embodiment of the present invention comprises: obtaining a first fraction comprising particulate material derived from a pyrometallurgical process; obtaining a second fraction comprising particulate material derived from a pyrometallurgical process; wherein the first fraction has a lower iron oxide content than the second fraction, and the first fraction forms part of a feed material supplied to a cement kiln in the production of cement clinker; The second fraction is added to the cement mix after the cement kiln as a supplementary material. The present invention relates to a method for producing cement.

[0090] Further embodiments of the present invention are described in the following paragraphs: Embodiment 1 is (a) providing steelmaking slag; (b) subjecting the steelmaking slag to separation and crushing to obtain crushed steelmaking slag; (c) subjecting the crushed steel slag to at least one magnetic separation step to separate magnetic particles from non-magnetic particles and recovering the magnetic and non-magnetic particles; (d) subjecting the recovered non-magnetic particles to at least one separation step to at least partially separate Fe2+-loaded particles from Fe3+-containing particles into an Fe2+-containing particle fraction and an Fe3+-containing particle fraction, respectively; (e) optionally subjecting the Fe2+-loaded fraction and / or the Fe3+-loaded mineral fraction particles, respectively, to milling to obtain finely milled particles of the Fe2+-loaded fraction and / or the Fe3+-loaded mineral fraction, respectively; The present invention relates to a method for upgrading steelmaking slag, including:

[0091] Embodiment 2 relates to the method of embodiment 1, further comprising, prior to step (d), one or more classification steps followed by one or more separation steps to obtain at least one fine particle fraction comprising particles of a size between 0 and 3 mm, preferably between 1.5 and 2.5 mm.

[0092] Embodiment 3 relates to the method according to embodiment 1 or embodiment 2, wherein the separation and crushing method is high-impact dry crushing.

[0093] Embodiment 4 relates to the method of any one of embodiments 1 to 3, wherein the finely divided particles have a particle size of 3 μm to 200 μm.

[0094] Embodiment 5 relates to a method according to any one of embodiments 1 to 4, wherein a strong magnet is used in at least one magnetic separation step in step (c).

[0095] Embodiment 6 relates to the method according to any one of embodiments 1 to 5, wherein a weak magnet is used in at least one magnetic separation step in step (c).

[0096] Embodiment 7 relates to a method according to any one of embodiments 1 to 6, wherein a specific magnet is used in at least one magnetic separation step in step (d) to enrich the two different grades.

[0097] Embodiment 8 relates to the method of any one of embodiments 1 to 7, wherein the steelmaking slag is stainless steel slag, carbon steel slag, basic oxygen furnace (BOF) slag, electric arc furnace (EAF) slag, ladle furnace (LF) slag, desulfurization slag, or any combination thereof.

[0098] Embodiment 9 relates to the method of any one of embodiments 1 to 8, including one or more additional non-magnetic metal separation steps to separate heavy non-magnetic materials from light non-magnetic materials, the non-magnetic separation method being selected from eddy current separation, gravity separation, and airflow separation.

[0099] Embodiment 10 relates to the method of any one of embodiments 1 to 9, further comprising using the recovered non-magnetic particles, either immediately after magnetic separation or after further comminution step (d), as feed or part of a feed for producing cement clinker in a cement kiln, either directly in the kiln or at a later stage in clinker production.

[0100] Embodiment 11 relates to the method of embodiment 10, wherein one or more additional raw materials are selected from the list comprising limestone, gypsum, clay, shale, iron ore, bauxite, fly ash, BF slag.

[0101] Embodiment 12 relates to the method of embodiment 9 or embodiment 10, wherein the iron content of the feed is adjusted by adding steel slag to the feed.

[0102] Embodiment 13 relates to the method of any one of embodiments 1 to 12, further comprising using the recovered non-magnetic particles immediately after specific concentration (d) or after a further milling step (e) as a hexavalent chromium reducing agent for cement.

[0103] Embodiment 14 relates to an agent for reducing hexavalent chromium in cement, which can be obtained by the method according to any one of embodiments 1 to 13.

[0104] Embodiment 15 relates to a dry concrete premix for making concrete, comprising the agent for hexavalent chromium reduction according to embodiment 14.

[0105] Embodiment 16 relates to a cement comprising the agent for hexavalent chromium reduction according to embodiment 14.

[0106] The embodiment is illustrated in the following schematic drawing.

[0107] FIG. 1 illustrates one embodiment of the present invention. Material from an industrial pyrometallurgical process 1, for example, from a basic oxygen furnace in a steelworks, is subjected to a pretreatment process including a refinement step 2 and a separation step 3. The refined material is transferred from the refinement step 2 to the separation step 3. In the separation step 3, separation may be based on particle size and can be performed, for example, by sieving or screening. In the separation step 3, coarse particles are separated from particulate material 4, which contains oxides of iron and has a particle size Dv50 of less than 2 mm, preferably less than 1.5 mm. The coarse particles, for example, having a particle size Dv50 of more than 2.5 mm or more than 3 mm, are transferred to a partitioning step 9, where metal particles 10 are separated from agglomerated material 11. The metal particles 10 can be returned to the pyrometallurgical process 1, and the agglomerated material 11 can be returned to the refinement step 2.

[0108] Particulate material 4, which contains iron oxides and has a particle size Dv50 of less than 2 mm, is transferred to fractionation step 5, where the particulate material is divided into a first fraction and a second fraction. The first fraction has a lower iron oxide content than the second fraction. At least a portion of the first fraction is used to form part of the feed material for producing cement clinker 8 in cement kiln 6. At least a portion of the second fraction can be used as a supplementary material for producing cement and can be added to cement clinker 8 after cement kiln 6. It is also possible to add an organic acid to the second fraction in step 7 before it is used as a supplementary material.

[0109] The process described in this disclosure, particularly the features shown as 5, 6, 7, and 8 in FIG. 1, has been shown to significantly reduce the iron oxide content and increase the CaO content in the first fraction, thereby improving its usability in the production of cement clinker.

[0110] <Experiment> Embodiments of the present invention are described in the following non-limiting examples.

[0111] Example 1: Effect of separating fractions Steel slag from a European steel mill was subjected to a pretreatment process to crush the steel slag. Metal particles and agglomerates were separated from particulate material having a particle size Dv50 of less than 1 mm, referred to herein as demetallized slag. The demetallized slag was magnetically fractionated into a first fraction and a second fraction. Table 1 shows the content of the particulate material before fractionation and the content of the first fraction, as analyzed using an X-ray fluorescence (XRF) analyzer. All values ​​are expressed as weight percent.

[0112] As can be seen from Table 1, the iron oxide content in the first fraction is reduced by 20% compared to the particulate material before fractionation. Additionally, it can be seen that the calcium content in the first fraction is increased by 11.5%, and a 29% reduction in chromium content also occurs. This example demonstrates that the contents of the first fraction can be modified to form part of the feed material for producing cement clinker in a cement kiln. Table 1 [Table 1] * Ignition loss ** All iron is expressed as Fe2O3.

[0113] Example 2 The ability of steelmaking slag to reduce chromium(VI) to chromium(III) was tested.

[0114] Three different steelmaking slags were mixed with Portland cement containing clinker and gypsum. The compositions of the slags, analyzed using an X-ray fluorescence (XRF) analyzer, are shown in Table 2. All values ​​are expressed as weight percent.

[0115] In some samples, oxalic acid was used as a proton-donating chemical activator, which was added to the cement samples along with steel slag. The amount of chromium (VI) was measured after mixing (initial amount) and after 3 and 6 months. Chromium (VI) was measured using test method DIN EN 196-10:2016. The sample compositions and results are shown in Table 3. Table 2 Composition of steelmaking slag used in Examples 2 and 3 [Table 2] * Ignition loss ** All iron is expressed as Fe2O3. Table 3. Composition and results of samples from Example 2 [Table 3]

[0116] The results in Table 3 show that the use of steel slag can provide an initial reduction in chromium (VI) content in cement samples by reducing chromium (VI) to chromium (III). The obtained effect is enhanced when the steel slag is used in combination with a proton-donating chemical activator. The obtained effect does not significantly diminish during storage for six months.

[0117] Example 3 The ability of steelmaking slag to reduce chromium(VI) to chromium(III) was tested.

[0118] Steel slag 4, with the composition shown in Table 2, was mixed with Portland cement containing clinker and gypsum. Two proton-donating chemical activators were tested: oxalic acid and citric acid. The proton-donating chemical activators were added to the Portland cement along with the steel slag.

[0119] After adding steel slag and a proton-donating chemical activator, the amount of chromium(VI) in the cement samples was measured. Chromium(VI) was determined using test method DIN EN 196-10:2016.

[0120] The sample compositions and results are shown in Table 4. Table 4. Composition and results of samples from Example 3 [Table 4] * Value relative to total cement amount

[0121] From Table 4, it can be seen that the reducing effect of the steel slag was increased when the steel slag was used in combination with a proton-donating chemical activator.

[0122] Although the present invention has been described with reference to what are presently considered to be the most practical and preferred embodiments, it is understood that the present invention is not limited to the above-described embodiments, but is intended to encompass various modifications and equivalent technical solutions within the scope of the appended claims.

Claims

1. 1. Use of a particulate material as an activator for reducing chromium (VI) to chromium (III) in the production of cement, concrete or other similar materials, said particulate material originating from an industrial pyrometallurgical process, preferably a steelmaking process, and containing Fe, calculated on the dry weight of said particulate material. ２ O ３ The above-mentioned use, which contains at least 10% by weight of iron(II) and / or iron(III) converted thereto, and preferably not more than 5% by weight, more preferably not more than 3% by weight, of Fe(0).

2. 2. Use according to claim 1, characterized in that the particulate material is used in combination with a proton-donating chemical activator, preferably in the form of an acid.

3. 3. The use according to claim 2, characterized in that the proton-donating chemical activator is an organic acid or a salt thereof, preferably selected from the group comprising oxalic acid, acetic acid, formic acid, citric acid, tartaric acid, salts thereof, or any combination thereof.

4. Use according to claim 2 or claim 3, characterized in that the particulate material is used in combination with 0.1 to 50% by weight of the chemical activator, calculated on the total weight of the particulate material.

5. The particulate material contains Fe, calculated on the dry weight of the particulate material. ２ O ３ Use according to any one of the preceding claims 1 to 4, characterized in that it contains iron(II) and / or iron(III) in an amount calculated as 15% by weight or more, preferably 20% by weight or more, more preferably 30% by weight or more.

6. 6. Use according to any one of the preceding claims 1 to 5, characterised in that the particulate material comprises at least 5 wt.-%, preferably 10 wt.-%, more preferably 15 wt.-% iron(II), calculated as FeO from the dry weight of the particulate material.

7. 7. Use according to any one of the preceding claims 1 to 6, characterised in that the particulate material has a particle size Dv90 in the range of 3 to 200 μm, preferably 3 to 100 μm, more preferably 3 to 30 μm.

8. 8. Use according to any one of the preceding claims 1 to 7, characterized in that the particulate material derived from an industrial pyrometallurgical process is selected from ferrous slag, ferroalloy slag, base metal slag, pyrometallurgical tailings, or any combination thereof.

9. 9. Use according to any one of the preceding claims 1 to 8, characterized in that the particulate material is a steelmaking slag selected from basic oxygen furnace slag, electric arc furnace slag, ladle furnace slag, Linz-Donauwitz slag (LD slag), open hearth slag, blast furnace slag, desulfurization slag, or any combination thereof.

10. 1. A process for reducing chromium (VI) to chromium (III) in the production of cement, concrete, or other similar materials, comprising: Obtaining particulate material originating from an industrial pyrometallurgical process, preferably a steelmaking process, wherein said particulate material contains Fe, calculated on the dry weight of said particulate material. ２ O ３ Contains at least 10% by weight of iron (II) and / or iron (III), calculated as iron (II) and / or iron (III), and preferably not more than 5% by weight, more preferably not more than 3% by weight of Fe (0); adding said particulate material as an activator to a cement mix, concrete mix, or other similar material to reduce chromium (VI) to chromium (III); A method comprising:

11. 14. The method of claim 13, wherein a proton-donating chemical activator is contacted with the particulate material.

12. 12. The method of claim 11, wherein the proton-donating chemical activator is mixed with the particulate material prior to its addition to the cement mix, concrete mix, or other similar material.

13. 12. The method of claim 11, wherein the proton-donating chemical activator is added to the cement mix, concrete mix, or other similar material separately from the particulate material.

14. 1. A method for producing a particulate material suitable for use as an activator for the reduction of chromium (VI) to chromium (III) in the production of cement, concrete, or other similar materials, comprising: Obtaining starting particulate material originating from an industrial pyrometallurgical process, preferably from a steelmaking process, wherein said starting particulate material comprises iron(II) and / or iron(III), and fractionating the starting particulate material into at least a first fraction and a second fraction, wherein the first fraction and the second fraction have different contents of iron(II) and iron(III), and the second fraction has a content of Fe(II) calculated on the dry weight of the particulate material. ２ O ３ a particulate material comprising at least 10% by weight of iron (II) and / or iron (III), calculated as iron (II) and / or iron (III), and preferably not more than 5% by weight, more preferably not more than 3% by weight of Fe (0); A method comprising:

15. 15. The method of claim 14, wherein the starting particulate material is fractionated into the first and second fractions by using magnetic separation, density separation, size separation, electrostatic separation, flotation separation, eddy current separation, gravity separation, and air flow separation, or any combination thereof, preferably by using magnetic separation.

16. 16. The method according to claim 14 or claim 15, characterized in that the second fraction is subjected to micronization to obtain finely divided particles, said finely divided particles preferably having a particle size Dv90 in the range of 3 to 200 μm, preferably 3 to 100 μm, more preferably 3 to 30 μm.

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