Method for selectively removing heavy metals from flue gases of iron and / or steel making - Patent Application 20070122997

Abstract

The present invention relates to a method for selectively removing heavy metals from flue gases of iron and / or steel making, the method comprising the steps of: preparing a feedstock (FS) by blending or mixing a chloride precursor (CPM) with iron and / or steelmaking flue gas (ISFD) containing heavy metals, wherein the heavy metals are at least Pb and Zn, and optionally at least Pb, Zn and Cd; In a first reaction step in a first reactor (1), the FS is heat-treated at a temperature in the range of 700°C to 950°C to react the CPM with the ISFD, thereby removing at least 70 wt% of the Pb from the ISFD; In a subsequent second reaction step in a second reactor (2), the CPM is further reacted with ISFD by heat treating the FS at a temperature in the range of 850 ° C to 1200 ° C; and A step of obtaining a secondary solid material (8) after the second reaction step. The present invention also relates to a plant for carrying out the method of the present invention.

Description

[Technical Field]

[0001] The present invention relates to a process for selectively removing heavy metals from flue gases of iron and / or steel making by chlorination and vaporization of the heavy metals present in the flue gases of iron and / or steel making. The present invention also relates to a plant for carrying out the process of the present invention. [Background technology]

[0002] Blast furnace (BF) sludge is a by-product of the purification of flue gases generated during the production of pig iron in a blast furnace using a wet scrubber; the dried sludge is called flue gas dust or flue dust. The mineral composition of blast furnace sludge typically reflects that of the raw materials used in blast furnace ironmaking. Due to the extremely high temperatures encountered in the steelmaking process, blast furnace sludge contains volatile non-ferrous heavy metals and metalloids, such as zinc, lead, cadmium, and mercury, which are entrained by the process gases in the upper, cooler parts of the furnace, where they mix with and condense on solid particles. The zinc in the sludge primarily comes from the internal recycling of flue dust from ironmaking and / or steelmaking operations, including recycled and coated iron scrap, in, for example, the EAF or BOF. If the zinc content (usually in the form of ZnO or ZnS compounds) in the final BF sludge is too high (typically greater than about 2 wt%), the sludge cannot be recycled on-site by directly re-feeding it to the BF furnace after calcination. This is because vaporized metallic zinc easily condenses on the upper walls of the furnace, adversely affecting furnace operation. Heavy metals, such as lead, cadmium, and mercury, primarily originate from the large amounts of iron ore, coke, and coal used in blast furnace operations. Recycling of sludge or flue dust to the steelmaking process to recover the existing iron and carbon is very limited. This is because the ores used are also sources of the naturally occurring radionuclide lead-210. The accumulation of lead-210 as well as other toxic elements in the blast furnace sludge and subsequent flue dust significantly limits their reuse in the steelmaking process. Therefore, blast furnace sludge and flue dust rich in heavy metals are carefully and partially stored in settling ponds or landfills. Therefore, there is a strong need for a suitable recycling process that can at least partially ameliorate environmental pollution and recover the iron and carbon lost through landfilling of blast furnace sludge and flue dust.

[0003] Rotary hearth furnaces (RHFs) are known as an effective process for removing zinc from blast furnace (BF) flue dust or sludge and have been installed in several steel plants around the world, primarily in Asia. In the RHF process, zinc is removed via a high-temperature pyrometallurgical route, resulting in the zinc being concentrated in the RHF flue dust as a mixture with other heavy metals and harmful elements. This necessitates further processing for zinc extraction and final waste disposal. This requires operating temperatures exceeding 1250°C. Economically viable RHF plants require high initial investments and high production capacities. Although RHFs have been developed by several industrial companies, recycling secondary flue dust containing Zn, Pb, and other harmful elements remains extremely challenging.

[0004] The Waelz process is a method for recovering zinc and other low-boiling metals (e.g., lead and cadmium) from metallurgical waste, most commonly electric arc furnace (EAF) flue dust, using a rotary kiln. The process involves treating zinc-containing materials (zinc can be in the form of zinc oxide, zinc silicate, zinc ferrite, or zinc sulfide) with a carbon-containing reducing agent in a rotary kiln, typically at temperatures between about 1200°C and 1300°C. The kiln feed, containing zinc, flux, and reducing agent (i.e., coke), is typically pelletized before being added to the rotary kiln. In this chemical process, zinc compounds are reduced to elemental zinc, which has a boiling point of 907°C, which volatilizes and oxidizes to zinc oxide in the gas phase. The zinc oxide is collected from the kiln exhaust by filters, electrostatic precipitators, settling tanks, or the like. The Waelz process is typically carried out using oxygen-enriched air supplied countercurrently to the material being treated. The increasing use of galvanized steel has led to an increase in zinc concentrations in steel scrap and, consequently, in EAF flue gases. Currently, the Waelz process is the preferred and most widely used industrial-scale method for zinc recovery from EAF flue dust. However, recycling blast furnace sludge in the Waelz process is not economically attractive because the material does not contain sufficient Zn.

[0005] Patent document WO 2022 / 172495 A1 discloses a method for recovering zinc from electric arc steelmaking furnace dust containing zinc and iron. The method involves loading the dust into the rotating cylindrical kiln body of an indirectly heated rotary kiln, heat-treating it once within the kiln body at approximately 950-1000°C to vaporize the zinc contained in the dust, and then directing the vaporized zinc, along with other low-melting-point components, through an exhaust pipe at the discharge end of the rotary kiln to a treatment device, where the zinc is recovered. Furthermore, the residue resulting from the treatment in the kiln body is directed through a residue outlet at the discharge end of the rotary kiln to a burner device, where it is mixed with air and carbon and injected into an electric furnace for combustion. The disclosed zinc recovery method is a single heat treatment method and does not address the presence of other heavy metals in the electric arc furnace steelmaking dust.

[0006] Patent document WO2019 / 043261A1 discloses a method for purifying chlorine-containing waste or industrial by-products, in particular bypass dust from cement production, which method comprises the steps of: a) preparing a composition (C) by blending or mixing a chlorine-containing waste or industrial by-product (B) with one or more materials containing heavy metals (HM); b) reacting (B) with (HM) by a single heat treatment of (C); c) separating the evaporated heavy metal chloride compounds (HMCC); and d) obtaining a solid material after the heat treatment step, wherein the heavy metals (HM) are one or more of the following element group: Zn, Pb, Hg, Cu, Cd, Tl, In, Sn, Ni, and Co; and the single heat treatment is carried out at a temperature of 200 to 1500°C, most preferably 600 to 700°C, in a non-oxidizing atmosphere, to remove the heavy metals (HM). The material containing heavy metals (HM) and the chlorine-containing waste or industrial by-product (B) are mixed or blended in the presence of water, with 2 to 50 mass %, more preferably 10 to 20 mass %, of water being present in the overall composition (C). The ratio of the material containing heavy metals (HM) to the chlorine-containing waste or industrial by-product (B) is selected so that the chlorine content of composition (C) is 100 to 150%, most preferably 100 to 110%, of the amount required to stoichiometrically convert the heavy metals (HM) in the material containing heavy metals (HM) to chlorides. Alternatively, the ratio of the material containing heavy metals (HM) to the chlorine-containing waste or industrial by-product (B) is selected so that the chlorine content of composition (C) is 80 to 100%, most preferably 90 to 95%, of the amount required to stoichiometrically convert the zinc in the material containing heavy metals (HM) to chlorides. ZnCl2 is evaporated by heat treatment at 600 to 680°C. In one embodiment, the heat treatment is performed in combination with the Waelz process.

[0007] European Patent Publication EP3333272A1 discloses a wet chemical process for selectively reducing the amount of heavy metals, including Zn, from metallurgical plant waste containing Fe, the process comprising the steps of selectively leaching zinc by mixing the waste with a leach solution containing ammonia and ammonium salts and having a pH in the range of 8 to 12 to form a reaction mixture, controlling the pH of the reaction mixture to maintain the pH in the range of 8 to 12, separating the reaction mixture into a leach filtrate and a leach solid residue, and recovering ZnO from the leach filtrate.

[0008] Patent document US6,083,295 discloses a method for processing a finely divided material containing metal-based components, which comprises the steps of forming the finely divided material into pellets, drying the pellets, heating the pellets in a first rotary kiln at a temperature of 900-1200°C, preferably 1050-1200°C, and for a residence time sufficient to reduce and sinter the pellets and remove volatile first components, mainly lead oxide and any chlorides, from the pellets, removing the material in finely divided form from the sintered pellets, and heating the sintered pellets in a second rotary kiln in a reducing atmosphere with anthracite and some dolomite fines, whereby one or more second components, mainly zinc oxide, in the pellets are reduced to a volatile form and removed at a temperature of about 1080-1100°C, leaving one or more reduced third components. In this process, zinc oxide is reduced to metallic zinc, and the atmosphere in the kiln is maintained at a sufficient oxidizing condition to re-oxidize the metallic zinc, which is then carried away with the waste gas and recovered from the waste gas. The zinc oxide is said to be of high purity.

[0009] Patent document US5,547,490 discloses a method for removing lead and zinc from foundry dust material containing lead-containing components, zinc, and iron in the form of alkali chloride complexes, the method comprising the steps of: feeding the material to be treated to a lead treatment furnace; heating the material in the lead treatment furnace at a temperature of 900-1100°C, preferably 1000-1100°C, only until the lead-containing components evaporate, to produce a zinc-containing residual material from which the chloride fraction of the lead-containing components has been removed, wherein the lead-containing components are removed from the lead treatment furnace by a scavenging gas stream, and the scavenging gas stream loaded with the lead-containing components is cooled and filtered; then heating the zinc-containing residual material together with coal in a zinc treatment furnace under reducing conditions at a temperature in the range of 1100-1400°C, preferably 1150-1350°C, to reduce zinc oxide and form zinc metal vapor, wherein the zinc vapor is removed from the zinc treatment furnace by a scavenging gas stream in the presence of an oxygen-containing furnace atmosphere. The CO generated from the coal is oxidized to CO2 and the zinc metal is converted back to zinc oxide. The scavenging gas stream is cooled and filtered.

[0010] Patent document US 6,132,488 discloses a method for recovering metallic zinc from waste containing oxides of zinc, lead, chlorine, fluorine, and water. The method includes a mixing step in which the waste is mixed with a reducing agent to obtain a mixed material to be treated; a chlorine recovery step in which the mixed material is heated at temperatures between 40 and 600°C to recover chlorine and water; a lead recovery step in which the mixed material is heated under vacuum at temperatures between 200 and 600°C to recover fluorine and lead; a zinc recovery step in which the mixed material is heated under vacuum at temperatures between 600 and 1100°C to reduce and vaporize the zinc and recover metallic zinc; and a residue recovery step in which the residue of the mixed material is compressed into briquettes under vacuum to recover the residue of the mixed material to be treated. The vacuum level in each step is 0.001 to 20 Torr. Summary of the Invention

[0011] There is a need for improved methods for removing heavy metals from iron and / or steelmaking flue gases, i.e., flue gases generated from, for example, blast furnace (BF) operations.

[0012] As understood herein, in any description of a composition or preferred composition, all references to percentages are by weight unless otherwise specified.

[0013] It is an object of the present invention to provide an improved process for selectively removing heavy metals from iron and / or steelmaking by-products, particularly dust, sludge or filter cake (collectively referred to as "flue dust") obtained from gas scrubbing of iron and steel mill off-gases and arising from blast furnace operations, direct reduced iron manufacturing processes, electric arc furnace operations, electric reduction furnaces, HIsarna-type ironmaking processes or basic oxygen steelmaking operations.

[0014] These and other objects and further advantages are achieved or surpassed by the method according to claim 1, the use according to claims 11 and 12, respectively, the plant according to claim 13 and the preferred embodiments according to the dependent claims. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 shows a schematic process flow of the method according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] To achieve these objects, the present invention provides, in a first aspect, a method for selectively removing heavy metals from flue gases of iron and / or steel making, comprising the following steps: (i) preparing a feedstock (FS) by blending or mixing a chloride precursor (CPM) (16) with heavy metal-containing iron and / or steelmaking flue gas (ISFD) (15), wherein the heavy metals are at least Pb and Zn, and optionally at least Pb, Zn, and Cd; (ii) in a first reaction step in a first reactor (1), a step of reacting CPM with ISFD by heat treating FS at a temperature in the range of 700°C to 950°C, thereby reducing the Pd content of ISFD by removing at least 70% by weight of Pd present in the ISFD by chlorinating and evaporating Pb, and removing it (i.e., chlorinated Pb) from the first reactor (1) using the generated off-gas; (iii) in a subsequent second reaction step in a second reactor (2), the raw material (FS) resulting from the first reaction step in the first reactor (1) and added to the second reactor (2) is heat-treated at a temperature in the range of 850°C to 1200°C to further react the CPM (16) with the ISFD (15), and the Zn present in the ISFD is removed by chlorination and evaporation of the Zn, thereby reducing at least the Zn content of the ISFD, and removing it (i.e., chlorinated Zn) from the second reactor (2) using the generated off-gas; and (iv) obtaining a secondary solid material (8) substantially free of at least Pb, Zn and Cd after the second reaction step and removing it from the second reactor (2); The secondary solid material (8) contains high proportions of metallic iron, residual carbon, unreduced FeOx (hematite and magnetite), and inert gangue minerals, and very low levels of non-ferrous heavy metals, particularly lead, zinc, and cadmium, which have been removed from the ISFD (15).

[0017] The method of the present invention provides highly efficient and selective removal of non-ferrous heavy metals, particularly zinc, lead, and even cadmium, from ISFD 15. After the second reaction step, the remaining secondary solid material 8 contains a high proportion of metallic iron, residual carbon, unreduced FeOx, and inert gangue minerals, and can be reused in iron-making operations, such as blast furnace operations.

[0018] By separating the removal of heavy metals from the ISFD (15) into at least two separate reaction steps in separate reactors, the off-gas from each reaction step can be treated individually and separately to produce two separate fractions or portions of the flue dust: a lead-enriched flue dust fraction (5) from the first reaction step and a zinc-enriched flue dust fraction (7) from the second reaction step. The zinc-enriched flue dust fraction (7) is substantially free of lead and, therefore, lead-210, thereby increasing the value and usefulness of the flue dust fraction (7). Because the majority of the lead is concentrated in a single flue gas fraction (5), the total amount of lead-containing flue gas is significantly reduced, thereby contributing to a significant reduction in by-products from iron or steelmaking operations that must be considered environmentally unfriendly or even harmful. As a result, more than about 60%, typically more than about 70%, and in the best case more than about 80% of the ISFD (15) after treatment in accordance with the present invention continues to have commercial value as zinc-rich flue dust (7) from the second reaction or as secondary solid material (8) after the second reaction, and does not need to be disposed of, such as by landfilling. This is a significant improvement over a single thermal treatment process for blast furnace flue dust.

[0019] The method of the present invention advantageously enables the treatment of flue dust obtained from gas scrubbing of iron and steel mill off-gases from a wide range of operations, including blast furnace (BF) operations, direct reduced iron (DRI) manufacturing processes, electric reduction furnace (REF) operations, electric arc furnace (EAF) operations, HIsarna-type ironmaking processes, and basic oxygen steelmaking operations (BOF, BOS, or BOP).

[0020] The chloride precursor (16) is a compound or substance that can be converted to chloride. This conversion occurs by heating the chloride precursor (16), thereby providing chloride for the selective chlorination and vaporization of heavy metals from the ISFD (15). Examples of chloride precursors (16) include polyvinyl chloride (PVC), PVC-containing waste, chlorinated rubber or other chlorinated polymers, FeCl or FeCl, and CaCl. In a preferred embodiment, the chloride precursor (16) is FeCl (iron(II) chloride), specifically FeCl obtained as a by-product from steel pickling operations.

[0021] Preferably, the ISFD (15) and CPM (16) can be premixed to form the Feedstock (FS) prior to the first reaction step.

[0022] If the ISFD (15) and CPM (16) are premixed before being fed into a reactor, e.g., a rotary kiln, for the first reaction step, the ISFD and CPM can be compressed by (micro)granulation or pelletization to form the FS. Various binders, e.g., about 0.3-0.6 wt. % bentonite and a small amount of water, can be used. The diameter of the pellets can vary depending on the reactor volume and residence time within the reactor, but typically ranges from about 5 to 20 mm. The advantage of granulation or pelletization is that in industrial processes, the composition of the ISFD (15) is not constant over time, and the amount of CPM (16) added can be adjusted for each batch of FS and stored until use. This allows for considerable flexibility in blend recipes. The use of pellets also reduces the generation of dust containing heavy metals in the rotary kiln process and at the work site. In one embodiment, the granules or pellets are formed in an apparatus (3) comprising a granulator, pelletizer, or pelletizing plant.

[0023] When the first reactor (1), e.g. a rotary kiln, is fed separately, the feeding can be simultaneous or sequential, and can also be at the same inlet point of the rotary kiln or at different inlet points of the rotary kiln.

[0024] The first reaction step in the first reactor (1) removes at least substantial parts of the heavy metals (particularly lead and cadmium) from the ISFD by chlorination and evaporation and can be carried out in an oxidizing or non-oxidizing atmosphere. In a preferred embodiment, the first reaction step is carried out in a non-oxidizing atmosphere.

[0025] The second reaction step in the second reactor (2) removes at least a substantial portion of the heavy metal zinc from the ISFD by chlorination and vaporization and can be carried out in an oxidizing or non-oxidizing atmosphere. In a preferred embodiment, the second reaction step is carried out in a non-oxidizing atmosphere.

[0026] In the field of iron and steel metallurgy, the non-oxidizing atmosphere is required to have as low an oxygen partial pressure as possible. In one embodiment, the oxygen partial pressure of the non-oxidizing atmosphere is less than 1×10 when measured at 800° C. -8 atm, preferably less than 1×10 when measured at 800°C -10 atm, and more preferably less than 1×10 when measured at 800°C. -12 The non-oxidizing atmosphere may be comprised of nitrogen, a noble gas, CO2, CO, H, or a mixture of any of these.

[0027] A non-oxidizing atmosphere is preferred to avoid the formation of ZnO, which only evaporates at temperatures much above 1200°C, and the presence of ZnO reduces the yield of zinc removal in the process of the present invention. ZnO has a melting point of about 1974°C and a boiling point of about 2360°C. In a non-oxidizing atmosphere, carbon is used primarily as a reducing agent, and the unoxidized residual carbon can be utilized as a feedstock for hot metal carburization, for example, in subsequent high-temperature metal carburization in the REF.

[0028] In one embodiment of the method of the present invention, at least 70% of the lead is removed from the ISFD (15) during the first reaction step by evaporating PbCl at temperatures between 700°C and 950°C, preferably between 800°C and 900°C, and more preferably between 800°C and 890°C. Within this temperature range, a substantial portion of the lead and also other heavy elements such as cadmium and mercury are removed from the ISFD (15). By controlling the upper temperature limit of the first reaction, zinc removal, either after chlorination and subsequent evaporation or evaporation as elemental metal, is transferred to the second reaction step in the second reactor (2) as far as possible. Metallic zinc is evaporated at approximately 905°C.

[0029] In one embodiment of the method of the present invention, at least 80% by weight, preferably at least 90% by weight, more preferably at least 95% by weight of the lead is removed from the ISFD (15) by chlorination and evaporation during the first reaction step in the first reactor (1), when comparing the Pb content at the start of the first reaction step with the Pb content at the end of the first reaction step. Due to the process temperatures applied during the first reaction step, some zinc is also inevitably removed from the ISFD (15), but a substantial part of the zinc is removed only in the second reaction step in the second reactor (2).

[0030] In one embodiment of the process of the present invention, during the subsequent second reaction step in the second reactor (2), at least residual zinc is removed from the ISFD (15) by evaporating ZnCl at a temperature of about 850°C to 1200°C. In one embodiment, the upper temperature limit does not exceed 1100°C. In one embodiment, the temperature is at least 900°C, more preferably at least 950°C. These operating temperatures are significantly lower than those applied in the Waelz process, thereby providing cost advantages, e.g., fuel savings. Lower operating temperatures also limit well-known problems associated with accretion in the Waelz process.

[0031] It has been found that, according to the method of the present invention, a large proportion of the zinc present in the ISFD, preferably more than about 50% by weight, preferably more than about 60% by weight, i.e., the zinc content in the ISFD at the start of the first reaction step, is removed by chlorination and vaporization during the second reaction step in the second reactor (2). When treated according to the present invention, a total of more than 85% by weight, and in the best cases more than 95% by weight, of the zinc present in the ISFD (15) is removed from the ISFD (15) by chlorination and vaporization.

[0032] In one embodiment of the method of the present invention, each of the first and second reaction steps further comprises a step of purifying the off-gas produced during each reaction step using an off-gas treatment system (4, 6) connected to the reactor, as known in the art. Since both reaction steps are separated from each other, the off-gas treatment can be tailored to the composition and temperature of the off-gas, and the flue dust produced thereafter has a different composition and can be treated separately.

[0033] Because the majority of the lead is removed during the first reaction step, it is possible to form a lead-rich flue dust (5) following the first reaction step, resulting from off-gas treatments known in the art (e.g., gas scrubbing). This lead-rich flue dust fraction (5) is significantly different from the zinc-rich flue dust (7) resulting from off-gas treatments (e.g., gas scrubbing) in the second reaction step. This zinc-rich flue gas (7) is substantially free of cadmium and lead, and therefore is also substantially free of lead-210. This difference significantly increases the value of the zinc-rich flue dust (7), making it a valuable feedstock for processes known in the art for recovering metallic zinc from the flue dust (e.g., subsequent hydrometallurgical or electrolytic conversion processes). This is in contrast to processes known from the prior art (e.g. patent document WO 2019 / 043261 A1), in which ISFD is treated in a single thermal treatment and, after subsequent off-gas treatment, the resulting secondary flue dust fraction contains not only evaporated zinc but also significant amounts of lead, cadmium and other non-ferrous heavy metals, thereby generating significantly larger amounts of environmentally unfriendly by-products that have to be carefully treated and landfilled at considerable cost.

[0034] In one embodiment of the method of the present invention, the ratio of heavy metal-containing iron and / or steelmaking flue dust (ISFD) (15) and chloride precursor (CPM) (16) is selected so that the chloride content of the feedstock (FS) is 100% to 150%, preferably 100% to 130%, more preferably 100% to 110% of the amount required to stoichiometrically convert the heavy metals in the ISFD to chlorides.

[0035] The first and second reaction steps are carried out in separate reactors, the first reactor (1) and the second reactor (2), respectively, and the reaction conditions, including temperature and reaction atmosphere, are controlled to facilitate the control and consistent treatment of off-gases generated in each reactor (1, 2). In one embodiment, each reactor (1, 2) is a fluidized bed reactor, a rotary hearth furnace, a moving strand, or other gas-tight reactor that allows good control of temperature and off-gases.

[0036] In a preferred embodiment, each reactor (1, 2) is a rotary kiln. Typically, a rotary kiln has a cylindrical shape, with the length of the cylinder being much longer than the width. The rotary kiln rotates around an axis of rotation, which is usually inclined, allowing the raw materials to be heat-treated in the rotary kiln to move downward within the rotary kiln under the influence of gravity. The rotary kiln may be equipped with a burner assembly at its lower end for burning fuel to generate the heat required for pyro-processing, but indirect or electrical heating may also be applied. Flue gases or off-gases are generated in the rotary kiln together with volatile compounds and then discharged from the upper end of the rotary kiln, where they are then captured and treated in the off-gas treatment system (4, 6).

[0037] After the first reaction step, the raw material (FS) with reduced content of non-ferrous heavy metals (particularly lead and cadmium) is cooled and then fed to a second reactor (2) for the subsequent second reaction step, where the raw material is heat treated at a temperature in the range of 850-1200°C to further react CPM (16) with ISFD (15) and remove almost all of the remaining zinc.

[0038] In a preferred embodiment, the reactors (1, 2) for the first and second reaction steps are arranged in series to allow continuous feeding of the raw material from the first reactor (1) to the second reactor (2) and to avoid loss of thermal energy in the raw material.

[0039] Operating a rotary kiln reactor at high temperatures, especially above approximately 1100°C, can cause various operational problems, such as the deposition of iron components (e.g., Ca-ferrite and Fe-silicate) on the surface walls and sintering of pellets. Therefore, it is preferable to limit the temperature of the second reaction step to approximately 1100°C. Pyrometallurgical processes in rotary kilns tend to result in particle buildup and accumulation on the inner walls of the kiln, forming a "ring" of accumulated particles, known as a "kiln ring." Such kiln rings can significantly limit the production capacity of the kiln and lead to laborious cleaning operations that require the production process to be stopped. By reducing the cross-sectional area of ​​the kiln, the kiln rings prevent material from moving down the kiln under normal conditions. Furthermore, particle accumulation on the inner walls of the kiln reduces heat transfer. Periodic shutdowns to clean and / or remove the kiln rings result in lost production time.

[0040] The advantage of separating the removal of heavy metals from ISFD (15) into at least two separate reaction steps, i.e., a first reaction step at a relatively low temperature and a second reaction step at a higher temperature, preferably arranged in series with one another, is that fouling is not an issue in the first reaction step due to the relatively low operating temperature, and fouling in the second reaction step can be controlled by controlling the maximum operating temperature applied, which provides significant cost benefits and avoids operational problems related to buildup.

[0041] The solid residue or secondary solid material (8) obtained after the second reaction step and removed from the second reactor (2) contains a high proportion of metallic iron, residual carbon, unreduced FeOx and inert gangue minerals, with very low levels of non-ferrous heavy metals, and can therefore be reused in steelmaking operations as an iron-bearing raw material and / or carbon source, preferably by direct injection or after agglomeration, e.g. as pellets or by briquetting as HBI (hot briquettes for DRI).

[0042] A second aspect of the invention relates to a plant for carrying out the method for selectively removing heavy metals from iron and / or steel making flue gases (15) according to the invention, said plant comprising: an apparatus (3) for preparing a feedstock by blending or mixing a CPM (16) with an ISFD (15), in one embodiment the apparatus (3) comprises a granulator, pelletizer or pelletizing plant; a first reactor (1) configured for a first reaction step, the first reactor (1) being provided with an off-gas treatment system (4) or connected to an off-gas treatment system (4); and A second reactor (2) configured for a second reaction step, the second reactor (2) being provided with or connected to an off-gas treatment system (6). Equipped with.

[0043] Preferably, the first reactor (1) and the second reactor (2) are arranged in series to facilitate continuous operation.

[0044] The present invention further comprises: at least one operation selected from the group comprising a blast furnace (BF) operation (13), a direct reduced iron (DRI) manufacturing operation (12), a reduction arc furnace (REF) operation (10), an electric arc furnace operation (10), a HIsarna-type steelmaking process (14), and a basic oxygen steelmaking operation (11) (BOF, BOS, or BOP); One or more operations involving off-gas generation, the operations being provided with an off-gas treatment system for capturing heavy metal-containing flue gas (ISFD), wherein the heavy metals are at least Pb and Zn, and optionally at least Pb, Zn, and Cd; Flue gas containing heavy metals (ISFD) which is blended or mixed with chloride precursors (CPM) in a suitable device (3) to prepare feedstock (FD); subjecting the feedstock (FD) to a heat treatment in a first reaction step in a first reactor (1) and a subsequent second reaction step in a second reactor (2) as described herein and in the claims; Reusing the secondary solid material (8) obtained after the second reaction step and removed from the second reactor (2) in iron-making operations (10, 12, 13, 14) as iron-containing raw material and / or carbon source, either by direct injection or after agglomeration, e.g., as pellets or briquettes. Preferably, the flue gas or off-gas of the second reaction step in the second reactor (2) is treated in a scrubbing step using an off-gas treatment system (6) to obtain a solid residue (7), which can be reused in a hydrometallurgical or electrolytic process or other zinc recovery process to recover zinc metal or zinc compounds.

[0045] In a preferred embodiment of an integrated steel industry plant, the chloride precursor (16) comprises at least FeCl2, preferably FeCl2 derived from a steel pickling operation.

[0046] The present invention is also embodied in the use or method of using the secondary solid material (8) obtained after the second reaction step in a steel making operation as an iron-bearing raw material and / or carbon source in the steel making operation, preferably by direct injection or after agglomeration (e.g. after agglomeration as pellets or briquettes).

[0047] The invention is also embodied in the use or method of using the flue dust of the second reaction step in the second reactor (2) to obtain a zinc-rich solid residue (7) in a hydrometallurgical or electrolytic conversion process and convert it into metallic zinc or other valuable zinc resources.

[0048] Detailed Description of the Drawings The invention will now be described with the aid of the following non-limiting figures.

[0049] 1 shows a schematic process flow of a method according to the present invention. Iron and / or steelmaking flue dust (ISFD) (15) containing heavy metals, particularly at least zinc, lead, and possibly cadmium, originating from one or more operations including blast furnace (BF) operations (13), direct reduced iron (DRI) manufacturing processes (12), electric reduction furnace (REF) operations (10), electric arc furnace (EAF) operations (10), HIsarna-type iron making processes (14), and basic oxygen steelmaking operations (BOF) (11) is mixed or blended with chloride precursor (CPM) (16), e.g., FeCl, in apparatus (3) to prepare feedstock (FD), e.g., feedstock (FD) in the form of pellets.

[0050] The feedstock is fed to a first reactor (1) (a rotary kiln in this embodiment). In a first reaction step, the CPM (16) is reacted with the ISFD (15) by thermally treating the feedstock at temperatures ranging from 700°C to 950°C, preferably within a narrower temperature range. The resulting off-gas is used to remove at least 70% by weight of the lead present from the ISFD by chlorination and evaporation of PbCl. The PbCl-containing off-gas produced during the first reaction step is then scrubbed in an off-gas treatment system (4), resulting in a lead-rich solid residue or flue dust (5) containing high fractions of lead and other heavy metals, such as cadmium and mercury, as well as some zinc. This heavy metal-rich solid residue or flue dust (5) has no immediate commercial value and is carefully stored in landfills at high cost. However, the total amount of heavy metal-rich solid residue or flue dust (5) is still significantly less than the solid residue resulting from, for example, the process disclosed in WO 2019 / 043261 A1, in which the ISFD is treated in a single thermal treatment and, after off-gas treatment, the resulting flue dust or solid residue contains not only evaporated zinc but also significantly larger amounts of lead, cadmium, and other toxic non-ferrous heavy metals originally contained in the ISFD. Due to the high contamination levels of lead and other toxic non-ferrous heavy metals, such solid residue is not suitable for reuse in the zinc recovery industry and must be disposed of, for example, by landfill.

[0051] According to the present invention, the raw material resulting from the first reaction step is then subjected to a subsequent second reaction step in a second reactor (2) (in this embodiment a rotary kiln) arranged in series with the first reactor, in which the CPM (16) is further reacted with the ISFD (15) by heat treating the raw material at a temperature in the range of 850°C to 1200°C, preferably in a narrower temperature range, and a substantial majority of the zinc present in the ISFD is removed by chlorination and evaporation of ZnCl.

[0052] The off-gas from the second reaction is scrubbed in a scrubbing step using a separate off-gas treatment system (6) to obtain a zinc-rich solid residue or flue dust (7) with a very high weight fraction of zinc compounds. The zinc-rich solid residue or flue dust (7) is highly pure due to the very low presence of other heavy non-ferrous metals, especially lead, cadmium, and mercury, most of which are already concentrated in the lead-rich solid residue or flue dust (5) resulting from the first reaction step. The zinc-rich solid residue or flue dust (7) has high added value and can be easily reused in hydrometallurgical processes (not shown) or electrolytic processes (not shown) or other zinc recovery processes known in the field of zinc recovery to recover zinc metal or zinc compounds. The product of the second reaction is the so-called secondary solid material (8), which has very low levels of non-ferrous heavy metals and a high proportion of metallic iron, residual carbon, unreduced FeOx, and inert gangue minerals, and can be easily reused in steelmaking operations (10, 12, 13, or 14) as iron-bearing raw material and / or carbon source by direct injection or after agglomeration, e.g., as pellets or briquettes, thereby avoiding the detrimental accumulation of lead and other toxic heavy metals in the steelmaking operations. [Example]

[0053] The present invention will now be described in detail with reference to non-limiting embodiments thereof.

[0054] Blast furnace flue dust generated from an industrial steelmaking operation, the composition (dry mass) of which is listed in Table 1, was pelletized into raw material for micropellets 3-5 mm in diameter using approximately 0.5 wt. % bentonite as a binder material and approximately 4.6 wt. % FeCl2, a chloride precursor generated as a by-product of steel pickling. The composition of the micropellets is also listed in Table 1. All compositions listed in Table 1 were determined using thermogravimetric analysis (TGA) and inductively coupled plasma (ICP) techniques well known to those skilled in the art.

[0055] Small 15g batches of these pellets were heat-treated at 800°C for 1 hour in a quartz glass tube under a flowing, non-oxidizing, inert nitrogen atmosphere in a laboratory-scale first reaction step to chlorinate and vaporize at least lead, cadmium, and some zinc. The flue dust from this first reaction step was rich in lead, containing approximately 4.54 wt% lead and 15.43 wt% chlorine, as shown in Table 1. The flue gas was also enriched in Cd. Given the presence of high levels of toxic heavy metals, this flue gas, a by-product of the first reaction step, has no commercial value in iron and / or steelmaking operations. The micropellets or solid residue (i.e., feedstock) after this first reaction step had a very low lead content of approximately 0.01 wt%, and approximately 2.14 wt% zinc remained, compared to 2.73 wt% zinc in the original BF flue dust. The product of the first reaction step is used as the feedstock for the subsequent second reaction step, in which the solid material is held at 1000°C for 1 hour under a flowing, non-oxidizing, inert nitrogen atmosphere to chlorinate and vaporize zinc and other remaining heavy metals. The flue dust from this second reaction step contains approximately 17.26% zinc by weight, as shown in Table 1, making it rich in Zn and very low in lead (approximately 0.02% by weight), making it a valuable by-product usable in the zinc recovery industry. The secondary solid residue (8) obtained after the second reaction step has very low zinc and lead contents (0.04% by weight and 0.01% by weight, respectively) and is cadmium-free. Meanwhile, the original blast furnace flue dust contains approximately 2.73% zinc and 0.54% lead by weight. Due to its high iron content, high carbon content, and very low zinc and lead contents, the solid residue obtained after the second reaction step can be reused in the steelmaking process.

[0056] The calculated mass balance for the experiment according to the present invention is: Residual solid mass after 800℃: approx. 86% Gas produced at 800°C: approx. 13% Residual solid mass after 1000℃: approx. 72% Gas produced at 1000°C: approx. 25% is.

[0057] Conventionally, blast furnace flue dust had to be disposed of due to its composition, but by using the method of the present invention, at least two usable by-products are extracted from the blast furnace flue dust, namely flue dust from the second reaction step (7) and secondary solid residue (8) obtained after the second reaction step, thereby significantly reducing the total amount of steelmaking by-products that have to be disposed of.

[0058] [Table 1-1]

[0059] [Table 1-2]

[0060] The above description is intended to merely illustrate the methods of the present invention and should not be construed as limiting the scope of the appended claims to any particular embodiment or group of embodiments. Accordingly, the specification and drawings should be considered as illustrative, and are not intended to limit the scope of the appended claims. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. The mere fact that certain measures are recited in different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope of the appended claims. [Explanation of symbols]

[0061] 1. First reactor 2. Second reactor 3. Blender / Mixer 4. Off-gas treatment system connected to the first reactor 5. Lead-rich flue dust 6. Off-gas treatment system connected to the second reactor 7. Zinc-rich flue dust 8. Secondary solid materials 10. Reduction furnace operation 11. Basic oxygen steelmaking operation 12. Direct reduced iron manufacturing process 13. Blast furnace operation 14.HIsarna Steelmaking Process 15. Iron and / or steelmaking flue gases 16. Chloride Precursors

Claims

1. 1. A method for selectively removing heavy metals from flue gases of iron and / or steel making, comprising: The following steps: preparing a feedstock (FS) by blending or mixing a chloride precursor (CPM) with iron and / or steelmaking flue gas (ISFD) containing heavy metals, wherein the heavy metals are at least Pb and Zn, and optionally at least Pb, Zn and Cd; In a first reaction step in a first reactor (1), the CPM is reacted with ISFD by heat treating the FS at a temperature in the range of 700°C to 950°C, and at least 70% by weight of the Pb is removed from the ISFD by chlorination and evaporation of the Pb, and the generated off-gas is utilized to remove it from the first reactor (1); In a subsequent second reaction step in the second reactor (2), the CPM is further reacted with the ISFD by heat treating the FS at a temperature in the range of 850°C to 1200°C, and the Zn is removed from the ISFD by chlorination and evaporation of the Zn, and the generated off-gas is utilized to remove it from the second reactor (2); and Obtaining and removing a secondary solid material (8) from the second reactor (2) after the second reaction step. A method comprising:

2. During the first reaction step, PbCl is reacted in a non-oxidizing atmosphere at a temperature of 700°C to 950°C, preferably 800°C to 900°C. ２ 10. The method of claim 1, wherein at least 70% of the Pb is removed from the ISFD by evaporating the

3. 3. The process according to claim 1 or 2, wherein at least 80 wt. %, preferably at least 90 wt. %, of the Pb is removed from the ISFD during the first reaction step.

4. During the second reaction step, ZnCl is reacted in a non-oxidizing atmosphere at a temperature of 850°C to 1200°C, preferably 900°C to 1100°C. ２ 4. The method of claim 1, wherein Zn is removed from the ISFD by evaporating

5. 5. The method according to any one of claims 1 to 4, wherein the off-gas produced in the first reaction step in the first reactor (1) is treated in an off-gas treatment system (4) to obtain a lead-rich flue gas (5).

6. 6. The method according to any one of claims 1 to 5, wherein the off-gas produced in the second reaction step in the second reactor (2) is treated in an off-gas treatment system (6) to obtain zinc-rich flue gas (7).

7. 7. The method according to any one of claims 1 to 6, wherein the proportions of ISFD and iron and / or steel making flue gases comprising CPM are selected so that the chloride content of the FS is between 100% and 150%, preferably between 100% and 130%, of the amount required for stoichiometric conversion of heavy metals in the ISFD to chlorides.

8. Chloride precursors (CPMs) include polyvinyl chloride (PVC), PVC-containing waste, chlorinated rubber or other chlorinated polymers, FeCl ２ , FeCl ３ and CaCl ２ The method of any one of claims 1 to 7, wherein the compound is selected from the group comprising:

9. The chloride precursor (CPM) is FeCl ２ The method according to any one of claims 1 to 8, wherein

10. The method according to any one of claims 1 to 9, wherein each of the first and second reaction steps is carried out in a rotary kiln.

11. Use of the secondary solid material (8) obtained after the second reaction step according to any one of claims 1 to 10 as iron-containing raw material and / or carbon source in iron-making operations.

12. 11. Use of zinc-rich flue gas from the second reaction step in the second reactor according to any one of claims 1 to 10 in a hydrometallurgical or electrolytic process for recovering zinc metal or zinc compounds.

13. A plant for carrying out the method for selectively removing heavy metals from flue gases of iron and / or steel making according to any one of claims 1 to 10, comprising: an apparatus (3) for preparing a feedstock (FS) by blending or mixing a CPM (16) with an ISFD (15); a first reactor (1) configured for a first reaction step, the first reactor (1) being provided with an off-gas treatment system (4); and A second reactor (2) configured for a second reaction step, the second reactor (2) being provided with an off-gas treatment system (6). A plant equipped with:

14. 14. The plant according to claim 13, wherein the first reactor (1) and the second reactor (2) are arranged in series, preferably each of the first reactor (1) and the second reactor (2) being a rotary kiln.

15. at least one operation selected from the group comprising a blast furnace operation (13), a direct reduced iron production operation (12), a reduction electric furnace operation (10), an electric arc furnace operation (10), a HIsarna type iron making process (14) and a basic oxygen steelmaking operation (11); one or more operations involving off-gas generation, the operations being provided with an off-gas treatment system for capturing heavy metal containing flue gas (ISFD), wherein the heavy metals are at least Pb and Zn, and optionally at least Pb, Zn and Cd; 15. An apparatus (3) according to claim 13 or 14, a first reactor (1) and a second reactor (2); ISFD blended or mixed with chloride precursor (CPM) in unit (3) to prepare feedstock (FD); subjecting the feedstock (FD) to a heat treatment in a first reaction step in a first reactor (1) and a subsequent second reaction step in a second reactor (2) according to any one of claims 1 to 10; Reusing the secondary solid material (8) obtained after the second reaction step and removed from the second reactor (2) as iron-containing raw material in iron-making operations (10, 12, 13, 14) by direct injection or after agglomeration.

15. The plant according to claim 13 or 14, comprising:

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