Method for capturing acidic pollutants by recycling steel slag as adsorbent

Abstract

The invention relates to a method for capturing acidic pollutants from flue gas by recycling steel slag generated in a steelmaking process of a steel plant as an adsorbent. The acidic pollutants comprise HCl, HF, SOx and / or NOx. In order to improve the efficiency of capturing nitrogen oxides, the steel slag contains crystalline calcium silicate and a calcium magnesium silicate phase. Furthermore, the method for producing the adsorbent should comprise the steps of: producing a particulate steel slag material from the steel slag, the particulate steel slag material having a first particle size distribution having a D50 mesh size value of less than 70 m and a first specific surface area; and increasing the first specific surface area of the particulate steel slag material to a second specific surface area higher than 5 m2 / g by carbonating the particulate steel slag material with a gas comprising carbon dioxide. The flue gas is then contacted with at least a portion of the carbonated granular steel slag material as the adsorbent to trap the acidic contaminants in the carbonated granular steel slag material.

Description

[0001] This invention relates to a method for recovering and utilizing steel slag generated during the steelmaking process in steel plants as an adsorbent to capture acidic pollutants from flue gas (especially through a dry process), the acidic pollutants including HCl, HF, and SO. x and / or NO x .

[0002] During steel production, especially carbon steel and stainless steel production, a significant amount of byproducts are generated, primarily in the form of steel slag. Typically, this is achieved by relatively slowly cooling liquid steel slag to solidify it, resulting in a non-metallic slag phase comprising a crystalline slag phase. Steelmaking slags are classified according to the production process that yields them. The production of carbon steel (also known as ordinary steel) produces specific types of slags: electric arc furnace slags (EAF slag), basic oxygen furnace slags (BOF slag), and ladle metallurgy slags (LM slag). BOF slags particularly include LD slag, a byproduct of steel production via the Linz-Donawitz process. Slag used in the manufacture of stainless steel is obtained during stainless steel production and contains chromium, and optionally other alloying elements such as nickel and molybdenum. The slag used in the manufacture of stainless steel includes electric arc furnace slag (EAF slag), argon oxygen decarburization slag (AOD slag), vacuum oxygen decarburization slag (VOD slag), ladle metallurgical slag (LM slag), and slag produced in the tundish (for continuous casting of molten steel).

[0003] Therefore, steel slag includes ordinary steel slag and stainless steel slag. Ordinary steel slag includes electric arc furnace slag (EAF slag), basic oxygen furnace slag (BOF slag), LD slag, and ladle metallurgical slag (LM slag). Stainless steel slag includes electric arc furnace slag (EAF slag), argon-oxygen decarburization slag (AOD slag), vacuum oxygen decarburization slag (VOD slag), ladle metallurgical slag (LM slag), and slag generated in the tundish.

[0004] After solidification, stainless steel slag undergoes processing to recover the metals it contains (approximately 5%). To recover the metals entrained in the slag, it is crushed. After metal recovery, approximately 70% of the slag can be recycled as coarse or fine aggregate for concrete or asphalt. However, approximately 25% of the slag is very fine grain (<0.5 mm), which is difficult to reuse due to its high chromium and molybdenum content. This powder fraction also cannot be used in asphalt or concrete due to its high water absorption. The powder fraction does indeed consist of so-called slag powder, which has a high dicalcium silicate (γ-C2S) content, increasing its water absorption. The amount of slag powder produced depends on the slag's chemical properties / alkalinity and the solidification process.

[0005] Some patent publications, such as EP 3 990 414, disclose the use of fine stainless steel slag powder as a binder to produce carbonate-bonded building materials, such as building blocks. Stainless steel slag binders can indeed be cured by carbon dioxide gas and therefore can be used as an alternative to cement binders. For these applications, the steel slag powder is preferably relatively fresh so that at most only a portion of the carbon dioxide-reactive phase has already reacted with atmospheric carbon dioxide through natural carbonation. For example, after prolonged storage of fine steel slag fractions, such as stockpiling for years or even decades, most of the calcium oxide contained in free lime but also primarily in other slag phases may have already reacted with atmospheric carbon dioxide through natural carbonation, thereby reducing the bonding properties of the steel slag binder. Currently, large quantities of fine steel slag are stockpiled or landfilled in specialized landfills. Therefore, further methods for the cost-effective recycling of fine steel slag fractions remain needed.

[0006] One approach involves using steel slag as an adsorbent to capture acidic pollutants from flue gas. The use of LD slag for flue gas desulfurization has been disclosed in numerous publications, particularly in several patent publications, such as US 4,191,731. However, most of these processes are wet processes.

[0007] The use of stainless steel slag for flue gas purification is also well known. For example, WO 2009 / 039393 discloses a dry adsorption process for flue gas purification in which stainless steel slag is used as the adsorbent. In the only embodiment described in that patent publication, stainless steel slag is mixed with cement in a 90 / 10 ratio. 30% water is added to the mixture, and the mixture is granulated in a mixer to produce granulated particles with an average diameter of 2 to 6 mm. A packed bed reactor is made using the granulated particles, and flue gas from a coal-fired boiler is introduced into the filter. The carbon dioxide content in the flue gas is reduced by about 31%. Since the stainless steel slag reacts with only a relatively small amount of carbon dioxide (e.g., about 10 wt.%), and the flue gas has a relatively high carbon dioxide concentration (e.g., about 10 vol.%), a relatively large amount of steel slag material is obviously used per Nm³ of flue gas in this embodiment. With this amount of stainless steel slag, the sulfur oxide concentration is reduced by about 85%, but the nitrogen oxide concentration is reduced by only about 25%. Calcium carbonate and calcium sulfate are produced by the reaction of stainless steel slag with sulfur dioxide and carbon dioxide, primarily on the surface of agglomerated solid material. WO 2009 / 039393 does indeed teach the removal of the surface of agglomerated solid material particles containing calcium carbonate and sulfate by surface grinding and sieving, so that the solid material can be reused in a reactor bed. Alternatively, as disclosed in that patent document, the used agglomerated solid material particles can be ground and then mixed with a new binder component to re-form solid material particles.

[0008] A drawback of this known technology is that the pores of the agglomerated material are rapidly blocked by the generated carbonates during the carbonation reaction, limiting the reaction with sulfur dioxide to the outer layer of the agglomerated solid material particles. Another drawback is the rather limited removal efficiency of nitrogen oxides. The purification process appears to be primarily attributed to the chemical reaction between carbon dioxide and sulfur dioxide and the active calcium oxide phase contained in the steel slag material. However, capturing nitrogen oxides from flue gas requires other technologies, such as alkaline or acid absorption, activated carbon absorption, or selective and non-selective catalytic reduction, as described in, for example, Wanpeng Yang's article "Summary of flue gas denitration technology for coal-fired power plants" (doi:10.1088 / 1755-1315 / 300 / 3 / 032054).

[0009] The purpose of this invention is to provide a novel method for recycling steel slag as an adsorbent to capture acidic pollutants. This method can capture nitrogen oxides with higher efficiency, especially in dry adsorption processes (including dry adsorption injection processes and dry adsorption filter bed processes).

[0010] Therefore, the method of the present invention is characterized in that: the steel slag contains a non-metallic slag phase, at least 40 wt.% of the non-metallic slag phase is a crystalline non-metallic slag phase, the crystalline non-metallic slag phase includes at least a crystalline calcium silicate phase and a crystalline calcium magnesium silicate phase; and the method includes the following steps: - Granular steel slag material is produced from the steel slag, the granular steel slag material being composed of steel slag particles and having D 50 The first particle size distribution with sieve aperture sizes less than 70 µm, and especially less than 5 μm. 2 The first specific surface area per g; - By carbonating the granular steel slag material with a gas containing carbon dioxide, the first specific surface area of ​​the granular steel slag material is increased to a value greater than 5 m². 2 The second specific surface area per g; and - The flue gas is contacted with at least a portion of a carbonized granular steel slag material, which serves as the adsorbent, to capture the acidic pollutants in the carbonized granular steel slag material.

[0011] The first and second specific surface areas were determined by nitrogen adsorption pressure measurement according to the BET method conforming to ISO 9277:2022(E), especially after vacuum degassing at 190°C for at least two hours.

[0012] According to the present invention, it has been found that the capture level of various gaseous acidic pollutants can be improved by carbonating steel slag materials. Firstly, in the case of acidic pollutants such as sulfur dioxide (SO2), hydrochloric acid (HCl), and especially hydrofluoric acid (HF), they may chemically react with the carbonates contained in the carbonated particulate steel slag materials. Furthermore, the capture level of nitrogen oxides can also be improved, and considering that nitrogen oxides obviously do not react with carbonates, this level can even be improved to unexpectedly high levels.

[0013] To achieve this high capture level, steel slag comprises a nonmetallic slag phase, wherein the nonmetallic slag correspondingly includes at least 40 wt.% of its total amount of crystalline nonmetallic slag phase. In other words, steel slag from which all metals (i.e., iron or steel) have been removed, leaving only the nonmetallic slag phase, should include at least 40 wt.% of the crystalline nonmetallic slag phase, and therefore should include less than 60 wt.% of the amorphous nonmetallic slag phase. Steel slag is a silicate slag, and its crystalline nonmetallic slag phase includes at least crystalline calcium silicate and calcium magnesium silicate phases. These calcium silicate and calcium magnesium silicate phases react with carbon dioxide. In particular, calcium oxide can be extracted from these phases, and calcium oxide can react with carbon dioxide to form calcium carbonate on the surface of the slag particles.

[0014] Steel slag should be carbonated in the form of fine-grained steel slag material, which has D... 50 The first particle size distribution has a sieve aperture size of less than 70 µm. This fine-grained steel slag material can be produced by grinding the steel slag and / or separating this fine fraction from the remaining coarser particles in the steel slag. In both cases, it is preferable to first crush the solidified steel slag. It has been found that the fine-grained steel slag material can be carbonated to a higher degree compared to the coarse-grained steel slag fraction, i.e., more calcium oxide can be extracted from the steel slag particles and converted into carbonates on the surface of the steel slag particles. It has also been found that the BET specific surface area of ​​this fine-grained steel slag material can be significantly increased to 5 m² through the carbonation step. 2 / g or even higher values, such as increasing to above 10, 15 or 20 mg 2 / g. Furthermore, it was found that the increase in specific surface area was associated with an improved level of gaseous contaminant capture, not only acidic contaminants, but especially nitrogen oxides. Therefore, the generated carbonates not only react with acidic contaminants, but they also appear to provide an increased surface area suitable for adsorbing gaseous contaminants, including nitrogen oxides. Moreover, and perhaps more importantly, pores, particularly nanopores, are generated in the calcium-depleted outer regions of steel slag materials by extracting / leaching calcium oxide from the silicate phase, within which gaseous contaminants, such as sulfur oxides and especially nitrogen oxides, can be physically captured.

[0015] In embodiments of the method according to the invention, the gas used for carbonicating granular steel slag material, including carbon dioxide, is free of HCl or contains less than 10 mg / Nm³. 3 HCl, free of HF or containing less than 1 mg / Nm 3 HF, free of SO2 or containing less than 50 mg / Nm 3 SO x , NO-free x Or contains less than 200 mg / Nm 3 NO x .

[0016] The advantage of this implementation scheme is that in carbonated granular steel slag materials, activated calcium oxide primarily reacts only with carbon dioxide to form carbonates. Therefore, other compounds such as chlorides, sulfites, and sulfates are not or minimally generated. In this way, the steel slag adsorbent has a high carbonate content, which may still react with substances such as HCl, HF, and SO₂ present in the flue gas. x It reacts with acidic pollutants such as SO2. Furthermore, the additional surface area generated during carbonation is not affected by acidic pollutants (especially SO2). x and NO xThe carbonated granular steel slag material retains its absorption capacity to the maximum extent, and preferably remains free of acidic contaminants.

[0017] The carbon dioxide-containing gas used for carbonating granular steel slag materials can be pure carbon dioxide or include pure carbon dioxide. However, it can also be flue gas, preferably flue gas generated by processes that primarily produce carbon dioxide, such as flue gas from kilns, especially lime kilns or cement kilns. The flue gas is preferably not flue gas generated by incinerators, especially not flue gas generated by waste incinerators or coal incinerators.

[0018] In an embodiment of the method according to the invention, or in a previous embodiment, the second specific surface area, i.e., the specific surface area of ​​the carbonated granular steel slag material (in which at least a portion is used as an adsorbent), is greater than 10 m². 2 / g, preferably higher than 15 m 2 / g, more preferably higher than 20 m 2 / g.

[0019] It was found that the higher specific surface area was associated with higher adsorbent efficiency. In fact, the second specific surface area is typically below 70 m². 2 / g.

[0020] In an embodiment of the method according to the invention, or in any of the foregoing embodiments, the granular steel slag material is carbonated until the granular steel slag material has a carbonate content (expressed as a dry weight percentage of carbon dioxide) of at least 2.0 wt.%, preferably at least 4.0 wt.%, more preferably at least 6.0 wt.%, and most preferably at least 8.0 wt.%. In an alternative embodiment of the method according to the invention, or in any of the foregoing embodiments, the granular steel slag material is carbonated until the granular steel slag material has a carbonate content (expressed as a dry weight percentage of carbon dioxide) that is at least 50% of its maximum carbonate content (expressed as a dry weight percentage of carbon dioxide), particularly by carbonating a sample of granular steel slag material with a water content of 15 wt.% (dry weight percentage) at 23°C for 24 hours with 100% carbon dioxide gas at a pressure of 0.5 bar, preferably at least 70% of its maximum carbonate content, and more preferably at least 90% of its maximum carbonate content.

[0021] It was found that the higher the degree of carbonation of granular steel slag materials, the higher their BET surface area and the higher their capture level of different acidic pollutants.

[0022] In an embodiment of the method according to the present invention, or in any of the foregoing embodiments, the D of the first particle size distribution 50The sieve aperture size (i.e., the particle size distribution of the carbonated steel slag granular material) is less than 60 µm, preferably less than 50 µm, more preferably less than 40 µm, and most preferably less than 30 µm. Preferably, it is greater than 1.0 µm.

[0023] It was found that the finer the particle size of granular steel slag, the higher its degree of carbonation. Finer particle size corresponds to a higher external surface area, especially a higher Blaine value. Carbonates appear to be formed primarily on the outer surface of the granular steel slag particles during the carbonation step; therefore, a larger total surface area of ​​the granular steel slag particles allows for the formation of more carbonates during the carbonation process.

[0024] In an embodiment of the method according to the invention, or in any of the foregoing embodiments, the granular steel slag material is uniformly carbonated. Monolithically carbonated granular steel slag material refers to carbonated granular steel slag, wherein the size measured before carbonatedation is greater than D of the granular steel slag. 10 Almost all particles of the sieve aperture size are carbonized.

[0025] Steel slag contains only a limited amount of calcium compounds that can react with carbon dioxide. Therefore, by uniformly carbonating a specific steel slag material, the maximum amount of carbonates and the maximum amount of pores can be generated on the surface of the granular steel slag material.

[0026] In embodiments of the method according to the invention, or in any of the foregoing embodiments, the carbon dioxide content of the carbon dioxide and the gas used for carbonating the granular steel slag material is less than 5.0 vol.%, preferably less than 3.0 vol.%, more preferably less than 1.0 vol.%, and said gas is, in particular, atmospheric gas. Typically, it contains at least 0.03 vol.% carbon dioxide.

[0027] Using a gas with a relatively low carbon dioxide concentration helps avoid the formation of a hard shell on the outer surface of the large amount of carbonized granular steel slag. A hard shell forms when carbonates are generated in the pores between the granular steel slag particles, causing these particles to adhere to each other and hindering further penetration of the carbon dioxide-containing gas into the granular steel slag. Therefore, using a gas with a relatively low carbon dioxide concentration makes it easier to achieve uniform carbonation of the granular steel slag. It has been found that carbonation of granular steel slag using atmospheric air, i.e., natural carbonation, can achieve relatively uniform carbonation of large piles of carbonized granular steel slag throughout the pile. The lower carbon dioxide concentration in the carbonation gas requires a longer time for carbonation of the steel slag, but because fewer pores on the material surface are closed by accelerated carbonation, larger masses of granular steel slag can be carbonized more uniformly. Especially when the granular steel slag is carbonized to 90% or more of its maximum carbonation level, the granular steel slag is carbonized very uniformly when using a gas with a relatively low carbon dioxide content, particularly when using atmospheric carbonation.

[0028] In an alternative embodiment of the method according to the invention, the carbon dioxide content of the gas used for carbonating the particulate steel slag material is greater than 5.0 vol.%, preferably greater than 10.0 vol.%, more preferably greater than 15.0 vol.%. The maximum carbon dioxide content is 100 vol.%.

[0029] This implementation scheme enables the carbonation of granular steel slag materials more quickly.

[0030] In an embodiment of the method according to the present invention, or according to any of the foregoing embodiments, in the carbonation step, the granular steel slag material is arranged in a pile or bed.

[0031] In the method according to the invention, it is not necessary to manufacture a compact with a certain green strength before carbonating the granular steel slag material. In fact, it is not intended to produce block or granular products from the steel slag material that require compaction to reduce their porosity and thus increase their strength. Instead, the carbonated granular steel slag material is preferably in bulk. By not compacting the granular steel slag material in the pile or bed, the porosity of the pile or bed of granular steel slag material does not decrease except due to its own gravity, thus allowing carbon dioxide-containing gas to more easily permeate into the pile or bed, thereby avoiding or at least reducing the tendency to form a hard shell on the surface of the pile or bed through the carbonation process. The pile can be placed on a surface or in a container, for example, in a bag preferably made of a breathable material.

[0032] Preferably, the granular steel slag material is loosely piled in the pile or the bed.

[0033] In this embodiment, no external pressure is applied to the pile or bed of granular steel slag material. Furthermore, the pile or bed of granular steel slag material may also be compacted without vibration.

[0034] Advantageously, the first particle size distribution of granular steel slag material has D 60 sieve aperture size and D 10 The sieve aperture size value, where D 60 sieve aperture size and D 10 The ratio of sieve aperture size values ​​(i.e., the grain size uniformity coefficient U) is less than 15, preferably less than 14, more preferably less than 13, and most preferably less than 12. A smaller grain size uniformity coefficient is preferred, for example, less than 10 or 8, or even less than 6. The uniformity coefficient is typically greater than 2.

[0035] The porosity of a stockpile or bed of granular steel slag material depends in part on the particle size uniformity coefficient U, i.e., D. 60 sieve aperture size and D 10 The ratio of sieve aperture size values ​​(D) 60 / D 10 This is especially evident when granular steel slag is compacted to a certain extent, such as when it is compacted into a large pile under its own weight. According to the equation proposed by Vukovic and Soro in "Determination of hydraulic conductivity of porous media from grain-size distribution" (Colorado, Water Resources Publications, LLC, 1992), the porosity n equals 0.255(1+0.83). U When the particle size uniformity coefficient U is less than 15, even if the pile or bed is compacted under its own weight, the porosity of the granular steel slag material in the pile or bed will be greater than 27%. Since only a limited amount of carbonate is produced in the carbonated granular steel slag material, the pores of the granular steel slag will not be completely filled with carbonate during the carbonated process. A lower particle size uniformity coefficient is preferred because the minimum porosity of the granular steel slag material can be even greater; for example, greater than 28% when the particle size uniformity coefficient is equal to 12, and greater than 30% when the particle size uniformity coefficient is equal to 9. A smaller particle size uniformity coefficient can be obtained by selecting a narrower particle size fraction from the steel slag material.

[0036] In an embodiment of the method according to the present invention, or according to any of the foregoing embodiments, the granular steel slag material is stirred once or multiple times in the carbonation step.

[0037] Particulate materials can be continuously or intermittently stirred. Stirring mixes the materials, resulting in more uniform carbonation. Secondly, stirring the particulate materials can prevent or reduce the agglomeration of steel slag particles. This is especially important when the adsorbent must be a fine material, such as when it may be injected into flue gas. It has indeed been found that when the carbonated particulate material is at least partially deagglomerated, for example by crushing or grinding, the BET specific surface area obtained in the carbonation step may decrease again. Studies have found that reducing the particle size of the particulate steel slag material before the carbonation step has a positive effect on the BET specific surface area, while reducing the particle size of agglomerated steel slag material after the carbonation step has a negative effect on the BET specific surface area.

[0038] In embodiments of the method according to the invention, or according to any of the foregoing embodiments, carbon dioxide and a gas for carbonating the granular steel slag material are passed through the bed of granular steel slag material to agitate the steel slag particles, thereby preventing or reducing their agglomeration. The granular steel slag material is particularly likely to form a fluidized bed.

[0039] In this embodiment, the granular steel slag material can be carbonized rapidly and uniformly, while avoiding or minimizing the formation of granular (agglomerated) steel slag particles.

[0040] In an embodiment of the method according to the invention, or according to any of the foregoing embodiments, the particles of the granular steel slag material are at least partially agglomerated in the carbonation step to produce a granular material containing granular steel slag material granules (agglomerates).

[0041] The resulting carbonated granular material is preferably suitable for use as an adsorbent in a packed filter. Optionally, after crushing the carbonated granular steel slag material, the desired particle size can be sieved from the carbonated granular material. In the granular carbonated steel slag material, additional pores are created between the carbonated particles of the granular steel slag material.

[0042] Preferably, the size of the carbonated granular steel slag material is reduced at least partially after the carbonation step and before the contact step.

[0043] The reduced particle size allows flue gas to penetrate the pores of the carbonated material more quickly.

[0044] Preferably, at least a portion of the granules is used to form a packed filter bed, and the flue gas is guided through the packed filter bed during the contact step.

[0045] Carbonated granular steel slag material is quite porous, thus effectively capturing acidic pollutants from flue gas flowing through a packed filter bed. One advantage of packed filter bed applications is that the contact time between the filter bed and the adsorbent can be easily increased by increasing the amount of adsorbent in the filter bed.

[0046] Alternatively, a portion of the carbonated granular steel slag material used as the adsorbent may be injected into the flue gas stream, particularly according to dry adsorption injection technology.

[0047] The advantage of this flue gas purification process is that it eliminates the need for additional filters in the flue gas purification system. Furthermore, there is no need to periodically replace the adsorbent material in the packed bed filter. The adsorbent can be easily injected and collected by existing dust filters, especially bag filters. The injected adsorbent particles have very effective contact with the flue gas. If increased contact time is required, the collected adsorbent can be re-injected into the flue gas stream.

[0048] Preferably, the portion of the carbonated granular steel slag material injected into the flue gas stream as the adsorbent has a D 90 The second particle size distribution has a sieve aperture size of less than 2000 µm, preferably less than 1000 µm, more preferably less than 500 µm, and most preferably less than 250 µm.

[0049] Fine particles / granules can be easily carried by the flue gas flow and thus collected by dust filters. Larger particles are aggregated granules with higher porosity and therefore lower density, so they are also easily carried away by the flue gas flow.

[0050] The flue gas is preferably generated within the furnace of an incinerator, particularly a municipal solid waste incinerator, and directed to a dust filter. A portion of a carbonized steel slag material, used as an adsorbent, is injected into the flue gas backflow upstream of the dust filter, which is preferably a fabric filter, and in particular a fabric filter.

[0051] The adsorbent can be injected into the furnace itself and / or into the flue gas flow between the furnace and the dust filter. When injected into the furnace, the flue gas has the highest temperature, causing the adsorbent material to be rapidly heated. Therefore, moisture contained in the adsorbent slag material can be rapidly removed from it. Furthermore, if some heavier particles are present in the adsorbent material, these particles may fall into the furnace and be collected in the bottom ash. However, most of the adsorbent material will be collected on the dust filter. It forms a layer on the dust filter before falling into it. Therefore, the residence time on the dust filter increases its contact time with the flue gas. A significant advantage of adsorbents made from carbonated granular steel slag material is that calcium carbonate reacts with hydrochloric acid to form calcium chloride hydrate. CaCl2·4H2O and CaCl2·6H2O have low melting points, so they become viscous and adhere to the dust filter. This is a well-known problem with commercially available slaked lime adsorbents. However, the steel slag adsorbent of the present invention is composed of particles / granules mainly composed of other phases, so even if some calcium chloride forms on its surface, they will not adhere firmly to the dust filter.

[0052] In an embodiment of the method according to the invention, or according to any of the foregoing embodiments, the carbonated granular steel slag material used as the adsorbent is dried to a moisture content of less than 10 wt.%, preferably less than 7 wt.%, and more preferably less than 4 wt.%, after the carbonation step but before contact with the flue gas.

[0053] It was found that reducing the water content of carbonated steel slag adsorbents can improve the capture level of acidic pollutants. This may be because water fills the nanopores present in the carbonated granular steel slag material, preventing gaseous pollutants from being captured immediately.

[0054] In an embodiment of the method according to the invention, or according to any of the foregoing embodiments, the granular steel slag material is produced from stainless steel slag and contains more than 1500 mg / kg, especially more than 2000 mg / kg, and even more particularly more than 2500 mg / kg of chromium.

[0055] The chromium content is expressed as Cr(III) or Cr(VI) in mg Cr(III) or (VI) / kg of nonmetallic slag phase. The fine fraction of stainless steel slag is more problematic due to its high chromium content compared to carbon steel slag (such as LD slag). Most prior art literature disclosing the use of steel slag as an adsorbent for acidic pollutants describes the application of carbon steel slag. These slags do indeed contain more free lime than stainless steel slag. However, the inventors have discovered that when steel slag (especially stainless steel slag) is carbonated, carbonates are produced and nanopores are formed, making the carbonated granular steel slag material very effective at capturing acidic pollutants from flue gas, even though the free lime is indeed converted to carbonates during carbonation. Furthermore, because stainless steel slag contains less free lime, it reacts readily with carbon dioxide, thereby reducing the pores formed in the silicate phase due to calcium consumption in these salt phases. Therefore, more micropores can be generated in the silicate phase through the carbonation process.

[0056] In an embodiment of the method according to the invention, or according to any of the foregoing embodiments, the granular steel slag material comprises a crystalline nonmetallic steel slag phase, wherein at least 3 wt.%, preferably at least 5 wt.%, and more preferably at least 7 wt.%, of the crystalline nonmetallic steel slag phase is dicalcium γ-silicate. Typically, the content of dicalcium γ-silicate is less than 20 wt.%.

[0057] The advantage of using a portion of steel slag with such a high γ-dicalcium silicate content is that, during the solidification and cooling process of the steel slag, the conversion of β-dicalcium silicate to γ-dicalcium silicate is accompanied by a 12% increase in the volume of the dicalcium silicate phase, leading to the fragmentation of the dicalcium silicate phase. Therefore, the portion of steel slag containing such a high γ-dicalcium silicate content is automatically pulverized, forming so-called solidified steel slag fines. Thus, this portion requires little or no further grinding and can be used as the granular steel slag material in the method of this invention. Furthermore, the presence of some small cracks in the steel slag particles in this portion may increase the reactivity of the steel slag particles to carbon dioxide. Finally, the alkalinity of this portion may be slightly higher, i.e., the CaO / SiO2 ratio, thus allowing more calcium to be available for the carbonation reaction.

[0058] In an embodiment of the method according to the invention, or according to any of the foregoing embodiments, after the contact step, the carbonated granular steel slag material is mixed with a binder, and the mixture of the carbonated granular steel slag material and the binder is hardened to produce a shape-retaining block, wherein the binder may be, in particular, a hydraulic binder that cures in the presence of water; a granular carbonateable material, in particular, a steel slag material that cures with carbon dioxide; or an asphalt binder.

[0059] Granular steel slag material can be, in particular, powdered steel slag material remaining after removing coarse and fine fractions (sand) from crushed steel slag. Therefore, due to its high water absorption, this powdered steel slag material is unsuitable for bonding applications such as concrete or asphalt. However, according to the method of the present invention, the granular steel slag material is carbonized before being used as an adsorbent, and even if not completely carbonized, it is further carbonized by the carbon dioxide contained therein during contact with flue gas. When used in the production of carbonized products, it can be added as a binder by carbon dioxide-cured, carbonatable granular material, since the granular steel slag material used as an adsorbent cannot be further carbonized. The advantage of incorporating the used adsorbent material into the shape-retaining substance is that not only is the leaching of heavy metals (such as chromium, nickel, and molybdenum) contained in the carbonized granular steel slag material prevented or at least reduced, but also the leaching of pollutants captured from the flue gas is prevented or at least reduced.

[0060] Shape-retaining materials are molded articles or any in-situ produced materials that have a compressive strength of at least 2 MPa, as measured according to Belgian standard NBN B 15-220:1990.

[0061] Other details and advantages of the invention will become apparent from the following description of some specific embodiments of the method according to the invention. Reference numerals used in this specification refer to the drawings, wherein: Figure 1A and 1B It is used to produce powdered stainless steel slag (granular steel slag material, which is carbonated to increase its BET specific surface area to 5 m²). 2 The flowchart of the specific implementation plan of the method (which can be used as an adsorbent after reaching / g) consists of two parts; Figure 2 A packed filter bed device is schematically shown for cleaning flue gas produced by brick kilns; Figure 3 An apparatus for cleaning flue gas produced by a waste incinerator is schematically shown, which generates energy in the form of electricity and heat by injecting an adsorbent into the flue gas stream. Figure 4 To show the passage Figure 1A and Figure 1B A graph showing the relationship between the percentage of particles smaller than 63 µm in the powdered stainless steel slag produced by the method shown and the maximum carbon dioxide absorption of the powdered stainless steel slag. Figure 5 To show the passage Figure 1A and Figure 1B A graph showing the relationship between the content of dicalcium γ-silicate in the powdered stainless steel slag produced by the method shown and the percentage of particles smaller than 63 µm in the powdered stainless steel slag. Figure 6 To illustrate the use of Figure 1A and Figure 1B A graph showing the relationship between the carbonate content (expressed as a percentage of carbon dioxide) after carbonation in the powdered stainless steel slag prepared by the method shown, and the BET specific surface area of ​​the carbonated stainless steel slag material; and Figure 7 This demonstrates the BET specific surface area of ​​the carbonated powdered steel slag fraction and the NO capture from flue gas components by the carbonated granular steel slag material. x A graph showing the relationship between SO2 and HCl levels.

[0062] In this specification and claims, unless otherwise stated, % or wt.% refers to dry weight percentage.

[0063] The term "slag phase" refers to a non-metallic slag phase, which can be amorphous or crystalline. Therefore, the term "slag phase" does not encompass metallic phases or metallic particles. These metallic particles can be embedded within the non-metallic slag phase or can consist of individual steel particles that may coat or cover the slag phase.

[0064] Chromium content is expressed in mg Cr / kg dry weight, especially in mg / kg dry weight of the non-metallic slag phase, unless explicitly stated that it relates to the amount of Cr₂O₃. Therefore, the metallic phase / particles were first removed from the steel slag. The amount of chromium was determined by ICP after complete destruction of the non-metallic slag phase with an acid mixture of HNO₃, HCl, and HBF₄, as described in CMA / 2 / II / A.3 and CMA / 2 / I / B.1 for sampling and analysis of waste and soil samples (both published in the Belgian Official Gazette / Moniteur on January 11, 2021). ICP analysis, especially ICP-OES analysis, was performed.

[0065] This invention generally relates to a method for recycling steel slag generated during the steelmaking process in a steel plant. The steel slag is recycled and used as an adsorbent to capture acidic pollutants such as HCl, HF, SO2, SO3, NO2, and NO in flue gas. Specifically, this is carried out according to a dry adsorption process, including so-called semi-dry processes. Therefore, the adsorbent in contact with the flue gas is anhydrous or contains only a small amount of water, which evaporates from the adsorbent when the flue gas is heated. Wet processes are not included, in which the adsorbent is applied to a liquid through which the flue gas passes. Therefore, in this specification and claims, the dry adsorption process also covers so-called semi-wet processes. A characteristic of the dry process is that the adsorbent forms a dry product after contact with the flue gas, and in particular, the moisture content of this dry product is at most 5 wt.%.

[0066] Steel slag can be slag produced in the carbon steel production process at a steel plant, especially EAF slag, BOF slag, or LD and LM slag, but preferably slag produced in the stainless steel production process, especially EAF slag, AOD slag, VOD slag, LM slag, or tundish slag. Steel slag material is typically generated during the steel production process, forming a protective layer on the steel bath to protect the molten steel from oxidation. The slag also purifies the steel by absorbing oxides and impurities. In addition to the actual slag material, steel slag contains steel particles of varying sizes that can be recycled, especially after the slag has been crushed and optionally ground and solidified.

[0067] Steel slag, a byproduct of steelmaking plants, mainly comes from two sources.

[0068] First, during steel production, a certain amount of steel slag spills onto the steel plant floor. This occurs, for example, when molten slag is poured from a furnace or ladle into a slag pot, and when it is skimmed from a transfer ladle or poured into a bucket and then into a slag pot. Additionally, some molten slag splashes out of the furnace and onto the area around and below the furnace floor during the in-furnace steelmaking process, when slag-forming agents are added to the furnace (especially the EAF). Liquid steel also reaches the steel plant floor in this way. During the removal of refractory linings from furnaces and ladles within the steel plant, small pieces of refractory material also fall onto the floor. Waste is collected during the cleaning of the steel plant floor; this waste includes steel slag mixed with smaller amounts of other materials, such as approximately 5 to 10 wt.% of other materials, like scrap refractory material.

[0069] Waste collected from the steel plant floor can be further mixed with the fine fraction (e.g., 1 to 10 mm) of the refractory material, which is separated from the coarser fraction of the dismantled refractory lining. The method of the present invention can use not only waste collected from the steel plant floor that primarily contains (i.e., especially more than 90 wt.%) steel slag material, but also mixed waste, as it still contains steel slag material. The mixed waste preferably contains more than 50 wt.%, and more preferably more than 60 wt.% steel slag material. When steel slag is included in a mixture with another material (e.g., the fine fraction of waste refractory material from the dismantled refractory lining), the parameters of the steel slag material described or claimed in this specification and claims (e.g., the weight percentage of crystalline nonmetallic slag phase contained in the steel slag) refer only to the steel slag material contained in the mixture, i.e., excluding other materials that may be present in the mixture.

[0070] Besides waste collected from the steel plant surface, the main steel slag byproduct from steel plants is steel slag obtained by solidifying liquid steel slag collected in slag pots. After proper cooling and crushing, most of the liquid steel slag products can be recycled as building aggregates, including coarse and fine aggregates. These fine aggregates are practically free of fine particles, especially particles smaller than 0.5 mm. Therefore, fine particles are left over during the production of these aggregates. These fine particles, especially those consisting of 0-0.5 mm portions, are byproducts and are currently mainly used as carbonated binders in the production of artificial stone. Therefore, it is necessary to find new uses for these fine particles. Steel slag fines are not only continuously generated in large quantities, but there are also long-standing single landfills filled with steel slag fines for years or even decades. In particular, several single landfills are filled with stainless steel slag fines because, compared to, for example, LD slag, stainless steel slag fines have too high a heavy metal content and are unsuitable for use as soil conditioners.

[0071] The steel slag used in the method according to the invention must contain a non-metallic slag phase, of which at least 40 wt.% must be a crystalline non-metallic slag phase. The maximum content of the crystalline non-metallic slag phase is 100 wt.% of the total non-metallic slag phase. This steel slag is not a rapidly hardening steel slag, such as granular steel slag, because such slag contains an excessive amount of amorphous slag phase, i.e., more than 60 wt.% of amorphous slag phase. The crystalline non-metallic slag phase must contain at least a crystalline calcium silicate phase and a crystalline calcium magnesium silicate phase. The calcium silicate phase refers to a phase containing at least CaO and SiO2. Examples of crystalline calcium silicate phases are monocalcium silicate and dicalcium silicate (CaSiO3, Ca2SiO4), including γ-dicalcium silicate and β-dicalcium silicate, as well as cuspidine (Ca4Si2O7F2). The calcium magnesium silicate phase is a phase containing at least CaO, MgO, and SiO2. Examples of crystalline calcium magnesium silicate phases are leucosite (Ca7Mg(SiO4)4), merosite (Ca3Mg(SiO4)2), and magnesian feldspar (Ca2MgSi2O7).

[0072] In the method of this invention, granular steel slag material is produced from steel slag. This granular steel slag material has D... 50 The first particle size distribution is characterized by sieve aperture sizes less than 70 µm. Granular steel slag materials, in particular, exhibit particle size distributions below 5 µm. 2 The first specific surface area per g.

[0073] D 50 The sieve aperture size value represents the particle size at which 50% of the volume passes through. Particle size distribution can be tested using a sieve with square openings, according to ASTM D6913 / D6913M-17. The volume percentage of particles can be calculated, in particular, by dividing the weight of the particles passing through the sieve by the average density of the material forming the particles. Alternatively, particle size distribution can also be determined using laser technology.

[0074] The specific surface area was determined by the BET method according to ISO 9277:2022(E). This was accomplished by nitrogen adsorption pressure measurement after vacuum degassing at 190°C for at least two hours to remove any free moisture from the material.

[0075] Small particle sizes can be obtained, for example, by grinding steel slag. By grinding the steel slag to this size, most of the steel particles / inclusions are released and can be separated from the non-metallic slag phase. In particular, waste collected from the ground of steel mills, optionally mixed with fine waste refractory materials, can be ground in this way to recover the steel contained therein.

[0076] However, the steel slag produced by solidifying the liquid steel slag collected in the slag pot is first used to produce the valuable aggregate portion. This is especially true for stainless steel slag, as it contains less free lime compared to ordinary steel slag, and the free lime can be adequately neutralized to avoid any expansion problems when the aggregate portion is used as a building material, particularly as aggregate in concrete or asphalt. The remaining fines, or even finer fractions separated from it, can be used as is in the method according to the invention, or after some additional grinding. Air-cooled steel slag is produced by pouring liquid steel slag into a slag dump and allowing it to solidify. Preferably, the cooling of the solidified steel slag is accelerated, especially by spraying water onto the solidified steel slag. This air-cooling method results in slower solidification of the liquid steel slag compared to granulation methods. Thus, the solidified steel slag is not entirely amorphous, but contains a crystalline slag phase, and usually, but not necessarily, contains an amorphous slag phase. The nonmetallic components of the solidified steel slag correspondingly contain at least 40 wt.%, preferably at least 50 wt.%, of a crystalline nonmetallic slag phase, i.e., a mineral phase. They may also contain amorphous nonmetallic slag phases, particularly at least 15 wt.%, and more particularly at least 20 wt.%.

[0077] The material used in the method according to the invention for generating granular steel slag (D) 50 Some steel slag material with a sieve aperture size less than 70 µm can be separated from the steel slag during solidification. The solidified steel slag does indeed contain a certain amount of particles with a sieve aperture size less than 0.5 mm.

[0078] Liquid steel slag from various ladles and furnaces in steel production plants is poured into cooling pools via slag pots in the slag yard, where it is air-cooled, allowing it to slowly solidify and cool. During the cooling process, water can be sprayed onto the solidified slag to accelerate the cooling process to some extent, especially towards the end. Due to the relatively slow solidification, the slag does not solidify almost entirely in an amorphous phase, but rather largely in a crystalline phase. One of the mineral phases of steel slag is dicalcium silicate (C2S). When crystalline dicalcium silicate is cooled, it undergoes several polymorphic processes: α, which has a hexagonal crystal structure αH', which has an orthorhombic crystal structure αL', which has an orthorhombic crystal structure β, which has a monoclinic crystal structure, and γ has an orthorhombic crystal structure.

[0079] Under laboratory conditions, for pure dicalcium silicate, a transformation from αL'-dicalcium silicate to β-dicalcium silicate occurs at 675°C, followed by a transformation from β-dicalcium silicate to γ-dicalcium silicate at 490°C. Since the transformation from β-dicalcium silicate to γ-dicalcium silicate involves a 12% increase in volume due to their different crystal structures, this disrupts the dicalcium silicate phase. This causes partial pulverization of the slag and produces fine particles. This transformation also creates microcracks in the powdery particles, which seems to explain why the resulting fine particles can absorb and retain large amounts of water. These water-absorbing properties make these fine particles highly unsuitable for most applications in construction. However, according to the present invention, it has been found that these fine particles can be converted into adsorbents (especially by simply carbonizing these fine particles) for capturing acidic pollutants in flue gas. To increase the yield of valuable aggregates and limit the formation of fines during the cooling process, the cooling process can be accelerated, especially by spraying water onto the solidified steel slag, which cools the slag more quickly, particularly from temperatures above 500°C, and allows less β-dicalcium silicate to be converted into γ-dicalcium silicate.

[0080] In the process shown in Figure 1, solidified steel slag 31 is stored in a slag bin 32. The steel slag 31 is fed into a hopper 33, which includes a grid to prevent any excessively large slag lumps 34, in this particular case, larger than 300 mm. Since these excessively large lumps can damage the crusher used in subsequent processes, they are removed for later specific treatment, such as crushing and extracting large metal portions with hammers before being fed back into the hopper 33.

[0081] Slag particles 35 smaller than 300 mm fall through hopper 34 onto a conveyor belt and are transported to a first manual metal pickup chamber 36, where the operator removes large metal pieces 37 from the slag particles 35 on the conveyor belt. Figure 1AIn the next step (not shown), the steel slag particles 35 can be screened to remove fine particles or a portion thereof with a particle size of less than 0.5 mm. These fine particles can be used as granular steel slag material in the method according to the invention. The steel slag particles 35, or the remaining steel slag particles, are crushed in the first crusher 38 to produce crushed slag material 39, which is conveyed along the first metal separation tape 40 to the first screen 42, from which metal particles 41 are removed. The slag particles 39 then pass through the first screen 42, which separates them into three parts: particles 43 larger than 35 mm, particles 44 between 10 and 35 mm, and particles 45 smaller than 10 mm. The portion of particles 43 larger than 35 mm is carried away by the second conveyor belt through the second metal pickup chamber 46, where more metal fragments 47 are removed. The particles 43 larger than 35 mm are then returned to the first crusher 38. A portion of particles 44 between 10 and 35 mm enters the second crusher 48 to produce further crushed steel slag material 49, which is fed to the second screen 50. The further crushed steel slag material 49 is separated into three portions in the second screen 50: a portion 51 containing particles larger than 20 mm, a portion 52 containing particles smaller than 10 mm, and a portion 53 containing particles between 10 and 20 mm. The portion 53 containing particles between 10 and 20 mm is carried away by a third conveyor belt via a second metal separation tape 54, where more metal 55 is removed, and then returned to the second crusher 48. The portion 51 containing particles larger than 20 mm is carried away by a third metal separation tape 56, where more metal 57 is removed, and then stored in a box 58. This portion 51 is valuable coarse aggregate for building and road construction. The portion 45 of particles smaller than 10 mm from the first sieve 42 and the portion 52 of particles smaller than 10 mm from the second sieve 50 are combined to form 0-10 mm granular material 59, which is stored in bin 60.

[0082] like Figure 1B As shown, granular slag material 59 is supplied to a third screen 61, which is a 2 mm screen that separates the 0-10 mm stainless steel slag granular material 59 into a fine portion 62 of particles smaller than 2 mm and a coarser portion 63 of particles between 2 and 10 mm.

[0083] The coarser portion 63 is fed into a wet vibratory separator or vibratory separator, where metal particles 65 are removed from the 2-10 mm coarser portion 63. The vibratory separator 64 is preferably an online pressure vibratory separator as described in the following article: Andrew Falconer, “Gravity Separation: Old Techniques / New MethodsPublished in Physical Separation in Science and Engineering, 2003, Vol. 12, No. 1, pp. 31-48. A winnowing separator 64 is filled with water, in which steel slag particles are winnowed, causing heavier metal particles 65 to separate from lighter slag particles 66 by gravity. The lighter slag particle fraction 66 passes through a fourth metal separation tape 67, where a metal-rich fraction 68 is removed, and the slag particle fraction 66 is stored in a box 69. This fraction 66 is a valuable finer aggregate for building and road construction.

[0084] Preferably, the metal-rich portion 68 is ground or crushed by a grinder 96 and then fed to a metal separator 97, wherein the steel particles 99 are separated from the finely ground steel slag portion 98.

[0085] The third screen 61 is preferably a wet screen in which water is supplied. Therefore, the fine material portion 62 is mixed with water to produce an aqueous mixture 70. This aqueous mixture is also produced using water 71 from a winnowing machine 64, which contains fine slag material washed away from the coarser slag portion 63.

[0086] The aqueous mixture 70 is fed into flotation unit 72. The working principle of flotation unit 72 is also explained in Andrew Falconer's article "Gravity Separation: Old Techniques / New Methods The process is described in section 72. In flotation machine 72, a steel-rich fraction 73 is separated from the aqueous mixture 70. This steel-rich fraction 73 is fed into a first gravity separation screw 74, from which overflow 75 is added back into the aqueous mixture 70, while underflow 76 is fed into a ball mill crusher 77, from which slag material adhering to the steel particles is removed. The crushed material 78 exiting the ball mill crusher 77 is fed into a second gravity separation screw 79. The overflow 80 of this second gravity separation screw 79 is added back into the aqueous mixture 70, while the underflow is the valuable fine steel fraction 81.

[0087] An aqueous mixture 70, comprising slag portions 75 and 80 removed from the steel section 73, is fed into a dewatering classifier, particularly a dewatering screw 82, where, as underflow, a sand portion 83, particularly 0.5-2 mm sand particles, is removed from the aqueous mixture 70. This sand portion 83 can be used as fine aggregate in the production of concrete or asphalt. The overflow exiting the dewatering screw 82 is an aqueous dispersion 84 of fine slag particles in water.

[0088] To remove fine particles from the aqueous dispersion 84, the aqueous dispersion 84 is fed into the hydrocyclone 85. The operating principle of the flotation unit 72 is explained in Andrew Falconer's article "Gravity Separation: Old Techniques / New Methods As described in the text, the underflow 86 of the hydrocyclone 85 is filtered through a disc filter 87 to remove fine slag particles that form the powdery steel slag portion 88. The overflow 89 of the hydrocyclone 85 is further processed in a thickener 90, and the overflow 91 of the thickener is pumped into a reservoir 92, while the underflow 93 is processed by the disc filter 87. Therefore, other fine slag particles removed by the thickener 90 also reach the powdery steel slag portion 88. The filtrate 94 leaving the disc filter 87 is also supplied to the reservoir 92.

[0089] The purified water contained in the reservoir 92 can be reused to supply water to the wet screen 61 and the winnowing machine 64. In the reservoir 92, other fine steel slag material will settle to the bottom to produce precipitate 95. This precipitate can be removed from the reservoir 92 from time to time and can be added to the powdered steel slag section 88.

[0090] In the method of the present invention, granular steel slag material is produced from steel slag. As described above, this can be achieved by simply grinding the steel slag (e.g., waste collected from the ground of a steel plant) and removing the metallic portion from the ground steel slag; or the steel slag can be crushed, removing the coarser portion and the metallic portion, leaving a powdery steel slag portion. This powdery steel slag portion can be further ground, or it can be separated into finer and coarser portions. One or more coarser steel slag portions can also be ground into a powdery steel slag portion. In particular, it is preferable to further grind the aforementioned metal-rich portion 68 in order to remove the finely ground slag phase (i.e., the finely ground steel slag portion 98) from the steel particles 99 contained in the metal-rich portion 68. For example, the D of the finely ground steel slag portion 98 90 The particle size is approximately 80 µm, D 50 The particle size is approximately 25 µm, D 10 The particle size is approximately 2 µm. Prior to carbonation, this finely ground steel slag fraction with its specific particle size distribution has a BET specific surface area of ​​2.4 m². 2 / g. The ground slag phase 98 absorbs less moisture compared to the powdered steel slag portion 88, and therefore can be used as a filler, for example, in concrete or asphalt. However, they can also be used as granular steel slag materials in the methods of this invention.

[0091] A key characteristic of granular steel slag materials formed from steel slag is that they should be fine materials, meaning that granular materials possess D... 50Particle size distribution with sieve aperture sizes less than 70 µm. This particulate material has a relatively low primary specific surface area, especially less than 5 µm, measured by nitrogen adsorption pressure measurement at 190 °C after vacuum degassing for at least two hours according to the BET method of ISO 9277:2022(E). 2 The first specific surface area per g.

[0092] For non-porous spherical particles, the particle size D[3,2] (in nm), i.e., the surface average particle size (i.e., the average diameter of spheres with the same surface area as the particles), can be determined by the BET specific surface area A of the material. BET (Unit: m) 2 / g) and density ρ (unit: g / cm³) 3 ) is calculated using the following formula: D[3, 2] = 6000 / A BET ·ρ.

[0093] The density of steel slag is 3.28 g / cm³. 3 In the case of non-porous spherical particles, the particle size of D[3,2] should be equal to 365 nm (= 0.3 µm) in order to have 5 m 2 The BET specific surface area is / g. Producing this fine-grained granular steel slag material is economically infeasible. Because the particles of the aforementioned granular steel slag material have only limited porosity, their BET specific surface area is too low to effectively capture acidic pollutants from flue gas using dry adsorption processes.

[0094] However, the inventors have discovered that by carbonating granular steel slag materials, their BET specific surface area can be increased, especially to a value exceeding 5 m². 2The value of / g is quite surprising, as the formation of carbonates reduces the pore volume of granular steel slag materials. Quoc Tri Phung, in his doctoral dissertation "Effects of carbonation and calcium leaching on microstructure and transport properties of cement pastes," points out that most published studies report a decrease in specific surface area after carbonation. In his experiments, the BET specific surface area of ​​cement paste samples containing limestone filler decreased, while that of cement paste samples without limestone filler increased. Regarding a possible explanation for the increase in BET specific surface area, he mentions that CSH carbonation in cement paste significantly promotes calcite formation, resulting in the potential opening of small necks in CSH gel pores, or ink bottle-shaped pores. An increase in BET specific surface area may occur when the opening of gel pores dominates the change in microporous structure compared to the pore filling caused by calcium carbonate precipitation. Due to the lower Ca / Si ratio resulting from CSH carbonation, the structure of CSH was found to become more porous and more easily infiltrated by nitrogen.

[0095] Although steel slag itself does not contain the CSH phase, the increase in BET specific surface area observed by the inventors could also be explained by the fact that calcium is extracted from the calcium silicate or calcium magnesium silicate phase through the carbonation process, thereby creating calcium-depleted external regions on the outer surface of the steel slag particles. The study also found that carbonation of steel slag produces amorphous phases, such as amorphous silica. The micropores in these calcium-depleted regions may be the cause of the increased BET specific surface area. However, this explanation is proposed only as a possible theory and is not intended to limit the scope of the invention.

[0096] The inventors have discovered a correlation between BET specific surface area and the degree of carbonation. Due to the high temperatures in steelmaking furnaces, fresh steel slag does not contain carbonates. It contains small amounts of free lime and periclase, as well as a relatively large amount of calcium silicate and calcium magnesium silicate phases, which can react with carbon dioxide.

[0097] Both ordinary steel slag and stainless steel slag contain high levels of CaO and MgO. In the article "Mechanical and environmental properties of carbonated steel slag compacts as a function of mineralogy and CO2 uptake" published by P. Librandi et al. in the 2019 issue of the *Journal of CO2 Utilization* (Vol. 33), the CaO content of BOF steel slag was 51 wt.% and the MgO content was 3.5 wt.%, while the CaO content of EAF stainless steel slag was 45 wt.% and the MgO content was 12 wt.%. For stainless steel slag, the maximum CO2 uptake is approximately 10 wt.%, equivalent to approximately 12.7 wt.% CaO, which only accounts for a portion (approximately 22%) of the total CaO and MgO content in stainless steel slag. For BOF steel slag, the maximum CO2 uptake is approximately 18 wt.%, equivalent to approximately 23 wt.% CaO, but this still only accounts for a portion (approximately 42%) of the total CaO and MgO content in BOF steel slag. Furthermore, compared to stainless steel slag, BOF slag contains more free lime, specifically 2.1 wt.% compared to 0 wt.%. In the method of the present invention, stainless steel slag is preferred because ordinary steel slag contains more free lime, resulting in more carbon dioxide reacting with the free lime in the ordinary steel slag without creating pores in the calcium silicate and calcium magnesium silicate phases.

[0098] It appears that only the outer surface of the steel slag particles is carbonated to form an amorphous phase, and only the outer edges of these particles are calcium-depleted, providing micropores. These micropores are considered the cause of the significant increase in the BET specific surface area of ​​the granular steel slag material. It was also found that the increase in BET specific surface area is correlated with the capture level of acidic contaminants, especially HCl and SO₂. x and NO x Absorption-related.

[0099] Before the carbonation step begins, the granular steel slag material has D 50 Particle size distribution with sieve aperture size less than 70 µm. Preferably, D 50 The sieve aperture size is smaller, especially less than 60 µm, preferably less than 50 µm, more preferably less than 40 µm, and most preferably less than 30 µm. It has been found that the finer the particles of the granular steel slag material at the start of the carbonation process, the higher the maximum amount of carbonate that can be produced, thus achieving a higher BET specific surface area. Preferably, the granular steel slag material is carbonated until its BET specific surface area exceeds 10 m². 2 / g, preferably higher than 15 m 2 / g, more preferably higher than 20 m 2 / g.

[0100] Preferably, the granular steel slag material is carbonated until its carbonate content (expressed as a percentage of dry weight of carbon dioxide) is at least 2.0 wt.%, preferably at least 4.0 wt.%, more preferably at least 6.0 wt.%, and most preferably at least 8.0 wt.%. The carbonate content can be easily determined by simultaneous thermal analysis (STA, DIN 51004, DIN 51006, and DIN 51007).

[0101] Preferably, the maximum carbonate content of the granular steel slag is first determined by analyzing at least one sample of the granular steel slag material, and then the granular steel slag material is carbonated until the maximum carbonate content is reached to at least 50%, preferably at least 70%, and more preferably at least 90%.

[0102] For example, the maximum carbonate content corresponds to the maximum carbonate content obtained through the following test. Dry the steel slag sample at 110°C until there is no further weight loss. Then sieve the sample through a 250µm sieve. Place 10 g of sample in a cup, do not compact the sample, and add 1.5 g of water to mix with the steel slag. Place the cup in an autoclave, which is purged with 100% CO2 gas and pressurized to 0.5 barg (=1.5 bara). Maintain the autoclave at approximately 23°C for 24 hours. Perform STA analysis on the carbonated sample from 0–1000°C. The weight loss between 550°C and 850°C is due to the release of carbon dioxide from the decomposition of carbonates. Divide this weight loss by the initial weight of the dried sample and multiply by 100 to obtain the maximum carbonate content of the carbonated granular steel slag material, expressed as a percentage of dry weight carbon dioxide. The degree of carbonation can be determined using the same test method when carbonated granular steel slag material.

[0103] Based on the chemical properties and fineness of granular steel slag, it contains only a limited amount of calcium compounds that can react with carbon dioxide. Therefore, by uniformly carbonating a specific type of steel slag, the maximum amount of carbonates can be produced, resulting in the maximum number of pores on the surface of the granular steel slag particles.

[0104] For example, when carbonating a large quantity of granular steel slag (e.g., a large heap of steel slag), it is preferable to use a carbonation gas with a relatively low carbon dioxide content, particularly, less than 5.0 vol.%, preferably less than 3.0 vol.%, more preferably less than 1.0 vol.%. The carbonation gas can be particularly present in the atmosphere, where the carbon dioxide content is approximately 0.04 vol.%. By using a carbonation gas with a higher carbon dioxide content, the carbonation process of the granular steel slag is accelerated. During this process, the external pores of a large number of granular steel slag blocks are filled with carbonates more quickly, thereby hindering the carbonation of the interior of the large quantity of granular steel slag and making it more difficult to achieve uniform carbonation. The inventors have discovered that under natural carbonation, i.e., carbonation under atmospheric conditions, a large heap (stockpile) of granular steel slag material can be uniformly carbonized over several years until the center of the heap. Although the granular steel slag material is loosely piled in the heap, it is compacted at the bottom of the heap under its own weight.

[0105] Granular steel slag materials can also be carbonated in smaller piles, such as in blocks contained in large bags permeable to carbonation gas. In these smaller piles, especially in large bags, the contained granular steel slag materials can be carbonated within a few days with carbonation gas containing less than 5 vol.% carbon dioxide.

[0106] However, granular steel slag materials can also be carbonated with a carbonation gas containing more than 5 vol.% carbon dioxide. They can then be loosely stacked into piles or beds. A pile can be defined as having a height greater than its width, while a bed can be defined as having a height less than its width. Both piles and beds can be elongated; in this case, the width must be measured perpendicular to its longitudinal direction. To further accelerate the carbonation reaction, the carbon dioxide content of the carbonation gas is preferably greater than 10.0 vol.%, more preferably greater than 15.0 vol.%.

[0107] To avoid clogging of the external pores of the granular steel slag material in the pile or bed, it is preferable to agitate a large quantity of the granular steel slag material once or multiple times during the carbonation step. "Agitation" must be understood in the broadest sense herein. It also includes any type of mixing of the granular steel slag material contained in the pile or bed. Agitation can also be achieved, particularly by blowing carbonated material through the granular steel slag material at a certain flow rate to stir the steel slag particles. The steel slag particles can be agitated to a certain extent, thereby avoiding or at least reducing the agglomeration of the granular steel slag material. Agglomeration of the steel slag material can be avoided by keeping the particles in a fluidized bed.

[0108] Typically, at least a portion of the particles in granular steel slag material agglomerates during carbonation. This yields a granular material containing carbonated granular steel slag particles, where the slag particles are bound together by carbonates formed on their surfaces. Alternatively, the granular steel slag material can be granulated before carbonation. In this case, the slag particles also agglomerate during the carbonation step, resulting in a granular material containing carbonated steel slag particles, where the slag particles are bound together by carbonates formed on their surfaces. When granulating the granular steel slag material before carbonation, it is preferable to use a carbonation gas with a relatively low carbon dioxide content, particularly below 5.0 vol.%, preferably below 3.0 vol.%, and more preferably below 1.0 vol.%. By using such a low carbon dioxide concentration, the granulated steel slag particles can be carbonated more uniformly, i.e., it is easier to prevent the formation of a hard shell.

[0109] The inventors have discovered that when producing granular materials containing carbonated granular steel slag particles, a higher BET specific surface area can be achieved, i.e., in the pores formed between the steel slag particles.

[0110] The resulting granular material can be used as an adsorbent to capture acidic pollutants. If the granular material is too coarse, the particle size can be reduced. Preferably, it is crushed rather than ground. In this way, the BET specific surface area can be retained to the maximum extent after the crushing step. On the other hand, fine grinding of carbonated materials may reduce the BET specific surface area of ​​the carbonated materials.

[0111] To reduce the interparticle bonding strength in carbonated granular steel slag materials, a higher porosity can be formed between the particles. This can be achieved by producing materials with a lower D... 60 The sieve aperture size value and its D 10 This is achieved by using granular steel slag material with a ratio of sieve aperture size values, i.e., by producing granular steel slag material with a steeper particle size distribution curve. This can be achieved by sieving out the granular steel slag fraction with a smaller particle size range. Preferably, the D of the granular steel slag material... 60 / D 10 The ratio, i.e., its uniformity coefficient, is less than 15, preferably less than 14, more preferably less than 13, and most preferably less than 12. The D of granular steel slag material 60 / D 10 The ratio is preferably greater than 2.0, and more preferably greater than 3.0.

[0112] The carbonation gas used for carbonating granular steel slag materials may contain a certain amount of acidic contaminants, but preferably, only a limited amount. In particular, it is preferably free of HCl or contains less than 10 mg / Nm³. 3 HCl, free of SO2 or containing less than 50 mg / Nm³ of SO2. x , NO-free x Or containing less than 200 mg / Nm³ of NO x Therefore, clean gases or flue gas can be used, provided they contain only limited amounts of acidic pollutants. Acidic pollutants include HCl and SO₂. x It does reduce the formation of carbonates, instead forming chlorides and sulfites / sulfates, while the NO present in the carbonation gas... x It will occupy the micropores formed in the carbonized granular steel slag material.

[0113] In the method of this invention, the flue gas comes into contact with, or at least a portion thereof, a carbonated particulate steel slag material. The flue gas includes acidic pollutants such as HCl, HF, and SO₂. x and NO x Flue gas can be generated by different types of processes, such as in kilns, like lime kilns, cement kilns, or ceramic brick kilns. However, incinerators (such as municipal solid waste incinerators) produce more polluting flue gas.

[0114] Existing flue gas treatment processes can be divided into three categories: wet flue gas purification processes, semi-dry flue gas purification processes, and dry flue gas purification processes. The method of this invention preferably employs a semi-dry or dry flue gas purification process because, compared to wet processes, they require lower investment, and the carbonated granular steel slag material used in this method performs poorly in wet flue gas purification processes. In this specification and claims, dry and semi-dry flue gas purification processes are referred to as dry adsorption processes because in both processes, the adsorbent after the reaction is a dry product. The adsorbent in contact with the flue gas can be a dry or wet product, but a wet product will dry out upon contact with high-temperature flue gas.

[0115] Carbonated granular steel slag material can be arranged in a packed filter bed to guide flue gas through the filter bed during the contact step. In this embodiment, the carbonated granular steel slag material is preferably a granular material comprising aggregated granular steel slag material particles. Because the aggregated carbonated steel slag material particles are coarser than the steel slag particles contained within these particles, the granular carbonated steel slag material has larger pores and is therefore more permeable than the initial granular steel slag material, thus allowing flue gas to flow through the packed filter bed. The advantage of a packed filter bed is that, by providing a larger filter bed, the residence time of the flue gas in the filter can be increased. The carbonated granular steel slag material can also be contacted with the flue gas until the required amount of acidic pollutants is adsorbed. The packed filter bed can then be replaced, but the carbonated granular steel slag material can also be continuously replaced by using a so-called moving filter bed, which is a type of packed filter bed in which new adsorbent (carbonated granular steel slag material) is fed from the top and used adsorbent is removed from the bottom.

[0116] Figure 2 An embodiment of a flue gas purification device with a moving packed filter bed is illustrated schematically. Flue gas 100 is generated in a kiln 101 used for firing bricks, tiles, pottery, etc. The hot flue gas 100 can be guided through a heat recovery system 102, in which the flue gas is cooled to a temperature of, for example, 160 to 270°C. The flue gas is then guided through a filter 103, which comprises a packed filter bed 104 composed of adsorbent material 105 (i.e., carbonized granular steel slag material 105). Figure 2 The filter bed 104 shown is a moving filter bed 104. In this moving filter bed 104, adsorbent material 105 is continuously fed from the funnel 106 into the top of the filter bed 104. At the bottom of the filter bed 104, the adsorbent material 105 that has captured acidic pollutants is continuously collected and conveyed through an endless screw conveyor 107 to a container 108 for the used adsorbent material 105. In the filter 103, a baffle structure 109 is preferably provided to create open spaces within the bed of adsorbent material 105. Through these open spaces, the flue gas 100 can diffuse more easily, resulting in a more uniform distribution within the bed of adsorbent material 105. If the residence time of the adsorbent material 105 is too short, a portion of the used adsorbent material 105 can be recovered back into the funnel 106. The flow of flue gas 100 through the flue gas purification device is generated by passing the flue gas 100 through the filter 103 and blowing it into the chimney 111 by the blower 110.

[0117] In addition to being placed in a packed filter bed, carbonated granular steel slag material can also be injected into the flue gas stream. Figure 3An embodiment of a flue gas purification device is schematically illustrated, wherein adsorbent material 105 is injected into the flow of flue gas 100. Flue gas 100 is generated in an incinerator 112 for incinerating waste 113 (e.g., municipal solid waste). Therefore, the device can be a Municipal Solid Waste Incinerator (MSWI). The incinerator 112 may include a moving grate 114 that carries the burning waste 113 and conveys it to a container 115 to collect bottom ash 116. The hot flue gas 100 generated from burning the waste 113 rises and passes through a boiler 117. In this boiler 117, steam can be generated to drive a steam turbine (not shown), particularly a steam turbine for a generator (not shown). Furthermore, in this device, the flow of flue gas 100 is generated by a fan 110 located upstream of a chimney 111.

[0118] A reactor 118 can be installed downstream of boiler 117. For example, water can be sprayed onto flue gas 100 to regulate flue gas 100, i.e., control its temperature and moisture content. Alkaline compound slurry (e.g., quicklime) can also be injected into flue gas 100 in reactor 118 to help neutralize acidic pollutants.

[0119] In boiler 117, some dust particles contained in flue gas 100 can be removed from flue gas 100 and collected as boiler ash 119 in boiler ash container 120. A fabric filter 121 (preferably a so-called bag filter) is provided downstream of optional reactor 118 to remove remaining dust particles from flue gas 100. These dust particles are collected as fly ash 122 in fly ash container 123.

[0120] In such a flue gas purification device, carbonated granular steel slag material can be injected as a dry adsorbent material into different locations in the flue gas flow 100. It can initially be injected into the top of the incinerator 112 via injector 124. At this location, the flue gas 100 still has a very high temperature. The advantage of injecting the adsorbent material 105 at this location in the flue gas flow 100 is that it allows for the maximum contact time between the adsorbent material 105 and the flue gas 100. Furthermore, when the adsorbent material 105 contains some moisture, it dries rapidly in the flue gas flow 100, simultaneously increasing the moisture content of the flue gas. This increased moisture content in the flue gas may increase the reactivity of the adsorbent material 105 with acidic pollutants. When using carbonated granular steel slag material as the adsorbent material 105, it has been found that drier adsorbent material 105 is more effective at capturing acidic pollutants from the flue gas.

[0121] Alternatively, the adsorbent material 105 can be injected into other locations in the flow of flue gas 100, such as in boiler 117, reactor 118, or the location between reactor 118 and fabric filter 121, as indicated by arrow 125. The advantage of using fabric filter 121 is that dust contained in the flue gas 100 is collected on fabric filter 121. This dust contains the injected adsorbent material 105. Since the dust forms a layer on fabric filter 121 before falling off, the presence of fabric filter 121 significantly increases the contact time between the flue gas and the adsorbent material. A mixture of ordinary fly ash and the used adsorbent material is collected in fly ash container 123. However, a portion of this mixture can be re-injected into the flow of flue gas 100 upstream of fabric filter 121 via injector 126, allowing adsorbent material 105 to capture a larger amount of acidic pollutants.

[0122] Preferably, when carbonated granular steel slag material is injected into the flue gas stream, its particle size distribution D 90 The sieve aperture size is less than 2000 µm, preferably less than 1000 µm, more preferably less than 500 µm, and most preferably less than 250 µm. The smaller the particle size of the steel slag, the better the carrying effect with the flue gas flow. In cases where relatively coarse particles / granules exist in the carbonated granular steel slag material, it is preferable to inject them above the incinerator. Heavier particles that are not carried by the flue gas flow fall into the incinerator, where they may capture acidic contaminants and reach the bottom ash. The D of the carbonated granular steel slag material... 90 The sieve aperture size is preferably greater than 50 µm, more preferably greater than 75 µm. This allows the filter to more effectively remove carbonated granular steel slag material from the flue gas stream. Carbonated granular steel slag material will reduce filter clogging problems, especially when the flue gas has a relatively high moisture content. It has indeed been found that when calcium chloride forms in the adsorbent material, the higher hydrate content of calcium chloride can make it viscous, which is particularly problematic when the calcium chloride concentration is high in small, lightweight adsorbent particles.

[0123] The carbonated granular steel slag material used as the adsorbent is preferably dried to a moisture content of less than 10 wt.%, preferably less than 7 wt.%, and more preferably less than 4 wt.%, after the carbonation step but before contact with the flue gas. Higher moisture content has been found to reduce the capture level of acidic pollutants. Therefore, the carbonated granular steel slag material can be used to purify flue gas at lower temperatures because it does not require drying (as is the case with semi-wet processes). Since the carbonation step requires the presence of water in the granular steel slag material, preferably more than 10 wt.%, a drying step is necessary to achieve the preferred moisture content. The carbonated granular steel slag material in contact with the flue gas has a moisture content greater than or equal to 0 wt.%.

[0124] The moisture content of the carbonated granular steel slag material was determined by keeping a 10 g sample of the material at 110°C for 24 hours, measuring the weight loss, and calculating the weight loss as a percentage of the initial weight.

[0125] Experimental data Parameters of granular steel slag materials Following the method described above, refer to... Figure 1A and 1B Starting with stainless steel slag collected in slag pots and solidified in the slag yard, stainless steel slag aggregate and powdered steel slag fractions were produced. Over a nine-month period, the composition of 88% of the powdered steel slag fraction was analyzed weekly. The volume percentage passing through different filters was determined by dry sieving. Furthermore, calcite content and maximum carbon dioxide uptake were determined by carbonating 10 g samples each time using the aforementioned test methods. The average, minimum, and maximum values ​​of these measurements are listed in Table 1.

[0126] Table 1 Particle size distribution, calcite content, maximum carbon dioxide absorption, total maximum carbon dioxide absorption, and dicalcium γ-silicate content of powdered stainless steel slag 88.

[0127]

[0128] Total carbon dioxide content is the sum of calcite content (expressed as a percentage of carbon dioxide dry weight) and maximum carbon dioxide uptake. Gamma C2S content (γ-C2S) is the weight percentage of γ-C2S in the total crystalline slag phase. This content is determined by XRD.

[0129] The inventors have discovered that the finer the particle size distribution, the higher the maximum carbonate content (total CO2) of the granular steel slag. From Figure 4 This positive correlation can be seen in the weekly analysis results shown. The figure illustrates the correlation between the volume percentage of particles smaller than 63 µm and the maximum carbonate content (expressed as a percentage of CO2 dry weight). Similar correlations exist between the volume percentage of particles smaller than 45 µm or smaller than 125 µm and the maximum carbonate content. Smaller particle sizes correspond to larger surface areas, such as larger blaine surface areas, which favors the reaction with carbon dioxide to form carbonates. Smaller particle sizes can be obtained by grinding granular steel slag. However, the inventors have found that smaller particle sizes are associated with higher γ-C2S content. Figure 5This correlation can be observed. When selecting steel slag fractions with higher γ-C2S content, it is easier to produce granular steel slag fractions with smaller particle sizes, thereby obtaining higher carbonate content without grinding granular steel slag materials.

[0130] Relationship between BET specific surface area and carbonate content of granular steel slag For many years, powdered steel slag component 88 has been produced and has been stored in large piles (at least 10 meters high) in the open air under atmospheric conditions. Over these years, the powdered steel slag component 88 has therefore undergone natural carbonation.

[0131] Research found that over many years, granular steel slag material 88 carbonated to the center of the pile. Samples were collected from different piles. Fresh samples of granular steel slag material 88 were also collected. Due to its production process (such as... Figure 1A and 1B As shown, these samples had been carbonized to a certain extent. Some fresh granular steel slag material samples (88) were further carbonized with carbon dioxide. Finally, two finely ground steel slag fractions (98) were also collected as different types of granular steel slag material.

[0132] Carbonate content was measured by STA (Symptom Analysis) and expressed as a percentage of CO2 dry weight from all samples, and BET (Best Equivalent Surface Area) was also measured. Two samples from the fine-ground steel slag fraction 98 had the lowest carbonate content and BET values, i.e., twice the carbonate content of 0.16 wt.% CO2, with BET values ​​of 1.7 and 2.4 m², respectively. 2 / g. Due to the extremely fine particle size of this finely ground steel slag portion (98%), especially D... 50 The sieve aperture size is 25.9 µm, resulting in relatively high BET values. A sample of fresh granular steel slag material 88 also exhibits similar D values. 50 The sieve aperture size, i.e., D. 50 The sieve aperture size is 20.6 µm, but the carbonate content is slightly higher at 0.77 wt.% CO2, and slightly higher at 2.93 µm. 2 The BET specific surface area was [value missing] g. The sample was finely ground to D [value missing]. 50 With a sieve aperture size of 3.4 µm, the BET specific surface area can be increased to 4.17 m². 2 / g. Therefore, fine grinding of granular steel slag materials to increase their BET specific surface area is beneficial for obtaining a surface area greater than 5 m². 2 In terms of BET specific surface area per g, this is not an economically feasible method.

[0133] However, the inventors have discovered that carbonation of granular steel slag materials can effectively increase the BET specific surface area of ​​the granular steel slag materials.

[0134] Figure 6 The relationship between the carbonate content and the BET specific surface area of ​​granular steel slag materials is shown. The curve fitted from these data is an exponential curve. For lower carbonate contents, the increase in BET specific surface area is quite limited. This is likely because free lime (including calcium hydroxide) undergoes carbonation first, which does not create additional porosity in the calcium and calcium magnesium silicate phases.

[0135] After carbonation, granular steel slag can be crushed, but fine grinding is preferred. A sample of granular steel slag stored in a pile for several years agglomerated through a natural carbonation process. The agglomerated material was then crushed to obtain finer granular material with a D... 10 The sieve aperture size is 60.7 µm, D 50 The sieve aperture size is 503.3 µm, D 90 The sieve aperture size is 1243.2 µm. The BET specific surface area of ​​this granular material is 46.4 m². 2 / g. The granular material is then finely ground to obtain D. 10 The sieve aperture size is 0.9 µm, D 50 The sieve aperture size is 6.4 µm, D 90 The material is fine with a sieve aperture size of 81.9 µm. Despite the extremely fine particle size, the BET specific surface area decreased after fine grinding, specifically to 8.6 m². 2 / g. Clearly, this fine grinding process may disrupt the pore structure of the carbonated granular steel slag material, or the carbonate structure formed on the surface of the steel slag particles within the pores of the granular material. However, a coarse crushing process can be used to reduce the particle size of the granular material produced by the carbonation process.

[0136] Effect of increasing BET specific surface area on the capture level of acid pollutants in flue gas composition Four types of carbonated granular steel slag materials have been tested, and their BET specific surface area and carbonate content have been determined. Figure 6 The figure shows these granular steel slag materials. Figure 1A and 1B The described method involves the production of stainless steel slag. Granular steel slag material is taken from powdered steel slag portion 88. Two of these materials are newly produced; one (slag A) was naturally aged for several weeks, and the other (slag B) was first carbonized with carbon dioxide for 24 hours. Two other materials (slag C and slag D) are taken from piles of powdered steel slag portion 88 that have been stored for 6 to 10 years.

[0137] All slag materials contained some agglomerated particles / clumps, which were broken up before the contaminant adsorption tests. Slag A and Slag D were manually crushed, and particles larger than 4 mm were removed by sieving. Slag B and Slag C had a higher degree of carbonation. These slags were crushed using a jaw crusher, and then fine particles smaller than 710 µm and coarser particles larger than 4 mm were removed by sieving.

[0138] A packed filter bed was prepared and placed in a reactor, each filter bed containing 200g of dried slag material. A three-gas mixture was prepared, namely the first gas mixture, which contained 1000 mg / m³ of slag material. 3 Air containing NO2 gas; a second gas mixture containing 1000 mg / m³ 3 Air containing SO2 gas; a third gas mixture containing 2000 mg / m³ 3 Nitrogen gas and HCl gas were simultaneously passed through a packed filter bed in the reactor at a flow rate of 2 Nl / min for 60 minutes. The reactor was heated to approximately 80°C using an external electric heating mantle before the test began. During the test, the reactor was further heated. At the end of the test, the temperature inside the reactor had risen to approximately 105°C. The gas exiting the reactor was sequentially passed through two bottles containing ultrapure water to capture residual acidic gases in the flue gas composition. The levels of sulfate, sulfide, nitrate, nitrite, and chloride in the water were determined. The test was also conducted using an empty reactor to calculate the capture levels of different acidic contaminants. As a comparative example, a sample containing 200 g of Sorbacal was also tested. ® Testing of a packed filter bed composed of SP. Sorbacal ® SP consists of over 93% hydrated lime and has a minimum thickness of 40 m. 2 / g high BET specific surface area and over 0.20cm 3 / g total pore volume (0-1000 Å). It is particularly suitable for dry flue gas treatment to capture SO2, HCl and HF.

[0139] The following results were obtained after performing two or three different tests.

[0140] Table 2 Results of acid contaminant capture tests in packed beds.

[0141]

[0142] Figure 7 SO2, HCl and NO are shown xThe average capture level is shown in the graph of the BET specific surface area of ​​the granular carbonate slag material. It can be seen that the capture level of different acidic pollutants is closely related to the BET specific surface area of ​​the slag material. x The trend line has the steepest slope, which may be because NO x HCl primarily adsorbs onto the surface of carbonated granular steel slag, while HCl mainly reacts with carbonates already formed on the surface of the granular steel slag particles. The SO2 curve lies between the other two curves, exhibiting a moderate slope, which seems to indicate that SO2 is adsorbed on the surface and may also react with carbonates.

[0143] Slag B exhibits the highest BET specific surface area. XRD analysis indicates its crystalline phase comprises 20.3% CaCO3. On average, the total amount of acidic contaminants captured in 200 g of sample during a 60-minute test was approximately 0.45 g. The average HCl capture level of slag B is comparable to that of Sorbacal. ® SP's average HCl capture level is roughly the same. However, its average SO2 capture level is even higher. Surprisingly, its NO... x The capture level is much higher, roughly the same as the SO2 capture level. This can be explained by the fact that the carbonated slag B contains micropores in which NO2 can be captured because, unlike SO2 and HCl, NO2 does not react with carbonates.

[0144] The article "Flue gas treatment in the ceramic industry" by M. Sindram, X. Pettiau, and O. Barthe describes the use of a packed bed filter composed of ground limestone for purifying flue gas containing HF, HCl, and SO2. A 95-98% HF reduction can be achieved, but only a 10-20% SO2 reduction is possible. According to this article, ground limestone can be used to capture HF from flue gas, but when SO2 is present... x Increase to above approximately 300 mg / Nm 3 At concentrations of, or except for SO x Furthermore, when HCl removal is required, ground limestone is no longer suitable. Based on current test results, it is clear that the carbonated granular steel slag material used in the method of this invention is effective not only due to its carbonate content, but especially due to its (micro)pores and increased BET specific surface area. It has been found that the pores in the silicate phase can even trap NO. x .

[0145] Further testing was conducted using slag C. The slag contained 1000 mg / m³. 3A mixture of SO2 gases was passed at a flow rate of 5 Nl / min through a 200 g filter bed in a reactor heated to approximately 80°C at the start of the test for 60 minutes. Unlike the use of ultrapure water to capture SO2 remaining in the gas after passing through the reactor, the SO2 content in the gas was continuously measured using an ecom-J2KNpro flue gas analyzer. Within the first 15 minutes, 100% of the SO2 was captured by the filter bed. During the next 45 minutes, the capture level decreased linearly to approximately 80%. In this test, approximately 0.28 g of SO2 was captured from a 200 g sample of slag C.

[0146] The same test was performed on slag C with 8% added water. From the start of the test, the SO2 capture level dropped linearly and dramatically from 100% to approximately 70%.

[0147] The first test, using a combination of three gases, was also repeated with slag C containing 8% added water instead of dry slag C. During the test, the moisture content of the slag decreased. At the end of the test, the moisture content of the filter bed was 2.4%. This test was conducted only once, achieving SO2 capture levels of 54%, HCl capture levels of 90%, and NO... x The capture level reached 75%. These three values ​​are low due to the high water content. Therefore, water appears to have filled some of the smaller pores and reduced the surface area of ​​the slag, which could be used for adsorption and / or reaction of acidic contaminants with the carbonated slag material.

[0148] Neutralization of Sorbacal as an adsorbent in carbonized steel slag at high temperature ® HCl and SO adsorbed in SP 2 Quantity The granular steel slag material is taken from the powdered steel slag portion 88, which is obtained through... Figure 1A and Figure 1B The method described herein produces the slag from stainless steel slag. The fine fraction is sieved through a 63 µm sieve. The fine fraction is completely dried at 105 °C. Water is added to a moisture content of 15%. The wet slag fraction is spread into a thin layer / bed and carbonated at 40 °C with >80% CO2 gas for 24 hours. Thus, the slag is completely carbonated. The slag particles do not agglomerate. The total carbonate content in the carbonated slag fraction is equal to approximately 12.5 wt.% CO2.

[0149] By containing 1200 mg HCl / Nm 3 A mixture of HCl gas and N2 containing 3363 mg SO2 / Nm 3 The adsorption of HCl and SO2 in a mixture of SO2 gases was measured. 50 mg of carbonized fine steel slag fraction and 30 mg of Sorbacal were used as adsorbents. ®SP samples. The size and isothermal exposure differences between the two sample types are due to the packing density of the samples in the crucible, Sorbacal. ® SP has a much lower packing density.

[0150] For each test, one sample was placed in a STA analyzer, specifically a Netzch %STA 409 PC. The sample was heated from 20°C to 180°C at a rate of 10°C / min, with an air flow rate of 30 ml / min. Then, a mixture of HCl or SO2 gases was introduced into the analyzer at a flow rate of 150 ml / min for 75 or 45 minutes for steel slag samples, and for Sorbacal samples... ® SP samples were subjected to treatment for 45 or 25 minutes (considering the small sample volume). The samples were then cooled from 180°C to 20°C at a rate of 20°C / min with an air flow rate of 30 ml / min. Samples removed from the analyzer were exposed to ambient air to absorb moisture for at least 8 hours. EDXRF measurements were used to determine the amounts of chloride and sulfate in the samples.

[0151] The following results were obtained from different tests.

[0152] Table 3 Results of acid contaminant capture tests in packed beds.

[0153]

[0154] It can be seen that carbonated granular steel slag can adsorb approximately 1.5% to 2% of acidic pollutants. In further tests, for SO2, an adsorption percentage of approximately 3% was obtained with increasing reaction time. It appears that after rapid SO2 adsorption, SO2 capture increases slowly due to the required reaction between carbonates and SO2. For HCl, no initial rapid adsorption was observed, and HCl capture appears to be primarily due to chemical reactions with carbonates.

[0155] The adsorption of HF has not yet been determined. However, considering the reactivity between HF and carbonates, and the high BET surface area of ​​carbonated granular steel slag, it should be able to adsorb relatively large amounts of HF, especially given the BET specific surface area of ​​less than 5 m² disclosed in the aforementioned article by M. Sindram et al. 2 The adsorption capacity of ground limestone is higher per g.

Claims

1. A method for recycling steel slag (31) generated during the steelmaking process of a steel plant as an adsorbent (105) for capturing acidic pollutants from flue gas (100), particularly by means of a dry adsorption process, said acidic pollutants including HCl, HF, SO₂. x and / or NO x , Its features are, The steel slag (31) comprises a non-metallic slag phase, of which at least 40 wt.% is a crystalline non-metallic slag phase, wherein the crystalline non-metallic slag phase comprises at least a crystalline calcium silicate phase and a crystalline calcium magnesium silicate phase, and wherein... The method includes the following steps: - Granular steel slag materials (88, 98) are produced from the steel slag (31), the granular steel slag materials (88, 98) being composed of steel slag particles and having D 50 First particle size distribution and first specific surface area with sieve aperture size less than 70 µm; - By carbonating the granular steel slag materials (88, 98) with a gas containing carbon dioxide, the first specific surface area of ​​the granular steel slag materials (88, 98) is increased to above 5 m². 2 Specific surface area per g; and - The flue gas (100) is contacted with at least a portion of a carbonated granular steel slag material, which serves as the adsorbent (105), to capture the acidic pollutants in the carbonated granular steel slag material. In the method, the first specific surface area and the second specific surface area are specific surface areas determined by nitrogen adsorption pressure measurement using the BET method according to ISO 9277:2022(E).

2. The method according to claim 1, characterized in that, The gas containing carbon dioxide does not contain HCl or contains less than 10 mg / Nm³. 3 HCl, free of HF or containing less than 1 mg / Nm 3 HF, free of SO2 or containing less than 50 mg / Nm 3 SO x and NO-free x Or contains less than 200 mg / Nm 3 NO x .

3. The method according to claim 1 or 2, characterized in that, The second specific surface area is higher than 10 m² 2 / g, preferably higher than 15 m 2 / g, more preferably higher than 20 m 2 / g.

4. The method according to any one of claims 1 to 3, characterized in that, The granular steel slag material (88, 98) is carbonated until the granular steel slag material has a carbonate content expressed as a percentage of dry weight of carbon dioxide of at least 2.0 wt.%, preferably at least 4.0 wt.%, more preferably at least 6.0 wt.%, and most preferably at least 8.0 wt.%.

5. The method according to any one of claims 1 to 3, characterized in that, The granular steel slag material (88, 98) is carbonated until the granular steel slag material has a carbonate content, expressed as a percentage of dry weight of carbon dioxide, that is at least 50%, preferably at least 70%, and more preferably at least 90% of its maximum carbonate content, obtained, in particular, by carbonating a sample of the granular steel slag material with a water content of 15 wt.% at 23°C with 100% carbon dioxide gas at a pressure of 0.5 bar for 24 hours.

6. The method according to any one of claims 1 to 5, characterized in that, The D of the first particle size distribution 50 The sieve aperture size is less than 60 µm, preferably less than 50 µm, more preferably less than 40 µm, and most preferably less than 30 µm.

7. The method according to any one of claims 1 to 6, characterized in that, The granular steel slag materials (88, 98) are uniformly carbonized.

8. The method according to any one of claims 1 to 7, characterized in that, The gas has a carbon dioxide content of less than 5.0 vol.%, preferably less than 3.0 vol.%, more preferably less than 1.0 vol.%, and the gas is, in particular, atmospheric air.

9. The method according to any one of claims 1 to 7, characterized in that, The gas has a carbon dioxide content greater than 5.0 vol.%, preferably greater than 10.0 vol.%, and more preferably greater than 15.0 vol.%.

10. The method according to any one of claims 1 to 9, characterized in that, During the carbonation step, the granular steel slag materials (88, 98) are arranged in piles or beds.

11. The method according to claim 10, characterized in that, The granular steel slag material (88, 98) is loosely stacked in the pile or the bed.

12. The method according to claim 10 or 11, characterized in that, The first particle size distribution has D 60 sieve aperture size and D 10 The sieve aperture size value, wherein D 60 The sieve aperture size value and the D 10 The ratio of the sieve aperture size values ​​is less than 15, preferably less than 14, more preferably less than 13, and most preferably less than 12.

13. The method according to any one of claims 10 to 12, characterized in that, In the carbonation step, the granular steel slag material (88, 98) is stirred once or multiple times.

14. The method according to any one of claims 10 to 13, characterized in that, The gas passes through the bed of the granular steel slag material (88, 98) to agitate the steel slag particles to avoid or reduce their agglomeration.

15. The method according to any one of claims 1 to 14, characterized in that, The particles of the granular steel slag material (88, 98) at least partially agglomerate during the carbonation step to produce a granular material containing granular carbonated granular steel slag material.

16. The method according to claim 15, characterized in that, The granules were at least partially reduced in size after the carbonation step and before the contact step.

17. The method according to claim 15 or 16, characterized in that, The packed filter bed (104) is made of at least a portion of the granules, and during the contact step, the flue gas (100) is guided through the packed filter bed (104).

18. The method according to any one of claims 1 to 16, characterized in that, The portion of the carbonated granular steel slag material used as the adsorbent (105) is injected into the flow of flue gas (100), particularly according to the dry adsorption injection technique.

19. The method according to claim 18, characterized in that, The portion of the carbonated granular steel slag material used as the adsorbent (105) has D 90 The second particle size distribution has a sieve aperture size of less than 2000 µm, preferably less than 1000 µm, more preferably less than 500 µm, and most preferably less than 250 µm.

20. The method according to claim 18 or 19, characterized in that, The flue gas (100) is generated in an incinerator (112), particularly a municipal solid waste incinerator (112), and is directed to a dust filter (121), wherein a portion of the carbonated granular steel slag material is injected into the flow of the flue gas (100) upstream of the dust filter (121), the dust filter being preferably a fabric filter (121).

21. The method according to any one of claims 1 to 20, characterized in that, The portion of the carbonated granular steel slag material used as the adsorbent (105) is dried to a moisture content of less than 10 wt.%, preferably less than 7 wt.%, and more preferably less than 4 wt.%, after the carbonation step but before contact with the flue gas (100).

22. The method according to any one of claims 1 to 21, characterized in that, The granular steel slag material (88, 98) is produced from stainless steel slag (31) and contains more than 1500 mg / kg, especially more than 2000 mg / kg, and more specifically more than 2500 mg / kg of chromium.

23. The method according to any one of claims 1 to 22, characterized in that, The granular steel slag material (88) comprises a crystalline nonmetallic steel slag phase, wherein at least 3 wt.%, preferably at least 5 wt.%, and more preferably at least 7 wt.%, of the crystalline nonmetallic steel slag phase is dicalcium γ-silicate.

24. The method according to any one of claims 1 to 23, characterized in that, Following the contact step, the carbonated granular steel slag material is mixed with a binder, and the mixture of the carbonated granular steel slag material and the binder is hardened to produce a shape-retaining block. The binder is, in particular, a hydraulic binder that cures in the presence of water; a carbonateable granular material, especially granular steel slag material cured with carbon dioxide; or an asphalt binder.

Images