Comprehensive utilization of steel slag

Abstract

The present invention relates to a technical field of comprehensive utilization of industrial waste slag, and in particular to a method for comprehensive utilization of steel slag, which includes the steps of leaching free calcium oxide in steel slag with a first ammonium chloride solution, obtaining a first leach residue and a first mineralization solution through solid-liquid separation, subjecting the first mineralization solution to CO2 absorption and mineralization to obtain calcium carbonate and an ammonium chloride solution, leaching the first leach residue with a second ammonium chloride solution, obtaining a second leach residue and a crude mineralization solution through solid-liquid separation, oxidizing the crude mineralization solution, adjusting the alkali and separating it, obtaining an iron-aluminum precipitate residue and a second mineralization solution, subjecting the second mineralization solution to CO2 absorption and mineralization to obtain crude calcium carbonate and an ammonium chloride solution, and leaching the iron-aluminum precipitate residue with a sodium hydroxide solution to separate iron and aluminum elements. This method can achieve efficient extraction and separation of major elements in steel slag, while also achieving the goal of reducing carbon emissions. The auxiliary agents are recyclable, the process is simple, the production cost is low, and industrial production is easy.

Description

[Technical Field]

[0001] The present invention relates to the technical field of comprehensive utilization of industrial waste slag, and more particularly to a method for comprehensive utilization of iron and steel slag. [Background technology]

[0002] Steel slag is molten slag discharged during the steelmaking process. It contains oxides formed by the oxidation of various elements in the metal charge, impurities in the metal charge, and the calcination products of conditioning materials such as limestone. Steel slag contains approximately 20% slag iron, as well as substances such as calcium, magnesium, and aluminum oxides and silicates. While the iron content of steel slag can be partially recycled through magnetic separation, the remaining substances such as calcium, magnesium, and aluminum oxides and silicates are used in cement and road paving, and large amounts of waste slag are still piled up for disposal.

[0003] The discharge of large amounts of steel slag causes serious environmental pollution and harm. First, piles of steel slag occupy a large amount of valuable land resources. Because some steel slag particles are small, they are prone to forming dust particles, causing dust pollution and harming human health. Furthermore, steel slag leaches into nearby land and rivers after mixing with water, causing serious environmental pollution. Therefore, how to reduce steel slag pollution, transform steel slag into valuable resources, and promote the efficient recycling and full utilization of steel slag has become an urgent issue that must be resolved.

[0004] Extraction and utilization of elements is an important method of recycling solid waste. The alkaline substances and silicates contained in steel slag, such as calcium oxide, magnesium oxide, calcium silicate, and magnesium silicate, can be used as raw materials for CO2 solidification to mineralize and fix CO2. The iron and aluminum contained in steel slag can be leached and concentrated with alkaline oxides, and then used as raw materials for flocculants and catalyst carriers, thereby realizing advanced recycling of steel slag.

[0005] At present, various methods for extracting calcium, magnesium, aluminum, and iron from steel slag and comprehensively utilizing the elements have been disclosed in literature and patents. For example, a Chinese invention patent with application number CN202010726836.5 discloses that steel slag is leached with ammonium chloride to obtain a CaCl2-NH4Cl-NH3-H2O system leachate and filtration residue, and the leachate is used to fix and seal the carbon dioxide gas produced by smelting in situ to produce high-purity calcium carbonate products. The filtration residue is then reduced at high temperature to extract iron, and the iron is melted. A comprehensive utilization method for steel slag has been disclosed, in which waste slag is directly used to produce diopside-phase microcrystalline glass. Although this method solves the problems of low utilization rate of steel slag and complicated process, the calcium extraction rate in the leaching stage is very low, the reaction time is long, and a high-temperature molten state of 1300-1500°C is required in the process of extracting iron element and producing microcrystalline glass, which results in high energy consumption, difficult operation, low degree of automation, and high requirements for equipment and materials, and therefore cannot meet the requirements for large-scale industrial production.

[0006] In the Chinese invention patent with application number CN20221042334.3, silicon, iron, calcium, titanium, vanadium, aluminum, magnesium and phosphorus contained in steel slag are extracted and used, and hydrochloric acid with a concentration of 30-36% is added to carry out an acid dissolution reaction with the steel slag. After filtration, the filter residue is dried and crushed to obtain silicon powder. The pH value of the filtrate is adjusted with ammonia water and filtered to obtain iron hydroxide precipitate and filtrate B. The filtrate B is reacted with sulfate and filtered to obtain calcium sulfate and filtrate C. Hydrochloric acid is added to the filtrate C to adjust the pH value, and titanium ions are extracted. This paper discloses a comprehensive method for recycling steel slag, which involves adsorbing and desorbing with an ion exchange resin to obtain filtrate E and a titanium-containing analytical solution, adjusting the pH of filtrate E with ammonia water, adsorbing and desorbing with a vanadium ion exchange resin to obtain filtrate H and a vanadium-containing analytical solution, adjusting the pH of filtrate H with ammonia water, and filtering the filtrate to obtain aluminum hydroxide and filtrate J. Adding ammonia water to filtrate J to adjust the pH while simultaneously adding ammonium salt, filtering the filtrate to obtain ammonium magnesium phosphate and filtrate K. Concentrating filtrate K by evaporation, the ammonium salt and distilled water are obtained for reuse. While this method achieves a significant degree of comprehensive utilization of steel slag, it consumes large amounts of concentrated hydrochloric acid (30-36%) and ammonia water. Furthermore, problems arise, such as coprecipitation occurring during element separation, resulting in low product purity. For example, during the process of adjusting the pH to 3-4 with ammonia water, some aluminum ions are precipitated, resulting in low iron product purity.

[0007] In response to the problems of conventional steel slag recovery technologies, such as the need to consume large amounts of acid and alkali, low calcium extraction rate and purity, low overall element utilization rate, and high energy and material consumption, the present invention provides a new method for comprehensively utilizing steel slag. Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the present invention is to provide a method for comprehensively utilizing iron and steel slag, which can significantly improve the overall utilization rate of elements and reduce the energy consumption and material consumption for production. [Means for solving the problem]

[0009] The present invention provides Step S1: leaching free calcium oxide in the steel slag with a first ammonium chloride solution, obtaining a first leaching residue and a first mineralization solution by solid-liquid separation, and subjecting the first mineralization solution to CO2 absorption and mineralization to obtain calcium carbonate and an ammonium chloride solution; Step S2: leaching the first leaching residue with a second ammonium chloride solution, obtaining a second leaching residue and a crude mineralization solution through solid-liquid separation, oxidizing the crude mineralization solution, adjusting the alkalinity and subjecting it to solid-liquid separation to obtain an iron-aluminum precipitate residue and a second mineralization solution, and subjecting the second mineralization solution to CO2 absorption and mineralization to obtain crude calcium carbonate and an ammonium chloride solution; The present invention provides a method for comprehensively utilizing iron and steel slag, comprising: step S3 of leaching iron-aluminum precipitate residue with a sodium hydroxide solution and obtaining an iron hydroxide precipitate and a sodium meta-aluminate solution by solid-liquid separation; subjecting the sodium meta-aluminate solution to CO2 absorption and mineralization to obtain an aluminum hydroxide precipitate and a sodium carbonate solution; and treating the sodium carbonate solution with carbide slag to obtain crude calcium carbonate and a sodium hydroxide solution.

[0010] In the method for comprehensive utilization of iron and steel slag according to the present invention, first, the free calcium oxide in the iron and steel slag is leached with ammonium chloride solution, followed by CO2 absorption and mineralization to obtain calcium carbonate product, and the chemical reaction is as follows: CaO+2NH4Cl→CaCl2+2NH3+H2O

[0011] After the slurry obtained by the above reaction is subjected to solid-liquid separation, a first leaching residue and a first mineralizing solution are obtained. A CO2-containing gas is passed through the first mineralizing solution to carry out a mineralization reaction, producing calcium carbonate precipitate and ammonium chloride. After solid-liquid separation, calcium carbonate and ammonium chloride solutions are obtained. After the calcium carbonate is washed and dried, a calcium carbonate product can be obtained. The obtained ammonium chloride solution can be returned to the leaching step and reused.

[0012] Next, the insoluble calcium, magnesium, iron, aluminum, etc. in the primary leaching residue are further leached, and CO absorption and mineralization are carried out to obtain a crude calcium carbonate product and an iron-aluminum precipitate, and the chemical reaction is as follows: CaX n O m (MgX n O m ) + 2NH4Cl - CaCl2 (MgCl2) + X n O m-1 +2NH3+H2O Al2O3+6NH4Cl=2AlCl3+3H2O+6NH3 FeO + 2NH4Cl = FeCl2 + H2O + 2NH3 AlCl3+3NH3+3H2O=Al(OH)3+3NH4Cl FeCl3+3NH3+2H2O=Fe(OH)3+3NH4Cl CaCl2(MgCl2)+CO2+2NH3·H2O→CaCO3(MgCO3)+2NH4C1

[0013] The primary leaching residue is added to a second ammonium chloride solution to leach insoluble calcium, magnesium, aluminum, iron, etc., producing ammonia gas. The resulting slurry is subjected to solid-liquid separation to obtain a secondary leaching residue and a crude mineralization solution. The crude mineralization solution contains CaCl2 (MgCl2), AlCl3, and FeCl2. The ferrous ions in the slurry are completely oxidized to ferric ions through an oxidation reaction, and the pH of the slurry is adjusted to precipitate iron and aluminum elements in the form of hydroxide precipitates, producing ammonium chloride. After solid-liquid separation of the slurry, an iron-aluminum precipitate residue and a secondary mineralization solution containing calcium and magnesium elements are obtained. The secondary mineralization solution is then subjected to CO2 absorption and mineralization to produce carbonate precipitates and ammonium chloride. The carbonate and ammonium chloride solution are obtained through solid-liquid separation. After the carbonate is washed and dried, a crude calcium carbonate product is obtained. The resulting ammonium chloride solution can be returned to the leaching stage for reuse.

[0014] Finally, the iron and aluminum elements are separated from the iron-aluminum precipitation residue, and CO2 absorption and mineralization are carried out to obtain a crude calcium carbonate product and an iron-aluminum product, and the chemical reaction is as follows: Al(OH)3 + NaOH = NaAlO2 + 2H2O 2NaAlO2+3H2O+CO2=2Al(OH)3↓+Na2CO3 Na2CO3 + Ca(OH)2 = 2NaOH + CaCO3↓

[0015] The iron-aluminum precipitate residue is added to a sodium hydroxide solution of a specific concentration for leaching, and the aluminum hydroxide precipitate is dissolved into water-soluble sodium metaaluminate under specific conditions. The slurry obtained by the above reaction is subjected to solid-liquid separation to obtain an iron hydroxide precipitate and a sodium metaaluminate solution. The sodium metaaluminate is subjected to a mineralization reaction to obtain an aluminum hydroxide precipitate and a sodium carbonate solution. The sodium carbonate solution is treated with carbide slag (mainly composed of unreacted calcium hydroxide) to obtain a sodium hydroxide solution and a calcium carbonate precipitate. These are subjected to solid-liquid separation to obtain calcium carbonate and a sodium hydroxide solution. The calcium carbonate is washed and dried to obtain a crude calcium carbonate product, and the obtained sodium hydroxide solution can be returned to the leaching step and reused.

[0016] Therefore, the method for comprehensive utilization of steel slag of the present invention fully utilizes the properties of steel slag itself to realize the extraction and separation of the main elements in steel slag, and also achieve the purpose of reducing carbon emissions.

[0017] The present invention does not strictly limit the solid-liquid separation method, which includes, but is not limited to, sedimentation, filtration, centrifugation, and the like.

[0018] Furthermore, the CO2 used in the mineralization reaction in the present invention is preferably industrial exhaust gas, and the volume content of CO2 in the industrial exhaust gas is 5% to 100%.

[0019] In this technical solution, preferably, the leaching in step S1 is aimed only at extracting free calcium oxide in the steel slag, and in order to avoid other elements in the steel slag, such as iron and aluminum, from being mixed into the solution, the mass concentration of the first ammonium chloride solution used is 5 to 30%, preferably 8 to 25%, and during the leaching, the temperature of the reaction system is controlled to 5 to 55°C, preferably 10 to 40°C, and the pH value needs to be controlled to be greater than 9.

[0020] In this technical solution, preferably, the leaching in step S2 is aimed at extracting insoluble calcium, magnesium, iron, aluminum, etc. in the steel slag. Therefore, in order to promote the dissolution of the insoluble components in the steel slag, the mass concentration of the diammonium chloride solution used is 10 to 40%, preferably 10 to 35%. During the leaching, the temperature of the reaction system is controlled to 90 to 125°C, preferably 100 to 120°C, and the pH value is controlled to be less than 2.5.

[0021] In this technical solution, preferably, in step S2, in order to dissolve and extract as much of the insoluble components in the first leaching residue as possible with ammonium chloride, the molar ratio of ammonium chloride in the second ammonium chloride solution to the soluble components in the first leaching residue is (2~6):1, and the soluble components are calculated as calcium / magnesium silicate, aluminum oxide, and iron oxide. The reaction molar ratios of calcium / magnesium silicate to ammonium chloride are 1:2, the reaction molar ratios of aluminum oxide to ammonium chloride are 1:6, and the reaction molar ratios of iron oxide to ammonium chloride are 1:2. Therefore, in combination with the content of the insoluble components in the first leaching residue, the molar ratio of ammonium chloride to the soluble components in the first leaching residue is preferably (3~5):1.

[0022] In this technical solution, preferably, in step S2, when the primary leaching residue is leached with the second ammonium chloride solution, the ammonia gas generated by the reaction is discharged from the reaction system, and the discharge method includes any of inert gas stripping, evaporation, and ultrasonic waves. During the leaching, the ammonia gas is continuously released from the liquid phase by the above method, which not only promotes the progress of the reaction toward dissolution, but also allows the obtained ammonia-containing gas to be used in the subsequent alkali adjustment and mineralization reaction.

[0023] In the present technical solution, preferably, in step S2, during the oxidation, air is passed through the crude mineralization liquor or an oxidizing agent is added to completely oxidize the ferrous ions in the crude mineralization liquor to ferric ions.

[0024] During the alkalinity adjustment, ammonia gas collected during the leaching process is passed through the oxidized mineralized crude liquor to adjust the pH value to 5-6, causing iron and aluminum elements to precipitate in the form of hydroxide precipitates, and producing ammonium chloride.

[0025] During the CO2 absorption and mineralization, CO2 gas and ammonia gas collected during the leaching process are passed through the second mineralization fluid.

[0026] When a second mineralizing fluid containing calcium and magnesium elements is subjected to a mineralization reaction, CO2 gas is passed through the second mineralizing fluid, and ammonia gas collected during the leaching process is also passed through the second mineralizing fluid, thereby obtaining carbonate precipitates and ammonium chloride solution, which not only reduces the amount of ammonia consumed in this process, but also improves the overall utilization rate of ammonia.

[0027] In this technical solution, preferably, in step S3, the iron hydroxide precipitate and the aluminum hydroxide precipitate are washed and calcined respectively to obtain an iron oxide product and an alumina oxide product.

[0028] In this technical solution, preferably, in steps S1 and S2, the produced ammonium chloride solution is returned to the leaching stage to form a closed loop, and in step S3, the produced sodium hydroxide solution is returned to the leaching stage to form a closed loop.

[0029] In this technical solution, the slurry reactor preferably used in the present invention for leaching includes, but is not limited to, a mechanically stirred tank, a loop reactor, a bubble tower, and a three-phase fluidized bed reactor. The slurry reactor specifically includes a jacketed reactor, a stirring device, and an aeration mechanism. The jacketed reactor has an air inlet, an air outlet, and a supply port at the top, and an outlet and a discharge port at the bottom. Both the stirring device and the aeration mechanism are installed inside the jacketed reactor. One or more baffles are installed at the bottom inside the jacketed reactor to further improve the dispersion effect of the mixed slurry, reduce the formation of an inert layer on the particle surface, increase the probability of the extraction solution diffusing on the particle surface, and improve the efficiency of element leaching.

[0030] In this technical solution, preferably, the aeration mechanism includes an aeration coil and an aeration base, the aeration coil is spirally installed on the inner wall of the jacketed reactor, the aeration base is fixed to the inner bottom of the jacketed reactor, the aeration base is a concentric coil, and a plurality of aeration holes are uniformly opened in the concentric coil.

[0031] The aeration coil on the inner wall of the jacketed reactor and the concentric coil on the inner bottom of the jacketed reactor are provided to further increase the turbulence of the mixed slurry, improving the dispersion effect of the mixed slurry and thereby increasing the leaching rate of the elements.

[0032] The jacketed reactor of the slurry reactor of the present invention has a circulating liquid inlet and an outlet on the outer surface thereof, and an electric heating device is connected to the jacketed reactor, which can be used to heat the circulating liquid in the jacket.

[0033] The method for comprehensively utilizing iron and steel slag of the present invention has at least the following technical effects: 1. This invention achieves the extraction and separation of major elements such as calcium, magnesium, aluminum, and iron in steel slag by analyzing the properties of the steel slag raw material and controlling the process parameters. Then, through CO2 absorption and mineralization, the mineralization products calcium carbonate and crude calcium carbonate are obtained, respectively. Furthermore, by introducing carbide slag and sodium hydroxide circulation aid, the separation of iron and aluminum elements is achieved, and high-purity iron oxide products and alumina oxide products are obtained, respectively. At the same time, CO2 absorption and mineralization are carried out, further achieving the purpose of reducing carbon emissions. 2. In the method for comprehensively utilizing iron and steel slag according to the present invention, the circulation aid can be recycled without the need for extraction and separation of organic reagents, and without the need for high-temperature decomposition or other operations, making the process simple and easy to scale up. 3. In the method for comprehensive utilization of iron and steel slag according to the present invention, the escape of ammonia in the gas phase form from the solution is promoted, which not only improves the efficiency of the leaching reaction, but also reduces the amount of ammonia required in subsequent processes, thereby improving the overall utilization rate of ammonia. 4. In the method for comprehensive utilization of iron and steel slag according to the present invention, the leaching of insoluble elements such as calcium, magnesium, iron, and aluminum in iron and steel slag is achieved by using a uniquely designed slurry reactor, which improves the leaching efficiency and comprehensive utilization rate of the elements. The method is simple to operate and easy to implement for industrial production. [Brief explanation of the drawings]

[0034] In order to more clearly describe the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces drawings necessary for describing the specific embodiments or the prior art. Obviously, the drawings described below are some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any creative work.

[0035] [Figure 1] 1 is a schematic diagram of a slurry reactor of the present invention. [Figure 2] 1 is a schematic diagram of an aeration base of the present invention. [Figure 3] 1 is a process flowchart of step S1 of the present invention. [Figure 4] 1 is a process flowchart of step S2 of the present invention. [Figure 5] 1 is a process flowchart of step S3 of the present invention.

[0036] 1: Jacketed reactor, 2: Stirring device, 3: Air inlet, 4: Air outlet, 5: Supply port, 6: Discharge port, 7: Discharge port, 8: Baffle, 9: Aeration coil, 10: Aeration base. DETAILED DESCRIPTION OF THE INVENTION

[0037] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art.

[0038] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly dictates otherwise, the singular forms include the plural forms, and further, when used herein, the terms "comprises" and / or "comprises" are to be understood as indicating the presence of features, steps, operations, devices, components and / or combinations thereof.

[0039] The technical solutions of the present invention will be described clearly and completely below with reference to the embodiments, but obviously, the described embodiments are not all the embodiments but only a part of the embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present invention.

[0040] Example 1 Steel slag was selected as the calcium / magnesium-containing silicate mineralization raw material. The steel slag was collected from a steel mill in Hebei Province, and its main components were determined by fusion X-ray fluorescence analysis and are shown in Table 1.

[0041] [Table 1]

[0042] According to YB / T 4328-2012 "Method for determining the content of free calcium oxide in steel slag", the mass fraction of free calcium oxide in steel slag is determined to be 66%. Take an appropriate amount of steel slag and grind it to 100 mesh.

[0043] S1: A 10% mass fraction of ammonium chloride solution was added to a slurry reactor (Figures 1 and 2) according to the free calcium oxide content. The solution temperature was controlled at 25°C and the pH was maintained at 9 or higher. After 0.5 hours of low-speed stirring, the slurry was discharged and allowed to settle. This resulted in a primary leaching residue rich in iron, aluminum, and some insoluble calcium, and a calcium-containing primary mineralization solution. Power plant flue gas with a 12% CO2 content was passed through the calcium-containing primary mineralization solution to produce a calcium carbonate precipitate and an ammonium chloride solution. The calcium carbonate precipitate was separated using a plate-and-frame filter press to obtain calcium carbonate and ammonium chloride solutions. The calcium carbonate was then dried in a drum to obtain a micronized calcium carbonate product. The separated ammonium chloride solution could be reused for steel slag leaching (Figure 3).

[0044] Here, the extraction rate of free calcium is 98.5%, and the micronized calcium carbonate product has a purity of 99.96%, a whiteness of 98.4, and a median diameter D50 of 2.5 μm.

[0045] S2: The second leaching residue obtained above, which is rich in iron, aluminum, and a portion of the insoluble calcium, is added to a slurry reactor (Figures 1 and 2). A 20% mass fraction of second ammonium chloride solution is added at a chemical reaction molar ratio of 2:1 based on the calcium, magnesium, iron, and aluminum contents of the first leaching residue. Circulating water is passed through the jacket to control the reaction temperature of the solution at 90°C. Air is passed through the jacketed reactor through the air inlet, the pH of the solution is controlled at 2 to 2.5, and the aeration rate is automatically adjusted according to the pH of the solution. Ammonia-containing air is discharged through the air outlet and collected. After stirring for 1 hour, the resulting slurry was separated by pressure filtration to obtain a second leaching residue and a mineralized crude solution containing calcium, magnesium, iron, and aluminum. An appropriate amount of hydrogen peroxide was added to the mineralized crude solution while stirring, with the amount of hydrogen peroxide added being 1.1 times the reaction stoichiometric ratio according to the iron ion content in the mineralized crude solution. After the reaction was completed, the collected ammonia-containing air was pressurized and passed through the mineralized crude solution to adjust the pH value of the crude solution to 6, causing iron and aluminum elements to precipitate in the form of hydroxides to produce ammonium chloride, and the resulting iron-aluminum precipitate was separated by pressure filtration. The second mineralization solution is then passed through a plate and frame filter press to separate the carbonate precipitate, which is then mixed with a crude calcium carbonate solution and an ammonium chloride solution. The crude calcium carbonate is then further washed and dried in a drum to obtain a micron crude calcium carbonate product. The ammonium chloride solution is then returned to the slurry reactor for reuse (Figure 4).

[0046] Here, the micron crude calcium carbonate product has a calcium carbonate content of 67.4%, a magnesium carbonate content of 32.6%, a median diameter D50 of 2.2 μm, a whiteness of 96.5, a total calcium extraction rate of 99.86%, and a magnesium extraction rate of 96.2%.

[0047] In S3, the separated iron-aluminum precipitate residue is added to a 10% sodium hydroxide solution in a slurry reactor (Figures 1 and 2), thoroughly stirred and dissolved, and filtered to separate the precipitate. This yields an iron hydroxide precipitate and a sodium metaaluminate solution. The iron hydroxide precipitate is then washed and calcined to obtain the iron oxide product. A 30% mass fraction of exhaust gas from a cement plant is passed through the separated sodium metaaluminate solution to produce aluminum hydroxide and sodium carbonate. This is then filtered to separate the aluminum hydroxide precipitate and a sodium carbonate solution. The aluminum hydroxide precipitate is then washed and calcined to obtain the alumina oxide product. Carbide slag (94% calcium hydroxide) is added to the resulting sodium carbonate solution, thoroughly stirred, and filtered to obtain the sodium hydroxide solution and calcium carbonate precipitate. This is then filtered under pressure to obtain the crude calcium carbonate product and a sodium hydroxide solution. The sodium hydroxide solution is then returned to the slurry reactor for reuse (Figure 5).

[0048] Here, the iron oxide product has an Fe2O3 content of 99.8%, a total calcium content (calculated as CaO) of 0.2%, and an iron extraction rate of 97.6%.

[0049] The aluminum oxide product has an Al2O3 content of 99.9% and an Fe2O3 content of 0.1%, with an aluminum extraction rate of 98.4%.

[0050] The crude calcium carbonate product has a calcium carbonate content of 94.71%, a magnesium carbonate content of 1.57%, an iron oxide content of 0.15%, a silica content of 3.58%, a whiteness index of 94.5, and a median diameter D50 of 4.9 μm.

[0051] Example 2 The steel slag used in Example 1 is used as the raw material, and the operation steps are almost the same as those in Example 1, with the difference being that in step S2, thermal oil is added to the jacket of the slurry reaction vessel, and the heating device is turned on at the same time to control the temperature of the reaction solution at 105-115°C, and air is not allowed to pass through. The ammonia generated by evaporation is allowed to overflow from the solution, maintaining the pH value of the solution at 2-2.5. At the same time, water is added to keep the liquid level stable, and the ammonia-containing water vapor is condensed and collected for use in the iron-aluminum precipitation process and mineralization process.

[0052] The micron crude calcium carbonate product obtained in step S2 has a calcium carbonate content of 67.9%, a magnesium carbonate content of 32.1%, a median diameter D50 of 2.1 μm, a whiteness of 95.5, a total calcium extraction rate of 99.94%, a magnesium extraction rate of 94.1%, an iron extraction rate of 98.2%, and an aluminum extraction rate of 98.7%.

[0053] Comparative Example 1 In step S1, the first ammonium chloride solution has a mass concentration of 10% and a pH value of 7 to 8, and the other experimental steps are the same as those in Example 1.

[0054] In step S1, the free calcium extraction rate is 97.4%, and the micronized calcium carbonate product has a purity of 91.4%, a whiteness of 86.3, and a median diameter D50 of 3.3 μm.

[0055] Comparative Example 2 In step S2, the second ammonium chloride solution has a mass concentration of 20% and a pH value of 4 to 5, and the other experimental steps are the same as those in Example 1.

[0056] In step S2, the micron crude calcium carbonate product has a calcium carbonate content of 77.4%, a magnesium carbonate content of 22.6%, a median diameter D50 of 2.5 μm, a whiteness of 97.3, a total calcium extraction rate of 54.8%, and a magnesium extraction rate of 43.2%.

[0057] Comparative Example 3 In the leaching process, a conventional jacketed slag reactor equipped only with a stirring device is used, and the treatment method and process parameters are the same as in Example 1.

[0058] In step S1, the free calcium extraction rate is 97.8%, and the micronized calcium carbonate product has a purity of 99.92%, a whiteness of 96.5, and a median diameter D50 of 2.8 μm.

[0059] In step S2, the micron crude calcium carbonate product has a calcium carbonate content of 60.1%, a magnesium carbonate content of 39.9%, a median diameter D50 of 3.2 μm, a whiteness of 96.3, a total calcium extraction rate of 60.6%, and a magnesium extraction rate of 51.3%.

[0060] In step S3, the iron oxide product has an Fe2O3 content of 98.2%, a total calcium content (calculated as CaO) of 1.8%, and an iron extraction rate of 20.6%.

[0061] The aluminum oxide product has an Al2O3 content of 98.9% and an Fe2O3 content of 1.1%, with an aluminum extraction rate of 10.4%.

[0062] The crude calcium carbonate product has a calcium carbonate content of 95.38%, a magnesium carbonate content of 0.85%, an iron oxide content of 0.13%, a silica content of 3.99%, a whiteness index of 95.7, and a median diameter D50 of 5.4 μm.

[0063] As described above, the method for comprehensive utilization of steel slag of the present invention uses a uniquely designed slurry reactor, and by analyzing the properties of the steel slag raw material and controlling the process parameters, it achieves the leaching and separation of major elements such as calcium, magnesium, aluminum, and iron in the steel slag, greatly improving the leaching efficiency and comprehensive utilization rate of the elements, while simultaneously achieving the purpose of reducing carbon emissions.

[0064] Finally, it should be explained that the above embodiments are only used to describe the technical solutions of the present invention, and do not limit the present invention; although the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or part or all of the technical features thereof can be replaced with equivalents, and these modifications or replacements will not cause the essence of the corresponding technical solutions to depart from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for comprehensively utilizing iron and steel slag, comprising: The free calcium oxide in the steel slag is leached with a first ammonium chloride solution, and a first leaching residue and a first mineralization solution are obtained by solid-liquid separation. CO ２ Step S1: carrying out absorption and mineralization to obtain a calcium carbonate and ammonium chloride solution; The first leaching residue is leached with a second ammonium chloride solution, and a second leaching residue and a mineralized crude solution are obtained by solid-liquid separation. The mineralized crude solution is then oxidized, alkali-adjusted, and solid-liquid separated to obtain an iron-aluminum precipitate residue and a second mineralized solution. The second mineralized solution is then treated with CO ２ Step S2: Absorption and mineralization to obtain crude calcium carbonate and ammonium chloride solution; The iron-aluminum precipitate residue is leached with a sodium hydroxide solution, and an iron hydroxide precipitate and a sodium metaaluminate solution are obtained by solid-liquid separation. CO ２ and step S3 of absorbing and mineralizing the slag to obtain aluminum hydroxide precipitate and sodium carbonate solution, and then treating the sodium carbonate solution with carbide slag to obtain crude calcium carbonate and sodium hydroxide solution.

2. 2. The method for comprehensively utilizing iron and steel slag according to claim 1, wherein in step S1, the mass concentration of the first ammonium chloride solution is 5 to 30%, and during the leaching, the temperature of the reaction system is controlled to be 5 to 55°C, and the pH value is controlled to be greater than 9.

3. 2. The method for comprehensively utilizing iron and steel slag according to claim 1, wherein in step S2, the mass concentration of the second ammonium chloride solution is 10 to 40%, and during the leaching, the temperature of the reaction system is controlled to 90 to 125°C, and the pH value is controlled to be less than 2.

5.

4. 2. The method for comprehensively utilizing iron and steel slag according to claim 1, wherein in step 2, the molar ratio of ammonium chloride in the second ammonium chloride solution to the soluble components in the first leaching residue is (2-6):1, and the soluble components are calculated as calcium / magnesium silicate, aluminum oxide, and iron oxide.

5. 2. The method for comprehensively utilizing iron and steel slag according to claim 1, wherein in step S2, ammonia gas generated by the reaction during leaching of the first leaching residue with the second ammonium chloride solution is discharged from the reaction system, and the discharge method includes any one of inert gas stripping, evaporation, and ultrasonic waves.

6. In step S2, during the oxidation, air is passed through the mineralized crude liquid or an oxidizing agent is added; During the alkalinity adjustment, ammonia gas collected during the leaching process is passed through the oxidized mineralized crude liquor to adjust the pH value to 5-6; The CO ２ During absorption and mineralization, CO ２ 6. The method for comprehensively utilizing iron and steel slag according to claim 5, wherein the gas and ammonia gas collected during the leaching process are passed through the second mineralization solution.

7. 2. The method for comprehensively utilizing iron and steel slag according to claim 1, wherein in step S3, the iron hydroxide precipitate and the aluminum hydroxide precipitate are washed and calcined, respectively, to obtain an iron oxide product and an alumina oxide product.

8. In steps S1 and S2, the produced ammonium chloride solutions are returned to the leaching stage, respectively, to form a closed loop; 2. The method for comprehensively utilizing iron and steel slag according to claim 1, wherein in step S3, the produced sodium hydroxide solution is returned to the leaching stage, forming a closed loop.

9. The leaching is performed using a slurry reactor, which comprises a jacketed reactor (1), an agitator (2) and an aeration mechanism, the jacketed reactor (1) having an air inlet (3), an air outlet (4) and a supply port (5) at the top, and an outlet (6) and a discharge port (7) at the bottom, and both the agitator (2) and the aeration mechanism are installed inside the jacketed reactor (1); The method for comprehensively utilizing iron and steel slag according to claim 1, characterized in that one or more baffles (8) are installed at the bottom of the inside of the jacketed reactor (1).

10. The aeration mechanism includes an aeration coil (9) and an aeration base (10); 10. The method for comprehensively utilizing iron and steel slag according to claim 9, wherein the aeration coil (9) is spirally installed on the inner wall of the jacketed reactor (1), the aeration base (10) is fixed to the inner bottom of the jacketed reactor (1), the aeration base (10) is a concentric coil, and a plurality of aeration holes are uniformly opened in the concentric coil.

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