Comprehensive Utilization Methods for 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 particularly to a method for comprehensive utilization of steel slag.

Background Art

[0002] Steel slag is molten slag discharged during the ironmaking process, and includes oxides formed by oxidation of various elements in the metal charge, impurities in the metal charge, and calcined products of regulating substances such as limestone. Steel slag contains about 20% slag iron, and substances such as calcium, magnesium, aluminum oxides, and silicates. Although the iron content of steel slag can be partially recycled by magnetic separation, etc., the remaining substances such as calcium, magnesium, aluminum oxides, and silicates are used in cement and road paving, etc., and a large amount of waste slag is still piled up for disposal.

[0003] The large discharge of steel slag causes serious environmental pollution and hazards. First, the piling up of steel slag occupies a large amount of precious land resources. Since some of the steel slag particles are small, it is easy to form a dust generation phenomenon, causing dust pollution and harming human health. In addition, after being leached by rainwater, steel slag mixes with water and flows into adjacent land, rivers, etc., causing serious environmental pollution. Therefore, how to reduce the pollution of steel slag, turn steel slag into a treasure, and promote the efficient recycling and complete utilization of steel slag has become an urgent problem to be solved at present.

[0004] Elemental extraction and utilization is one of the important methods of resource recovery for solid waste. Alkaline substances and silicates contained in steel slag, such as calcium oxide, magnesium oxide, calcium silicate, and magnesium silicate, may be used as raw materials for solidifying CO2 for mineralization and fixation, and the iron and aluminum contained therein may be leached out and concentrated with alkali oxides, and then used as raw materials for flocculants and catalyst carriers, thereby realizing advanced resource recovery for steel slag.

[0005] Currently, various methods for extracting calcium, magnesium, aluminum, and iron from steel slag and utilizing the elements comprehensively are disclosed in literature and patents. For example, in the Chinese invention patent application no. CN202010726836.5, steel slag is leached with ammonium chloride to obtain a CaCl2-NH4Cl-NH3-H2O leachate and a filtered residue. Carbon dioxide gas produced by smelting is then fixed and sealed in place using the leachate to produce a high-purity calcium carbonate product. Next, the filtered residue is reduced at high temperature to extract iron, and then melted. A comprehensive steel slag utilization method has been disclosed that directly produces diopside-phase microcrystalline glass from waste slag. While this method solves problems such as the low utilization rate of steel slag and the complexity of the process, it has drawbacks: the calcium extraction rate in the leaching stage is very low, the reaction time is long, a high-temperature molten state of 1300-1500°C is required in the iron element extraction process and the microcrystalline glass production process, energy consumption is high, operation is difficult, the degree of automation is low, and the requirements for equipment and materials are high, making it unable to meet the requirements for large-scale industrial production.

[0006] In the Chinese invention patent application number CN20221042334.3, silicon, iron, calcium, titanium, vanadium, aluminum, magnesium, and phosphorus contained in steel slag are extracted and used, and mainly 30-36% hydrochloric acid is added to carry out an acid dissolution reaction with the steel slag, and after filtration the filtered residue is dried and pulverized to obtain silicon powder, the pH of the filtrate is adjusted with ammonia water and filtered to obtain iron hydroxide precipitate and filtrate B, filtrate B is reacted with sulfate and filtered to obtain calcium sulfate and filtrate C, hydrochloric acid is added to filtrate C to adjust the pH and titanium ions A comprehensive method for the resource utilization of steel slag is disclosed, which involves adsorption and desorption using an exchange resin to obtain filtrate E and titanium-containing analytical solution, adjusting filtrate E with ammonia water, adsorption and desorption using a vanadium ion exchange resin to obtain filtrate H and vanadium-containing analytical solution, adjusting the pH of filtrate H with ammonia water and filtering to obtain aluminum hydroxide and filtrate J, adjusting the pH of filtrate J by adding ammonia water, simultaneously adding an ammonium salt and filtering to obtain magnesium ammonium phosphate and filtrate K, and evaporating and concentrating filtrate K to obtain an ammonium salt and distilled water for reuse. This method realizes a large degree of comprehensive utilization of multiple elements in steel slag, but it consumes large amounts of concentrated hydrochloric acid (30-36%) and ammonia water in the process, and problems such as coprecipitation occurring in the element separation process resulting in low purity of the product occur. For example, in the process of adjusting the pH to 3-4 with ammonia water, some aluminum ions precipitate, resulting in low purity of the iron product.

[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 elemental utilization rate, and high energy and material consumption, the present invention provides a new method for the comprehensive utilization of steel slag. [Overview of the project] [Problems that the invention aims to solve]

[0008] The objective of the present invention is to provide a comprehensive steel slag utilization method that significantly improves the overall utilization rate of elements and reduces energy consumption and material consumption for manufacturing. [Means for solving the problem]

[0009] The present invention Step S1 involves leaching free calcium oxide from steel slag with a first ammonium chloride solution, obtaining a first leaching residue and a first mineralization liquid by solid-liquid separation, and then performing CO2 absorption and mineralization on the first mineralization liquid to obtain calcium carbonate and an ammonium chloride solution. Step S2 involves leaching the first leaching residue with a second ammonium chloride solution, obtaining a second leaching residue and a crude mineralization solution by solid-liquid separation, oxidizing, alkali adjusting, and solid-liquid separation of the crude mineralization solution to obtain an iron-aluminum precipitate residue and a second mineralization solution, and then performing CO2 absorption and mineralization on the second mineralization solution to obtain crude calcium carbonate and an ammonium chloride solution. The present invention provides a comprehensive method for utilizing steel slag, which includes step S3: leaching the iron-aluminum precipitate residue with a sodium hydroxide solution, obtaining iron hydroxide precipitate and sodium metaaluminate solution by solid-liquid separation, performing CO2 absorption and mineralization on the sodium metaaluminate solution to obtain aluminum hydroxide precipitate and sodium carbonate solution, treating the sodium carbonate solution with carbide slag, and then obtaining crude calcium carbonate and sodium hydroxide solution.

[0010] In the present invention's comprehensive steel slag utilization method, free calcium oxide in the steel slag is first leached with a solution of ammonium monochloride, CO2 absorption and mineralization are carried out to obtain a calcium carbonate product, and the chemical reaction is as follows: CaO + 2NH4Cl → CaCl2 + 2NH3 + H2O

[0011] After separating the slurry obtained from the above reaction into solid and liquid components, a first leaching residue and a first mineralization solution are obtained. A gas containing CO2 is passed through the first mineralization solution to carry out a mineralization reaction, producing calcium carbonate precipitate and ammonium chloride. After separating these into solid and liquid components, calcium carbonate and ammonium chloride solutions are obtained. After washing and drying the calcium carbonate, the calcium carbonate product can be obtained, and the resulting ammonium chloride solution can be returned to the leaching stage and reused.

[0012] Next, insoluble calcium, magnesium, iron, aluminum, etc., in the first leaching residue are further leached, CO2 absorption and mineralization occur, and crude calcium carbonate product and iron-aluminum precipitate are obtained. The chemical reactions are 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 first leaching residue is added to the second ammonium chloride solution to leach insoluble calcium, magnesium, aluminum, iron, etc., generating ammonia gas. The slurry obtained by the above reaction is subjected to solid-liquid separation to obtain the second leaching residue and the crude mineralization liquid. The crude mineralization liquid contains CaCl2 (MgCl2), AlCl3, and FeCl2. Through oxidation reactions, the ferrous ions in the slurry are completely oxidized to ferric ions, the pH value of the slurry is adjusted, and iron and aluminum elements are precipitated in the form of hydroxide precipitates to produce ammonium chloride. After solid-liquid separation of the slurry, an iron-aluminum precipitate residue and a second mineralization liquid containing calcium and magnesium elements can be obtained. CO2 absorption and mineralization are performed on the second mineralization liquid to produce a carbonate precipitate and ammonium chloride. Solid-liquid separation is performed to obtain carbonate and ammonium chloride solution. After washing and drying the carbonate, a crude calcium carbonate product can be obtained, and the obtained ammonium chloride solution can be returned to the leaching stage and reused.

[0014] Finally, the iron and aluminum elements are separated from the iron-aluminum precipitate residue, CO2 absorption and mineralization are performed to obtain crude calcium carbonate product and 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 leached in a sodium hydroxide solution of a specific concentration, the aluminum hydroxide precipitate is dissolved in water-soluble sodium metaaluminate under specific conditions, the slurry obtained by the above reaction is subjected to solid-liquid separation to obtain iron hydroxide precipitate and sodium metaaluminate solution, the sodium metaaluminate is subjected to a mineralization reaction to obtain aluminum hydroxide precipitate and sodium carbonate solution, and the sodium carbonate solution is treated with carbide slag (whose main component is unhydrated calcium hydroxide) to obtain sodium hydroxide solution and calcium carbonate precipitate, which are then subjected to solid-liquid separation to obtain calcium carbonate and sodium hydroxide solution, the calcium carbonate is washed and dried to obtain crude calcium carbonate product, and the obtained sodium hydroxide solution can be returned to the leaching stage and reused.

[0016] Therefore, the present invention's comprehensive steel slag utilization method fully combines the properties of the steel slag itself to achieve extraction and separation of major elements in the steel slag, while also achieving the objective of reducing carbon emissions.

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

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

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

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

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

[0022] As a technical solution, preferably, in step S2, when leaching the first leaching residue with the second ammonium chloride solution, the ammonia gas generated by the reaction is discharged from the reaction system, and the discharging method includes any one of inert gas stripping, evaporation, and ultrasonic waves. During the leaching, by the above method, ammonia gas can be continuously released from the liquid phase, which can not only promote the progress of the reaction in the dissolution direction, but also the obtained ammonia-containing gas can be used in subsequent alkali adjustment and mineralization reactions.

[0023] As a technical solution, preferably, in step S2, during the oxidation, air is passed through the crude mineralized liquid or an oxidizing agent is added to completely oxidize the ferrous ions in the crude mineralized liquid to ferric ions.

[0024] During the alkali adjustment, the ammonia gas collected in the leaching process is passed through the oxidized crude mineralized liquid to adjust the pH value to 5-6, so that iron and aluminum elements are precipitated in the form of hydroxide precipitates to generate ammonium chloride.

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

[0026] When the second mineralized liquid containing calcium and magnesium elements is subjected to a mineralization reaction, by passing CO2 gas through the second mineralized liquid and passing the ammonia gas collected in the leaching process, carbonate precipitates and an ammonium chloride solution can be obtained, which not only reduces the consumption of ammonia in this process, but also improves the overall utilization rate of ammonia.

[0027] As a technical solution, preferably, in step S3, the iron hydroxide precipitate and the aluminum hydroxide precipitate are washed and calcined respectively to obtain iron oxide products and aluminum oxide products.

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

[0029] Preferably, the slurry reactor used in the leaching process in the present invention includes, but is not limited to, a mechanical stirring tank, a loop reactor, a bubble tower, and a three-phase fluidized bed reactor. Specifically, the slurry reactor used in the present invention includes a jacketed reaction vessel, a stirring device, and an aeration mechanism. The jacketed reaction vessel has an air inlet, an air outlet, and a supply port at the top, and a discharge port and an outlet at the bottom. Both the stirring device and the aeration mechanism are provided inside the jacketed reaction vessel. One or more baffles are provided at the bottom inside the jacketed reaction vessel 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 diffusion of the extraction solution onto the particle surface, and improve elemental leaching efficiency.

[0030] Preferably, the aeration mechanism includes an aeration coil and an aeration base, wherein the aeration coil is spirally arranged on the inner wall of the jacketed reaction vessel, the aeration base is fixed to the inner bottom of the jacketed reaction vessel, the aeration base is a concentric coil, and a plurality of aeration holes are uniformly formed in the concentric coil.

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

[0032] The outer surface of the jacketed reaction vessel of the slurry reactor of the present invention is provided with a circulating liquid inlet and a circulating liquid outlet, and an electric heating device may be connected to the jacketed reaction vessel and used to heat the circulating liquid inside the jacket.

[0033] The present invention provides a comprehensive method for utilizing steel slag, which has at least the following technical effects: 1. The present invention achieves the extraction and separation of major elements such as calcium, magnesium, aluminum, and iron from steel slag by analyzing the properties of the steel slag raw material and controlling process parameters. Through CO2 absorption and mineralization, calcium carbonate and crude calcium carbonate are obtained as mineralization products. Furthermore, by introducing carbide slag and a sodium hydroxide circulation aid, the separation of iron and aluminum elements is achieved, yielding high-purity iron oxide products and aluminum oxide products, while simultaneously performing CO2 absorption and mineralization, thereby further achieving the objective of reducing carbon emissions. 2. In the steel slag comprehensive utilization method of the present invention, the circulation aid does not require the extraction and separation of organic reagents, nor does it require operations such as high-temperature decomposition, thus the process is simple and easy to scale up. 3. In the steel slag integrated utilization method of the present invention, by promoting the release of ammonia in the form of a gaseous phase from the solution, not only is the leaching reaction efficiency improved, but the amount of ammonia administered in subsequent processes is also reduced, thereby improving the overall utilization rate of ammonia. 4. In the present invention's comprehensive steel slag utilization method, the leaching of insoluble elements such as calcium, magnesium, iron, and aluminum from the steel slag is achieved using a uniquely designed slurry reactor, improving element leaching efficiency and overall utilization rate. This method is easy to operate and facilitates industrial production. [Brief explanation of the drawing]

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

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

[0036] 1: Jacketed reaction vessel, 2: Agitator, 3: Air inlet, 4: Air outlet, 5: Feed port, 6: Discharge port, 7: Outlet, 8: Baffle, 9: Aeration coil, 10: Aeration base. [Modes for carrying out the invention]

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

[0038] The terms used herein are solely for the purpose of describing specific embodiments and are not intended to limit the exemplary embodiments described herein. As used herein, unless the context explicitly indicates otherwise, the singular form includes the plural form, and furthermore, where the terms “includes” and / or “equipment” are used herein, they should be understood to indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

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

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

[0041] [Table 1]

[0042] According to YB / T 4328-2012, "Method for Measuring the Free Calcium Oxide Content in Steel Slag," the mass fraction of free calcium oxide in steel slag was measured to be 66%, and an appropriate amount of steel slag was taken and polished to 100 mesh.

[0043] S1, a 10% mass fraction of ammonium chloride solution is added to a slurry reactor (Figures 1 and 2) according to the free calcium oxide content. The solution temperature is controlled to 25°C, the pH of the solution is controlled to 9 or higher, and the mixture is stirred at low speed for 0.5 hours to allow the reaction to proceed. After the reaction, the slurry is released, and sedimentation separation is performed on the slurry to obtain a first leaching residue rich in iron, aluminum, and some insoluble calcium, and a first mineralization liquid containing calcium. Power plant exhaust gas with a CO2 content of 12% is passed through the first mineralization liquid containing calcium to carry out a calcification reaction, obtaining a calcium carbonate precipitate and an ammonium chloride solution. The obtained calcium carbonate precipitate is separated by a plate and frame filter press to obtain calcium carbonate and an ammonium chloride solution. The calcium carbonate is dried in a drum to obtain micronized calcium carbonate products, and the separated ammonium chloride solution can be reused for leaching steel slag (Figure 3).

[0044] Here, the extraction rate of free calcium was 98.5%, and the micron-sized calcium carbonate product had 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 some insoluble calcium, is added to a slurry reaction vessel (Figures 1 and 2). Depending on the calcium, magnesium, iron, and aluminum content in the first leaching residue, a 20% mass fraction ammonium chloride solution is added in a chemical reaction molar ratio of 2:1. The reaction temperature of the solution is controlled to 90°C by passing circulating water through a jacket, air is passed through the jacketed reaction vessel from the air inlet, the pH value of the solution is controlled to 2-2.5, the amount of air to be passed through is automatically adjusted according to the pH value of the solution, and air containing ammonia is discharged and collected from the air outlet. After stirring for 1 hour to allow the reaction to proceed, the resulting slurry was separated by pressure filtration to obtain a second leaching residue and a crude mineralization solution containing calcium, magnesium, iron, and aluminum. An appropriate amount of hydrogen peroxide was added to the crude mineralization 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 crude mineralization solution. After the reaction was complete, the collected ammonia-containing air was pressurized and passed through the crude mineralization solution to adjust the pH of the crude solution to 6, and the iron and aluminum elements were precipitated in the form of hydroxides to produce ammonium chloride. The resulting iron-aluminum precipitate was separated by pressure filtration. This process yields an iron-aluminum precipitate residue and a second mineralization solution containing calcium and magnesium elements. The second mineralization solution is then passed through the power plant exhaust gas with a mass fraction of 12% and the collected ammonia-containing air to carry out a mineralization reaction, yielding a carbonate precipitate and ammonium chloride. The obtained carbonate precipitate is separated by a plate-and-frame filter press to obtain crude calcium carbonate and ammonium chloride solution. The crude calcium carbonate is further washed and dried in a drum to obtain a micron-sized crude calcium carbonate product. The obtained ammonium chloride solution is returned to the slurry reaction vessel 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, in a slurry reactor (Figures 1 and 2), the separated iron-aluminum precipitate residue is added to a 10% sodium hydroxide solution, stirred thoroughly to dissolve, filtered and separated to obtain iron hydroxide precipitate and sodium metaaluminate solution. The iron hydroxide precipitate is further washed and calcined to obtain iron oxide products. Exhaust gas from a cement plant with a mass fraction of 30% is passed through the separated sodium metaaluminate solution to react and produce aluminum hydroxide and sodium carbonate. After filtering and separation, aluminum hydroxide precipitate and sodium carbonate solution are obtained. The aluminum hydroxide precipitate is further washed and calcined to obtain aluminum oxide products. Carbide slag (containing 94% calcium hydroxide) is added to the obtained sodium carbonate solution, stirred thoroughly and filtered to obtain sodium hydroxide solution and calcium carbonate precipitate. After separation by pressure filtration, crude calcium carbonate product and sodium hydroxide solution are obtained. The sodium hydroxide solution is returned to the slurry reaction vessel for reuse (Figure 5).

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

[0049] The aluminum oxide product has an Al2O3 content of 99.9%, a Fe2O3 content of 0.1%, and 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 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 operating steps are almost the same as in Example 1. The difference is that in step S2, heat transfer oil is added to the jacket of the slurry reaction vessel, and at the same time the heating device is turned on to control the temperature of the reaction solution to 105-115°C, and the ammonia generated is overflowed from the solution by evaporation without allowing air to pass through, maintaining the pH value of the solution at 2-2.5, and at the same time water is supplied to keep the liquid level stable, and the water vapor containing ammonia is condensed and collected and used in the iron-aluminum precipitation process and mineralization process.

[0052] The micron-sized 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 ammonium chloride solution has a mass concentration of 10% and a pH of 7-8, and the other experimental steps are the same as in Example 1.

[0054] In step S1, the free calcium extraction rate was 97.4%, and the micron calcium carbonate product had 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 ammonium chloride solution has a mass concentration of 20% and a pH of 4-5, and the other experimental steps are the same as 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 was used, and the processing method and process parameters were the same as in Example 1.

[0058] In step S1, the free calcium extraction rate was 97.8%, and the micron calcium carbonate product had 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 in terms of CaO) of 1.8%, and an iron extraction rate of 20.6%.

[0061] The aluminum oxide product has an Al2O3 content of 98.9%, an Fe2O3 content of 1.1%, and 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 of 95.7, and a median diameter D50 of 5.4 μm.

[0063] As described above, the present invention's comprehensive steel slag utilization method utilizes a uniquely designed slurry reactor and, through analysis of the properties of the steel slag raw material and control of process parameters, achieves the leaching and separation of major elements such as calcium, magnesium, aluminum, and iron in the steel slag, significantly improving elemental leaching efficiency and overall utilization rate, while simultaneously achieving the objective of reducing carbon emissions.

[0064] Finally, it should be noted that the above embodiments are used solely to illustrate the technical solutions of the present invention and do not limit the invention. While the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that it is still possible to modify the technical solutions described in the above embodiments or to replace some or all of their technical features with equivalents, and that such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A comprehensive method for utilizing steel slag, Free calcium oxide in steel slag is leached with a solution of ammonium chloride (III), and solid-liquid separation is performed to obtain a first leaching residue and a first mineralization liquid. CO2 is then added to the first mineralization liquid. ２ Step S1 involves absorption and mineralization to obtain a calcium carbonate and ammonium chloride solution, The first leachate residue is leached with a second ammonium chloride solution, and solid-liquid separation is performed to obtain the second leachate residue and the mineralization crude liquid. The mineralization crude liquid is then oxidized, alkalinized, and separated again to obtain the iron-aluminum precipitate residue and the second mineralization liquid. CO2 is then added to the second mineralization liquid. ２ Step S2 involves absorption and mineralization to obtain crude calcium carbonate and ammonium chloride solution, The iron-aluminum precipitate residue was leached with a sodium hydroxide solution, and solid-liquid separation was performed to obtain an iron hydroxide precipitate and a sodium metaaluminate solution. CO2 was then added to the sodium metaaluminate solution. ２ The process includes step S3, in which absorption and mineralization are carried out to obtain an aluminum hydroxide precipitate and a sodium carbonate solution, and the sodium carbonate solution is treated with carbide slag to obtain crude calcium carbonate and a sodium hydroxide solution. In step S1, the mass concentration of the first ammonium chloride solution is 5-30%, the temperature of the reaction system is controlled to 5-55°C during leaching, and the pH value is controlled to be greater than 9. In step S2, the mass concentration of the second ammonium chloride solution is 10-40%, and when the first leaching residue is leached, the temperature of the reaction system is controlled to 90-125°C, and the pH value is controlled to be less than 2.

5. Furthermore, during the leaching in step S2, A slurry reactor is used, and the slurry reactor includes a jacketed reaction vessel (1), a stirring device (2), and an aeration mechanism. The jacketed reaction vessel (1) has an air inlet (3), an air outlet (4), and a supply port (5) at the top, and a discharge port (6) and an outlet (7) at the bottom. Both the stirring device (2) and the aeration mechanism are provided inside the jacketed reaction vessel (1). One or more baffles (8) are provided at the bottom of the inside of the jacketed reaction vessel (1). The aeration mechanism includes an aeration coil (9) and an aeration base (10). The aeration coil (9) is spirally mounted on the inner wall of the jacketed reaction vessel (1), the aeration base (10) is fixed to the inner bottom of the jacketed reaction vessel (1), the aeration base (10) is a concentric coil, and multiple aeration holes are uniformly formed in the concentric coil. A comprehensive method for utilizing steel slag, characterized by the following features.

2. The method for comprehensive utilization of steel slag according to claim 1, characterized in that, 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 to be calcium silicate / magnesium silicate, aluminum oxide, and iron oxide.

3. The comprehensive steel slag utilization method according to claim 1, characterized in that, in step S2, when the first 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 ultrasound.

4. In step S2, during the oxidation, air is passed through the crude mineralization liquid or an oxidizing agent is added. During the alkali adjustment process, the ammonia gas collected during the leaching process is passed through the oxidized crude mineralization solution to adjust the pH value to 5-6. The aforementioned CO ２ During absorption and mineralization, CO ２ The comprehensive steel slag utilization method according to claim 3, characterized in that the gas and ammonia gas collected during the leaching process are passed through the second mineralization liquid.

5. The method for comprehensive utilization of steel slag according to claim 1, characterized in that in step S3, the iron hydroxide precipitate and the aluminum hydroxide precipitate are washed and calcined to obtain an iron oxide product and an alumina product.

6. In steps S1 and S2, the generated ammonium chloride solution is returned to the leaching stage, respectively, forming a closed loop. The method for comprehensive utilization of steel slag according to claim 1, characterized in that in step S3, the generated sodium hydroxide solution is returned to the leaching stage, forming a closed loop.

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