Steel slag treatment method for preparing light calcium carbonate through iron recovery, calcium leaching and carbonation

Abstract

The invention provides a steel slag treatment method for preparing light calcium carbonate through iron recovery, calcium leaching and carbonation. The method comprises the following steps: (1) mixing biomass and steel slag, and carrying out microwave reduction to obtain an iron product and calcium-rich tailings; (2) mixing the calcium-rich tailings with an ammonium salt solution, and reacting under the action of microwaves to obtain calcium-rich supernate and silicon-rich tailings; and (3) adjusting the pH value of the calcium-rich supernate to 9-11 by using ammonia water, carrying out carbonation reaction in a carbonation reactor, carrying out solid-liquid separation to obtain light calcium carbonate and an ammonium chloride solution, and applying the ammonium chloride solution to the step (2). According to the method, separation and utilization of iron, calcium and silicon can be well achieved, the pre-reduction iron extraction rate is about 80%, the Ca < 2 + > leaching rate reaches 80% or above, the carbonization rate reaches 98%, the purity of obtained light calcium carbonate is higher than 98%, and no waste gas or waste water is discharged in the whole process.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of metallurgy and calcification, in particular to a method for microwave-enhanced "steel slag pre-reduction iron extraction-ammonium salt leaching calcium extraction-CO2 chemical adsorption for preparing light calcium carbonate", and more particularly to a method for steel slag treatment including iron recovery, calcium leaching and carbonation for preparing light calcium carbonate. BACKGROUND

[0002] At present, the production of each ton of crude steel is accompanied by about 150-250 kg of steel slag by-products and 1.9 tons of carbon dioxide, which causes serious pollution to the environment and also wastes a large amount of land resources. The mass fraction of CaO in steel slag is 20-60%, and the calcium-containing phases mainly include calcium silicate (CaSiO3, CS), dicalcium silicate (Ca2SiO4, C2S), calcium ferrum aluminate and magnesium iron phase solid solution (RO), and a small amount of tricalcium silicate (Ca3SiO5, C3S), free CaO and free MgO, which is an excellent carbon dioxide capture raw material, but the calcium phase is complex, and if the carbon capture capacity is to be improved, the steel slag needs to be treated for calcium extraction. In addition, the steel slag contains rich iron elements, with a mass fraction of Fe2O3 of 10-50%, mainly existing in silicate phases, coexisting with calcium, which is difficult to extract. Therefore, in the pretreatment process of calcium extraction, comprehensive recovery and utilization of iron, calcium and other useful elements in the steel slag is an important means to reduce the environmental pollution in the production of crude steel.

[0003] Current steel slag calcium extraction technologies are mainly based on strong acid, weak acid and ammonium salt leaching systems. Although the strong acid leaching system (such as HCl, H2SO4) can achieve efficient dissolution of calcium elements (leaching rate > 95%), its non-selectivity leads to the simultaneous leaching of Fe 3+ , Al 3+ , Mg 2+ , SiO3 2- and other impurity ions, making it difficult to separate calcium and iron. At the same time, the strong acid system has technical bottlenecks such as serious equipment corrosion and high energy consumption for waste liquid treatment. The weak acid system (such as acetic acid, citric acid) can selectively leach calcium components (Ca 2+ leaching rate 60-75%) by adjusting the pH (2.5-5.0), but its weak coordination ability leads to incomplete dissociation of silicate minerals, and subsequent impurity removal needs to be achieved through multi-stage precipitation (such as calcium oxalate step-by-step crystallization) or ion exchange. The ammonium salt system (such as NH4Cl, NH4NO3) uses the ion exchange mechanism of NH 4+ and Ca 2+ to achieve selective leaching of calcium under near-neutral conditions (pH 6-8), and its environmental compatibility and alkaline characteristics (pH 8.5-9.5) of the leaching solution can improve the efficiency of CO2 chemical absorption by 30-50% compared with acidic systems, so ammonium salt is a better leaching medium compared with strong acid and weak acid.

[0004] However, the leaching rate of calcium ions in the converter slag by ammonium salt is only 60-70%, which has not achieved good results and still needs to be further improved. SUMMARY

[0005] Based on the research of the inventors on the above problems, the present application provides a steel slag treatment method, in particular a method for treating steel slag containing iron recovery, calcium leaching and preparation of light calcium carbonate by carbonation. The method uses microwave biomass enhanced reduction and microwave ammonium salt system to improve the separation and recovery strategy of calcium carbonate leaching to obtain calcium-rich leaching solution. Micro-bubble system is used for the third step of carbonation to prepare high-purity light calcium carbonate. Thus, while achieving CO2 emission reduction in the steel industry, high-value-added calcium carbonate products and secondary-use iron-rich slag are produced, achieving the purpose of waste treatment and high-quality utilization of steel slag.

[0006] As a first aspect of the present application, the present application provides a method for treating steel slag containing iron recovery, calcium leaching and preparation of light calcium carbonate by carbonation, the method comprising: (1) mixing biomass with steel slag and carrying out microwave reduction to obtain a reduction product, the mass of the biomass accounting for 30-40% of the mass of the steel slag, the power of the microwave reduction being 3-4 KW, the treatment time being 30-80 min, and the reduction product being subjected to magnetic separation to obtain an iron product and a calcium-rich tailing, the CO2 flue gas generated participating in the carbonation reaction in step (3); (2) mixing the calcium-rich tailing and an ammonium salt solution, the solid-liquid mixing ratio of the calcium-rich tailing and the ammonium salt solution being 10-40 g / ml, and carrying out a reaction under the action of microwaves to obtain a calcium-rich supernatant and a silicon-rich tailing, the temperature of the reaction being 30-90 ℃, the microwave power being 0-800 W, and the reaction being kept for 30-150 min after the reaction, the ammonia gas generated participating in the pH adjustment of the calcium-rich supernatant in step (3); (3) adjusting the pH value of the calcium-rich supernatant to 9-11 by using ammonia water, introducing CO2 into the carbonation reactor at a flow rate of 5-15 L / (min·L) to carry out a carbonation reaction, and obtaining light calcium carbonate and an ammonium chloride solution after solid-liquid separation, and using the ammonium chloride solution in step (2).

[0007] The method can better realize the separation and utilization of iron, calcium and silicon, the pre-reduction iron recovery rate is about 80%, the Ca 2+ The leaching rate is more than 80%, the carbonation rate is 98%, and the purity of the light calcium carbonate obtained is higher than 98%, and there is no waste gas and waste water emission in the whole process.

[0008] According to the embodiments of the present application, the particle size of the steel slag and the biomass is independently 58-75 µm. Thus, the effect of microwave reduction can be further improved.

[0009] According to an embodiment of the present application, the biomass includes at least one of straw, fruit shell, vinasse, wood chip, wood, forestry waste and processing waste, the steel slag includes converter slag, refining slag, electric furnace slag and other solid waste generated in steelmaking process, the mass percentage of total Fe in the steel slag is 10-50%, the mass percentage of CaO in the steel slag is 20-60%, and the calcium-containing phase in the steel slag includes monocalcium silicate, dicalcium silicate and calcium ferrite. Thus, the effect of microwave reduction can be further improved.

[0010] According to an embodiment of the present application, the microwave treatment in step (1) further includes a heating treatment, the heating rate of the heating treatment is 15-35 ℃ / min, the heating temperature is 900-1100 ℃, and the reduction time is 30-80 min.

[0011] According to an embodiment of the present application, the magnetic field strength of the magnetic separation in step (1) is 0.10-0.5 T.

[0012] According to an embodiment of the present application, step (2) satisfies: the concentration of the ammonium salt solution is 1-4 mol / L; the reaction of the calcium-rich tailing and the ammonium salt under the microwave is carried out under stirring, and the stirring rate is 0-300 rpm; the reaction time is 0.5-2.5 h; the pH value of the obtained calcium-rich supernatant is 6-8.

[0013] According to an embodiment of the present application, in step (3), the carbonation process is carried out at a carbon dioxide gas flow of 1-15 L / (min·L), the carbonation time is 5-30 min, and the reaction temperature is 30-80 ℃.

[0014] According to an embodiment of the present application, step (2) further includes collecting the generated ammonia gas to obtain ammonia water, and the ammonia water is introduced into the carbonation reactor in step (3).

[0015] In another aspect of the present application, a calcium carbonate obtained based on steel slag is provided. The calcium carbonate is obtained by the method described above, and the purity of the calcium carbonate is not less than 98%. BRIEF DESCRIPTION OF DRAWINGS

[0016] In the drawings, like reference numerals refer to like elements throughout the various drawings. The drawings are not necessarily to scale, the emphasis instead being placed upon illustrating the principles of the application. It should be understood that the drawings are merely depictions of some embodiments of the present application and should not be construed as limiting the scope of the present application.

[0017] Figure 1 System structure diagram of the whole method proposed in the embodiments of the present application; Figure 2 Process flow chart of the method described in the present application; Figure 3 TG-DSC result of the calcium carbonate product obtained according to the embodiment 13 of the present application; Figure 4 Scanning electron microscope photo of the calcium carbonate product obtained according to the embodiment 13 of the present application. DETAILED DESCRIPTION

[0018] The embodiments of the technical solutions of the present application will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, and cannot limit the protection scope of the present application.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs; the terms used herein are only for the purpose of describing specific embodiments, and are not intended to limit the present application; the terms "include" and "have" and any variations thereof in the specification and claims of the present application and the above description of drawings are intended to cover non-exclusive inclusion.

[0020] In this paper, the "embodiment" means that the specific features, structures or characteristics described in conjunction with the embodiment can be included in at least one embodiment of the present application. The phrase appears in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment to other embodiments. The skilled person in the art explicitly and implicitly understands that the embodiments described herein can be combined with other embodiments.

[0021] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the character " / " in this paper generally represents that the front and rear associated objects are a "or" relationship.

[0022] In the description of the embodiments of the present application, the term "a plurality of" refers to two or more (including two), and similarly, "a plurality of groups" refers to two or more groups (including two groups), and "a plurality of pieces" refers to two or more pieces (including two pieces).

[0023] The terms used in the present application have the commonly understood meanings known to those skilled in the art, unless otherwise indicated. The values of the parameters mentioned in the present application can be measured by various measuring methods commonly used in the art, unless otherwise indicated (for example, the tests can be performed according to the methods given in the examples of the present application).

[0024] In a first aspect of the present application, a method for processing steel slag to produce light calcium carbonate by iron recovery, calcium leaching and carbonation is provided, the method comprising: (1) mixing biomass with steel slag and performing microwave reduction to obtain a reduction product, the mass of the biomass accounting for 30-40% of the mass of the steel slag, the microwave reduction being performed at a power of 3-4 KW for 30-80 min, and the reduction product being subjected to magnetic separation to obtain an iron product and a calcium-rich tailing, and CO2 flue gas generated in the process being used in the carbonation reaction in step (3); (2) mixing the calcium-rich tailing with an ammonium salt solution, the solid-liquid mixing ratio of the calcium-rich tailing and the ammonium salt solution being 10-40 g / ml, and the mixture being subjected to microwave reaction to obtain a calcium-rich supernatant and a silicon-rich tailing, the reaction being performed at a temperature of 30-90 ℃ and a microwave power of 0-800 W, and the mixture being kept for 30-150 min after the reaction, and ammonia gas generated in the process being used to adjust the pH of the calcium-rich supernatant in step (3); (3) adjusting the pH of the calcium-rich supernatant to 9-11 using ammonia water, and introducing CO2 into a carbonation reactor at a flow rate of 5-15 L / (min·L) to perform carbonation reaction, and separating the light calcium carbonate and the ammonium chloride solution, and using the ammonium chloride solution in step (2).

[0025] The method can achieve good separation of calcium and iron, the leaching rate of Ca ions can be as high as 80% or even higher, the light calcium carbonate obtained has high purity, the process is simple and efficient, various intermediate products can be recycled, the method has good recovery and processing effects, and the generated ammonium chloride solution and ammonia water can be recycled and utilized.

[0026] According to the embodiments of the present application, the particle size of the steel slag and the biomass is independently 58-75 µm. In this way, the effect of microwave reduction can be further improved.

[0027] According to an embodiment of the present application, the biomass includes agricultural and forestry wastes such as straw, fruit shell, vinasse, sawdust, wood, and processing waste, and specifically can include agricultural biomass such as straw, fruit shell, rice husk, bagasse, corn cob, and the like, forestry biomass such as sawdust, sawdust, offcut, sawdust, waste wood (processing waste), branches, leaves, roots (felling waste), and the like, household garbage such as organic kitchen garbage, and processing-generated biomass such as vinasse, vinegar dregs, medicinal dregs, and rapeseed meal.

[0028] The steel slag includes converter slag, refining slag, electric furnace slag, and the like, and solid waste generated in other steelmaking links, the mass percentage of total Fe in the steel slag is 10-50%, the mass percentage of CaO is 20-60%, and the calcium-containing phase includes monocalcium silicate, dicalcium silicate, and calcium ferrite aluminate. Thus, the effect of microwave reduction can be further improved.

[0029] According to an embodiment of the present application, the calcium-containing phase, calcium ferrite aluminate, and magnesium iron phase solid solution in the steel slag, and a small amount of dicalcium ferrite, f-CaO, and f-MgO, these iron- and calcium-containing phases are reduced with the biomass under the action of a microwave field, and through the regulation of microwave synergistic reduction parameters, iron and calcium elements can be effectively separated, thereby creating convenient conditions for subsequent calcium extraction.

[0030] In some embodiments, the content of each main chemical component in the steel slag can be as shown in Table 1: Table 1

[0031] According to an embodiment of the present application, the heating rate of microwave reduction in step (1) is 25-35 ℃ / min, and the heating temperature is 900-1100 ℃. Thus, in step (1), the difference in dielectric response of Fe3O4 / Fe2O3 and calcium silicate is utilized, a local high-temperature field (900-1100 ℃) is constructed with the aid of biomass reducing agent, iron oxides are preferentially reduced to metallic iron phase, and H2 / CO reducing atmosphere generated by the decomposition of biomass volatiles is simultaneously utilized, so that the exponential increase of reaction kinetics is realized, thereby obtaining metallic iron that can be directly recycled.

[0032] According to an embodiment of the present application, the magnetic field strength of the magnetic separation in step (1) is 0.15-0.2 T. Thus, the calcium-rich tailings obtained by magnetic separation and the microwave-ammonium salt synergistic leaching system can be jointly subjected to classification treatment, thereby further improving the efficiency and effect of the treatment.

[0033] According to the embodiment of the present application, in step (2), the calcium-rich tailings obtained in step (1) can contain part of the aforementioned iron, calcium, silicon and other multi-phase components, which react with the ammonium chloride solution to generate calcium chloride and ammonia gas, thereby realizing selective extraction of calcium, obtaining ammonia gas for subsequent steps, and obtaining a silicon-containing tailings. The reaction equation in the above step (1) and step (2) can include: .

[0034] Specifically, in step (1), the steel slag mixture reacts with biomass (containing C) to obtain calcium oxide, iron metal, and produce carbon dioxide. The ferrous oxide can be further reduced to iron metal under the action of carbon. The calcium oxide in the obtained calcium-rich tailings can generate calcium chloride and ammonia gas under the action of ammonium salt solution, and the calcium-rich tailings can also react with ammonium salt to obtain a silicon-rich tailings containing silicon dioxide. At the same time, step (2) can also produce ammonia gas. The carbon dioxide produced in step (1) can be recycled and used in step (3). Similarly, the ammonia gas produced in step (2) can also be recycled, such as dissolving in water to form ammonia water, and used in the subsequent step (3) to adjust the pH value.

[0035] According to the embodiment of the present application, step (2) can be carried out under the action of microwave. The microwave can promote the ion exchange rate of NH 4+ to Ca 2+ , realizing efficient leaching of calcium components.

[0036] In order to further improve the effect of step (2), according to the embodiment of the present application, the concentration of ammonium salt can be 1-4 mol / L, preferably 2-4 mol / L, for example, it can be 1, 1.5, 2, 2.5, 3, 4 mol / L.

[0037] According to the embodiment of the present application, the solid-liquid mixing ratio of calcium-rich tailings and ammonium chloride solution is 10-40 g / ml, for example, the mass ratio of calcium-rich tailings to ammonium chloride solution is 1:10-30 g / mL, for example, it can be 1:10, 1:15, 1:20, 1:25, 1:30 g / mL.

[0038] According to the embodiment of the present application, the power of the microwave in step (2) can be 0-800 W, for example, it can be 240, 320, 400, 480, 560, 640, 720, 800 W.

[0039] According to an embodiment of the present application, the reaction of the calcium-rich tailings and ammonium chloride under the action of microwaves is carried out under stirring, the stirring rate can be 0-300 rpm (not 0), the reaction time is 0.5-2.5 h, for example, it can be 0.5, 1, 1.5, 2, 2.5 h. The reaction temperature is 30-80 ℃, for example, it can be 30, 40, 50, 60, 70, 80 ℃. The pH value of the calcium-rich supernatant obtained in this step can be 6-8.

[0040] This step can also obtain Si-rich tailings, which can be used to prepare low-carbon cementitious materials, thereby further improving the economic benefits of the method and improving the atomic utilization rate.

[0041] According to an embodiment of the present application, in step (3), the calcium-rich supernatant is obtained by filtration, and the pH value of the calcium-rich supernatant is adjusted to 9-11 by using ammonia water in a carbonation reactor, and then a carbonation reaction is carried out, CO2 and generated ammonia gas are introduced into the carbonation reactor to generate white precipitate, and high-purity light calcium carbonate and ammonium chloride solution are obtained by solid-liquid separation, and the ammonium chloride solution can be recycled in step 2. Further, the carbon dioxide gas in this step can be derived from, but not limited to, emissions from steel enterprises, emissions in the steel production process, specifically, the carbon dioxide generated in the aforementioned step (1) can be used; the ammonia gas generated in step 2 is introduced into an ammonia water solution pool, and the ammonia water in the solution pool is introduced into the carbonation reactor for pH adjustment.

[0042] According to an embodiment of the present application, in step (3), the carbon dioxide gas flow during the carbonation process is 5-15 L / (min·L), the carbonation time is 5-30 min, and the reaction temperature is 30-80 ℃.

[0043] By adjusting the alkalinity of the calcium-rich leaching solution with ammonia water (pH 10-12) and coupling the CO2-NH3 gas-liquid mass transfer process, the crystal form of calcium carbonate can be controlled. In order to further improve the effect of this step, the gas flow and the amount of carbon dioxide and ammonia gas introduced during the carbonation reaction can be controlled. In the gas-liquid-solid three-phase interface reaction, the nucleation-growth kinetics of calcite, aragonite and vaterite is controlled by supersaturation and solution ion strength, and high-purity light calcium carbonate (purity ≥98%, whiteness >97%) with a specific surface area >12 m² / g, particle size d<2 μm and adjustable morphology (cube, spindle, needle-like, etc.) can be prepared.

[0044] According to an embodiment of the present application, the pH value of the ammonia water can be 9-11, for example, can be 9, 9.5, 10, 10.5, 11. The temperature of the carbonation process is 30-80 ℃, for example, can be 30, 40, 50, 60, 70 ℃. The gas flow of the carbonation process is 5-15 L / (min·L), for example, can be 5, 10, 14.4 L / (min·L). The time of the carbonation process is 5-30 min, for example, can be 5, 10, 15, 20, 25, 30 min.

[0045] For example, according to some embodiments of the present application, referring to Figure 1 , the method can specifically include three main processes, i.e., microwave reduction iron extraction, microwave-ammonium salt synergistic calcium extraction, and carbon dioxide capture to prepare calcium carbonate.

[0046] Referring to Figure 1 and Figure 2 , in the microwave reduction iron extraction process, the steel slag biomass is mixed in proportion to prepare steel slag biomass pellets, microwave reduction, the generated carbon dioxide gas is collected through pipeline 2 into the gas collection tank 3 for storage, and the gas collection tank 3 can also store the carbon dioxide discharged by the steel enterprise. The reduction product is subjected to magnetic separation 4 to obtain metallic iron 5 and calcium-rich slag 6. Subsequently, the calcium-rich slag 6 is subjected to microwave-ammonium salt synergistic calcium extraction treatment, which is added into an ammonium chloride solution and can be reacted under the action of microwaves. After passing through the solid-liquid separation device 8, the silicon-rich tailings 9 and the calcium-rich leaching solution are obtained and stored in the calcium-rich leaching solution pool 10. The silicon-rich tailings 9 (i.e., the calcium-rich filter residue in Figure 2 ) can be used to prepare low-carbon gel materials. The ammonia gas generated in this step can be supplied to the ammonia water pool 14 through pipeline 13 for recycling. The calcium-rich leaching solution in the calcium-rich leaching solution pool 10 enters the porous micro-bubble generator 12 to prepare calcium carbonate, and the copper dioxide collected in the previous step can be supplied to the porous micro-bubble generator 12 for use. The ammonia gas generated in this step can also be supplied to the ammonia water pool 14 through pipeline 13. The ammonia water prepared in the ammonia water pool 14 can be supplied to the porous micro-bubble generator 12 for use. The product of the porous micro-bubble generator 12 can be subjected to solid-liquid separation using the same solid-liquid separator 8 as in the previous step to obtain high-purity calcium carbonate product 15, and the liquid ammonium chloride solution can be stored in the ammonium chloride solution pool 7 for use in microwave-ammonium salt synergistic calcium extraction. In general, the method proposed in the present application has the following advantages: (1) The present application uses microwaves to pre-reduce the steel slag, and the dicalcium ferrite, calcium ferrite, and other iron-calcium compounds in the steel slag that do not react with ammonium salt are reduced, and the metallic iron product and calcium-rich tailings that can be directly reused for steelmaking are obtained by magnetic separation.

[0047] (2) The application promotes the separation of calcium and other elements in the steel slag by using microwave-ammonium salt, to obtain a calcium-rich leaching solution and a silicon-rich filter residue, the calcium leaching rate is greater than 90%, the calcium purity of the leaching solution is greater than 98%, and the silicon-rich filter residue can be used for preparing low-carbon cementing materials for the building materials industry.

[0048] (3) The application uses inexpensive ammonium chloride as a leaching agent to realize selective leaching of calcium under near-neutral conditions (pH 6-8), and the alkaline characteristics of the leaching solution can significantly enhance the CO2 chemical absorption efficiency; at the same time, the generated ammonia gas can be used to adjust the alkalinity of the calcium-rich supernatant in the carbonation reactor, which not only has low production cost, but also can be recycled, and the NH4Cl regeneration rate is greater than 95%.

[0049] (4) The application is a whole process of recycling, which combines microwave dielectric heating, the carbon-neutral characteristics of the biomass reducing agent, and the closed-loop recycling system of ammonium salt, to form a full-chain value-added utilization mode of "reduction separation-leaching carbonation-medium regeneration" of the iron and calcium components of the steel slag, and there is no waste gas, waste water and waste residue emission in the whole process.

[0050] (5) The application realizes the value-added utilization of steel slag, provides a clean production technology scheme with dual benefits of solid waste resource utilization and carbon emission reduction for the steel industry, and achieves the purpose of waste treatment.

[0051] In another aspect of the application, the application provides a calcium carbonate obtained by recycling steel slag. The calcium carbonate is obtained by the method described above, and the purity of the calcium carbonate is not less than 98%.

[0052] Next, the foregoing content will be described in detail according to specific embodiments.

[0053] Example 1 obtains iron products and calcium-rich tailings The steps of obtaining iron products and calcium-rich tailings are as follows: The biomass and the steel slag powder are mixed, the mass of the biomass accounts for 30% of the mass of the steel slag, the microwave power is 3.6 KW, the heating temperature is 900 ℃, the reduction time is 50 min, the grinding is to 58-75 µm, the magnetic separation intensity is 0.2 T, and the iron products and the calcium-rich tailings are separated.

[0054] Example 2 obtains iron products and calcium-rich tailings The microwave pre-reduction of the steel slag in this embodiment is different from that in example 1 in that the mass of the biomass accounts for 35% of the mass of the steel slag.

[0055] Example 3 obtains iron products and calcium-rich tailings The microwave pre-reduction of the steel slag in this embodiment is different from that in example 3 in that the heating temperature is 1000 ℃.

[0056] Example 4 obtains iron products and calcium-rich tailings The microwave pre-reduction of the steel slag in this example is different from example 3 in that the reduction time is 60 min.

[0057] The detection results of the metallization rates of examples 1-4 are shown in table 2 below: Table 2

[0058] Example 5 microwave-ammonium salt leaching of calcium elements The calcium-rich tailings come from example 4 with the highest metallization rate. The calcium-rich tailings with a particle size of 58-75 µm are mixed with an ammonium chloride solution under the conditions of a solid-liquid ratio of 1:30 g / ml, a rotation speed of 300 rpm, an ammonium salt concentration of 3 mol / L, and a temperature of 50 ℃ for 2 h. The calcium-rich supernatant is obtained by filtration. At this time, the calcium ion leaching rate is 53.35%, and no iron, aluminum, and silicon elements are detected.

[0059] Example 6 microwave-ammonium salt leaching of calcium elements The microwave-ammonium salt leaching of calcium elements in this example is different from example 5 in that a microwave field is added, and the microwave power is 720 W.

[0060] Example 7 microwave-ammonium salt leaching of calcium elements The microwave-ammonium salt leaching of calcium elements in this example is different from example 6 in that the reaction time is 1 h.

[0061] Example 8 microwave-ammonium salt leaching of calcium elements The microwave-ammonium salt leaching of calcium elements in this example is different from example 7 in that the ammonium chloride concentration is 2 mol / L.

[0062] Example 9 microwave-ammonium salt leaching of calcium elements The microwave-ammonium salt leaching of calcium elements in this example is different from example 8 in that the reaction temperature is 80 ℃.

[0063] The detection results of the calcium element leaching rates obtained in examples 5-9 are shown in table 3: Table 3

[0064] Example 10 carbonation for preparing high-purity light calcium carbonate The calcium-rich leaching solution comes from example 9 with the optimal leaching rate. The pH of the calcium-rich leaching solution is adjusted to 9 with ammonia water, and then placed in a carbonation reactor. Subsequently, blast furnace flue gas and ammonia gas are introduced into the carbonation reactor at a rate of 5 L / (min·L) to simulate the carbonation reaction. The carbonation reaction is carried out at 30 ℃ for 20 min. After filtration, calcium carbonate precipitate and ammonium chloride solution are obtained. The calcium carbonate product is analyzed by TG-DSC to obtain the purity of the calcium carbonate.

[0065] Example 11 carbonation for preparing high-purity light calcium carbonate The difference between this embodiment, which uses carbonation to prepare high-purity light calcium carbonate, and Example 10 is that the pH of the leachate is 10.

[0066] Example 12: Preparation of high-purity light calcium carbonate by carbonation The difference between this embodiment and Example 11 in that the reaction time is 10 min, which is used to prepare high-purity light calcium carbonate by carbonation.

[0067] Example 13: Preparation of high-purity light calcium carbonate by carbonation The difference between this embodiment and Example 12 in that the reaction temperature is 30°C, which is used to prepare high-purity light calcium carbonate by carbonation.

[0068] Table 4 shows the test results for calcium carbonate: Table 4

[0069] The calcium carbonate product in Example 13 was analyzed by TG-DSC and scanning electron microscopy, and the purity was as high as 98.86%. The results are as follows: Figure 3 As shown in Figure 4.

[0070] Comparative analysis shows that after microwave pre-reduction treatment, iron and calcium compounds such as C2F and Ca2(Al,Fe)2O5 in steel slag that do not react with ammonium salts are reduced. At the same time, CS and C3S are transformed into C2S, which is more readily reacted with ammonium salts. Magnetic separation for iron removal not only facilitates the recovery of iron but also further improves the leaching rate of calcium.

[0071] Ammonium salts can selectively leach calcium from steel slag, and the leachate is alkaline, which is conducive to the carbonation reaction.

[0072] Microwave on Ca in steel slag 2+ Leaching rate has a promoting effect, at 720 W Ca 2+ The leaching rate was 90.3%, compared to 63.35% without microwave treatment, Ca... 2+ The leaching rate was increased by 27.95%, the reaction time was shortened by 60 min, the concentration of the leaching agent was reduced to 1 / 3, and the production cost was reduced.

[0073] Adjusting the pH of the leachate with ammonia water yields high-purity calcium carbonate. The high pH of the calcium-rich supernatant promotes the carbonation reaction. As the reaction temperature increases, the CaCO3 crystal form transforms from calcite to aragonite, and the particle size decreases from 12-15 µm to 2-4 µm. Aragonite-type calcium carbonate products can be used in cutting-edge fields such as medical materials and food.

[0074] The preferred embodiments of the present application are described in detail above, but the present application is not limited to the specific details described in the above embodiments, and various simple modifications can be made to the technical solutions of the present application within the technical concept of the present application, and these simple modifications all belong to the protection scope of the present application.

[0075] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction, and in order to avoid unnecessary repetition, various possible combinations are not described again in the present application.

[0076] In addition, various different embodiments of the present application can also be combined in any manner, as long as it does not deviate from the idea of the present application, and it should also be considered as disclosed in the present application.

Claims

1. A method for steel slag treatment for producing light calcium carbonate by iron recovery, calcium leaching and carbonation, the method comprising: (1) mixing biomass with steel slag and performing microwave reduction to obtain a reduction product, the mass of the biomass accounting for 30-40% of the mass of the steel slag, the microwave reduction being performed at a power of 3-4 KW for 30-80 min, and the reduction product being subjected to magnetic separation to obtain an iron product and a calcium-rich tailing, and CO2 flue gas generated in the process being used in a carbonation reaction in step (3); (2) mixing the calcium-rich tailing with an ammonium salt solution, the solid-liquid mixing ratio of the calcium-rich tailing and the ammonium salt solution being 10-40 g / ml, and the mixture being subjected to a reaction under the action of microwaves to obtain a calcium-rich supernatant and a silicon-rich tailing, the reaction being performed at a temperature of 30-90 ℃ and a microwave power of 0-800 W, and the mixture being kept for 30-150 min after the reaction, and ammonia gas generated in the process being used for pH adjustment of the calcium-rich supernatant in step (3); (3) adjusting the pH of the calcium-rich supernatant to 9-11 using ammonia water, and introducing CO2 into a carbonation reactor at a flow rate of 5-15 L / (min·L) to perform a carbonation reaction, and obtaining light calcium carbonate and an ammonium chloride solution after solid-liquid separation, and using the ammonium chloride solution in step (2).

2. The method of claim 1, wherein, The particle size of the steel slag and the biomass is independently 58-75 µm.

3. The method of claim 1, wherein, The biomass comprises at least one of straw, fruit shell, vinasse, wood chips, wood, agricultural and forestry waste and processing waste, the steel slag comprises converter slag, refining slag, electric furnace slag and other solid waste generated in the steelmaking process, and the mass percentage of total Fe in the steel slag is 10-50%, and the mass percentage of CaO is 20-60%.

4. The method of claim 1, wherein, In step (1), the microwave reduction is performed at a heating rate of 15-35 ℃ / min, a reduction temperature of 900-1100 ℃ and a reduction time of 30-80 min.

5. The method of claim 1, wherein, In step (1), the magnetic field strength for the magnetic separation is 0.10-0.5 T.

6. The method of claim 1, wherein, In step (2), the concentration of the ammonium salt solution is 1-4 mol / L; The reaction of the calcium-rich tailing and the ammonium chloride under the action of microwaves is performed under stirring at a stirring rate of 0-300 rpm; The reaction time is 0.5-2.5 h; The pH of the obtained calcium-rich supernatant is 6-8. In step (3), the flow rate of the carbon dioxide gas in the carbonation process is 1-15 L / (min·L), the carbonation time is 5-30 min, and the reaction temperature is 30-80 ℃.

7. The method of claim 1, wherein, Step (2) further comprises collecting the generated ammonia gas to obtain ammonia water, and introducing the ammonia water into the carbonation reactor in step (3).

8. The method of claim 1, wherein, The calcium carbonate is obtained by the method of any one of claims 1-8, and the purity of the calcium carbonate is not less than 98%.

9. A calcium carbonate recovered based on steel slag, characterized in that, ​

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