Method for activating and converting waste lithium iron phosphate battery material calcium salt and high-value utilization

Abstract

The application discloses a method for activating and converting calcium salt of waste lithium iron phosphate battery material and high-value utilization, which comprises the following steps: calcium salt activation, iron-lithium fine separation, compound transformation and forming maintenance, adopting chemical properties stable oxidizing calcium salt such as calcium hypochlorite or super calcium oxide to assist mechanical chemical activation to strengthen lithium iron phosphate phase deconstruction, then through dilute sulfuric acid system to strengthen lithium element selective leaching, and simultaneously realize directional enrichment of phosphorus, iron elements and calcium, sulfur elements introduced into the system, not only shorten the process, but also reduce the tail liquid disposal cost caused by repeated addition of chemical reagents to adjust pH in the leaching liquid and reduce the loss of lithium elements, which is environment-friendly in operation, high in lithium element recovery rate, and beneficial to industrial application and popularization, and has remarkable economic benefits.

Description

Technical field:

[0001] The present invention relates to the technical field of comprehensive utilization of waste lithium iron phosphate battery materials, and in particular to a method for activation, conversion and high-value utilization of calcium salts of waste lithium iron phosphate battery materials. Background technology:

[0002] Waste lithium iron phosphate battery materials are often subjected to enhanced leaching using a strong acid-base system supplemented with an oxidant to achieve the purpose of lithium iron phosphate decomposition. This disposal process often produces a large amount of secondary solid waste enriched in elements such as iron, calcium, and phosphorus, which has low added value and is prone to pollution. Publication No. CN 114229812 A discloses a method for extracting iron and phosphorus from waste lithium iron phosphate materials. The waste lithium iron phosphate is subjected to enhanced leaching using an acidic oxidant system, resulting in a low-purity lithium-rich solution and iron phosphate slag. The iron phosphate slag is then activated and transformed using a reducing agent and an auxiliary agent to produce iron powder and phosphate. This method achieves an iron and phosphorus recovery rate of only approximately 95%, and the recovery process involves oxidation followed by reduction, making it difficult to achieve atomic economy and economic benefits. Furthermore, the iron-phosphorus-rich product obtained from industrially enhanced leaching of waste lithium iron phosphate battery materials is also used to prepare battery materials. However, due to the high impurity content and low purity of the iron phosphate, the resulting active material is difficult to meet commercial requirements.

[0003] Geopolymers are polymer gels made from minerals or solid waste. Due to their wide adaptability to raw material sources, particularly their compatibility with secondary solid waste rich in calcium, iron, phosphorus, and sulfur, and their excellent mechanical properties and resistance to fire, heat, acid, and alkali, they have broad application prospects in the disposal of bulk industrial solid waste. Based on the above analysis, it is of great significance to consider whether the byproducts generated during the recycling of waste lithium iron phosphate battery materials can be used to replace natural minerals as raw materials for geopolymer production, thereby transforming low-value-added products in the lithium iron phosphate recycling industry into high-value-added products.

[0004] Therefore, it is necessary to develop a high-efficiency, low-pollution recycling system to solve the problem of clean recycling of waste lithium iron phosphate battery materials and high-value utilization of all components. Summary of the invention:

[0005] The purpose of the present invention is to provide a method for activating, converting and high-value utilization of calcium salt of waste lithium iron phosphate battery materials.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for activating, converting and high-value utilization of calcium salt of waste lithium iron phosphate battery materials, the method comprising the following steps:

[0008] (1) Calcium salt activation: The waste lithium iron phosphate battery material and the oxidizing calcium salt are fully mixed in a high-speed ball mill for calcium salt activation;

[0009] (2) Iron-lithium separation: the product after calcium salt activation in step (1) is added to dilute sulfuric acid for slurry preparation, mechanically strengthened stirring is performed, and then diaphragm filter press is used to achieve iron-lithium separation to obtain an iron-calcium rich body and a lithium-rich liquid, and the lithium-rich liquid is returned to the lithium salt purification process;

[0010] (3) Compounding and transformation: the iron-calcium enriched body obtained in step (2) is mixed with aggregate, activator, stimulator, and tap water in a certain proportion in a blender and mechanically stirred for compounding and transformation to obtain a slurry prepolymer; based on the total mass percentage of the raw materials being 100%, the content of the iron-calcium enriched body is 20-30%, the content of the aggregate is 10-20%, the content of the activator is 10-17%, the content of the stimulator is 5-15%, and the content of the tap water is 32-40%;

[0011] (4) Molding and curing: the slurry precursor obtained in step (3) is injected into a mold, and the mold is placed in a constant temperature and humidity chamber for molding and curing, and then demolded to obtain a calcium iron-based geopolymer.

[0012] Preferably, the waste lithium iron phosphate battery material is scraps generated during the production process of lithium iron phosphate batteries and / or the positive electrode material after disassembly and sorting of retired lithium iron phosphate batteries.

[0013] Preferably, the oxidizing calcium salt described in step (1) is calcium hypochlorite and / or super calcium oxide, and the amount of oxidizing calcium salt added is 10wt% to 50wt% of the mass of the waste lithium iron phosphate battery material.

[0014] Preferably, the rotation speed of the high-speed ball mill in step (1) is 500 rpm to 850 rpm, and the reaction time is 20 min to 65 min.

[0015] Preferably, the liquid-to-solid ratio of the product after activation of the dilute sulfuric acid and calcium salt in step (2) is 10:1 to 15:1 L / Kg.

[0016] Preferably, the mechanical stirring speed in step (2) is 180 rpm to 300 rpm, and the stirring time is 30 min to 90 min.

[0017] Preferably, the concentration of the dilute sulfuric acid in step (2) is 0.1M to 1.0M, more preferably 0.3M.

[0018] Preferably, the aggregate in step (3) is at least one of coal gangue, fly ash, and iron aluminum alum slag.

[0019] Preferably, the activator in step (3) is at least one of volcanic ash and desulfurization gypsum.

[0020] Preferably, the activator in step (3) is at least one of water glass and quicklime.

[0021] Preferably, the mechanical stirring speed in step (3) is 1000 rpm to 1800 rpm, and the stirring time is 5 to 25 min.

[0022] Preferably, the temperature in the constant temperature and humidity chamber in step (4) is 55° C. to 65° C., the humidity is 70% to 95%, and the curing time is 18 h to 48 h.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] 1. Compared with the traditional liquid-solid reaction using a volatile hydrochloric acid system to add an oxidant such as hydrogen peroxide, hypochlorous acid or chlorine, the present invention uses chemically stable oxidizing calcium salts such as calcium hypochlorite and super calcium oxide to assist in mechanical chemical activation to enhance the physical deconstruction of lithium iron phosphate, and then uses a dilute sulfuric acid system to enhance the selective extraction of lithium elements, thereby simultaneously achieving the targeted enrichment of phosphorus, iron elements, and calcium and sulfur elements introduced into the system. This not only shortens the process, but also reduces the tail liquid disposal cost caused by repeated addition of chemical reagents to adjust the pH of the leachate neutralization reaction and reduces the loss of lithium elements. It has a friendly operating environment, a high lithium element recovery rate, is conducive to industrial application and promotion, and has significant economic benefits.

[0025] 2. The present invention uses the iron-calcium-rich aggregates enriched in phosphorus, iron, calcium, and sulfur produced in the recycling process of waste lithium iron phosphate battery materials as geopolymer precursors, and couples typical industrial solid wastes such as volcanic ash, desulfurized gypsum, coal gangue, fly ash, and iron aluminum alum slag as aggregates and activators for the geopolymers. Through the depolymerization and polycondensation reactions of oxides such as silicon, aluminum, calcium, and iron in the mixed system, a new type of calcium-iron-based polymer gel material with a high degree of polymerization is obtained, achieving the effects of "waste treatment" and high-value utilization. In particular, the iron-calcium-rich aggregates produced in the recycling process of waste lithium iron phosphate battery materials can provide abundant phosphorus, iron, calcium, and sulfur elements, avoiding the mining of natural ores and reducing the disposal risks and costs of secondary pollutants such as the iron-calcium-rich aggregates. In addition, the main elements in the calcium-iron-rich aggregates exist in the form of insoluble stable compounds, which improves the structural stability of high-value-added products and ensures the stable chemical properties of the calcium-iron-based enriched aggregates, resulting in new building materials with high value, low carbon, and environmental protection.

[0026] Therefore, the technical solution proposed in the present invention is a linkage coupling method, which is particularly suitable for the comprehensive disposal of solid waste in the production, processing and recycling of waste lithium iron phosphate batteries, as well as the low-carbon and clean production of new calcium-iron-based geopolymer building materials. It has the characteristics of low carbon, environmental protection, high comprehensive resource utilization rate, low disposal cost and easy industrial application and promotion. Description of the drawings:

[0027] Figure 1It is a process flow chart of the present invention;

[0028] Figure 2 This is the XRD phase composition diagram of the iron-calcium rich body obtained in Example 3 of the present invention. Specific implementation method:

[0029] The following is a further description of the present invention, but not a limitation of the present invention.

[0030] The composition of the waste lithium iron phosphate battery materials used in Examples 1-6 is shown in Table 1.

[0031] Table 1

[0032]

[0033]

[0034] Example 1:

[0035] like Figure 1 As shown, a method for activating, converting and high-value utilization of calcium salt of waste lithium iron phosphate battery materials includes the following steps:

[0036] (1) Calcium salt activation: The scraps generated during the production of lithium iron phosphate batteries were fully mixed with calcium hypochlorite in a high-speed ball mill for calcium salt activation, wherein the amount of calcium hypochlorite added was 10 wt % of the mass of the scraps generated during the production of lithium iron phosphate batteries, the speed of the high-speed ball mill was 500 rpm, and the reaction time was 20 min;

[0037] (2) Iron-lithium separation: The product after calcium salt activation in step (1) is added to a 0.1M dilute sulfuric acid for slurry preparation, and after mechanical intensive stirring, the iron-lithium separation is achieved by diaphragm filter pressing to obtain an iron-calcium enriched mass and a lithium-rich solution, and the lithium-rich solution is returned to the lithium salt purification process; wherein the liquid-to-solid ratio of the product after dilute sulfuric acid and calcium salt activation is 10:1 L / Kg, the mechanical stirring speed is 180 rpm, and the stirring time is 30 min;

[0038] (3) Compounding and transformation: the iron-calcium enriched body obtained in step (2) is mixed with aggregate coal gangue, activator volcanic ash, activator water glass, and tap water in a mass percentage of 25:20:15:5:35 wt% in a blender, and stirred at a stirring speed of 1000 rpm for 5 min to compound and transform, thereby obtaining a slurry prepolymer;

[0039] (4) Molding and curing: The slurry precursor obtained in step (3) was injected into a 15 mm × 15 mm × 25 mm mold, and the mold was placed in a constant temperature and humidity chamber at a temperature of 55°C and a humidity of 70% for molding and curing, and then demolded. The curing time was 18 hours to obtain a calcium iron-based geopolymer.

[0040] Example 2

[0041] like Figure 1 As shown, a method for activating, converting and high-value utilization of calcium salt of waste lithium iron phosphate battery materials includes the following steps:

[0042] (1) Calcium salt activation: The cathode material after disassembly and sorting of retired lithium iron phosphate batteries was fully mixed with super calcium oxide in a high-speed ball mill for calcium salt activation, wherein the amount of super calcium oxide added was 50 wt% of the mass of the cathode material after disassembly and sorting of retired lithium iron phosphate batteries, the high-speed ball mill speed was 850 rpm, and the reaction time was 65 min;

[0043] (2) Iron-lithium separation: The product after calcium salt activation in step (1) was added to dilute sulfuric acid with a concentration of 1.0 M to prepare a slurry, and after mechanical intensive stirring, the iron-lithium separation was achieved by diaphragm filter pressing to obtain an iron-calcium enriched mass and a lithium-rich solution, and the lithium-rich solution was returned to the lithium salt purification process, wherein the liquid-to-solid ratio of the product after dilute sulfuric acid and calcium salt activation was 15:1 L / Kg, the mechanical stirring speed was 300 rpm, and the stirring time was 90 min;

[0044] (3) Compounding and transformation: the iron-calcium enriched body obtained in step (2) is mixed with aggregate fly ash, activator desulfurization gypsum, activator quicklime, and tap water in a mass percentage of 30:10:10:10:40 (wt%) in a blender, and stirred at a stirring speed of 1800 rpm for 25 minutes to perform compounding and transformation to obtain a slurry prepolymer;

[0045] (4) Molding and curing: The slurry precursor obtained in step (3) was injected into a 15 mm × 15 mm × 25 mm mold, and the mold was placed in a constant temperature and humidity chamber at a temperature of 65°C and a humidity of 95% for molding and curing, and then demolded. The curing time was 48 hours to obtain a calcium iron-based geopolymer.

[0046] Example 3

[0047] like Figure 1 As shown, a method for activating, converting and high-value utilization of calcium salt of waste lithium iron phosphate battery materials includes the following steps:

[0048] (1) Calcium salt activation: The scraps generated during the production of lithium iron phosphate batteries were fully mixed with super calcium oxide in a high-speed ball mill for calcium salt activation, wherein the amount of super calcium oxide added was 20 wt% of the mass of the scraps generated during the production of lithium iron phosphate batteries, the high-speed ball mill speed was 600 rpm, and the reaction time was 30 min;

[0049] (2) Iron-lithium separation: The product after calcium salt activation in step (1) is added to a 0.3M dilute sulfuric acid for slurry preparation, and after mechanical intensive stirring, the iron-lithium separation is achieved by diaphragm filter pressing to obtain an iron-calcium rich body and a lithium-rich liquid, and the lithium-rich liquid is returned to the lithium salt purification process; wherein the liquid-solid ratio of the product after dilute sulfuric acid and calcium salt activation is 11:1 L / Kg, the mechanical stirring speed is 200 rpm, and the stirring time is 40 min. The XRD phase composition of the obtained iron-calcium rich body is as follows Figure 2 As shown;

[0050] (3) Compounding and transformation: the iron-calcium enriched mass obtained in step (2) is mixed with the aggregate iron aluminum alum slag, the activator volcanic ash, the activator quicklime, and tap water in a blender at a mass percentage (wt%) of 20:15:15:15:15:35, and the mixture is stirred at a stirring speed of 1200 rpm for 10 minutes to obtain a slurry prepolymer;

[0051] (4) Molding and curing: The slurry precursor obtained in step (3) was injected into a 15 mm × 15 mm × 25 mm mold, and the mold was placed in a constant temperature and humidity chamber at a temperature of 60°C and a humidity of 75% for molding and curing, and then demolded. The curing time was 24 hours to obtain a calcium iron-based geopolymer.

[0052] Example 4

[0053] like Figure 1 As shown, a method for activating, converting and high-value utilization of calcium salt of waste lithium iron phosphate battery materials includes the following steps:

[0054] (1) Calcium salt activation: The cathode material of the disassembled and sorted retired lithium iron phosphate batteries was fully mixed with calcium hypochlorite in a high-speed ball mill for calcium salt activation, wherein the amount of calcium hypochlorite added was 45 wt% of the weight of the scraps generated during the production of the lithium iron phosphate batteries, the high-speed ball mill speed was 750 rpm, and the reaction time was 50 min;

[0055] (2) Iron-lithium separation: The product after calcium salt activation in step (1) is added to a 0.8M dilute sulfuric acid for slurry preparation, and after mechanical intensive stirring, the iron-lithium separation is achieved by diaphragm filter pressing to obtain an iron-calcium enriched mass and a lithium-rich solution, and the lithium-rich solution is returned to the lithium salt purification step; wherein the liquid-to-solid ratio of the product after dilute sulfuric acid and calcium salt activation is 14:1 L / Kg, the mechanical stirring speed is 250 rpm, and the stirring time is 75 min;

[0056] (3) Compounding and transformation: the iron-calcium enriched body obtained in step (2) is mixed with aggregate fly ash, activator desulfurization gypsum, activator water glass, and tap water in a blender at a mass percentage (wt%) of 28:18:17:5:32, and stirred at a stirring speed of 1600 rpm for 20 minutes to compound and transform, thereby obtaining a slurry prepolymer;

[0057] (4) Molding and curing: The slurry precursor obtained in step (3) was injected into a 15 mm × 15 mm × 25 mm mold, and the mold was placed in a constant temperature and humidity chamber at a temperature of 65°C and a humidity of 80% for molding and curing, and then demolded. The curing time was 30 hours to obtain a calcium iron-based geopolymer.

[0058] Example 5

[0059] like Figure 1 As shown, a method for activating, converting and high-value utilization of calcium salt of waste lithium iron phosphate battery materials includes the following steps:

[0060] (1) Calcium salt activation: The cathode material after disassembly and sorting of retired lithium iron phosphate batteries was fully mixed with calcium hypochlorite in a high-speed ball mill for calcium salt activation, wherein the amount of calcium hypochlorite added was 25 wt% of the mass of the cathode material after disassembly and sorting of retired lithium iron phosphate batteries, the speed of the high-speed ball mill was 650 rpm, and the reaction time was 35 min;

[0061] (2) Iron-lithium separation: The product after calcium salt activation in step (1) is added to a 0.5M dilute sulfuric acid for slurry preparation, and after mechanical intensive stirring, the iron-lithium separation is achieved by diaphragm filter pressing to obtain an iron-calcium enriched mass and a lithium-rich solution, and the lithium-rich solution is returned to the lithium salt purification process; wherein the liquid-to-solid ratio of the product after dilute sulfuric acid and calcium salt activation is 12:1 L / Kg, the mechanical stirring speed is 220 rpm, and the stirring time is 50 min;

[0062] (3) Compounding and transformation: the iron-calcium enriched mass obtained in step (2) is mixed with the aggregate iron aluminum alum slag, the activator volcanic ash, the activator quicklime, and tap water in a blender at a mass percentage (wt%) of 26:13:11:13:37, and stirred at a stirring speed of 1500 rpm for 15 minutes to perform compounding and transformation to obtain a slurry prepolymer;

[0063] (4) Molding and curing: The slurry precursor obtained in step (3) was injected into a 15 mm × 15 mm × 25 mm mold, and the mold was placed in a constant temperature and humidity chamber at a temperature of 55°C and a humidity of 90% for molding and curing, and then demolded. The curing time was 36 hours to obtain a calcium iron-based geopolymer.

[0064] Example 6

[0065] like Figure 1 As shown, a method for activating, converting and high-value utilization of calcium salt of waste lithium iron phosphate battery materials includes the following steps:

[0066] (1) Calcium salt activation: The scraps generated during the production of lithium iron phosphate batteries were fully mixed with super calcium oxide in a high-speed ball mill for calcium salt activation, wherein the amount of super calcium oxide added was 35 wt% of the mass of the scraps generated during the production of lithium iron phosphate batteries, the high-speed ball mill speed was 550 rpm, and the reaction time was 45 min;

[0067] (2) Iron-lithium separation: The product after calcium salt activation in step (1) is added to a 0.6M dilute sulfuric acid for slurry preparation, and after mechanical intensive stirring, the iron-lithium separation is achieved by diaphragm filter pressing to obtain an iron-calcium enriched mass and a lithium-rich solution, and the lithium-rich solution is returned to the lithium salt purification process; wherein the liquid-to-solid ratio of the product after dilute sulfuric acid and calcium salt activation is 13:1 L / Kg, the mechanical stirring speed is 270 rpm, and the stirring time is 60 min;

[0068] (3) Compounding and transformation: the iron-calcium enriched body obtained in step (2) is mixed with aggregate coal gangue, activator desulfurization gypsum, activator quicklime, and tap water in a blender at a mass percentage (wt%) of 24:11:13:14:38, and stirred at a stirring speed of 1500 rpm for 17 minutes to perform compounding and transformation to obtain a slurry prepolymer;

[0069] (4) Molding and curing: The slurry precursor obtained in step (3) was injected into a 15 mm × 15 mm × 25 mm mold, and the mold was placed in a constant temperature and humidity chamber at a temperature of 62°C and a humidity of 85% for molding and curing, and then demolded. The curing time was 40 hours to obtain a calcium iron-based geopolymer.

[0070] Comparative Example 1

[0071] Refer to Example 1, except that no oxidizing calcium salt is added in the calcium salt activation process in step (1), and tap water is used instead of dilute sulfuric acid solution in the iron-lithium separation process in step (2). The remaining processes and parameters are the same as those in Example 1.

[0072] Since no oxidizing calcium salt was added for calcium salt activation in Comparative Example 1, and tap water was used as the solvent in the iron-lithium separation process, the decomposition of lithium iron phosphate was incomplete, the lithium recovery rate was low, and the obtained leaching residue failed to enrich the necessary geopolymer components such as calcium and sulfur, resulting in poor flexural and compressive strength of the obtained geopolymer, the product was unqualified, and the purpose of high value was not achieved.

[0073] Comparative Example 2

[0074] Refer to Example 3, except that in step (2), the iron-lithium fine separation process uses 0.3M dilute nitric acid instead of dilute sulfuric acid solution, and in step (3), the iron-calcium enriched body and the aggregate iron aluminum alum slag, the activator volcanic ash, the activator (not used), and the tap water are mixed in a blender at a mass percentage (wt%) of 20:20:20:0:40, and the blending transformation is carried out at a stirring speed of 1000 rpm for 30 minutes. The remaining processes and parameters are the same as those in Example 3.

[0075] Since 0.3M dilute nitric acid is used instead of dilute sulfuric acid solution in the iron-lithium fine separation process in Comparative Example 2, although the lithium element has a higher leaching rate, the nitrification effect of nitric acid causes the leaching residue to fail to enrich the necessary geopolymer components such as calcium and sulfur, and the addition of nitric acid causes the dispersion of the iron element, the iron content in the leaching residue decreases, and the iron concentration in the leachate increases, resulting in incomplete separation of lithium and iron, requiring an additional impurity removal process to improve the purity of lithium in the leachate. In addition, since activators such as quicklime or water glass are not used in the composite transformation process, demolding is difficult during the molding and curing process, and the molded geopolymer cannot be obtained, the product is unqualified, and the purpose of high value cannot be achieved.

[0076] The lithium recovery rates in Examples 1 to 6 and Comparative Examples 1 to 2 and the 3-day and 7-day performance test indicators of the obtained calcium-iron-based polymers are shown in Table 2:

[0077] Table 2

[0078]

[0079]

[0080] The description of the above embodiments is only used to help understand the technical solution and core ideas of the present invention. It should be pointed out that for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention. These improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for activation, conversion and high-value utilization of calcium salt of waste lithium iron phosphate battery materials, characterized in that: The method comprises the following steps: (1) Calcium salt activation: The waste lithium iron phosphate battery material and the oxidizing calcium salt are fully mixed in a high-speed ball mill for calcium salt activation; (2) Iron-lithium separation: The product after calcium salt activation in step (1) is added to dilute sulfuric acid to prepare a slurry, and after mechanical intensive stirring, the iron-lithium separation is achieved by diaphragm filter pressing to obtain an iron-calcium rich body and a lithium-rich liquid, and the lithium-rich liquid is returned to the lithium salt purification process; (3) Compounding and transformation: the iron-calcium enriched mass obtained in step (2) is mixed with aggregate, activator, stimulator and tap water in a certain proportion in a blender and mechanically stirred for compounding and transformation to obtain a slurry prepolymer; the raw materials are calculated based on the total mass percentage of 100%, the content of the iron-calcium enriched mass is 20-30%, the content of the aggregate is 10-20%, the content of the activator is 10-17%, the content of the stimulator is 5-15%, and the content of the tap water is 32-40%; the aggregate is at least one of coal gangue, fly ash and iron aluminum alum slag; the activator is at least one of volcanic ash and desulfurized gypsum; the stimulator is at least one of water glass and quicklime; (4) Molding and curing: the slurry precursor obtained in step (3) is injected into a mold, the mold is placed in a constant temperature and humidity chamber for molding and curing, and then demolded to obtain a calcium iron-based geopolymer.

2. The method according to claim 1, characterized in that The waste lithium iron phosphate battery material is the scraps generated during the production process of lithium iron phosphate batteries and / or the positive electrode material after disassembly and sorting of retired lithium iron phosphate batteries.

3. The method according to claim 1, characterized in that The oxidizing calcium salt is calcium hypochlorite, and the amount of the oxidizing calcium salt added is 10wt% to 50wt% of the mass of the waste lithium iron phosphate battery material.

4. The method according to claim 1, wherein The speed of the high-speed ball mill in step (1) is 500 rpm to 850 rpm, and the reaction time is 20 min to 65 min.

5. The method according to claim 1, wherein The liquid-to-solid ratio of the product after activation of the dilute sulfuric acid and calcium salt in step (2) is 10:1~15:1 L / kg.

6. The method according to claim 1, characterized in that The concentration of dilute sulfuric acid in step (2) is 0.1 M to 1.0 M.

7. The method according to claim 1, characterized in that The mechanical stirring speed in step (2) is 180 rpm to 300 rpm, and the stirring time is 30 min to 90 min.

8. The method according to claim 1, characterized in that The mechanical stirring speed in step (3) is 1000 rpm~1800 rpm, and the stirring time is 5~25 min.

9. The method according to claim 1, characterized in that The temperature in the constant temperature and humidity chamber in step (4) is 55°C to 65°C, the humidity is 70% to 95%, and the curing time is 18 h to 48 h.

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