Method for improving lithium yield in extraction of lithium from lepidolite ore

Abstract

The invention relates to a method for increasing the lithium yield in lithium extraction from lepidolite ore, and belongs to the technical field of mineral processing. The method is used for solving the problems of harsh lithium extraction conditions, high energy consumption and certain lithium loss of the existing roasting method. The method comprises the following steps: crushing lepidolite ore, and sieving to obtain lepidolite powder; the method comprises the following steps: adding lepidolite powder into a reaction kettle, adding water and an alkali activator into the reaction kettle, and stirring; sealing the reaction kettle, heating to 75-85 DEG C, and keeping the temperature for reaction; after the reaction is completed, opening the reaction kettle, filtering a mixture in the reaction kettle to obtain primary filtrate and primary filter residues, and drying the primary filter residues; uniformly mixing the primary filter residue with composite sulfate and a calcium oxide auxiliary agent, and roasting; crushing the roasted primary filter residues, adding the crushed primary filter residues into a reaction kettle, adding water and sodium hydroxide into the reaction kettle, and uniformly stirring and mixing; raising the temperature to 75-85 DEG C and preserving heat for 2-3 hours; after the reaction is completed, opening the reaction kettle, and filtering to obtain secondary filtrate and secondary filter residues; the method provided by the invention can improve the lithium yield.

Description

Technical Field

[0001] The invention relates to the technical field of mineral processing, and in particular to a method for improving the lithium yield in lithium extraction from lepidolite ore. Background Art

[0002] In recent years, with the widespread application of lithium-ion batteries, the demand for lithium and its compounds has been growing. There are two main methods for obtaining lithium in industry: one is to enrich lithium in brine and make lithium salt products; the other is to extract lithium from ore, which is mainly roasting to dissolve the lithium-containing compounds in the form of soluble lithium salts and then make lithium salt products.

[0003] my country's domestic salt lake lithium resources are poor, with low lithium content and high magnesium-lithium ratio. Therefore, the main source of lithium and its compounds is lithium-containing ores, usually spodumene and lepidolite.

[0004] The key to lithium extraction from lithium-containing ores is to destroy the original aluminosilicate structure in the ore. The traditional process for extracting lithium from spodumene is to roast it at 1000°C to convert it into β-spodumene, then roast it with concentrated acid and extract lithium by water leaching. This method not only has a complicated process flow, but also greatly increases energy consumption and environmental pollution.

[0005] The common process for extracting lithium from lithium mica is sulfate roasting, because it is necessary to take into account the benefits of fluorine fixation, preventing material sintering, and promoting lithium leaching during the sintering process. The formula used in the sulfate roasting method is usually more complicated, the roasting temperature is relatively high (generally between 900-980°C), and the lithium yield is highly dependent on the stability of the raw material components. For example, a slight increase in the fluorine content of lithium mica will lead to insufficient calcium salt for fluorine fixation, which will reduce the activation effect and also produce additional fluorine ions that will react with lithium to synthesize volatile lithium fluoride and damage the kiln. This requires the factory to test the lithium content of each batch of lithium slag that has undergone the leaching process in order to monitor the leaching effect and avoid the waste of raw materials caused by too low a leaching rate. In addition, the crystal transformation process during high-temperature roasting is energy-intensive, long, and costly, and there is a certain amount of lithium loss. This results in higher production and management costs, which is not conducive to the widespread application of lithium mica resources. Summary of the invention

[0006] In view of the above analysis, the present invention aims to provide a method for improving the lithium yield in lithium extraction from lepidolite ore, which is used to solve at least one of the following technical problems: the existing roasting method for lithium extraction has harsh conditions, high temperature, high energy consumption, and a certain lithium loss problem.

[0007] The purpose of the present invention is mainly achieved through the following technical solutions:

[0008] In one aspect, the present invention provides a method for improving the lithium yield in lithium extraction from lepidolite ore, comprising the following steps:

[0009] S1, crushing the lepidolite ore and sieving it to obtain lepidolite powder;

[0010] S2, the lepidolite powder is added into the reactor, water and alkali activator are added thereto, and stirring is uniformly mixed;

[0011] S3, after sealing the reactor, raise the temperature to 75-85°C and keep it warm for reaction;

[0012] S4. After the reaction is completed, open the reactor, filter the mixture therein to obtain a primary filtrate and a primary filter residue, and dry the primary filter residue; then mix the primary filter residue with the composite sulfate and the calcium oxide additive, and calcine;

[0013] S5, crushing the primary filter residue after roasting, adding it into the reaction kettle, adding water and sodium hydroxide thereto, stirring and mixing evenly; heating to 75-85°C and keeping warm for 2-3h;

[0014] S6. After the reaction is completed, open the reactor and filter to obtain a secondary filtrate and a secondary filter residue.

[0015] Furthermore, the alkali activator is calcium oxide or sodium hydroxide.

[0016] Furthermore, in S2, the mass concentration of the alkali activator is controlled to be 1.5% to 2.5%.

[0017] Furthermore, in S2, the liquid-to-solid ratio in the reactor is 4 to 10:1.

[0018] Furthermore, in S3, the reaction time is 1 to 2 hours.

[0019] Furthermore, in S4, the composite sulfate includes sodium sulfate and potassium sulfate.

[0020] Furthermore, the mass ratio of sodium sulfate to potassium sulfate is 1:1.9-2.1.

[0021] Furthermore, in S4, the mass ratio of the primary filter residue, the composite sulfate and the calcium oxide is 5:2.9 to 3.1:1.

[0022] Furthermore, in S4, the calcination temperature is 800°C to 860°C.

[0023] Furthermore, the reaction time in S5 is greater than the reaction time in S3.

[0024] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0025] The method of improving the lithium yield in lithium extraction from lithium mica of the present invention first uses an alkaline activator to treat the initial lithium mica powder, so that the components with relatively loose structures in the lithium mica powder are destroyed first, and a part of the lithium is released and dissolved into the alkaline solution. For components with compact structure and need to be activated by sulfate roasting, the pre-alkaline activation effectively improves the activation energy during the roasting activation process, and reduces the roasting temperature while maintaining the lithium yield; to a certain extent, it weakens the sintering phenomenon of other lithium-containing components that would otherwise occur due to the high roasting temperature, so that the lithium therein is no longer difficult to dissolve due to a large amount of conversion into a glass phase, thereby ensuring the lithium yield. Furthermore, in the method of the present invention, the lithium mica after roasting and activation is secondary activated to break the glass phase that may still exist, and further improve the lithium yield.

[0026] The method of the present invention fully considers the different requirements of different lithium-containing components in lepidolite for the process by precisely controlling each step and the process parameters in each step, splits different efficiencies, and reduces the high dependence of the activation process on the stability of the raw material components. The method of the present invention realizes the targeted activation of different lithium-containing components in lepidolite, thereby significantly improving the lithium yield and providing a new technical path for the efficient utilization of lepidolite resources.

[0027] In the method of the present invention, the temperature in the preliminary alkali activation reaction is relatively low, and the production safety is good. In the method of the present invention, the lithium yield is relatively high, which is above 89%, for example, 89.74% to 94.12%.

[0028] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents pointed out in the embodiments of the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings are only for the purpose of illustrating particular embodiments and are not to be construed as limiting the invention.

[0030] Figure 1 The XRD patterns of lepidolite calcined and calcined with calcium oxide and salt added;

[0031] Figure 2 This is an optical photograph of lithium mica after calcination and consolidation after adding additives after the first hydrothermal treatment. DETAILED DESCRIPTION

[0032] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0033] The present invention provides a method for improving the lithium yield in lithium extraction from lepidolite ore, comprising the following steps:

[0034] S1, crushing the lepidolite ore and sieving it to obtain lepidolite powder;

[0035] S2, the lepidolite powder is added into the reactor, water and alkali activator are added thereto, and stirring is uniformly mixed;

[0036] S3, after sealing the reactor, raise the temperature to 75-85°C and keep it warm for reaction;

[0037] S4. After the reaction is completed, open the reactor, filter the mixture therein to obtain a primary filtrate and a primary filter residue, and dry the primary filter residue; then mix the primary filter residue with the composite sulfate and the calcium oxide additive, and calcine;

[0038] S5, crushing the primary filter residue after roasting, adding it into the reaction kettle, adding water and sodium hydroxide thereto, stirring and mixing evenly; heating to 75-85°C and keeping warm for 2-3h;

[0039] S6. After the reaction is completed, open the reactor and filter to obtain a secondary filtrate and a secondary filter residue.

[0040] Specifically, in the above S1, the lithium mica ore includes lithium disilicate with a relatively tight lattice structure and 1M type lithium mica with a layered structure, and the interlayer bonding force is mainly van der Waals force. Considering that the powder particle size is too large, it is not conducive to its activation reaction, therefore, the lithium mica powder is controlled to pass through a 250 mesh sieve after crushing.

[0041] Specifically, the above S1 also includes testing and recording the lithium content in the lepidolite ore.

[0042] Specifically, in the above S2, the alkali activator can be calcium oxide or sodium hydroxide. When the mass concentration of the alkali activator increases to a certain amount, it will lose the effect of improving the lithium yield, and its mass concentration must be above a certain level to improve the lithium yield. Taking all factors into consideration, the mass concentration of the alkali activator is controlled to be 1.5% to 2.5%, for example, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, and 2.4%.

[0043] Specifically, in the above S2, considering that the liquid-solid ratio (the mass ratio of water to lithium mica powder) is too large, too much alkali activator will be required, which is not suitable for actual industrial production; if the liquid-solid ratio is too small, the lithium mica slurry will be too viscous, which is not conducive to its alkali activation reaction. Therefore, the liquid-solid ratio in the reactor is controlled to be (4-10):1, for example, 5:1, 6:1, 7:1, 8:1, 9:1.

[0044] Specifically, in the above S3, after the reactor is sealed (a high-pressure environment is formed after sealing), the reaction is carried out at 75-85°C, which can cause the components with relatively loose structures in the lithium mica powder to be destroyed first, releasing and dissolving a part of lithium into the alkaline solution; for components with compact structure that need to be roasted and activated, this step can effectively increase the activation energy during the roasting and activation process, and reduce the roasting temperature while maintaining the lithium yield. It should be noted that under alkaline conditions, the alkaline activator can provide a large amount of OH- ions, which can react with the silicon-oxygen bonds (Si-O) in silicate minerals, resulting in the breaking of Si-O bonds. The broken silicon-oxygen bonds will form silicate ions (such as [SiO 4 ] 4- ) and other oligomers, which are highly active and can be repolymerized into a silicate network with higher activity. Therefore, this step can effectively increase the activation energy during the roasting process. In addition, under the above temperature conditions, the rate of this reaction process will be significantly increased, and the solubility of the solvent will also be greatly increased, accelerating the breaking of silicon-oxygen bonds and the formation of oligomers while increasing the degree of depolymerization of the silicate network.

[0045] Specifically, in the above S3, considering that the reaction temperature is too high, it will produce extremely high pressure, which has high requirements for the reactor used, and there are also hidden dangers in production safety; if the reaction temperature is too low, the pressure generated is not high enough to achieve the destruction of the silicate structure; if the insulation time is too long, the production cost will increase, and if the time is too short, the alkali activation cannot be completed. Therefore, the reaction temperature is controlled to be 75-85°C, such as 76°C, 77°C, 78°C, 78°C, 80°C, 81°C, 82°C, 83°C, 84°C. The reaction time is controlled to be 1-2h, such as 1h, 1.2h, 1.5h, 1.7h.

[0046] Specifically, in the above S4, the composite sulfate includes sodium sulfate and potassium sulfate. Considering that the mass ratio of sodium sulfate to potassium sulfate is too large and the potassium sulfate content is too small, the effect of roasting activation will be reduced; while the mass ratio is too small and the potassium sulfate content is too high, the cost of roasting activation will be too high. Therefore, the mass ratio of sodium sulfate to potassium sulfate is controlled to be 1:1.9-2.1.

[0047] Specifically, if the amount of the composite sulfate in the above S4 is too small, the effect of roasting activation will be sharply reduced; however, if the amount of the composite sulfate increases to a certain extent, sintering will occur, which is also not conducive to lithium leaching. After in-depth research, the mass ratio of the primary filter residue, composite sulfate and calcium oxide is controlled to be 5:2.9-3.1:1.

[0048] Specifically, in the above S4, if the calcination temperature is too low, the effect of calcination activation will be reduced, and if the time is too short, it will be not conducive to the completion of calcination activation; if the calcination temperature is too high and the time is too long, it is easy to cause a large amount of lithium to be converted into a glass phase and difficult to dissolve; therefore, the calcination temperature is controlled to be 800°C to 860°C, for example, 810°C, 820°C, 830°C, 840°C, and 850°C; the calcination time is 1 to 2h, for example, 1.2h, 1.4h, 1.6h, and 1.8h.

[0049] Specifically, in the above S4, the phase after calcination mainly includes lithium potassium sulfate which is easily soluble in water, and lithium silicate which is slightly soluble in water but has good solubility in alkaline solution.

[0050] Specifically, in the above S5, considering that the powder particle size is too large, it is not conducive to the leaching of lithium in the calcined lithium mica and the breaking of the glass phase (a small amount of glass phase may be formed during calcination, and if there is a glass phase, this step can break the glass phase), the calcined lithium mica ore is crushed and passed through a 250 mesh sieve before being added to the reactor, and the liquid-solid ratio of the reactor is (4-10): 1, for example, 5: 1, 6: 1, 7: 1, 8: 1, 9: 1, and the reaction temperature is 75-85°C, for example, 76°C, 77°C, 78°C, 78°C, 80°C, 81°C, 82°C, 83°C, 84°C. The reaction time is controlled to be greater than the reaction time in S3, for example, the reaction time is 2-3h, for example, 2.2h, 2.5h, 2.7h.

[0051] Specifically, in the above S5, the concentration of sodium hydroxide is controlled to be 2.5% to 3.5%, for example, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, and 3.4%.

[0052] Specifically, in the above S6, the lithium content is tested after the secondary filter residue is dried. The lithium content in the final secondary filter residue is multiplied by the material mass magnification due to the introduction of composite sulfate and calcium oxide (the material mass loss is found to be less during the experiment, so it is chosen to be ignored) to obtain the lithium content per unit of lithium mica. The ratio of the lithium content per unit of lithium mica to the original lithium content is subtracted from 1 to obtain the lithium leaching rate, which is used to evaluate the effect of the method of the present invention.

[0053] The method of improving the lithium yield in lithium extraction from lithium mica of the present invention first uses an alkaline activator to treat the initial lithium mica powder, so that the components with relatively loose structures in the lithium mica powder are destroyed first, and a part of the lithium is released and dissolved into the alkaline solution. For components with compact structure and need to be activated by sulfate roasting, the pre-alkaline activation effectively improves the activation energy during the roasting activation process, and reduces the roasting temperature while maintaining the lithium yield; to a certain extent, it weakens the sintering phenomenon of other lithium-containing components that would otherwise occur due to the high roasting temperature, so that the lithium therein is no longer difficult to dissolve due to a large amount of conversion into a glass phase, thereby ensuring the lithium yield. Furthermore, in the method of the present invention, the lithium mica after roasting and activation is secondary activated to break the glass phase that may still exist, and further improve the lithium yield.

[0054] The method of the present invention fully considers the different requirements of different lithium-containing components in lepidolite for the process by precisely controlling each step and the process parameters in each step, splits different efficiencies, and reduces the high dependence of the activation process on the stability of the raw material components. The method of the present invention realizes the targeted activation of different lithium-containing components in lepidolite, thereby significantly improving the lithium yield and providing a new technical path for the efficient utilization of lepidolite resources.

[0055] In the method of the present invention, the temperature in the preliminary alkali activation reaction is relatively low, and the production safety is good. In the method of the present invention, the lithium yield is relatively high, which is above 89%, for example, 89.74% to 94.12%.

[0056] Example 1

[0057] This embodiment provides a method for improving the lithium yield in lithium extraction from lepidolite ore, the steps of which are:

[0058] S1. Crushing the lepidolite ore and passing it through a 250-mesh sieve to test the lithium content;

[0059] S2, weigh 5g of lithium mica powder, add it to the reactor with a capacity of 100mL, add 50mL of water and 1.25g of calcium oxide (mass concentration is 2.5%), stir and mix well;

[0060] S3, after the reactor is strictly sealed, the temperature is raised to 85°C and kept warm for 2h;

[0061] S4. After the reaction is completed, the reactor is opened, the mixture therein is filtered to obtain a primary filtrate and a primary filter residue, and the primary filter residue is dried; then the primary filter residue is evenly mixed with a composite sulfate (the mass ratio of sodium sulfate to potassium sulfate is 1:1.9) and calcium oxide in a ratio of 5:3:1, and then roasted at 850°C for 2h;

[0062] S5, crush the primary filter residue after roasting, pass it through a 250 mesh sieve, add it into a reactor, add 50 mL of water and 1.25 g of sodium hydroxide (mass concentration is 2.5%), stir and mix evenly; heat to 85 ° C and keep warm for 2.5 h to carry out lithium leaching process, and test the lithium content in the secondary filter residue after drying;

[0063] S6. The lithium yield was calculated to be 94.12%.

[0064] Example 2

[0065] This embodiment provides a method for improving the lithium yield in lithium extraction from lepidolite ore, the steps of which are:

[0066] S1. Crushing the lepidolite ore and passing it through a 250-mesh sieve to test the lithium content;

[0067] S2, weigh 5g of lithium mica powder, add it to a reactor with a capacity of 100mL, then add 50mL of water and 1g of calcium oxide (mass concentration is 2%), stir and mix evenly;

[0068] S3, after the reactor is strictly sealed, the temperature is raised to 82°C and kept warm for 2h;

[0069] S4. After the reaction is completed, the reactor is opened, the mixture therein is filtered to obtain a primary filtrate and a primary filter residue, and the primary filter residue is dried; then the primary filter residue is evenly mixed with a composite sulfate (the mass ratio of sodium sulfate to potassium sulfate is 1:2) and calcium oxide in a ratio of 5:2.9:1, and then roasted at 830°C for 1.5h;

[0070] S5. Crushing the primary filter residue after calcination, passing it through a 250-mesh sieve, adding it to a reactor, and then adding 50 mL of water and 1.5 g of sodium hydroxide (mass concentration of 3%), stirring and mixing evenly; after the reactor is strictly sealed, heating it to 85° C. and keeping it warm for 3 h;

[0071] S6. After the secondary reaction is completed, open the reactor, filter the mixture, and test the lithium content in the secondary filter residue after drying;

[0072] S7. The lithium yield was calculated to be 91.27%.

[0073] Example 3

[0074] This embodiment provides a method for improving the lithium yield in lithium extraction from lepidolite ore, the steps of which are:

[0075] S1. Crushing the lepidolite ore and passing it through a 250-mesh sieve to test the lithium content;

[0076] S2, weigh 5g of lithium mica powder, add it to the reactor with a capacity of 100mL, add 50mL of water and 0.75g of sodium hydroxide (mass concentration is 1.5%), and stir to mix evenly;

[0077] S3, after the reactor is strictly sealed, the temperature is raised to 85°C and kept warm for 2h;

[0078] S4. After the reaction is completed, the reactor is opened, the mixture therein is filtered to obtain a primary filtrate and a primary filter residue, and the primary filter residue is dried; then the primary filter residue is evenly mixed with a composite sulfate (the mass ratio of sodium sulfate to potassium sulfate is 1:2) and calcium oxide in a ratio of 5:3:1, and then roasted at 850°C for 2h;

[0079] S5. Crushing the primary filter residue after roasting, passing it through a 250-mesh sieve, adding it to the reactor, and then adding 50 mL of water and 1.25 g of sodium hydroxide (mass concentration of 2.5%), stirring and mixing evenly. After the reactor is strictly sealed, heating it to 85°C and keeping it warm for 3 hours;

[0080] S6. After the secondary reaction is completed, open the reactor, filter the mixture, and test the lithium content in the secondary filter residue after drying;

[0081] S7. The lithium yield was calculated to be 89.74%.

[0082] Comparative Example 1

[0083] Comparative Example 1 discloses a method with the same overall steps as in Example 1, except that:

[0084] The alkaline activator used in S2 is sodium hydroxide, with an amount of 0.5 g and a mass concentration of 1%. The obtained lithium yield is 84.31%, which indicates that too low a mass concentration of the alkaline activator has a negative impact on the lithium yield.

[0085] Comparative Example 2

[0086] Comparative Example 2 discloses a method with the same overall steps as in Example 1, except that:

[0087] The reaction temperature in S3 was 60°C and the reaction time was 3 hours. The lithium yield was 82.30%.

[0088] This comparative example shows that inappropriate reaction temperature control will reduce the lithium yield.

[0089] Comparative Example 3

[0090] Comparative Example 3 discloses a method with the same overall steps as in Example 2, except that:

[0091] In S4, the calcination temperature is 950°C and the holding time is 1h; in S5, the amount of sodium hydroxide used is 2.5g, the concentration is 5%, the temperature is 100°C, and the holding time is 4h. The lithium yield is 71.23%. This is because the calcination temperature is too high, resulting in a large amount of glass phase inside the primary filter residue, and the primary filter residue is solidified after adding additives to the calcination, which reduces its lithium yield.

[0092] Comparative Example 4

[0093] This comparative example discloses a method with the same overall steps as in Example 3, except that:

[0094] The amount of sodium hydroxide used in S2 is 0.25 g, and the concentration is 0.5%; the amount of sodium hydroxide used in S5 is 0.25 g, and the concentration is 0.5%. The insulation temperature is 70° C., the insulation time is 1 h, and the obtained lithium yield is 76.26%.

[0095] This comparative example shows that inappropriate material dosage and inappropriate reaction temperature will reduce the lithium yield.

[0096] Comparative Example 5

[0097] This comparative example provides a method for extracting lithium from lithium mica. The overall method is the same as that of Example 1, except that the reaction temperature in S3 is 150°C and the reaction time is 2 hours. The lithium yield obtained is 76.37%. This is because S3 has the function of extracting lithium from some loosely structured silicates and activating some compactly structured silicates at the same time. If the temperature is too high, the amount of lithium extracted from the loosely structured silicates reaches the upper limit, but the activation of the remaining components is too strong, so that more glass phases are produced under the same sintering process, and the subsequent reaction cannot break so many glass phases, so the lithium yield is reduced.

[0098] Comparative Example 6

[0099] This comparative example provides a method for extracting lithium from lepidolite, and the method of this comparative example is as follows:

[0100] S1, crush the lithium mica ore and pass it through a 250 mesh sieve;

[0101] S2, weigh 5g of lepidolite powder, mix the lepidolite powder with composite sulfate (the mass ratio of sodium sulfate and potassium sulfate is 1:1.9) and calcium oxide in a ratio of 5:3:1, and then calcine at 850°C for 2h;

[0102] The lithium yield obtained in this comparative example is 68.72%.

[0103] Comparative Example 7

[0104] This comparative example provides a method for extracting lithium from lepidolite. The overall method is the same as that in Example 1, except that:

[0105] Only S1-S4 are performed.

[0106] The lithium yield obtained in this comparative example was 82.12%.

[0107] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for improving the lithium yield in lithium extraction from lepidolite ore, characterized in that: The steps include: S1, crushing the lepidolite ore and sieving it to obtain lepidolite powder; S2, the lepidolite powder is added into the reactor, water and alkali activator are added thereto, and stirring is uniformly mixed; S3, after sealing the reactor, raise the temperature to 75-85°C and keep it warm for reaction; S4. After the reaction is completed, open the reactor, filter the mixture therein to obtain a primary filtrate and a primary filter residue, and dry the primary filter residue; then mix the primary filter residue with the composite sulfate and the calcium oxide additive, and calcine; S5, crushing the primary filter residue after roasting, adding it into the reaction kettle, adding water and sodium hydroxide thereto, stirring and mixing evenly; heating to 75-85°C and keeping warm for 2-3h; S6. After the reaction is completed, open the reactor and filter to obtain a secondary filtrate and a secondary filter residue.

2. The method according to claim 1, characterized in that In S2, the alkali activator is calcium oxide or sodium hydroxide.

3. The method according to claim 1, characterized in that In the S2, the mass concentration of the alkali activator is controlled to be 1.5% to 2.5%.

4. The method according to claim 1, characterized in that In S2, the liquid-to-solid ratio in the reactor is 4 to 10:

1.

5. The method according to claim 1, characterized in that In S3, the reaction time is 1 to 2 hours.

6. The method according to claim 1, characterized in that In S4, the composite sulfate includes sodium sulfate and potassium sulfate.

7. The method according to claim 6, characterized in that The mass ratio of sodium sulfate to potassium sulfate is 1:1.9-2.

1.

8. The method according to claim 1, characterized in that In the S4, the mass ratio of the primary filter residue, the composite sulfate and the calcium oxide is 5:2.9 to 3.1:

1.

9. The method according to any one of claims 1 to 8, characterized in that: In the step S4, the calcination temperature is 800°C to 860°C.

10. The method according to any one of claims 1 to 8, characterized in that: The reaction time in S5 is greater than the reaction time in S3.

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