A method for resource utilization of lithium sinking mother liquor

Abstract

The application discloses a method for resource utilization of lithium precipitation mother liquor, and high-quality lithium phosphate products can be obtained by treating the lithium precipitation mother liquor through a phosphate precipitation method; residual lithium in filtrate can be treated through bipolar membrane electrodialysis to enter an alkali solution return system to realize recovery, all Li + in the lithium precipitation mother liquor is recovered in a closed circuit short process, and the economic benefits of enterprises are significantly improved. In the dephosphorization stage, the dephosphorization agent can come from calcium-containing desorption liquid produced in the calcium removal stage or calcium-containing materials produced in the main system, and calcium phosphate products produced at the same time can be sold, so that the comprehensive utilization of Ca 2+ is realized, and the cost of purchasing reagents is reduced. The acid and alkali required by the bipolar membrane electrodialysis production system can solve the problem of salt open circuit.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium extraction from salt lakes, and particularly relates to a method for resource utilization of lithium precipitation mother liquor. BACKGROUND

[0002] With the rapid expansion of the lithium battery industry, the world's demand for lithium is expected to increase year by year. Li2CO3 is the most widely used lithium source in the lithium battery industry in recent years, and it is also the lithium product with the highest proportion in the global lithium industry. It mainly comes from lithium ore and salt lake brine. At present, the lithium extraction from ore mainly adopts the sulfate roasting method. After roasting and leaching of lithium ore, a high-concentration lithium sulfate solution is obtained. This lithium sulfate solution can produce Li2CO3 after lithium precipitation by sodium carbonate. The lithium extraction from salt lake is mainly divided into two categories: solar pond concentration and direct extraction.

[0003] Solar pond concentration refers to the removal of most of the sodium and potassium salts in the brine after solar evaporation concentration, and then obtaining a high-concentration lithium sulfate or lithium chloride solution through a chemical impurity removal process. Finally, Li2CO3 is produced through a sodium carbonate lithium precipitation process. Direct extraction refers to the production of Li2CO3 after the brine is sequentially subjected to pre-extraction, concentration and impurity removal, and sodium carbonate lithium precipitation. The pre-extraction method includes extraction, adsorption and other methods. A large amount of lithium precipitation mother liquor is produced in the lithium precipitation stage, which is divided into sulfate type and chloride type. Due to the solubility of lithium carbonate, the lithium precipitation rate in the lithium precipitation stage is only 70-90%, and the lithium concentration in the lithium precipitation mother liquor is still 1-3 g / L, with high alkalinity and high sodium characteristics. For solar pond concentration of salt lake, the lithium in the lithium precipitation mother liquor can be recovered by returning the lithium precipitation mother liquor to the solar pond concentration stage. However, there are disadvantages such as prolonging the evaporation period and prolonging the lithium recovery period.

[0004] For ore extraction and direct extraction of salt lake, if the lithium precipitation mother liquor is also directly returned to the main system, a large amount of impurities in the lithium precipitation mother liquor will be returned to the system, which may cause problems such as system water swelling, increased impurity removal pressure and decreased Li2CO3 product quality. In addition, since salt lakes and lithium deposits are often located in places such as highlands that are rarely visited and have weak ecological systems, if the lithium precipitation mother liquor is recovered and treated on site, the recovery process used needs to consider water, electricity and environmental protection issues.

[0005] Chinese patent application CN117285050A discloses a method for recovering lithium sink mother liquor, which first uses lithium-sodium resin to preliminarily separate and purify lithium-sodium in lithium sink mother liquor, and then produces lithium chloride solid after the desorption solution is mixed with a certain amount of KCl and sequentially subjected to reduced pressure evaporation crystallization, freeze crystallization and high temperature evaporation crystallization. This method frequently uses evaporation crystallization and freeze crystallization methods, consumes a large amount of potassium chloride, and has high energy consumption. In addition, the lithium-sodium resin may have problems such as excessive acid consumption, poor long-term stability and low lithium adsorption rate. Chinese patent application CN116354358A discloses a preparation method of battery-grade lithium dihydrogen phosphate and boric acid. Carbonate-type raw brine or lithium sink mother liquor is first treated by a titanium-based or manganese-based adsorbent to obtain a desorption solution, the desorption solution is concentrated by forward osmosis, impurities are removed by nanofiltration, and the lithium-rich solution containing 8-20 g / L of lithium is obtained after concentration by electrodialysis. The battery-grade lithium dihydrogen phosphate and boric acid are obtained after boron removal, pH adjustment and MVR evaporation crystallization. In this method, the source of phosphorus is not mentioned, but battery-grade lithium dihydrogen phosphate product is produced. The manganese-based adsorbent is not suitable for lithium sink mother liquor in an alkaline system, and the disclosure does not mention adjusting the pH. In addition, there is a problem of increased calcium and magnesium ion content after electrodialysis, which may cause the calcium and magnesium in the lithium dihydrogen phosphate product to exceed the standard. Chinese patent application CN116924438A discloses a method for recovering lithium from lithium sink mother liquor and battery-grade lithium carbonate. The method uses a composite extractant to treat lithium sink mother liquor produced from a sulfate system, and then produces lithium carbonate after back extraction and lithium sink with sodium carbonate. In this method, the back-extracted solution is not washed and deoiled, which may cause the TOC of lithium carbonate to exceed the standard, and due to environmental protection problems, the extraction method is difficult to implement in places with fragile ecology. Chinese patent application CN116425133A discloses a method for preparing high-purity lithium phosphate from lithium sink mother liquor. The lithium sink mother liquor is first treated by a chemical method to remove calcium and magnesium, and then sent to a bipolar electrodialysis device to obtain a lithium hydroxide solution. The lithium phosphate is prepared by mixing the lithium hydroxide solution with phosphoric acid and sodium hydroxide solution, and finally washed and dried to obtain high-purity lithium phosphate. This method does not mention the destination of the acid produced by the bipolar membrane electrodialysis, and uses expensive phosphoric acid as a lithium sink agent, which consumes a large amount of sodium hydroxide and has high cost.

[0006] In summary, the recovery of lithium sink mother liquor has always been a concern for industry personnel, but the main focus is on the recovery of lithium, and systematic consideration is not given. In addition to lithium-sodium, the content of other impurities in lithium sink mother liquor is very low, so it is also a high-quality sodium resource. Therefore, it is urgent to develop an efficient and low-cost lithium-sodium resource comprehensive utilization technology for lithium sink mother liquor. SUMMARY

[0007] In view of the deficiencies of the prior art, the present application aims to provide a method for resource utilization of lithium sink mother liquor.

[0008] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0009] A method for resource utilization of lithium precipitation mother liquor, comprising the following steps:

[0010] S1, lithium precipitation: adding phosphate mixture to the lithium precipitation mother liquor for reaction, and then performing solid-liquid separation to obtain crude lithium phosphate solid and filtrate;

[0011] S2, acidification: adding acid to the filtrate obtained in step S1 for acidification to remove carbonate in the filtrate, to obtain decarbonated brine, and absorbing CO2 gas released by alkali liquor to obtain mixed alkali solution;

[0012] S3, dephosphorization: adding calcium and / or magnesium-containing material to the decarbonated brine obtained in step S2, and then adding alkali liquor to increase the pH, and then filtering to obtain crude calcium phosphate and / or magnesium phosphate solid and dephosphorized brine;

[0013] S4, calcium and magnesium removal: sending the dephosphorized brine obtained in step S3 to a calcium and magnesium removal resin to remove residual calcium and / or magnesium ions, and then desorbing the loaded resin to finally obtain calcium and / or magnesium removed brine and calcium and / or magnesium containing desorption liquor, which is returned to step S3 as calcium and / or magnesium containing material for dephosphorization;

[0014] S5, acid and alkali preparation: treating the calcium and / or magnesium removed brine obtained in step S4 by bipolar membrane electrodialysis to obtain acid and alkali liquor; at least part of the acid is returned to step S2 for acidification and / or returned to step S4 for resin desorption, and at least part of the alkali liquor is returned to step S2 for CO2 gas absorption and / or returned to step S3 for pH increase.

[0015] Further, in step S1, the lithium precipitation mother liquor is the residual solution after lithium carbonate precipitation, including chloride system and sulfate system, and the lithium concentration is 1-3 g / L.

[0016] Further, in step S1, the reaction temperature is 60-95℃, and the reaction time is 0.5-4h.

[0017] Further, in step S1, the phosphate includes one or more of sodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate, and the amount of addition is 0.5-1.5 times the theoretical mass of the required phosphate. + Further, in step S1, the phosphate includes one or more of sodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate, and the amount of addition is 0.5-1.5 times the theoretical mass of the required phosphate.

[0018] Further, in step S2, the pH of the filtrate is adjusted to 3.0-4.5 by adding acid; and the mixed alkali solution is returned to a double alkali process for calcium and magnesium removal as double alkali and / or returned to a resin calcium and magnesium removal process as a post-transformation agent after resin regeneration.

[0019] Further, in step S3, the total mass of calcium and / or magnesium in the calcium-containing material and / or magnesium-containing material is 1-1.2 times the theoretical mass of calcium and / or magnesium required for removing all phosphorus in the decarburization brine; when the phosphorus concentration in the decarburization brine produced in step S2 is less than 2 mg / L, steps S3-S4 are not performed.

[0020] Further, in step S3, after the decarburization brine is added to the calcium-containing material and / or magnesium-containing material, the pH is raised to 10.5-12.0 by adding an alkali solution.

[0021] Further, the crude lithium phosphate solid obtained in step S1 and the crude calcium phosphate and / or magnesium phosphate solid obtained in step S3 are washed, filtered and dried, respectively, to obtain qualified lithium phosphate product and calcium phosphate and / or magnesium phosphate product, wherein the lithium phosphate product is used as a raw material product for preparing high-purity lithium phosphate, battery-grade lithium carbonate and / or battery-grade lithium hydroxide monohydrate; and the calcium phosphate and / or magnesium phosphate product is used as a fertilizer or a raw material product for preparing food-grade calcium phosphate and / or magnesium phosphate.

[0022] Further, in step S4, the decalcified and demagnified brine is treated by using one or a combination of a fixed bed system and a continuous ion exchange system to remove calcium and / or magnesium.

[0023] Further, in step S5, the H + concentration of the acid obtained by the bipolar membrane electrodialysis is 1.0-2.2 mol / L, and the OH - concentration of the alkali solution is 1.0-2.2 mol / L.

[0024] The present application has the following advantages:

[0025] (1) The present application can obtain high-quality lithium phosphate product by treating the lithium precipitation mother liquor by the phosphate precipitation method, and the residual lithium in the filtrate can be recovered by the bipolar membrane electrodialysis treatment into the alkali solution return system, realizing the closed-circuit short-flow high-efficiency recovery of all Li + in the lithium precipitation mother liquor, and significantly improving the economic benefits of the enterprise.

[0026] (2) In the present application, the calcium-containing and / or magnesium-containing material used in the phosphorus removal stage can come from the calcium-containing and / or magnesium-containing desorption liquid produced in the calcium and / or magnesium removal stage or the calcium-containing and / or magnesium-containing material produced in the production main system. For salt lake enterprises producing lithium carbonate or lithium hydroxide monohydrate by the precipitation method, the production main process generally includes the stages of solar evaporation, membrane treatment and lithium precipitation. The calcium-containing and / or magnesium-containing material such as calcium chloride hexahydrate produced in the solar evaporation stage (for high-calcium salt lakes) and the dialysis nanofiltration calcium-containing and / or magnesium-containing concentrated water produced in the nanofiltration membrane calcium and / or magnesium removal stage can be used as the phosphorus removal agent of the present application, and the simultaneously produced calcium phosphate and / or magnesium phosphate product can be sold externally, realizing the comprehensive utilization of Ca 2+ and Mg 2+ and reducing the cost of purchasing reagents.

[0027] (3) The application can solve the problem of salt open circuit by using the acid and base required by the bipolar membrane electrodialysis production system. The acid can be returned to the acidification stage and the calcium and magnesium removal stage, the alkali solution can be returned to the dephosphorization stage as a pH adjuster, and can also be returned to the acidification stage as a CO2 receiving liquid. It can also be further returned to the main production system, wherein the acid can be returned to the adsorption stage or the extraction stage of the main system for use as a desorption liquid or a stripping liquid, and can also be returned to other processes as a pH adjuster; the alkali solution can be returned to the double-alkali method calcium and magnesium removal process or the resin calcium and boron removal stage of the main system, and can also be returned to other processes as a pH adjuster. Therefore, the application not only realizes efficient short-process recovery of lithium in the lithium precipitation mother liquor, but also reduces the cost of purchasing acid and alkali and the emission of CO2, and has high matching with the main production system. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The overall flowchart of the method described in Embodiment 1-3 of the application;

[0029] Figure 2 The overall flowchart of the method described in Embodiment 4 of the application. DETAILED DESCRIPTION

[0030] The application will be further described below with reference to the accompanying drawings. It should be noted that the embodiments are based on the technical solutions, and detailed implementation methods and specific operation processes are given, but the protection scope of the application is not limited to the embodiments.

[0031] Embodiment 1

[0032] The laboratory-prepared sulfate-type lithium precipitation mother liquor is used as the raw material, and the main chemical composition is: Li 1.6 g / L, Na 73.1 g / L, K 7.1 g / L, CO3 2- 17.4 g / L. In this embodiment, the lithium precipitation mother liquor is resourcefully utilized, as shown in the following steps: Figure 1

[0033] (1) Lithium precipitation: the lithium precipitation mother liquor is heated to 95℃ and stirred, and then sodium dihydrogen phosphate is added to precipitate all Li + in the lithium precipitation mother liquor. After 2h of reaction, solid-liquid separation is performed to obtain crude lithium phosphate solid and phosphorus-containing filtrate, and the lithium recovery rate is 92.2%. The crude lithium phosphate is washed, filtered and dried to obtain lithium phosphate product meeting the Li2PO4-3 level in the YS / T 637-2022 standard;

[0034] (2) Acidification: sulfuric acid is added to the phosphorus-containing filtrate obtained in step (1) to acidify and reduce the pH to 4.1, thereby removing CO3 2- ​, obtaining a decarbonized sulfate solution in which the phosphorus concentration is 0.16 g / L, and simultaneously using a sodium hydroxide solution to absorb the discharged CO2 gas to obtain a mixed alkali solution (a mixed solution of sodium hydroxide and sodium carbonate);

[0035] (3) Dephosphorization: adding a calcium-containing desorption liquid to the decarbonized sulfate solution obtained in step (2), wherein the calcium content in the calcium-containing desorption liquid is 1 times the theoretical mass of calcium required to remove all phosphorus in the decarbonized sulfate solution, and then adding a sodium hydroxide solution to raise the pH to 11.0. After filtering, a crude calcium phosphate solid and a dephosphorized sulfate solution are obtained, wherein the phosphorus precipitation rate is 99.1%. The crude calcium phosphate solid is washed, filtered, and dried to obtain a calcium phosphate product with a purity of 98.6%;

[0036] (4) IX decalcification: The dephosphorized sulfate solution obtained in step (3) is fed into the decalcification resin process to remove the residual Ca 2+ , then desorb, finally get calcium-removing sulfate solution and calcium-containing desorption solution, calcium in the calcium-removing sulfate solution 2+ Mg 2+ The concentration is less than 0.05 mg / L, which has reached the feed requirement of bipolar membrane electrodialysis equipment (Ca 2+ Mg 2+ <0.5 mg / L);

[0037] (5) Acid and base preparation: The decalcified sulfate solution obtained in step (4) is treated by bipolar membrane electrodialysis to obtain sulfuric acid and sodium hydroxide solution. + Concentration and sodium hydroxide solution OH - The concentrations are 2.02 mol / L and 1.95 mol / L, respectively. The sulfuric acid solution is returned to step (2) for acidification and step (4) for resin desorption, and the sodium hydroxide solution is returned to step (2) and step (3) for use as a CO2 receiving solution and a pH adjuster, respectively.

[0038] Example 2

[0039] The raw material is the chloride-type lithium precipitation mother solution prepared in the laboratory. Its main chemical composition is: Li 1.0g / L, Na 105.5g / L, K 6.3g / L, CO3 2- 20.7g / L. This embodiment makes resource utilization of the lithium precipitation mother liquor, such as Figure 1 As shown, the following steps are included:

[0040] (1) Lithium precipitation: Heat the lithium precipitation mother liquor to 95 ° C and stir, then add the amount of lithium precipitated in the lithium precipitation mother liquor to precipitate all the lithium +Sodium phosphate 1.2 times the theoretical mass required was reacted for 2 hours and then solid-liquid separation was performed to obtain crude lithium phosphate solid and phosphorus-containing filtrate with a lithium recovery rate of 95.2%. The crude lithium phosphate was washed, filtered and dried to obtain a lithium phosphate product that met the Li2PO4-3 grade in the "YS / T 637-2022" standard;

[0041] (2) Acidification: Add hydrochloric acid to the phosphorus-containing filtrate obtained in step (1) to acidify it to reduce its pH to 3.9 and remove CO3 in the filtrate. 2- , obtaining a decarbonized chloride salt solution, wherein the phosphorus concentration is 0.31 g / L, and simultaneously using a sodium hydroxide solution to absorb the discharged CO2 gas to obtain a mixed alkali solution (a mixed solution of sodium hydroxide and sodium carbonate);

[0042] (3) Dephosphorization: adding a calcium-containing desorption liquid and calcium chloride hexahydrate to the decarbonized chloride salt solution obtained in step (2), wherein the total amount of calcium contained in the calcium-containing desorption liquid and the calcium chloride hexahydrate is 1.1 times the theoretical mass of calcium required to remove all phosphorus in the decarbonized chloride salt solution, and then adding a sodium hydroxide solution to raise the pH to 10.5. After filtering, a crude calcium phosphate solid and a dephosphorized chloride salt solution are obtained, and the phosphorus precipitation rate is 99.1%. The crude calcium phosphate is washed, filtered, and dried to obtain a calcium phosphate product with a purity of 98.71%;

[0043] (4) IX decalcification: The dephosphorized chloride solution obtained in step (3) is fed into the decalcification resin process to remove the residual Ca 2+ , and then desorb, finally get calcium-removing chloride salt solution and calcium-containing desorption solution, calcium in the calcium-removing chloride salt solution 2+ Mg 2 + The concentration is less than 0.05 mg / L, which has reached the feed requirement of bipolar membrane electrodialysis equipment (Ca 2+ Mg 2+ <0.5 mg / L);

[0044] (5) Acid and base preparation: The calcium-removed chloride solution obtained in step (4) is treated by bipolar membrane electrodialysis to obtain hydrochloric acid and sodium hydroxide solution. + Concentration and sodium hydroxide solution OH - The concentrations are 1.05 mol / L and 1.08 mol / L, respectively. The hydrochloric acid is returned to step (2) for acidification and to step (4) for resin desorption, and the sodium hydroxide solution is returned to step (2) and step (3) for use as a CO2 receiving solution and a pH adjuster, respectively.

[0045] Example 3

[0046] The main chemical components of the laboratory-prepared chlorinated salt type lithium precipitation mother liquor are: Li 1.3 g / L, Na 92.7 g / L, K 8.3 g / L, CO3 2- 17.0 g / L. In this embodiment, the lithium precipitation mother liquor is resourcefully utilized, as shown in the following steps: Figure 1

[0047] (1) Lithium precipitation: the lithium precipitation mother liquor is heated to 60°C and stirred, and then sodium bicarbonate in an amount of 1.5 times the theoretical mass of all Li + required phosphates is added, and after 0.5 h of reaction, solid-liquid separation is performed to obtain crude lithium phosphate solid and phosphorus-containing filtrate, with a lithium recovery rate of 93.17%, and the crude lithium phosphate is washed, filtered and dried to obtain lithium phosphate products meeting the Li2PO4-3 level in the YS / T637-2022 standard;

[0048] (2) Acidification: hydrochloric acid is added to the phosphorus-containing filtrate obtained in step (1) to acidify it to a pH of 4.5, and CO3 2- in the filtrate is removed to obtain a decarburized chlorinated salt solution with a phosphorus concentration of 0.88 g / L, and a mixed alkali solution (a mixture of sodium hydroxide and sodium carbonate) is obtained by absorbing the discharged CO2 gas with a sodium hydroxide solution;

[0049] (3) Dephosphorization: calcium-containing desorption solution and calcium-containing dialysis nanofiltration concentrated water are added to the decarburized chlorinated salt solution obtained in step (2), the total amount of calcium in the calcium-containing desorption solution and the calcium-containing dialysis nanofiltration concentrated water is 1.2 times the theoretical mass of calcium required to remove all phosphorus in the decarburized salt water, and then sodium hydroxide solution is added to raise the pH to 12.0, and after filtration, crude calcium phosphate solid and dephosphorized chlorinated salt solution are obtained, with a phosphorus precipitation rate of 99.67%, and the crude calcium phosphate is washed, filtered and dried to obtain a calcium phosphate product with a purity of 98.6%;

[0050] (4) IX calcium removal: the dephosphorized chlorinated salt solution obtained in step (3) is sent to a calcium removal resin process to remove residual Ca 2+ in it to obtain a calcium-removed chlorinated salt solution and calcium-containing desorption solution, and the concentrations of Ca 2+ and Mg 2+ in the calcium-removed chlorinated salt solution are both <0.05 mg / L, which has reached the feed requirements of the bipolar membrane electrodialysis equipment (Ca 2+ and Mg 2+ <0.5 mg / L);

[0051] (5) Acid-alkali preparation: the calcium-removed chlorinated salt solution obtained in step (4) is treated by bipolar membrane electrodialysis to obtain hydrochloric acid and sodium hydroxide solution, and the concentrations of H + in the hydrochloric acid and OH - ​1.94 mol / L and 1.99 mol / L, respectively. The hydrochloric acid is returned to step (2) for acidification, and the sodium hydroxide solution is returned to step (2) and step (3) for CO2 receiving liquid and pH adjuster, respectively.

[0052] Example 4

[0053] The sulfate type lithium precipitation mother liquor prepared in the laboratory is used as the raw material, and the main chemical composition thereof is: Li 2.8 g / L, Na 76.3 g / L, K 6.7 g / L, CO3 2- 18.4 g / L. In this embodiment, the lithium precipitation mother liquor is resourcefully utilized, as shown in the following steps: Figure 2

[0054] (1) Lithium precipitation: the lithium precipitation mother liquor is heated to 60°C and stirred, and then sodium phosphate with a dosage of 0.8 times the theoretical mass of the required phosphate is added. After 4 h of reaction, solid-liquid separation is performed to obtain crude lithium phosphate solid and filtrate, and the lithium recovery rate is 78.1%. The phosphorus concentration in the filtrate is <2 mg / L, and no dephosphorization and calcium removal treatment is required. The crude lithium phosphate is washed, filtered and dried to obtain lithium phosphate products meeting the Li2PO4-3 level in the standard YS / T 637-2022; +

[0055] (2) Acidification: sulfuric acid is added to the filtrate obtained in step (1) to acidify the filtrate to a pH of 3.0, so as to remove CO3 2- in the filtrate, to obtain a decarburized sulfate solution with a phosphorus concentration of 83 mg / L. Meanwhile, the discharged CO2 gas is absorbed by a sodium hydroxide solution to obtain a mixed alkali solution (a mixed solution of sodium hydroxide and sodium carbonate);

[0056] (3) Acid-alkali preparation: the decarburized sulfate solution obtained in step (2) is treated by bipolar membrane electrodialysis to obtain sulfuric acid and a sodium hydroxide solution. The H + concentration of the sulfuric acid and the OH - concentration of the sodium hydroxide solution are 2.08 mol / L and 2.10 mol / L, respectively. The sulfuric acid is returned to step (2) for acidification, and the sodium hydroxide solution is returned to step (2) for CO2 receiving liquid.

[0057] The chemical compositions of the lithium phosphate products produced in Examples 1-4 are shown in Table 1.

[0058] Table 1

[0059]

[0060]

[0061] ​​As shown in Table 1, the purity of the lithium phosphate product produced by Examples 1-4 is more than 95%, and the highest can reach 97.4%, and the contents of the remaining impurity elements such as Cl and Na meet the standard requirements of YS / T 637-2022.

[0062] For those skilled in the art, various corresponding changes and modifications can be made to the above technical solutions and concepts, and all these changes and modifications should be included in the protection scope of the claims of the present application.

Claims

1. A method for resource utilization of a lithium precipitation mother liquor, characterized in that, The method comprises the following steps: S1, lithium precipitation: adding phosphate mixture into the lithium precipitation mother liquor for reaction, and then performing solid-liquid separation to obtain crude lithium phosphate solid and filtrate; S2, acidification: adding acid into the filtrate obtained in step S1 for acidification to remove carbonate in the filtrate, to obtain decarbonated brine, and absorbing the released CO2 gas with lye to obtain mixed alkali solution; S3, dephosphorization: adding calcium and / or magnesium-containing material into the decarbonated brine obtained in step S2, and then adding lye to adjust the pH to 10.5-12.0, and then filtering to obtain crude calcium phosphate and / or magnesium phosphate solid and dephosphorized brine; S4, calcium and magnesium removal: sending the dephosphorized brine obtained in step S3 into a calcium and magnesium removal resin to remove residual calcium and / or magnesium ions, and then desorbing the loaded resin to finally obtain calcium and / or magnesium removed brine and calcium and / or magnesium containing desorption liquid, which is returned to step S3 as calcium and / or magnesium containing material for dephosphorization; S5, acid and alkali preparation: treating the calcium and / or magnesium removed brine obtained in step S4 by bipolar membrane electrodialysis to obtain acid and lye; at least part of the acid is returned to step S2 for acidification and / or returned to step S4 for resin desorption, and at least part of the lye is returned to step S2 for CO2 gas absorption and / or returned to step S3 for pH adjustment.

2. The method for recycling lithium sink solution according to claim 1, characterized in that, In step S1, the lithium precipitation mother liquor is the residual solution after lithium carbonate precipitation, including chloride system and sulfate system, and the lithium concentration is 1-3 g / L.

3. The method for recycling lithium sink solution according to claim 1, characterized in that, In step S1, the reaction temperature is 60-95℃, and the reaction time is 0.5-4 h.

4. The method for recycling lithium sink solution according to claim 1, characterized in that, In step S1, the phosphate includes one or more of sodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, and the amount of addition is 0.5-1.5 times the theoretical mass of the required phosphate + 0.5-1.5 times the theoretical mass of the required phosphate.

5. The method for recycling lithium sink solution according to claim 1, characterized in that, In step S2, the filtrate is added with acid to adjust the pH to 3.0-4.5; and the mixed alkali solution is returned to a double alkali process for calcium and magnesium removal as double alkali and / or returned to a resin calcium and magnesium removal process as resin regeneration post-transformation agent.

6. The method for recycling lithium sink liquor resources according to claim 1, characterized in that, In step S3, the total mass of calcium and / or magnesium in the calcium and / or magnesium containing material is 1-1.2 times the theoretical mass of calcium and / or magnesium required for removing all phosphorus in the decarbonated brine.

7. The method for recycling lithium sink liquor resources according to claim 1, characterized in that, The crude lithium phosphate solid obtained in step S1 and the crude calcium phosphate and / or magnesium phosphate solid obtained in step S3 are washed, filtered and dried respectively to obtain qualified lithium phosphate product and calcium phosphate and / or magnesium phosphate product, wherein the lithium phosphate product is used as raw material product for preparing high-purity lithium phosphate, battery-grade lithium carbonate and / or battery-grade lithium hydroxide monohydrate; and the calcium phosphate and / or magnesium phosphate product is used as fertilizer or raw material product for preparing food-grade calcium phosphate and / or magnesium phosphate.

8. The method for recycling lithium sink liquor resources according to claim 1, characterized in that, In step S4, one or a combination of fixed bed system and continuous ion exchange system is used to remove calcium and / or magnesium from the dephosphorized brine by calcium and magnesium removal resin.

9. The method for recycling lithium sink liquor resources according to claim 1, characterized in that, H of the acid obtained by bipolar membrane electrodialysis in step S5 + OH of the alkali solution has a concentration of 1.0-2.2 mol / L - OH of the alkali solution has a concentration of 1.0-2.2 mol / L.

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