Method for resource utilization of lithium precipitation mother liquor

Abstract

The invention discloses a method for recycling lithium precipitation mother liquor, which is characterized in that the lithium precipitation mother liquor is treated by a phosphate precipitation method to obtain a high-quality lithium phosphate product, and residual lithium in filtrate can be treated by bipolar membrane electrodialysis and enters an alkali liquor return system to realize recovery, so that closed-circuit short-process efficient recovery of all Li < + > in the lithium precipitation mother liquor is realized; and the economic benefits of enterprises are obviously improved. A dephosphorizing agent in the dephosphorizing stage can come from a calcium-containing desorption solution produced in the calcium removal stage or a calcium-containing material produced by a production main system, and meanwhile, the produced calcium phosphate product can be sold, so that the comprehensive utilization of Ca < 2 + > is realized, and the outsourcing cost of medicaments is reduced. The problem of salt open circuit can be solved by adopting acid and alkali required by a bipolar membrane electrodialysis production system.

Description

Technical Field

[0001] The invention relates to the technical field of lithium extraction applications in salt lakes, and in particular to a method for resource utilization of lithium precipitation mother liquor. Background Art

[0002] With the rapid expansion of the lithium battery industry, the global 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. 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, lithium ore is mostly extracted by sulfate roasting. After roasting and leaching, lithium ore is obtained to obtain a high-concentration lithium sulfate solution. This lithium sulfate solution can produce Li2CO3 after lithium precipitation with sodium carbonate. Lithium extraction from salt lakes is mostly "one lake, one policy", which is mainly divided into two categories: solar pond concentrated lithium extraction and direct lithium extraction.

[0003] Solar pond concentration and lithium extraction refers to the process of removing most of the sodium and potassium salts from brine by sun exposure, followed by chemical impurity removal to obtain a high-concentration lithium sulfate or lithium chloride solution, and finally producing Li2CO3 by sodium carbonate lithium precipitation. Direct lithium extraction refers to the process of producing Li2CO3 by pre-extraction of lithium, concentration and impurity removal, and sodium carbonate lithium precipitation. The pre-extraction methods include extraction and adsorption. A large amount of lithium precipitation mother liquor will be 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 generally only 70-90%, and the lithium concentration in the lithium precipitation mother liquor is still 1-3g / L, and it also has the characteristics of high alkalinity and high sodium. As for the concentration and lithium extraction in the salt lake solar pond, the lithium in the mother liquor can be recovered by returning the lithium precipitation mother liquor to the solar pond concentration stage. However, there are shortcomings such as extended exposure cycle and long lithium recovery cycle.

[0004] As for lithium extraction from ores and direct lithium extraction from salt lakes, if the mother liquor of lithium precipitation is directly returned to the main system, a large amount of impurities in the mother liquor of lithium precipitation will be returned to the system, which may cause system water expansion, increased impurity removal pressure and reduced quality of Li2CO3 products. In addition, since salt lakes and lithium deposits often exist in places such as plateaus where few people travel and where the ecosystem is weak, if the mother liquor of lithium precipitation is recycled on site, the recycling process used needs to consider issues such as water, electricity and environmental protection.

[0005] Chinese patent application CN117285050A discloses a method for recovering lithium precipitation mother liquor. The method first uses lithium sodium resin to preliminarily separate and purify lithium and sodium in lithium precipitation mother liquor. After a certain amount of KCl is added to the desorption liquid, lithium chloride solid is produced after vacuum evaporation crystallization, freezing crystallization and high-temperature evaporation crystallization. This method frequently uses evaporation crystallization and freezing crystallization, and consumes a large amount of potassium chloride, resulting in 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 method for preparing battery-grade lithium dihydrogen phosphate and boric acid. The carbonate-type raw brine or lithium precipitation mother liquor is first treated with a titanium-based or manganese-based adsorbent to obtain a desorption liquid. The desorption liquid is concentrated by forward osmosis, nanofiltration to remove impurities, and electrodialysis to obtain a lithium-rich solution containing 8-20g / L lithium. The solution is then subjected to boron removal, pH adjustment, and MVR evaporation and crystallization treatment to obtain battery-grade lithium dihydrogen phosphate and boric acid. In this method, the source of phosphorus is not mentioned, but a battery-grade lithium dihydrogen phosphate product is produced; manganese-based adsorbents are not suitable for lithium precipitation mother liquors in alkaline systems, and the pH adjustment is not publicly mentioned; in addition, there is a problem of increased calcium and magnesium ion content after electrodialysis treatment, which may lead to excessive calcium and magnesium in subsequent lithium dihydrogen phosphate products. Chinese patent application CN116924438A discloses a method for recovering lithium from lithium precipitation mother liquor and battery-grade lithium carbonate. The method uses a composite extractant to treat the lithium precipitation mother liquor produced by the sulfate system, and then produces lithium carbonate after stripping and sodium carbonate precipitation. In this method, the stripping solution is not washed and de-oiled, and there may be a problem of excessive TOC of lithium carbonate. Due to environmental protection issues, the extraction method is difficult to implement in places where the plateau ecology is fragile. Chinese patent application CN116425133A discloses a method for preparing high-purity lithium phosphate from lithium precipitation mother liquor. The lithium precipitation mother liquor is first treated by chemical method to remove calcium and magnesium, and then sent to bipolar electrodialysis to obtain lithium hydroxide solution, and then mixed with phosphoric acid and sodium hydroxide solution to obtain lithium phosphate, and finally washed and dried to obtain high-purity lithium phosphate. This method does not mention the problem of the destination of the acid produced by bipolar membrane electrodialysis, and uses expensive phosphoric acid as a lithium precipitation agent, and consumes a large amount of sodium hydroxide, which is costly.

[0006] In summary, the recovery of lithium precipitation mother liquor has always attracted much attention from industry insiders, but the main focus has been on the recovery of lithium without systematic consideration. In addition to lithium and sodium, the content of other impurities in lithium precipitation mother liquor is extremely low, so it is also a high-quality sodium resource. Therefore, it is urgent to develop an efficient and low-cost lithium and sodium resource comprehensive utilization technology for lithium precipitation mother liquor. Summary of the invention

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

[0008] In order to achieve the above object, the present invention adopts the following technical solution:

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

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

[0011] S2, acidification: adding acid to the filtrate obtained in step S1 for acidification, removing carbonate in the filtrate to obtain decarbonated brine, and using alkali solution to absorb the released CO2 gas to obtain a mixed alkali solution;

[0012] S3, dephosphorization: adding calcium and / or magnesium-containing materials to the decarbonized brine obtained in step S2, then adding alkali solution to adjust the pH value upward, and filtering to obtain crude calcium phosphate and / or magnesium phosphate solids and dephosphorized brine;

[0013] S4, calcium and magnesium removal: the dephosphorized brine obtained in step S3 is fed into a calcium and magnesium removal resin to remove residual calcium and / or magnesium ions therein, and then the loaded resin is desorbed to finally obtain a calcium and / or magnesium removal brine and a calcium and / or magnesium-containing desorption liquid, and the calcium and / or magnesium-containing desorption liquid is returned to step S3 as a calcium and / or magnesium-containing material for dephosphorization;

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

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

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

[0017] Furthermore, in step S1, the phosphate includes one or more of sodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate, and the amount of the phosphate added is 1:1 to 1:1. + 0.5-1.5 times the theoretical mass of phosphate required.

[0018] Furthermore, in step S2, acid is added to the filtrate to adjust the pH to 3.0-4.5; the mixed alkali solution is returned to the double alkali calcium and magnesium removal process for use as a double alkali and / or returned to the resin calcium and magnesium removal process for use as a transformation agent after resin regeneration.

[0019] Furthermore, 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 to remove all phosphorus in the decarbonated brine; when the phosphorus concentration in the decarbonated brine produced in step S2 is <2 mg / L, steps S3-S4 are not performed.

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

[0021] Furthermore, 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 to obtain qualified lithium phosphate products and calcium phosphate and / or magnesium phosphate products, 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; 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] Furthermore, in step S4, one or a combination of a fixed bed system and a continuous ion exchange system is used to remove calcium and / or magnesium from the dephosphorized brine using a calcium and magnesium removal resin.

[0023] Further, in step S5, the H + The concentration is 1.0-2.2 mol / L, the OH of the alkali solution - The concentration is 1.0-2.2mol / L.

[0024] The beneficial effects of the present invention are:

[0025] (1) The method of the present invention treats the lithium phosphate mother liquor by phosphate precipitation to obtain a high-quality lithium phosphate product. The residual lithium in the filtrate can be treated by bipolar membrane electrodialysis and enter the alkaline solution return system for recovery, thereby achieving the goal of recovering all the Li in the lithium phosphate mother liquor. + The closed-circuit short-process efficient recycling significantly improves the economic benefits of the enterprise.

[0026] (2) In the method of the present invention, the calcium and / or magnesium-containing materials used in the dephosphorization stage can come from the calcium and / or magnesium-containing desorption liquid output from the calcium and / or magnesium removal stage or the calcium and / or magnesium-containing materials output from the main production system. For salt lake enterprises that produce lithium carbonate or lithium hydroxide monohydrate by precipitation method, the main production process generally includes brine drying, membrane treatment and lithium precipitation steps. The calcium chloride hexahydrate output from the brine drying stage (for high-calcium salt lakes) and the dialysis nanofiltration calcium and magnesium-containing concentrated water output from the nanofiltration membrane calcium and magnesium removal stage can all be used as the dephosphorization agent of the present invention. At the same time, the calcium phosphate and / or magnesium phosphate products produced can be sold externally, realizing the Ca 2+ Mg 2+ Comprehensive utilization and reduction of external purchasing costs of medicines.

[0027] (3) The present invention uses the acid and alkali required by the bipolar membrane electrodialysis production system to solve the problem of salt open circuit. The acid can be returned to the acidification stage and the calcium and magnesium removal stage for use, and 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 for use, wherein the acid can be returned to the adsorption section or extraction section of the main system for use as a desorption liquid or stripping liquid, and can also be returned to other processes as a pH adjuster; the alkali solution can be returned to the main system for use in the double-alkali method for calcium and magnesium removal or the resin calcium and boron removal stage, and can also be returned to other processes as a pH adjuster. Therefore, in addition to realizing the efficient and short-process recovery of lithium in the lithium precipitation mother liquor, the present invention can also reduce the cost of purchasing acids and alkalis and the emission of CO2, and has a high compatibility with the main production system. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is an overall flow chart of the method described in Examples 1-3 of the present invention;

[0029] Figure 2 This is an overall flow chart of the method described in Example 4 of the present invention. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with the accompanying drawings. It should be noted that this embodiment is based on the technical solution and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to this embodiment.

[0031] Example 1

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

[0033] (1) Lithium precipitation: Heat the lithium precipitation mother liquor to 95°C and stir, then add all the Li + Sodium dihydrogen phosphate of 1 times the theoretical mass of the required phosphate is reacted for 2 hours and then solid-liquid separation is performed to obtain crude lithium phosphate solid and phosphorus-containing filtrate, with a lithium recovery rate of 92.2%. The crude lithium phosphate is washed, filtered and dried to obtain a lithium phosphate product that meets the Li2PO4-3 grade in the "YS / T 637-2022" standard;

[0034] (2) Acidification: Add sulfuric acid to the phosphorus-containing filtrate obtained in step (1) to acidify it, reduce its pH to 4.1, and remove CO3 in the filtrate. 2-, a decarbonized sulfate solution is obtained, wherein the phosphorus concentration is 0.16 g / L, and a sodium hydroxide solution is used 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, filtering to obtain a crude calcium phosphate solid and a dephosphorized sulfate solution, wherein the phosphorus precipitation rate is 99.1%, and washing, filtering, and drying the crude calcium phosphate solid to obtain a calcium phosphate product with a purity of 98.6%;

[0036] (4) IX Calcium Removal: The dephosphorized sulfate solution obtained in step (3) is fed into a calcium removal resin process to remove the residual Ca 2+ , and then desorb, finally obtaining calcium-removing sulfate solution and calcium-containing desorption solution. The calcium-removing sulfate solution contains Ca 2+ Mg 2+ The concentration is <0.05mg / L, which has reached the feed requirement of bipolar membrane electrodialysis equipment (Ca 2+ Mg 2+ <0.5mg / 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 the acidification of step (2) and the resin desorption of step (4), and the sodium hydroxide solution is returned to step (2) and step (3) for use as CO2 receiving liquid and pH adjusting agent 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 10 5.5g / L, K 6.3g / L, CO3 2- 20.7g / L. In this embodiment, the lithium precipitation mother liquor is recycled, 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 an amount of lithium precipitate to precipitate all the lithium in the lithium precipitation mother liquor. +Sodium phosphate of 1.2 times the theoretical mass required is reacted for 2 hours and then solid-liquid separation is performed to obtain crude lithium phosphate solid and phosphorus-containing filtrate, with a lithium recovery rate of 95.2%. The crude lithium phosphate is washed, filtered and dried to obtain a lithium phosphate product that meets 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 so that its pH drops to 3.9 and remove CO3 in the filtrate. 2- , a decarbonized chloride salt solution is obtained, wherein the phosphorus concentration is 0.31 g / L, and a sodium hydroxide solution is used 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, filtering to obtain a crude calcium phosphate solid and a dephosphorized chloride salt solution, wherein the phosphorus precipitation rate is 99.1%, and washing, filtering and drying the crude calcium phosphate to obtain a calcium phosphate product with a purity of 98.71%;

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

[0044] (5) Acid and base preparation: The decalcified 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 the acidification of step (2) and the resin desorption of step (4), and the sodium hydroxide solution is returned to step (2) and step (3) for use as CO2 receiving liquid and pH adjusting agent respectively.

[0045] Example 3

[0046] The raw material is the chloride-type lithium precipitation mother solution prepared in the laboratory. Its main chemical composition is: Li 1.3g / L, Na 92.7g / L, K 8.3g / L, CO3 2- 17.0g / L. In this embodiment, the lithium precipitation mother liquor is recycled, such as Figure 1 As shown, the following steps are included:

[0047] (1) Lithium precipitation: Heat the lithium precipitation mother liquor to 60°C and stir, then add an amount of lithium precipitate to precipitate all the lithium in the lithium precipitation mother liquor. + Disodium hydrogen phosphate with a theoretical mass of 1.5 times the required phosphate is reacted for 0.5 h and then solid-liquid separation is performed to obtain a crude lithium phosphate solid and a phosphorus-containing filtrate, with a lithium recovery rate of 93.17%. The crude lithium phosphate is washed, filtered and dried to obtain a lithium phosphate product that meets the Li2PO4-3 grade in the "YS / T637-2022" standard;

[0048] (2) Acidification: Add hydrochloric acid to the phosphorus-containing filtrate obtained in step (1) to acidify it so that its pH drops to 4.5 and remove CO3 in the filtrate. 2- , a decarbonized chloride salt solution is obtained, wherein the phosphorus concentration is 0.88 g / L, and a sodium hydroxide solution is used to absorb the discharged CO2 gas to obtain a mixed alkali solution (a mixed solution of sodium hydroxide and sodium carbonate);

[0049] (3) Dephosphorization: adding a calcium-containing desorption solution and a calcium-containing dialysis nanofiltration concentrated water to the decarbonized chloride salt solution obtained in step (2), wherein the total amount of calcium contained in the calcium-containing desorption solution and the dialysis nanofiltration concentrated water is 1.2 times the theoretical mass of calcium required to remove all phosphorus in the decarbonized brine, and then adding a sodium hydroxide solution to raise the pH to 12.0, filtering to obtain a crude calcium phosphate solid and a dephosphorized chloride salt solution, wherein the phosphorus precipitation rate is 99.67%, and washing, filtering and drying the crude calcium phosphate to obtain a calcium phosphate product with a purity of 98.6%;

[0050] (4) IX Calcium Removal: The dephosphorized chloride solution obtained in step (3) is sent to the calcium removal resin process to remove the residual Ca 2+ , and obtain calcium-removing chloride salt solution and calcium-containing desorption solution. The calcium in the calcium-removing chloride salt solution is 2+ Mg 2+ The concentration is <0.05mg / L, which has reached the feed requirement of bipolar membrane electrodialysis equipment (Ca 2+ Mg 2+ <0.5mg / L);

[0051] (5) Acid and base preparation: The decalcified 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 1.94 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 use as CO2 receiving liquid and pH adjuster respectively.

[0052] Example 4

[0053] The raw material is the sulfate lithium precipitation mother solution prepared in the laboratory, and its main chemical composition is: Li2.8g / L, Na76.3g / L, K 6.7g / L, CO3 2- 18.4g / L. In this embodiment, the lithium precipitation mother liquor is recycled, such as Figure 2 As shown, the following steps are included:

[0054] (1) Lithium precipitation: Heat the lithium precipitation mother liquor to 60°C and stir, then add an amount of lithium precipitate to precipitate all the lithium in the lithium precipitation mother liquor. + Sodium phosphate 0.8 times the theoretical mass of the required phosphate is reacted for 4 hours and then solid-liquid separation is performed to obtain crude lithium phosphate solid and filtrate, the lithium recovery rate is 78.1%, the phosphorus concentration in the filtrate is <2 mg / L, and no dephosphorization and decalcification treatment is required. The crude lithium phosphate is washed, filtered and dried to obtain a lithium phosphate product that meets the Li2PO4-3 grade in the "YS / T 637-2022" standard;

[0055] (2) Acidification: Add sulfuric acid to the filtrate obtained in step (1) to acidify it so that its pH drops to 3.0 and remove CO3 in the filtrate. 2- , a decarbonized sulfate solution is obtained, wherein the phosphorus concentration is 83 mg / L, and a sodium hydroxide solution is used to absorb the discharged CO2 gas to obtain a mixed alkali solution (a mixed solution of sodium hydroxide and sodium carbonate);

[0056] (3) Acid and alkali preparation: The decarbonized sulfate solution obtained in step (2) is treated by bipolar membrane electrodialysis to obtain sulfuric acid and sodium hydroxide solution. + Concentration and sodium hydroxide solution OH - The concentrations 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 use as CO2 receiving liquid.

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

[0058] Table 1

[0059]

[0060]

[0061] It can be seen from Table 1 that the purity of the lithium phosphate products produced in Examples 1-4 exceeds 95%, and can reach up to 97.4%, and the contents of other impurity elements such as Cl and Na meet the requirements of the "YS / T 637-2022" standard.

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

Claims

1. A method for resource utilization of lithium precipitation mother liquor, characterized in that: The steps include: S1, lithium precipitation: adding phosphate to the lithium precipitation mother liquor and mixing to react, and performing solid-liquid separation after the reaction to obtain crude lithium phosphate solid and filtrate; S2, acidification: adding acid to the filtrate obtained in step S1 for acidification, removing carbonate in the filtrate to obtain decarbonated brine, and using alkali solution to absorb the released CO2 gas to obtain a mixed alkali solution; S3, dephosphorization: adding calcium and / or magnesium-containing materials to the decarbonized brine obtained in step S2, then adding alkali solution to adjust the pH value upward, and filtering to obtain crude calcium phosphate and / or magnesium phosphate solids and dephosphorized brine; S4, calcium and magnesium removal: the dephosphorized brine obtained in step S3 is fed into a calcium and magnesium removal resin to remove residual calcium and / or magnesium ions therein, and then the loaded resin is desorbed to finally obtain a calcium and / or magnesium removal brine and a calcium and / or magnesium-containing desorption liquid, and the calcium and / or magnesium-containing desorption liquid is returned to step S3 as a calcium and / or magnesium-containing material for dephosphorization; S5, acid and alkali preparation: the calcium and / or magnesium-removed brine obtained in step S4 is treated by bipolar membrane electrodialysis to obtain acid and alkali solution; wherein, at least part of the acid is returned to step S2 for acidification and / or returned to step S4 for desorption of the resin, and at least part of the alkali solution is returned to step S2 for absorption of CO2 gas and / or returned to step S3 for increasing the pH.

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

3. The method for resource utilization of lithium precipitation mother solution according to claim 1, characterized in that: In step S1, the reaction temperature is 60-95° C., and the reaction time is 0.5-4 h.

4. The method for resource utilization of lithium precipitation mother solution according to claim 1, characterized in that: In step S1, the phosphate includes one or more of sodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate, and the amount of the phosphate added is to precipitate all the Li + 0.5-1.5 times the theoretical mass of phosphate required.

5. The method for resource utilization of lithium precipitation mother solution according to claim 1, characterized in that: In step S2, acid is added to the filtrate to adjust the pH value to 3.0-4.5; the mixed alkali solution is returned to the double alkali calcium and magnesium removal process for use as a double alkali and / or returned to the resin calcium and magnesium removal process for use as a transformation agent after resin regeneration.

6. The method for resource utilization of lithium precipitation mother solution according to claim 1, characterized in that: 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 to remove all phosphorus in the decarbonated brine; when the phosphorus concentration in the decarbonated brine produced in step S2 is <2 mg / L, steps S3-S4 are not performed.

7. The method for resource utilization of lithium precipitation mother solution according to claim 1, characterized in that: In step S3, after the calcium-containing material and / or magnesium-containing material is added to the decarbonated brine, the pH is raised to 10.5-12.0 by adding alkali solution.

8. The method for resource utilization of lithium precipitation mother solution 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 products and calcium phosphate and / or magnesium phosphate products, 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; 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.

9. The method for resource utilization of lithium precipitation mother solution according to claim 1, characterized in that: In step S4, calcium and / or magnesium are removed from the dephosphorized brine using a calcium and magnesium removal resin using one or a combination of a fixed bed system and a continuous ion exchange system.

10. The method for resource utilization of lithium precipitation mother solution according to claim 1, characterized in that: In step S5, the H + The concentration is 1.0-2.2 mol / L, the OH of the alkali solution - The concentration is 1.0-2.2mol / L.

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