Method for directional separation and recovery of lithium and sodium in lithium hydroxide evaporation mother liquor

Abstract

The application discloses a method for directional separation and recovery of lithium and sodium in lithium hydroxide evaporation mother liquor. + The lithium-precipitated solution is subjected to dephosphorization and evaporation crystallization treatment, and high-quality lithium phosphate, solid sodium hydroxide and calcium phosphate products are generated, the lithium recovery rate is high, the process is simple and efficient, compared with a traditional secondary lithium-containing solution treatment method, the application realizes efficient directional separation and recovery of lithium and sodium resources in the evaporation mother liquor, rather than only recovering lithium resources, meanwhile, crude lithium phosphate and crude calcium phosphate are washed by using subsequent evaporation crystallization stage to generate fresh water, therefore, the method can significantly improve economic benefits of enterprises, can greatly reduce purchasing cost of flaky alkali and save water resources, and is high in economy. In addition, the dephosphorization agent can come from calcium-containing desorption liquid generated in the calcium removal stage and calcium-containing materials generated in a main system, so that the purchasing cost of the dephosphorization agent is reduced, and the adaptability of the method to the main system is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium extraction from salt lakes, and particularly relates to a method for directional separation and recovery of lithium and sodium in lithium hydroxide evaporation mother liquor. BACKGROUND

[0002] LiOH H2O is one of the key raw materials for producing lithium batteries and has a huge market. At present, the preparation of LiOH generally includes the following steps: firstly, preparing a pure lithium-containing solution through pretreatment; secondly, producing a pure LiOH solution through causticization or electrolysis; and finally, producing LiOH H2O products through evaporation crystallization, washing, and drying. The evaporation crystallization process is accompanied by the generation of by-product evaporation mother liquor. The evaporation mother liquor has the characteristics of rich lithium and sodium resources, high sodium-lithium ratio, and high alkalinity, and the lithium and sodium contents are 12-20 g / L and 150-300 g / L, respectively. The evaporation mother liquor has great economic value and recovery potential. At present, there are few reports on the treatment method of lithium hydroxide evaporation mother liquor, and the mainstream treatment process mainly focuses on the recovery of LiOH H2O, without recycling the sodium resources. +

[0003] CN115571901A discloses a method for preparing lithium carbonate from lithium extraction evaporation mother liquor of salt lake. The method includes the following steps: firstly, diluting the evaporation mother liquor with pure water to meet the requirements of the downstream membrane treatment; secondly, removing suspended solids, colloidal macromolecular substances, and calcium and magnesium divalent ions through ultrafiltration and nanofiltration; thirdly, producing battery-grade lithium carbonate products through two-stage carbonization-thermal decomposition, solid-liquid separation, washing, drying, and magnetic removal. In the method, due to the high alkalinity of the evaporation mother liquor, the two-stage carbonization to prepare lithium bicarbonate solution leads to excessive consumption of carbon dioxide. If the direct carbonization is used to produce lithium carbonate solution, a large amount of carbon dioxide can be saved. However, due to the high Na + content in the thermal decomposition liquid, it is difficult to meet the requirements of battery grade after simple washing. In addition, the sodium resources are not recycled, which wastes a large amount of resources. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application aims to provide a method for directional separation and recovery of lithium and sodium in lithium hydroxide evaporation mother liquor.

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical solution:

[0006] A method for directional separation and recovery of lithium and sodium in lithium hydroxide evaporation mother liquor, comprising the following steps:

[0007] S1, heating the lithium hydroxide evaporation mother liquor to a constant temperature and maintaining stirring, then adding phosphate and continuing to stir and react; after the reaction is completed, solid-liquid separation is performed to obtain crude lithium phosphate solid and lithium precipitation liquid, and the crude lithium phosphate is washed with pure water, filtered, and dried to obtain lithium phosphate products; ​

[0008] S2, adding a calcium-containing material to the lithium precipitation post-liquid obtained in step S1, and obtaining a crude calcium phosphate solid and a dephosphorization post-liquid after filtration, and obtaining a calcium phosphate product after washing, filtering and drying treatment of the crude calcium phosphate solid;

[0009] S3, removing calcium from the dephosphorization post-liquid obtained in step S2 by using resin adsorption, and obtaining a calcium removal post-liquid after removing residual Ca + from the dephosphorization post-liquid; and desorbing the adsorbed resin to obtain a calcium-containing desorption liquid;

[0010] S4, evaporative crystallization of the calcium removal post-liquid obtained in step S3, returning the evaporated fresh water to washing of the crude lithium phosphate and the crude calcium phosphate, and obtaining a crude sodium hydroxide solid and mixed caustic after filtering the remaining slurry, and obtaining a solid sodium hydroxide product after washing, filtering and drying of the crude sodium hydroxide.

[0011] Further, in step S1, the phosphate salt includes one or more of sodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate, and the amount of the phosphate salt added is 1-1.5 times the theoretical mass of the calcium required for the removal of all Li + in the lithium hydroxide evaporation mother liquor.

[0012] Further, in step S1, the lithium hydroxide evaporation mother liquor is heated to 70-90°C and kept at constant temperature while maintaining stirring, and then the phosphate salt is added and the reaction is continued for 1-3h.

[0013] Further, the lithium phosphate product obtained in step S1 meets the Li2PO4-3 grade standard in the YS / T 637-2022 standard, and is used to prepare high-purity lithium phosphate, battery-grade lithium carbonate and / or as a raw material product for battery-grade lithium hydroxide monohydrate.

[0014] Further, in step S2, the amount of calcium-containing material added is 1-1.2 times the theoretical mass of calcium required for the removal of all phosphorus in the lithium precipitation post-liquid, based on the calcium contained therein.

[0015] Further, the calcium phosphate product obtained in step S2 has a purity of ≥98%, and can be used as a fertilizer or as a raw material product for food-grade calcium phosphate.

[0016] Further, in step S3, the resin adsorption for removing calcium is carried out by using one or a combination of the other of a fixed bed system and a continuous ion exchange system.

[0017] Further, in step S4, the evaporation loss rate of the evaporative crystallization is 40%-80%.

[0018] Further, the solid sodium hydroxide product obtained in step S4 meets the IS-IT-I type I grade qualified product indicators in GB 209-2006 Industrial Sodium Hydroxide.

[0019] Further, the calcium-containing material includes one or more of the calcium-containing desorption solution produced in step S2, calcium chloride hexahydrate produced in the solar salt stage of the lithium extraction process of a salt lake enterprise producing lithium carbonate and lithium hydroxide monohydrate, and the dialysis nanofiltration calcium-containing concentrated water produced in the nanofiltration membrane calcium and magnesium removal stage.

[0020] The present application has the beneficial effects that the present application first recovers Li + from the evaporation mother liquor by using the phosphate precipitation method, and then performs dephosphorization and evaporation crystallization treatment on the lithium-precipitated solution to produce high-quality lithium phosphate, solid sodium hydroxide and calcium phosphate products, the process has high lithium recovery rate and is simple and efficient, compared with the traditional secondary lithium-containing solution treatment method, the present application realizes efficient and directional separation and recovery of lithium and sodium resources in the evaporation mother liquor, rather than only recovering lithium resources, and the washing of the crude lithium phosphate and the crude calcium phosphate uses the fresh water produced in the subsequent evaporation crystallization stage, so that the present application method can significantly improve the economic benefits of the enterprise, greatly reduce the cost of purchasing piece alkali and save water resources, and has high economic efficiency. In addition, the dephosphorization agent can come from the calcium-containing desorption solution produced in the calcium removal stage, and can also come from the calcium-containing material produced in the main system, such as the calcium chloride hexahydrate produced in the solar salt stage of the lithium extraction main process of a salt lake enterprise producing lithium carbonate and lithium hydroxide monohydrate, and the dialysis nanofiltration calcium-containing concentrated water produced in the nanofiltration membrane calcium and magnesium removal section, so that the cost of purchasing the dephosphorization agent can be reduced, and the adaptability of the present application method to the production main system is also improved. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The process flowcharts of embodiments 1-3 of the present application are shown. DETAILED DESCRIPTION

[0022] The present application will be further described below with reference to the accompanying drawings, and it should be noted that the present embodiments are based on the technical solutions, and detailed implementation methods and specific operation processes are given, but the protection scope of the present application is not limited to the present embodiments.

[0023] Embodiment 1

[0024] The lithium hydroxide evaporation mother liquor produced by a certain salt lake enterprise is used as the raw material, and the main chemical components are: Li 14.9g / L, Na 173.0g / L, K 16.3g / L, OH - 13.4mol / L, and the lithium and sodium directional separation and recovery of the evaporation mother liquor is performed, as shown in FIG. 1, including the following steps: Figure 1

[0025] ​(1) first lithium hydroxide evaporation mother liquor to 70℃, then keep constant temperature and maintain stirring, then add 1.5 times the theoretical amount of sodium phosphate lithium sink to lithium hydroxide evaporation mother liquor, continue to keep constant temperature stirring reaction 1h after stirring, after the end of the solid-liquid separation, get crude lithium phosphate and lithium sink after liquid, process lithium recovery rate of 93.8%, crude lithium phosphate after washing, filtering, drying treatment get lithium phosphate product;

[0026] (2) to the lithium sink after liquid obtained in step (1) add calcium containing material dephosphorization, the calcium containing material is the calcium containing desorption liquid produced in step (3), the amount of calcium added is 1.2 times the theoretical amount. After filtration, crude calcium phosphate and dephosphorized liquid are obtained, the phosphorus precipitation rate is 99.4%, and the crude calcium phosphate is washed with pure water, filtered and dried to obtain a calcium phosphate product with a purity of 98.16%;

[0027] (3) the dephosphorized liquid produced in step (2) is sent to resin calcium removal to obtain calcium removed liquid and calcium containing desorption liquid, the calcium removed liquid Ca + , Mg + Concentration <0.05 mg / L, calcium containing desorption liquid returns to step (2) dephosphorization;

[0028] (4) the calcium removed liquid produced in step (3) is evaporated and crystallized, the evaporation weight loss rate is 79.1%, the evaporated water is returned for washing of crude lithium phosphate and crude calcium phosphate, and the slurry is filtered to obtain crude sodium hydroxide solid and mixed alkali. The crude sodium hydroxide is washed, filtered and dried to obtain solid sodium hydroxide product.

[0029] Example 2

[0030] The lithium hydroxide evaporation mother liquor produced by a certain salt lake enterprise is used as raw material, and its main chemical components are: Li 14.9 g / L, Na 173.0 g / L, K 16.3 g / L, OH - 13.4 mol / L. In this embodiment, lithium and sodium are directionally separated and recovered from the evaporation mother liquor, as shown in the following steps: Figure 1

[0031] (1) first lithium hydroxide evaporation mother liquor to 70℃, then keep constant temperature and maintain stirring, then add 1.5 times the theoretical amount of sodium phosphate lithium sink to lithium hydroxide evaporation mother liquor, continue to keep constant temperature stirring reaction 1h after stirring, after the end of the solid-liquid separation, get crude lithium phosphate and lithium sink after liquid, process lithium recovery rate of 93.8%, crude lithium phosphate after washing, filtering, drying treatment get lithium phosphate product;

[0032] ​(2) adding a calcium-containing material to the lithium precipitation liquid obtained in step (1) for dephosphorization, wherein the calcium-containing material includes the calcium-containing desorption liquid output in step (3) and the dialysis nanofiltration calcium-containing concentrated water produced by the lithium-containing brine nanofiltration membrane calcium and magnesium removal process, the amount of calcium added is 1 times the theoretical amount, and after filtering, crude calcium phosphate and dephosphorized liquid are obtained, the phosphorus precipitation rate is 99.0%, and the crude calcium phosphate is washed with pure water, filtered, and dried to obtain a calcium phosphate product with a purity of 98.1%;

[0033] (3) The dephosphorized liquid produced in step (2) is fed into a resin for adsorption and decalcification to obtain a decalcified liquid and a calcium-containing desorption liquid. The decalcified liquid Ca + Mg + If the concentration is less than 0.05 mg / L, the calcium-containing desorption solution is returned to step (2) for dephosphorization;

[0034] (4) The decalcified liquid produced in step (3) is evaporated and crystallized, and the evaporation weight loss rate is 41.6%. The fresh water produced by evaporation is returned for washing crude lithium phosphate and crude calcium phosphate. The slurry is filtered to obtain crude sodium hydroxide solid and mixed alkali. The crude sodium hydroxide is washed, filtered, and dried to obtain a solid sodium hydroxide product.

[0035] Example 3

[0036] The raw material is lithium hydroxide evaporation mother liquor produced by a salt lake enterprise. Its main chemical components are: Li 17.1g / L, Na 148.0g / L, K 13.6g / L, OH - 11.7 mol / L. In this embodiment, lithium hydroxide evaporation mother liquor is subjected to lithium and sodium directional separation and recovery, such as Figure 1 As shown, the following steps are included:

[0037] (1) first heating the lithium hydroxide evaporation mother liquor to 85° C., then maintaining the constant temperature and stirring, then adding 1.3 times the theoretical amount of sodium dihydrogen phosphate to the lithium hydroxide evaporation mother liquor to precipitate lithium, and continuing to maintain the constant temperature and stirring for 2 hours after the addition is completed. After the stirring is completed, solid-liquid separation is performed to obtain crude lithium phosphate and a lithium precipitation liquid. The lithium recovery rate of the process is 94.2%. The crude lithium phosphate is washed and dried to obtain lithium phosphate;

[0038] (2) adding a calcium-containing material to the lithium precipitation liquid obtained in step (1) for dephosphorization, wherein the calcium-containing material comprises the calcium-containing desorption liquid produced in step (3) and the calcium chloride hexahydrate solid produced in the brine salting stage, and the amount of calcium added is 1.15 times the theoretical amount. After filtering, crude calcium phosphate and dephosphorized liquid are obtained, and the phosphorus precipitation rate is 99.3%. The crude calcium phosphate is washed with pure water, filtered, and dried to obtain a calcium phosphate product with a purity of 98.7%;

[0039] (3) The dephosphorized solution from step (2) is sent to a resin calcium removal to obtain a calcium-removed solution and a calcium-containing desorption solution, and the calcium concentration of the calcium-removed solution is Ca + + <0.05 mg / L, and the calcium-containing desorption solution is returned to step (2) for dephosphorization;

[0040] (4) The calcium-removed solution from step (3) is subjected to evaporation crystallization, and the evaporation weight loss rate is 65.7%, and the evaporated fresh water is returned to be used for washing of the crude lithium phosphate and the crude calcium phosphate, and after the slurry is filtered, a crude sodium hydroxide solid and mixed alkali are obtained, the crude sodium hydroxide is washed, filtered and dried to obtain a solid sodium hydroxide product;

[0041] The chemical compositions of the lithium phosphate products and the solid sodium hydroxide products produced in examples 1-3 are shown in table 1 and table 2, respectively.

[0042] Table 1 Chemical composition of the lithium phosphate products produced in examples 1-3

[0043]

[0044]

[0045] Table 2 Chemical composition of the solid sodium hydroxide products produced in examples 1-3

[0046] Example 1 2 3 NaOH mass fraction / % 98.39 98.51 98.60 Na2CO3 mass fraction / % 0.33 0.42 0.15 NaCl mass fraction / % 0.02 0.02 0.04 Fe2O3 mass fraction / % 0.003 0.002 <0.001

[0047] For those skilled in the art, various corresponding changes and modifications can be given 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 application.​

Claims

1. A method for directional separation and recovery of lithium and sodium from lithium hydroxide evaporation mother liquor, characterized in that: The method comprises the following steps: S1, the lithium hydroxide evaporation mother liquor is heated to 70-90℃, then phosphate is added and the reaction is continued for 1-3 hours. The lithium phosphate product obtained in step S1 is used to prepare high-purity lithium phosphate, battery-grade lithium carbonate and / or as raw material product of battery-grade lithium hydroxide monohydrate. S3, removing calcium from the dephosphorized solution obtained in step S2 by using resin adsorption to remove residual Ca + , to obtain a calcium-removed solution; and desorbing the resin after adsorption to obtain a calcium-containing desorption solution; In step S2, the amount of calcium-containing material added is 1-1.2 times the theoretical mass of calcium required to remove all phosphorus in the lithium precipitation solution. The purity of the calcium phosphate product obtained in step S2 is ≥98%, which can be used as a fertilizer or as a raw material product of food-grade calcium phosphate.

2. The method of claim 1, wherein, In step S1, the phosphate includes one or more of sodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, and the amount of the phosphate added is 1-1.5 times the theoretical mass of the phosphate required to precipitate all Li + 1-1.5 times the theoretical mass of the phosphate required.

3. The method of claim 1, wherein, In step S3, resin adsorption calcium removal is carried out using one or a combination of fixed bed systems and continuous ion exchange systems.

4. The method of claim 1, wherein, In step S4, the evaporation loss rate of evaporation crystallization is 40%-80%.

5. The method of claim 1, wherein, ​ 6. The method of claim 1, wherein, ​ 7. The method of claim 1, wherein, ​ 8. The method of claim 1, wherein, ​

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