Method for extracting lithium from lithium precipitation mother liquor to obtain lithium phosphate

Abstract

The invention discloses a method for extracting lithium from lithium precipitation mother liquor to obtain lithium phosphate, which specifically comprises the following steps of: performing preliminary extraction on the lithium precipitation mother liquor, performing reverse extraction by adopting a composite reverse extraction agent consisting of phosphoric acid and acetylacetone in a molar ratio of (5-15): 1, controlling the pH value of a reverse extraction system to be 5-7, and performing phase splitting to obtain a lithium phosphate wet product; and finally, adding the lithium phosphate wet product into lithium hydroxide for reaction, and filtering to obtain lithium phosphate. According to the method, efficient enrichment of lithium ions in the lithium precipitation mother liquor is achieved through the extraction and reverse extraction processes, meanwhile, through optimization of a reverse extraction system in the reverse extraction process, formation of calcium phosphate impurities is reduced, the extraction purity of lithium is improved, the morphology of lithium phosphate can be regulated and controlled in the reverse extraction process, batch stability is achieved, and the product quality is improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium precipitation mother liquor extraction technology, and particularly relates to a method for extracting lithium from lithium precipitation mother liquor to obtain lithium phosphate. Background Technology

[0002] Lithium phosphate, as an important lithium compound, has attracted much attention due to its broad application prospects. Lithium phosphate is a white crystalline powder with a melting point of 837 ℃ and a density of 2.537 g / cm³. Its solubility in water at 25 ℃ is only 0.27 g / L, far lower than the solubility of other lithium salts and phosphates. The development of highly selective lithium extraction technology is key to overcoming the challenges of effectively utilizing low-quality lithium resources. Methods for extracting lithium salts from lithium precipitation mother liquor mainly include precipitation, adsorption, ion exchange, electrodialysis membrane methods, nanofiltration membrane methods, and solvent extraction. Among these, extraction is widely valued due to its high selectivity, simple process and equipment, continuous operation, and ease of automation.

[0003] The mother liquor for lithium precipitation contains calcium ions, which compete with lithium ion extraction. Furthermore, calcium ion extraction generates calcium phosphate precipitate, reducing the purity of the obtained lithium phosphate. To address the impact of calcium ions, existing techniques involve pre-treatment with calcium adsorption resin before extraction. However, in actual production line operation, it was found that although pre-treatment with adsorption resin was used, the low calcium ion content in the mother liquor itself was insufficient to achieve deep calcium removal, still affecting the purity of the subsequent lithium phosphate. Moreover, the morphology of the prepared lithium phosphate varied significantly across different batches, exhibiting substantial differences in performance.

[0004] Based on this, a novel method for extracting lithium from lithium precipitation mother liquor to obtain lithium phosphate has been studied. This method can not only improve the purity of the obtained lithium phosphate, but also achieve quality control between different batches. That is, the obtained lithium phosphate has a uniform morphology, achieving morphological similarity between batches and ensuring stable quality across different batches. Summary of the Invention

[0005] Purpose of the invention: The technical problem to be solved by the present invention is to provide a method for extracting and preparing lithium phosphate from lithium precipitation mother liquor, so as to improve the purity and controllable crystal morphology of lithium phosphate and achieve batch stability of production line.

[0006] Technical solution: The present invention provides a method for extracting lithium from lithium precipitation mother liquor to obtain lithium phosphate, comprising the following steps:

[0007] (1) The mother liquor containing lithium was extracted with an extractant to obtain Li-containing... + Ca 2+ Oil phase extract A and aqueous phase raffinate;

[0008] (2) Wash the oil phase extract A with phosphoric acid at a concentration of 0.05-0.5 mol / L to obtain oil phase extract B and aqueous washing residue;

[0009] (3) The oil phase extract B is back-extracted using a composite back-extracting agent composed of phosphoric acid and acetylacetone in a molar ratio of (5-15):1, and the pH of the back-extraction system is controlled at 5-7. The phase separation yields wet lithium phosphate product.

[0010] (4) Add the wet lithium phosphate product to lithium hydroxide to react, and filter to obtain the finished lithium phosphate product.

[0011] Furthermore, in step (1) of the extraction method of the present invention, the extractant is a composite extractant formed by mixing a main extractant, a co-extractant, and a diluent; wherein the molar ratio of the main extractant to the co-extractant is (0.5-3):1. Preferably, the main extractant used can be selected from at least one of benzoyltrifluoroacetone, 2-thiophenecarboxyltrifluoroacetone, 1-phenyl-1,3-decanedione, 2-naphthoyltrifluoroacetone, trifluoroacetylacetone, 1-(3,5-bis(trifluoromethylphenyl)-1,3-butanedione, 1-heptyl-3-phenyl-1,3-propanedione, dodecylphenyl-methyl-β-dione, dioctyl phthalate, and butyl salicylate. The co-extractant used may be selected from at least one of trioctylphosphine oxide, tributyl phosphate, di(2-ethylhexyl) phosphate, 2-ethylhexyl phosphate mono-2-ethylhexyl ester, di(2,4,4-trimethylpentyl) phosphate, and di(n-octyl) phosphate. The diluent used may be selected from at least one of 260# solvent oil, cyclohexanone, ethyl acetate, n-octanol, and sec-octanol.

[0012] Furthermore, in step (3) of the extraction method of the present invention, the O / A ratio of the back-extraction is (10-20):1. The phosphoric acid concentration in the composite back-extraction agent is 1-6 mol / L.

[0013] Furthermore, in step (4) of the extraction method of the present invention, after adding lithium hydroxide, the pH value is adjusted to 10-13.

[0014] Beneficial effects: Compared with the prior art, the significant advantages of the present invention are: the extraction and back-extraction process achieves efficient enrichment of lithium ions in the lithium precipitation mother liquor, while significantly reducing the content of impurities such as sodium, potassium and other anions; and in the back-extraction process, not only is the formation of calcium phosphate impurities reduced and the extraction purity of lithium improved, but the morphology can also be controlled and uniform, achieving batch-to-batch morphology similarity, batch stability, and improved product quality. Attached Figure Description

[0015] Figure 1 This is a morphology diagram of lithium phosphate obtained by the extraction method of Example 1 of the present invention;

[0016] Figure 2 This is a morphology diagram of lithium phosphate obtained by the extraction method of Comparative Example 1 of the present invention.

[0017] Figure 3 This is a morphology diagram of lithium phosphate obtained by the extraction method in Example 2 of the present invention;

[0018] Figure 4 This is a morphology diagram of lithium phosphate obtained by the extraction method of Comparative Example 2 of the present invention.

[0019] Figure 5 This is a morphology diagram of lithium phosphate obtained by the extraction method in Example 3 of the present invention;

[0020] Figure 6 This is a morphology diagram of lithium phosphate obtained by the extraction method of Comparative Example 3 of the present invention. Detailed Implementation

[0021] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the raw materials used in the extraction and back-extraction processes can be directly purchased from commercially available sources.

[0022] The extractant system used in the following embodiments and comparative examples of this invention is as follows:

[0023] Main extractants: benzoyltrifluoroacetone and dodecylphenyl-methyl-β-dione.

[0024] Co-extractant: di(2-ethylhexyl) phosphate;

[0025] Diluent: 2-octanol.

[0026] The extractant contains 0.5 mol / L benzoyltrifluoroacetone, 0.5 mol / L dodecylphenyl-methyl-β-diketone, and 0.8 mol / L di(2-ethylhexyl)phosphate. This means the molar ratio of the primary extractant to the co-extractant is 1.25:1.

[0027] Example 1

[0028] The main components of the lithium mother liquor stock solution in Example 1 are shown in Table 1.

[0029] Table 1. Content of main components in the lithium precipitation mother liquor stock solution of Example 1

[0030]

[0031] The method for extracting lithium from lithium precipitation mother liquor to prepare lithium phosphate in Example 1 is as follows:

[0032] (1) The mother liquor containing lithium was extracted using an extractant. The volume ratio of the extractant to the mother liquor was controlled at 1.2:1. There were 3 extraction stages, and the extraction time for each stage was 10 min. After phase separation, a lithium-loaded oil phase extract A with a lithium concentration of 2.107 g / L was obtained, and the lithium extraction rate was 99.9%.

[0033] (2) The lithium-loaded oil phase extract A was washed with a 0.1 mol / L phosphoric acid washing solution. The volume ratio of the lithium-loaded oil phase extract A to the washing solution was controlled at 12:1. The washing stage was 4 stages, and the washing time for each stage was 5 min. The oil phase extract B and the aqueous washing residue were obtained by phase separation.

[0034] (3) The oil phase extract B is back-extracted using a composite back-extracting agent. The O / A ratio of the back-extraction is 12:1, the number of back-extraction stages is 1, and the back-extraction stirring time is 20 min. The phase separation yields a wet lithium phosphate product. The composite back-extracting agent consists of phosphoric acid and acetylacetone in a molar ratio of 5:1. The concentration of phosphoric acid in the composite back-extracting agent is 1 mol / L. The O / A ratio of the back-extraction and the concentration of phosphoric acid in the composite back-extracting agent are used to make the pH of the back-extraction system 7, that is, the pH value of the system after back-extraction reaches 7.

[0035] (4) Add lithium hydroxide to the back-extraction solution of the wet lithium phosphate product, adjust the pH to 11, filter, wash, and dry to obtain the lithium phosphate product. The morphology of this lithium phosphate product is shown in the figure below. Figure 1 As shown.

[0036] Comparative Example 1

[0037] Comparative Example 1 is essentially the same as Example 1, except that the back-extraction agent used is only a 1 mol / L phosphoric acid solution, and calcium is pre-treated with a calcium adsorption resin to obtain the lithium phosphate product before extraction. Specifically, the steps include:

[0038] (1) The lithium precipitation mother liquor is subjected to deep calcium removal by calcium adsorption resin to obtain the calcium-removed lithium precipitation mother liquor.

[0039] (2) The mother liquor after calcium removal was extracted with an extractant. The volume ratio of the extractant to the mother liquor was controlled at 1.2:1. There were 3 extraction stages and the extraction time for each stage was 10 min. After phase separation, a lithium-loaded oil phase extract A with a lithium concentration of 2.094 g / L was obtained. The lithium extraction rate was 99.3%.

[0040] (3) The lithium-loaded oil phase extract A was washed with a 0.1 mol / L phosphoric acid washing solution. The volume ratio of the lithium-loaded oil phase extract A to the washing solution was controlled at 12:1. The washing stage was 4 stages, and the washing time for each stage was 5 min. The oil phase extract B and the aqueous washing residue were obtained by phase separation.

[0041] (4) The oil phase extract B was back-extracted with a phosphoric acid solution with a concentration of 1 mol / L. The O / A ratio of the back-extraction was 12:1, the number of back-extraction stages was 1, and the back-extraction stirring time was 20 min. The phase separation yielded a wet lithium phosphate product. The pH of the back-extraction system was controlled to be 6.5 by adjusting the concentration of the phosphoric acid solution and the O / A ratio of the back-extraction.

[0042] (5) Add lithium hydroxide to the back-extraction solution of the wet lithium phosphate product, adjust the pH to 11, filter, wash, and dry to obtain the lithium phosphate product. The morphology of this lithium phosphate product is shown in the figure below. Figure 2 As shown.

[0043] Example 2

[0044] The main components of the lithium mother liquor stock solution in Example 2 are shown in Table 2.

[0045] Table 2. Content of main components in the lithium precipitation mother liquor stock solution of Example 2

[0046]

[0047] The method for extracting lithium from lithium precipitation mother liquor to prepare lithium phosphate in Example 2 is as follows:

[0048] (1) The mother liquor containing lithium was extracted using an extractant. The volume ratio of the extractant to the mother liquor was controlled at 1.2:1. There were 3 extraction stages, and the extraction time for each stage was 10 min. After phase separation, a lithium-loaded oil phase extract A with a lithium concentration of 2.348 g / L was obtained, and the lithium extraction rate was 98.5%.

[0049] (2) The lithium-loaded oil phase extract A was washed with a 0.1 mol / L phosphoric acid washing solution. The volume ratio of the lithium-loaded oil phase extract A to the washing solution was controlled at 12:1. The washing stage was 4 stages, and the washing time for each stage was 5 min. The oil phase extract B and the aqueous washing residue were obtained by phase separation.

[0050] (3) The oil phase extract B was back-extracted using a composite back-extracting agent. The O / A ratio of the back-extraction was 20:1, the number of back-extraction stages was 1, and the back-extraction stirring time was 20 min. The phase separation yielded a wet lithium phosphate product. The composite back-extracting agent consisted of phosphoric acid and acetylacetone in a molar ratio of 10:1, and the concentration of phosphoric acid in the composite back-extracting agent was 3 mol / L. The pH of the back-extraction system was controlled to be 6.5 by the O / A ratio of the back-extraction and the concentration of phosphoric acid in the composite back-extracting agent.

[0051] (4) Add lithium hydroxide to the back-extraction solution of the wet lithium phosphate product, adjust the pH to 11, filter, wash, and dry to obtain the lithium phosphate product. The morphology of this lithium phosphate product is shown in the figure below. Figure 3 As shown.

[0052] Comparative Example 2

[0053] Comparative Example 2 is essentially the same as Example 2, except that only a 3 mol / L phosphoric acid solution is used as the back-extraction agent, and calcium is pre-treated with a calcium adsorption resin to obtain the lithium phosphate product. Specifically, the steps are as follows:

[0054] (1) The lithium precipitation mother liquor is subjected to deep calcium removal by calcium adsorption resin to obtain the calcium-removed lithium precipitation mother liquor.

[0055] (2) The mother liquor after calcium removal was extracted with an extractant. The volume ratio of the extractant to the mother liquor was controlled at 1.2:1. There were 3 extraction stages and the extraction time for each stage was 10 min. After phase separation, a lithium-loaded oil phase extract A with a lithium concentration of 2.350 g / L was obtained. The lithium extraction rate was 98.6%.

[0056] (3) The lithium-loaded oil phase extract A was washed with a 0.1 mol / L phosphoric acid washing solution. The volume ratio of the lithium-loaded oil phase extract A to the washing solution was controlled at 12:1. The washing stage was 4 stages, and the washing time for each stage was 5 min. The oil phase extract B and the aqueous washing residue were obtained by phase separation.

[0057] (4) The oil phase extract B was back-extracted with a 3 mol / L phosphoric acid solution. The O / A ratio of the back-extraction was 20:1, the number of back-extraction stages was 1, and the back-extraction stirring time was 20 min. The phase separation yielded a wet lithium phosphate product. The pH of the back-extraction system was controlled to 6.3 by the phosphoric acid solution and the back-extraction O / A ratio.

[0058] (5) Add lithium hydroxide to the back-extraction solution of the wet lithium phosphate product, adjust the pH to 11, filter, wash, and dry to obtain the lithium phosphate product. The morphology of this lithium phosphate product is shown in the figure below. Figure 4 As shown.

[0059] Example 3

[0060] The main components of the lithium mother liquor stock solution of Example 3 are shown in Table 3.

[0061] Table 3. Content of main components in the lithium precipitation mother liquor stock solution of Example 3

[0062]

[0063] The method for extracting lithium from lithium precipitation mother liquor to prepare lithium phosphate in Example 3 is as follows:

[0064] (1) The mother liquor containing lithium was extracted using an extractant. The volume ratio of the extractant to the mother liquor was controlled at 1.2:1. There were 3 extraction stages, and the extraction time for each stage was 10 min. After phase separation, a lithium-loaded oil phase extract A with a lithium concentration of 2.488 g / L was obtained, and the lithium extraction rate was 97.9%.

[0065] (2) The lithium-loaded oil phase extract A was washed with a 0.1 mol / L phosphoric acid washing solution. The volume ratio of the lithium-loaded oil phase extract A to the washing solution was controlled at 12:1. The washing stage was 4 stages, and the washing time for each stage was 5 min. The oil phase extract B and the aqueous washing residue were obtained by phase separation.

[0066] (3) The oil phase extract B was back-extracted using a composite back-extracting agent. The O / A ratio of the back-extraction was 20:1, the number of back-extraction stages was 1, and the back-extraction stirring time was 20 min. The phase separation yielded a wet lithium phosphate product. The composite back-extracting agent consisted of phosphoric acid and acetylacetone in a molar ratio of 15:1, and the concentration of phosphoric acid in the composite back-extracting agent was 4 mol / L. The pH of the back-extraction system could be controlled to 5.4 by adjusting the O / A ratio of the back-extraction and the concentration of phosphoric acid in the composite back-extracting agent.

[0067] (4) Add lithium hydroxide to the back-extraction solution of the wet lithium phosphate product, adjust the pH to 11, filter, wash, and dry to obtain the lithium phosphate product. The morphology of this lithium phosphate product is shown in the figure below. Figure 5 As shown.

[0068] Comparative Example 3

[0069] Comparative Example 3 is essentially the same as Example 3, except that only a 4 mol / L phosphoric acid solution is used as the back-extraction agent, and calcium is pre-treated with a calcium adsorption resin to obtain the lithium phosphate product. Specifically, the steps are as follows:

[0070] (1) The lithium precipitation mother liquor is subjected to deep calcium removal by calcium adsorption resin to obtain the calcium-removed lithium precipitation mother liquor.

[0071] (2) The mother liquor containing lithium was extracted using an extractant. The volume ratio of the extractant to the mother liquor was controlled at 1.2:1. There were 3 extraction stages, and the extraction time for each stage was 10 min. After phase separation, a lithium-loaded oil phase extract A with a lithium concentration of 2.471 g / L was obtained, and the lithium extraction rate was 97.2%.

[0072] (3) The lithium-loaded oil phase extract A was washed with a 0.1 mol / L phosphoric acid washing solution. The volume ratio of the lithium-loaded oil phase extract A to the washing solution was controlled at 12:1. The washing stage was 4 stages, and the washing time for each stage was 5 min. The oil phase extract B and the aqueous washing residue were obtained by phase separation.

[0073] (4) The oil phase extract B was back-extracted with a phosphoric acid solution of 4 mol / L. The O / A ratio of the back-extraction was 20:1, the number of back-extraction stages was 1, the back-extraction stirring time was 20 min, and the phase separation yielded a wet lithium phosphate product. The pH of the back-extraction system was controlled to be 5 by the phosphoric acid solution and the back-extraction O / A ratio.

[0074] (5) Add lithium hydroxide to the back-extraction solution of the wet lithium phosphate product, adjust the pH to 11, filter, wash, and dry to obtain the lithium phosphate product. The morphology of this lithium phosphate product is shown in the figure below. Figure 6 As shown.

[0075] Performance testing

[0076] The extraction rates and lithium phosphate product contents of the preparation methods in Examples 1-3 and Comparative Examples 1-3 are shown in Table 4, and the lithium extraction rate is calculated using the following formula: In the formula: C0 is the lithium content in the aqueous phase before extraction, and C1 is the lithium content in the aqueous phase after extraction, both in g / L.

[0077] Table 4 Extraction rate and content of prepared lithium phosphate products

[0078]

[0079] The 98% lithium phosphate content and impurity standards refer to YS / T 637-2022.

[0080] As shown in Table 4, the calcium ion content (13-17%) in Examples 1-3 using this method is significantly lower than the calcium ion content (56-92%) in Comparative Examples 1-3 using conventional extraction. Furthermore, comparing the morphology images of lithium phosphate prepared in Examples 1-3 and Comparative Examples 1-3, it can be seen that using the composite extractant of this invention, and under this specific reaction system, the prepared lithium phosphate consists entirely of uniformly sized needle-like crystals, resulting in lithium phosphate with a uniform and controllable morphology. Moreover, the morphology differences between different experiments are small, achieving batch stability in the production line. In contrast, back-extraction using a single acid solution according to conventional methods yields lithium phosphate of varying sizes, exhibiting agglomeration and lacking a clear crystal structure. Furthermore, the particle size of each batch of products in Comparative Examples 1-3 shows significant differences, and the product morphology is uncontrollable.

[0081] Based on the experimental results, further analysis reveals that the main differences between the two are as follows: This invention uses an extractant to fully extract lithium ions, while not limiting the extraction of competing ions such as calcium ions, allowing them to be extracted together with lithium ions. However, during the back-extraction process, a composite back-extraction agent composed of phosphoric acid and acetylacetone is used under specific phosphoric acid concentration conditions. This allows for the extraction of protons (H+) in the composite back-extraction agent during the back-extraction process. + The system replaces the metal cations in the extractant, increases the pH of the back-extraction solution, and promotes the acetylacetone to first complex the back-extracted calcium ions, thereby avoiding the formation of calcium phosphate, improving the purity of the final prepared lithium phosphate, and the substances in this system can also promote the regulation of the morphology of calcium phosphate.

[0082] In addition to the above embodiments, it should be noted that in the method for preparing lithium phosphate by lithium precipitation mother liquor extraction of the present invention, the main extractant may be one or more of benzoyltrifluoroacetone, 2-thiophenecarboxyltrifluoroacetone, 1-phenyl-1,3-decanedione, 2-naphthoyltrifluoroacetone, trifluoroacetylacetone, 1-(3,5-bis(trifluoromethylphenyl)-1,3-butanedione, 1-heptyl-3-phenyl-1,3-propanedione, dodecylphenyl-methyl-β-dione, dioctyl phthalate, and butyl salicylate; the co-extractant may be one or more of trioctylphosphine oxide, tributyl phosphate, di(2-ethylhexyl) phosphate, 2-ethylhexyl phosphate mono-2-ethylhexyl ester, di(2,4,4-trimethylpentyl) phosphate, and di(n-octyl) phosphate.

[0083] The technical effects claimed by this invention can be achieved by using the preparation process and the parameter range defined in this invention, so no further examples will be given to support this claim.

Claims

1. A process for the extraction of lithium from a lithium-laden mother liquor to obtain lithium phosphate, characterized in that, The method comprises the following steps: (1) The lithium-sink mother liquor is extracted by an extractant to obtain an oil-phase extract A containing Li + , Ca 2+ and an aqueous-phase raffinate; (2) washing the oil phase extraction liquid A with phosphoric acid with a concentration of 0.05-0.5 mol / L to obtain an oil phase extraction liquid B and a water phase washing residual liquid; (3) stripping the oil phase extraction liquid B with a composite stripping agent composed of phosphoric acid and acetylacetone with a molar ratio of (5-15):1, and controlling the pH of the stripping system to be 5-7 to obtain a lithium phosphate wet product by phase separation; (4) adding lithium hydroxide to the lithium phosphate wet product to react, and filtering to obtain a lithium phosphate product.

2. The process for extracting lithium from a lithium depleted liquor to obtain lithium phosphate according to claim 1, characterized in that, In step (1), the extraction agent is a composite extraction agent formed by mixing a main extraction agent, a co-extraction agent and a diluent; wherein the molar ratio of the main extraction agent to the co-extraction agent is (0.5-3):

1.

3. The process for extracting lithium from a lithium-laden mother liquor to obtain lithium phosphate according to claim 2, characterized in that, The main extraction agent is at least one selected from benzoyltrifluoroacetone, 2-thiophenecarbonyltrifluoroacetone, 1-phenyl-1,3-decanedione, 2-naphthoyltrifluoroacetone, trifluoroacetylacetone, 1-(3,5-bistrifluoromethylphenyl)-1,3-butanedione, 1-heptyl-3-phenyl-1,3-propanedione, dodecylphenyl-methyl-beta diketone, dioctyl phthalate, butyl salicylate.

4. The method of claim 2 for extracting lithium from a lithium-laden mother liquor to obtain lithium phosphate, characterized in that, The co-extraction agent is at least one selected from trioctylphosphine oxide, tributyl phosphate, di(2-ethylhexyl) phosphate, 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester, di(2,4,4-trimethylpentyl) phosphate, di(n-octyl) phosphate.

5. The method of claim 2 for extracting lithium from a lithium-laden mother liquor to obtain lithium phosphate, characterized in that, The diluent is at least one selected from 260# solvent oil, cyclohexanone, ethyl acetate, n-octanol, sec-octanol.

6. The process for extraction of lithium from a lithium depleted liquor to obtain lithium phosphate as claimed in claim 1 wherein, In step (3), the O / A ratio of the stripping is (10-20):

1.

7. The process for extraction of lithium from a lithium depleted liquor to obtain lithium phosphate as claimed in claim 6 wherein, The concentration of phosphoric acid in the composite stripping agent is 1-6 mol / L.

8. The method of extracting lithium from a lithium-laden mother liquor to obtain lithium phosphate according to claim 1, characterized in that, In step (4), after adding lithium hydroxide, the pH value is adjusted to 10-13.

Images