A method for preparing battery grade lithium chloride by lithium sink solution extraction

Abstract

This invention relates to the field of lithium extraction from lithium precipitated mother liquor, and provides a method for preparing battery-grade lithium chloride from lithium precipitated mother liquor, comprising: S1 cooling the lithium precipitated mother liquor and then performing precision filtration to remove solid particles; S2 adding a crown ether additive to the lithium precipitated mother liquor after filtration in step S1 to obtain a pretreated mother liquor; S3 performing multi-stage extraction on the pretreated mother liquor using a lithium extractant to obtain a loaded organic phase; S4 first performing multi-stage washing on the loaded organic phase with a mixed washing liquid, and then back-extracting to obtain a lithium chloride solution; S5 sequentially subjecting the lithium chloride solution to resin adsorption for oil removal and evaporation crystallization to obtain a battery-grade lithium chloride product. This method reduces sodium activity from the source by adding a crown ether additive in the extraction stage to reduce sodium co-extraction, and simultaneously adds a sodium replacement additive in the washing stage to chemically complex residual sodium ions to improve the efficiency of single-stage washing, thereby reducing the number of extraction stages and washing stages, significantly reducing equipment investment and operating costs compared to traditional processes.

Description

Technical Field

[0001] This invention relates to the field of lithium extraction technology from lithium precipitation mother liquor, and more specifically, to a method for preparing battery-grade lithium chloride by extraction from lithium precipitation mother liquor. Background Technology

[0002] Lithium precipitate mother liquor is a lithium-containing waste liquid generated during the production of lithium carbonate. It contains a certain amount of lithium ions as well as high concentrations of impurity ions such as sodium, potassium, and calcium. Solvent extraction has become one of the main technical means to extract lithium from lithium precipitate mother liquor due to its advantages such as high separation efficiency, strong operational continuity, and suitability for industrial production.

[0003] In existing technologies, a single lithium extractant may be used in combination with multi-stage extraction and multi-stage washing processes to achieve the standard of battery-grade lithium chloride. However, due to the limited lithium-sodium separation coefficient, sodium ions are easily co-extracted in the extraction stage. To reduce the sodium content of the product, multi-stage extraction is required, resulting in a large number of extraction stages and a complex process. At the same time, the washing stage is for deep sodium removal, which relies on multi-stage washing to form a concentration gradient, resulting in a large number of washing stages and high acid consumption, further increasing the complexity of the process and production costs.

[0004] Alternatively, a composite extractant can be used to reduce the number of extraction steps. For example, patent CN118206141A discloses a process for preparing battery-grade lithium carbonate by extracting mother liquor after lithium precipitation. Specifically, it uses a composite extractant composed of a mixture of organic phosphoric acid compounds and organic sulfoxide compounds. Battery-grade lithium carbonate is obtained through four-stage countercurrent continuous extraction, sulfuric acid solution washing, and two-stage countercurrent continuous back-extraction. This process does not require pre-carbon removal, which shortens the process flow to some extent. However, it still involves four extraction stages, making the process flow relatively complex. Furthermore, the washing stage only uses dilute sulfuric acid, resulting in low single-stage washing efficiency and difficulty in deeply removing impurities such as sodium. The final product is lithium carbonate, which does not meet the requirements for battery-grade lithium carbonate. Summary of the Invention

[0005] To address the aforementioned shortcomings in existing technologies, the core objective of this invention is to solve the technical problems of high acid consumption and high production costs caused by the limited lithium-sodium separation coefficient, easy sodium co-extraction in the extraction stage, and the need for multi-stage sodium removal in the washing stage, as well as the inability of existing composite extractants to meet the lithium extraction quality requirements of downstream battery-grade lithium carbonate. Specifically, by adding crown ether-type additives in the extraction stage to reduce sodium activity from the source and thus reduce sodium co-extraction, and by adding sodium replacement additives in the washing stage to chemically complex residual sodium ions to enhance single-stage washing efficiency, the invention ultimately achieves a significant reduction in the number of extraction and washing stages.

[0006] This invention is achieved through the following technical solution:

[0007] The purpose of this invention is to provide a method for preparing battery-grade lithium chloride by lithium precipitation mother liquor extraction, comprising the following steps: S1. Cool the lithium precipitation mother liquor to 35~45℃ and then filter it through precision to remove solid particles; S2. Add crown ether additives to the lithium precipitation mother liquor after filtration in step S1 to obtain pretreated mother liquor, wherein the concentration of crown ether additives is controlled at 0.2-1.0 g / L; S3. The pretreated mother liquor is subjected to multi-stage extraction using lithium extractant, and the loaded organic phase is obtained after separation. S4. First, the supported organic phase is washed in multiple stages with a mixed washing solution, then back-extracted with hydrochloric acid, and separated to obtain a lithium chloride solution; S5. The lithium chloride solution is subjected to resin adsorption for oil removal and evaporation for crystallization in sequence to obtain battery-grade lithium chloride product.

[0008] Further, in step S2, the crown ether auxiliaries are 15-crown-5 or benzo-15-crown-5. Even further, the crown ether auxiliaries are added after precision filtration and before entering the extraction process, and are uniformly mixed with the lithium precipitation mother liquor using a static mixer. Even further, by online monitoring of the crown ether concentration in the aqueous phase, when the concentration is below 0.2 g / L, crown ether auxiliaries need to be added promptly; and when the concentration is above 0.5 g / L, the crown ether concentration is maintained at 0.2~0.5 g / L through raffinate discharge regulation.

[0009] In this invention, the crown ether adjuvant selectively complexes sodium ions in the aqueous phase of the extraction stage to reduce sodium activity, thereby reducing the tendency for sodium to be co-extracted in the extraction section. Simultaneously, in the washing stage, the acidic environment of the washing solution protonates the crown ethers that have entered the organic phase and back-extracts them back into the washing aqueous phase, which is then returned to the extraction section with the washing liquid, enabling the recycling of crown ethers. Compared to existing technologies that necessitate multi-stage extraction to reduce sodium co-extraction rates due to the limited separation coefficient between lithium and sodium, this invention, by introducing crown ether adjuvants into the aqueous phase of the extraction section, reduces sodium activity at the source, effectively inhibiting sodium co-extraction behavior, thus effectively reducing the number of extraction stages while ensuring an ideal lithium extraction rate.

[0010] Further, in step S3, the lithium extractant is one or more of Pextal-02 extractant, LIX 54 extractant, and LIX 84 extractant. Further still, the extraction ratio, i.e., organic phase: aqueous phase, is 1:1 to 3:1, and the extraction time is 3 to 8 minutes. Further still, the raffinate obtained after extraction is adjusted to pH below 5 with dilute sulfuric acid, allowed to stand for layering, then subjected to oil removal via a polymerizing resin to recover the entrained extractant, and the crown ether in the raffinate is discharged with the aqueous phase.

[0011] Further, in step S4, the mixed washing solution includes dilute sulfuric acid and a sodium replacement agent, wherein the concentration of the dilute sulfuric acid is 0.8–1.5 mol / L. Even further, the amount of sodium replacement agent added is 0.05%–0.2% of the volume of the mixed washing solution. Even further, the sodium replacement agent is one or more selected from ethylenediaminetetraacetic acid, hypozoxytriacetic acid, aminotrimethylenephosphonic acid, and hydroxyethylidene diphosphonic acid.

[0012] In this invention, the sodium replacement agent forms a water-soluble complex with residual sodium ions in the organic phase under the acidic environment of the washing stage, transferring sodium from the organic phase to the washing aqueous phase. This, combined with dilute sulfuric acid, enhances the sodium removal efficiency, thereby effectively improving the single-stage washing efficiency. Compared to the traditional method in existing technologies where multi-stage washing is forced due to the decay of the washing concentration gradient and the gradual reduction of mass transfer driving force, in order to achieve a deeper level of impurity removal, this invention, through the chemical complexation effect of the sodium replacement agent, changes the removal of sodium in the washing stage from physical replacement to chemical replacement. This significantly improves the single-stage washing efficiency, allowing for a substantial reduction in the number of washing stages while achieving the same or better impurity removal effect, and significantly reducing washing acid consumption.

[0013] Further, in step S4, the concentration of the hydrochloric acid is 5~9 mol / L; even further, the back-extraction ratio is 1:0.3~1:1 for the organic phase and the aqueous phase, and the back-extraction time is 5~10 min.

[0014] After hydrochloric acid back-extraction, the separated organic phase is washed once with water to obtain a washing solution. This washing solution is used to prepare the mixed washing solution or as makeup water for the back-extraction process. Furthermore, the first washing uses pure water or deionized water, with an organic phase to aqueous phase ratio of 1:0.5 to 1:1, to remove chloride ions and trace amounts of calcium and sulfate ions carried in the organic phase, preventing impurities from accumulating in the system.

[0015] Furthermore, the washing liquid generated in step S4 is returned to the lithium precipitation mother liquor from step S1, so that the washing liquid is mixed with the fresh mother liquor and then re-extracted. Even further, the washing liquid is homogenized in a buffer tank before being returned to stabilize its composition and reduce disturbances to the extraction system's equilibrium.

[0016] Furthermore, in step S5, the resin adsorption for oil removal uses polystyrene-type adsorption resin or polyacrylate-type adsorption resin. Even further, the flow rate for adsorption oil removal is 3-10 resin bed volumes per hour.

[0017] Further, in step S5, the evaporation crystallization is carried out by evaporating the lithium chloride solution at an evaporation temperature of 70~95°C until the lithium chloride concentration reaches saturation, then cooling it to room temperature, and finally separating it to obtain battery-grade lithium chloride product.

[0018] The technical solutions of the embodiments of the present invention have at least the following advantages and beneficial effects: (1) The lithium chloride products obtained by this invention have a main content of more than 99.95%, a sodium content of less than 0.0013%, and impurities such as potassium, calcium, and sulfate are all superior to battery grade standards.

[0019] (2) This invention reduces sodium co-extraction by adding crown ether additives in the extraction stage to reduce sodium activity at the source, and adds sodium replacement additives in the washing stage to chemically complex residual sodium ions to enhance single-stage washing efficiency. Ultimately, the number of extraction stages and washing stages is reduced, which significantly reduces equipment investment and operating costs compared to traditional processes.

[0020] (3) The present invention replaces the traditional physical replacement with the chemical complexation of sodium replacement agent, which significantly improves the single-stage washing efficiency. Under the condition that the number of washing stages is reduced to 3, the washing acid consumption is lower than that of the existing multi-stage washing process.

[0021] (4) The present invention uses crown ether additives, which are recycled back to the extraction section with the washing liquid in the washing section. The sodium replacement additive forms a water-soluble complex with sodium ions and is discharged with the washing liquid, without the need for additional separation and recovery, and the consumption of auxiliary materials is low. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the core process of this invention. Detailed Implementation

[0023] Example 1 This embodiment provides a method for preparing battery-grade lithium chloride by lithium precipitation mother liquor extraction, including the following: The composition of the lithium precipitation mother liquor obtained from a certain batch of lithium carbonate production is shown in Table 1: Table 1. Composition of lithium precipitating mother liquor

[0024] Further steps include: S1. Cooling and Filtration: The lithium precipitation mother liquor was cooled to 40°C via a heat exchanger and then filtered through a precision filter to remove solid particles, resulting in a clear filtrate.

[0025] S2. Add crown ether adjuvant: The filtrate obtained in step S1 was passed through a static mixer, and 15-crown-5 adjuvant was continuously added to control its concentration in the mixture at 0.5 g / L, resulting in a pretreated mother liquor. During operation, the concentration of crown ether in the aqueous phase was monitored online. When the concentration was below 0.2 g / L, additional adjuvant was added; when the concentration was above 0.5 g / L, the concentration was adjusted by discharging the raffinate to maintain it between 0.2 and 0.5 g / L.

[0026] S3, Extraction: Two-stage lithium extraction was performed on the pretreated mother liquor using Pextal-02 extractant from Zhongke Pure Extraction. The organic phase:aqueous phase ratio was 1.2:1, the aqueous phase flow rate was 70 mL / min, the organic phase flow rate was 84 mL / min, and the residence time for each extraction stage was 5 min. After extraction, the loaded organic phase was separated. The raffinate was allowed to stand in an oil separator, the pH was adjusted to below 5 with dilute sulfuric acid, and then the oil was removed by a polymerizing resin to recover the entrained extractant. The crown ether in the raffinate was discharged with the aqueous phase.

[0027] S4. Washing and Back-Extraction: The loaded organic phase was subjected to three stages of washing with 0.8 mol / L dilute sulfuric acid as the washing solution, and 0.1% (by volume) of ethylenediaminetetraacetic acid (EDTA) was added as a sodium replacement agent. The organic phase to aqueous phase ratio was 1:0.5, and the washing flow rate was 5 mL / min. The washed solution was returned to the lithium precipitation mother liquor from step S1, homogenized in a buffer tank, and then mixed with fresh mother liquor for re-extraction.

[0028] After washing, the organic phase underwent four stages of back-extraction. The back-extraction solution was 8 mol / L hydrochloric acid, the organic phase:aqueous phase ratio was 1:0.6, the back-extraction flow rate was 4 mL / min, and the residence time was 6 min. A lithium chloride solution was obtained after separation. The organic phase was then washed once with pure water at a ratio of 1:0.8. The washing solution was used to prepare the washing solution or as makeup water for the back-extraction process.

[0029] S5. Degreasing and evaporation crystallization: The lithium chloride solution obtained in step S4 was passed through a chromatography column packed with polystyrene adsorption resin to remove oil at a flow rate of 5 resin bed volumes / hour. After oil removal, the solution was evaporated and concentrated at 85°C until crystals precipitated. Heating was then stopped, and the solution was cooled to room temperature and filtered to obtain battery-grade lithium chloride product.

[0030] Example 2 The difference between this embodiment and Embodiment 1 is that benzo-15-crown-5 is used instead of 15-crown-5 as the crown ether adjuvant.

[0031] Example 3 The difference between this embodiment and Example 1 is that aminotrimethylenephosphonic acid is used instead of ethylenediaminetetraacetic acid as the sodium replacement agent.

[0032] Example 4 The difference between this embodiment and Embodiment 1 is that the lithium extractant is replaced by LIX 54 extractant instead of Pextal-02 extractant.

[0033] Comparative Example 1 The difference between this comparative example and Example 1 is that no crown ether adjuvant is added in step S2, while the remaining steps and parameters are the same as in Example 1.

[0034] Comparative Example 2 The difference between this comparative example and Example 1 is that the mixed washing solution in step S4 does not contain sodium replacement agent, and only dilute sulfuric acid is used for washing. The remaining steps and parameters are the same as in Example 1.

[0035] Comparative Example 3 The difference between this comparative example and Example 1 is that the number of washing stages in step S4 is increased to 4, and no sodium replacement agent is added. The remaining steps and parameters are the same as in Example 1.

[0036] Comparative Example 4 The difference between this comparative example and comparative example 3 is that the number of washing stages in step S4 is increased to 6, and no sodium replacement agent is added. The remaining steps and parameters are the same as in example 1.

[0037] Comparative Example 5 The difference between this comparative example and comparative example 4 is that the number of washing stages in step S4 is increased to 8, and no sodium replacement agent is added. The remaining steps and parameters are the same as in example 1.

[0038] Experimental Example 1 This test used the evaporation crystallization products obtained in Examples 1-4 and Comparative Examples 1-5 as samples. The core indicators were tested according to the GB / T11064 series standards. The test results are shown in Table 2 below: Table 2 Test Results of Various Indicators

[0039] Analysis of the data in Table 2 shows that, under the conditions of two extraction stages and three washing stages, the sodium content of Comparative Example 1, which did not add any additives, was as high as 0.008543%, and the main lithium chloride content was only 98.62%, failing to meet the standards for all indicators. Furthermore, the sodium content of Comparative Example 2, which only added crown ether additives, was 0.003831%, and the main lithium chloride content was 99.25%, still failing to meet the standards. Even further, the sodium content of Comparative Example 3, which only added sodium replacement additives, was 0.004221%, and the main lithium chloride content was 99.18%, also failing to meet the standards. However, in Examples 1 to 4, which added both crown ether additives and sodium replacement additives, the sodium content of the products was reduced to below 0.0013%, and the main lithium chloride content was increased to above 99.90%, all meeting the battery-grade standards.

[0040] Without adding any additives, the sodium content in Comparative Example 1, with a washing stage of 3, was severely excessive. In Comparative Example 4, even after increasing the washing stage to 5, the sodium content remained below the standard at 0.002306%. In Comparative Example 5, the sodium content was reduced to 0.001243% and met the standard only after further increasing the washing stage to 8. This represents a significant increase in washing stages compared to the 3 stages in Examples 1 to 4. In summary, the crown ether additive and the sodium replacement additive have a significant synergistic effect; both are indispensable. This synergistic effect allows the present invention to achieve product purity comparable to or even better than high-wash-stage processes while reducing the extraction stage to 2 and the washing stage to 3, thus significantly simplifying the process.

[0041] Experimental Example 2 This experimental example uses the same process conditions as Example 1, and continuous operation is conducted to verify the process stability. Specifically, it runs continuously for 25 days, co-evaporating and crystallizing to prepare 10 batches of battery-grade lithium chloride. After the system stabilizes, each batch of product is tested, and the results are shown in the table below: Table 3 Test results for each batch

[0042] Analysis of the data in Table 3 shows that, using the same process conditions as in Example 1, namely, two-stage extraction, three-stage washing, addition of crown ether additives and sodium replacement additives, during 25 days of continuous operation, all batches of products consistently met the battery-grade lithium chloride standards for various indicators such as lithium chloride content, sodium, potassium, calcium, sulfate, iron, magnesium, and copper, and most indicators significantly exceeded the standard requirements. This further verifies the stability and reliability of the preparation process provided by this invention during long-term continuous operation.

Claims

1. A method for preparing battery-grade lithium chloride by extraction from lithium precipitation mother liquor, characterized in that, Includes the following steps: S1. Cool the lithium precipitation mother liquor to 35~45℃ and then filter it through precision to remove solid particles; S2. Add crown ether additives to the lithium precipitation mother liquor after filtration in step S1 to obtain pretreated mother liquor, wherein the concentration of crown ether additives is controlled at 0.2-1.0 g / L; S3. The pretreated mother liquor is subjected to multi-stage extraction using lithium extractant, and the loaded organic phase is obtained after separation. S4. First, the supported organic phase is washed in multiple stages with a mixed washing solution, then back-extracted with hydrochloric acid, and separated to obtain a lithium chloride solution; S5. The lithium chloride solution is subjected to resin adsorption for oil removal and evaporation for crystallization in sequence to obtain battery-grade lithium chloride product.

2. The method for preparing battery-grade lithium chloride by lithium precipitation mother liquor extraction according to claim 1, characterized in that, In step S2, the crown ether adjuvant is 15-crown-5 or benzo-15-crown-5.

3. The method for preparing battery-grade lithium chloride by lithium precipitation mother liquor extraction according to claim 1, characterized in that, In step S3, the lithium extractant is one or more of Pextal-02 extractant, LIX 54 extractant, and LIX 84 extractant.

4. The method for preparing battery-grade lithium chloride by lithium precipitation mother liquor extraction according to claim 1, characterized in that, In step S4, the mixed washing solution includes dilute sulfuric acid and sodium displacement agent, wherein the concentration of the dilute sulfuric acid is 0.8 to 1.5 mol / L.

5. The method for preparing battery-grade lithium chloride by lithium precipitation mother liquor extraction according to claim 1, characterized in that, The amount of sodium replacement agent added is 0.05% to 0.2% of the volume of the mixed washing liquid.

6. The method for preparing battery-grade lithium chloride by lithium precipitation mother liquor extraction according to claim 1, characterized in that, The sodium replacement aid is one or more of ethylenediaminetetraacetic acid, hyponitrotriacetic acid, aminotrimethylenephosphonic acid, and hydroxyethylidene diphosphonic acid.

7. The method for preparing battery-grade lithium chloride by lithium precipitation mother liquor extraction according to claim 1, characterized in that, In step S4, the concentration of the hydrochloric acid is 5~9 mol / L; And / or, after the hydrochloric acid back-extraction, the separated organic phase is washed once with water to obtain a washing solution, which is used to prepare the mixed washing solution or as supplementary water for the back-extraction process.

8. The method for preparing battery-grade lithium chloride by lithium precipitation mother liquor extraction according to claim 1, characterized in that, The washing liquid generated after washing in step S4 is returned to the lithium precipitation mother liquor in step S1, so that the washing liquid is mixed with the fresh mother liquor and then re-extracted.

9. The method for preparing battery-grade lithium chloride by lithium precipitation mother liquor extraction according to claim 1, characterized in that, In step S5, the resin adsorption for oil removal uses polystyrene-type adsorption resin or polyacrylate-type adsorption resin.

10. The method for preparing battery-grade lithium chloride by lithium precipitation mother liquor extraction according to claim 1, characterized in that, In step S5, the evaporation crystallization is carried out by evaporating the lithium chloride solution at an evaporation temperature of 70~95℃ until the lithium chloride concentration reaches saturation, cooling it to room temperature, and then separating it to obtain battery-grade lithium chloride product.

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