Method for treating lithium precipitation mother liquor based on eutectic solvent extraction-precipitation

Abstract

According to the method for treating the lithium precipitation mother liquor based on eutectic solvent extraction-precipitation, trioctylphosphine oxide and tetradecyl phosphoric acid are mixed to form a eutectic solvent system, trioctylphosphine oxide serves as a hydrogen bond acceptor, and the property of an eutectic solvent extraction-precipitation agent is regulated and controlled. Compared with an extraction-precipitation strategy of single tetradecyl phosphoric acid, by introducing trioctylphosphine oxide, the particle size of the precipitate is remarkably increased, an organic solvent is prevented from being used in the reverse extraction process, and meanwhile, the high-selectivity precipitation capacity of tetradecyl phosphoric acid TDPA to lithium is kept. The lithium can be enriched without isopropyl ether in the reverse extraction process, so that the isopropyl ether evaporation process in the extraction-precipitant circulation process is reduced, the overall energy consumption is reduced, and meanwhile, the performance attenuation of the extraction-precipitant caused by isopropyl ether oxidation is also avoided.

Description

Technical Field

[0001] This invention belongs to the field of lithium preparation technology, specifically relating to a method for treating lithium mother liquor based on eutectic solvent extraction-precipitation. Background Technology

[0002] Lithium precipitation mother liquor is a high-salt, lithium-containing wastewater generated during the sodium carbonate lithium precipitation process. It contains approximately 20%–30% residual lithium, along with high sodium content and high alkalinity. Traditional treatment methods typically involve acidification to remove carbonate, evaporation and concentration, and freeze crystallization to convert it into a lithium-rich solution for secondary lithium precipitation. This process suffers from high acid and alkali consumption, high lithium loss rates, low purity of the lithium carbonate product, and high energy consumption. Therefore, there is an urgent need to develop a low-cost, high-lithium-recovery method for treating lithium precipitation mother liquor.

[0003] The current consensus in industry and academia is to develop an efficient lithium selective extraction and enrichment technology to achieve selective separation of lithium ions in high-sodium systems and obtain high-concentration lithium solutions through a relatively simplified process for the preparation of high-purity lithium salt products. Lithium extraction technologies for lithium precipitation mother liquor include chemical precipitation, solvent extraction, lithium-ion sieve adsorption, and electroadsorption. Among these, synergistic solvent extraction technology based on (β-diketone-like) compounds has been industrially applied in lithium precipitation mother liquor from salt lakes and lepidolite extraction. However, diketone extraction systems typically suffer from high water solubility and high cost, leading to high initial investment, high operating costs, and high post-treatment costs for the raffinate. Furthermore, (β-diketone-like) extraction processes usually require maintaining a pH > 10 to fully extract lithium from the mother liquor; the existing carbonate ions cannot be directly utilized, typically requiring additional saponification or the addition of NaOH, further increasing costs.

[0004] Extraction-precipitation is a novel metal enrichment strategy proposed in recent years. This technology involves adding a solid organic precipitant with high selectivity for the target metal to the feed solution, allowing the metal to separate from the solution in a solid phase. Subsequently, under ultra-high solid-liquid ratio conditions, back-extraction is performed using an inorganic acid. The extraction-precipitant melts to form an oil phase, which naturally separates from the back-extraction solution, resulting in a highly concentrated target metal solution. Compared to traditional chemical precipitation or solvent extraction, this method offers significant advantages in terms of metal enrichment factor, control of organic pollution in the aqueous phase, and recycling of the precipitant. In previous studies, we found that long-chain alkylphosphonic acids can be used for selective precipitation of lithium mother liquor. However, the melting point of alkylphosphonic acids is close to the boiling point of water; therefore, isopropyl ether needs to be added during back-extraction to promote phase separation, reducing the process's economics and environmental friendliness. Furthermore, isopropyl ether is prone to oxidation during recycling, generating oxidation byproducts such as triacetone triperoxide and diacetone dimeroxide, leading to a gradual decline in the performance of the extraction-precipitant. Based on these issues, it is necessary to seek an alternative strategy that can effectively control the physicochemical properties of tetradecyl phosphoric acid without introducing additional organic solvents. Summary of the Invention

[0005] To improve the above-mentioned technical problems, the present invention provides a eutectic solvent that uses tri-n-octylphosphine oxide (TOPO) as a hydrogen bond acceptor (HBA) and tetradecylphosphonic acid as a hydrogen bond donor (HBD).

[0006] According to an embodiment of the present invention, the molar ratio of HBD to HBA is 1:(0.1-2), preferably 1:(0.6-1), and exemplary ratios are 1:0.1, 1:0.2, 1:0.4, 1:0.6, 1:0.8, 1:1, 1:1.5 or 1:2.

[0007] The present invention also provides a method for preparing the above-mentioned eutectic solvent, comprising mixing tri-n-octylphosphine oxide (TOPO) with tetradecylphosphonic acid to prepare the low eutectic solvent.

[0008] According to an embodiment of the present invention, the molar ratio of tetradecylphosphonic acid to tri-n-octylphosphine oxide (TOPO) is 1:(0.1-2), preferably 1:(0.2-1, and exemplary ratios are 1:0.1, 1:0.2, 1:0.4, 1:0.6, 1:0.8, 1:1, 1:1.5 or 1:2.

[0009] According to an embodiment of the present invention, the mixing temperature is 25~80°C, for example 70°C; the mixing time is 1~10 min, for example 5 min.

[0010] This invention also provides the application of the above-mentioned eutectic solvent in the precipitation and separation of metal ions such as lithium, cobalt, nickel, copper, and rare earth elements. For example, its application in the precipitation and separation of lithium from lithium precipitation mother liquor.

[0011] In this invention, the eutectic solvent can be directly used to precipitate and separate lithium in a carbonate system.

[0012] The present invention also provides a method for separating lithium, comprising mixing the above-mentioned eutectic solvent with a lithium-containing liquid and carrying out a precipitation reaction.

[0013] According to an embodiment of the present invention, the lithium-containing liquid also contains at least one of sodium and potassium. When at least one of sodium and potassium is present, after precipitation is completed, lithium can be separated from at least one of sodium and potassium, with lithium entering the precipitate and at least one of sodium and potassium remaining in the aqueous phase.

[0014] According to an embodiment of the present invention, after precipitation is completed, the process further includes back-extracting the lithium-containing precipitate using a back-extracting agent. For example, the back-extracting agent is selected from one or more of water, inorganic acids, oxalates, and oxalic acid. Preferably, the inorganic acid is selected from one or more of hydrochloric acid, nitric acid, and sulfuric acid, and the oxalate includes, but is not limited to, sodium oxalate and ammonium oxalate, more preferably sodium oxalate.

[0015] According to an embodiment of the present invention, the molar concentrations of the back-extraction agent, inorganic acid, oxalate, and oxalic acid, are between 1.5 and 3.0 mol / L, for example, 1.9 mol / L, 2.15 mol / L, 2.4 mol / L, 2.65 mol / L, or 3.0 mol / L.

[0016] According to an embodiment of the present invention, the precipitation temperature is 60-90°C, for example 60°C, 70°C, 80°C or 90°C; the precipitation time is 30-90 min, for example 30 min, 60 min or 90 min.

[0017] The present invention also provides a method for treating lithium precipitation mother liquor, comprising adding the above-mentioned eutectic solvent to the lithium precipitation mother liquor to carry out a precipitation reaction, and filtering to obtain filtrate and lithium-containing precipitate.

[0018] According to an embodiment of the present invention, the filtration temperature is room temperature to 95°C, for example, room temperature, 30°C, 60°C, 80°C, 90°C or 95°C.

[0019] According to an embodiment of the present invention, the processing method further includes washing the lithium-containing precipitate, and then adding an inorganic acid for back-extraction to obtain a eutectic mixture oil phase and a lithium-containing back-extraction solution.

[0020] According to an embodiment of the present invention, the inorganic acid used in the back-extraction includes at least one of sulfuric acid, hydrochloric acid and nitric acid, preferably sulfuric acid.

[0021] According to an embodiment of the present invention, the processing method further includes washing the oil phase of the eutectic mixture, evaporating the solvent, and drying to obtain a regenerated eutectic solvent.

[0022] According to an embodiment of the present invention, the processing method further includes neutralizing the lithium-containing back-extraction solution with alkali, and then subjecting the neutralized solution to deep impurity removal through an ion exchange resin to obtain a refined lithium solution for lithium precipitation.

[0023] According to an embodiment of the present invention, the processing method further includes precipitating lithium in the lithium solution used for lithium precipitation by reverse precipitation to prepare lithium carbonate and secondary lithium precipitation mother liquor; According to an embodiment of the present invention, the processing method further includes washing the obtained lithium carbonate.

[0024] According to an embodiment of the present invention, the processing method further includes evaporating and concentrating the obtained filtrate to obtain an evaporated lithium precipitation mother liquor.

[0025] According to an embodiment of the present invention, the processing method further includes mixing the evaporated lithium precipitation mother liquor and the secondary lithium precipitation mother liquor for use in the next cycle of lithium recovery process.

[0026] According to an embodiment of the present invention, the method for treating the lithium precipitation mother liquor includes the following steps: (1) Tetradecylphosphonic acid and trioctylphosphine oxide are heated and stirred to form a liquid; (2) Add eutectic solvent to lithium precipitation mother liquor to carry out precipitation reaction, and filter to obtain filtrate and lithium-containing precipitate filter cake; (3) The lithium-containing precipitate was washed and then an inorganic acid was added for back-extraction to obtain a eutectic mixture oil phase and a lithium-containing back-extraction solution; (4) The oil phase of the eutectic mixture is washed and dried to obtain the regenerated eutectic solvent; (5) The lithium-containing back-extraction solution is neutralized with alkali and then subjected to deep impurity removal through ion exchange resin to obtain a refined lithium solution for lithium precipitation. (6) The lithium solution used for lithium precipitation is prepared by reverse precipitation method to obtain lithium carbonate and secondary lithium precipitation mother liquor.

[0027] This invention extracts lithium from lithium precipitation mother liquor based on tetradecyl phosphate-trioctylphosphine oxide eutectic extraction-precipitation method. It not only maintains the high selective precipitation ability of tetradecylphosphonic acid for Li, but also avoids the use of organic solvents in the back-extraction process, which significantly improves the greenness and economy of the process.

[0028] According to an embodiment of the present invention, in step (1), the molar ratio of tetradecylphosphonic acid to trioctylphosphine oxide is 1:(0.1-2), preferably 1:(0.2-1), and exemplary ratios are 1:0.1, 1:0.2, 1:0.4, 1:0.6, 1:0.8 or 1:1.

[0029] According to an embodiment of the present invention, the molar ratio of tetradecylphosphonic acid in the eutectic solvent to lithium in the lithium precipitation mother liquor is 0.45~0.525, preferably 0.475~0.5; for example, 0.475, 0.5 or 0.525.

[0030] According to an embodiment of the present invention, in step (2), the lithium concentration in the lithium precipitation mother liquor is greater than 0.5 g / L, the Na concentration is within 30~100 g / L, the calcium and magnesium ion concentrations are within 10 mg / L, and the ratio of carbonate to lithium ions in the lithium precipitation mother liquor is greater than 0.5.

[0031] According to an embodiment of the present invention, in step (2), the reaction temperature during the precipitation process is 60~80℃, for example 60℃, 70℃, 80℃ or 90℃; the reaction time is 30~120 min, for example 30 min, 60 min or 90 min.

[0032] According to an embodiment of the present invention, in step (3), the washing method is rinsing, and the amount of washing water is 0.4 to 1.5 times the volume of the lithium precipitation mother liquor, for example, 0.4 times, 0.6 times, 0.8 times, 1.0 times, 1.2 times or 1.5 times.

[0033] According to an embodiment of the present invention, in step (3), the hydrogen concentration in the inorganic acid being back-extracted is 1.5~4 mol / L, the back-extraction liquid-solid ratio is 1:1~1:2, the back-extraction temperature is 40~90℃, for example 40℃, 60℃ or 90℃; the back-extraction time is 120~240min; for example 180min.

[0034] According to an embodiment of the present invention, in step (4), the washing solvent is water; the volume ratio of the washing water to the volume ratio of the back-extracted precipitate is 0.75 to 1.5 times, the washing time is 5 to 20 min, the washing temperature is 25 to 60 ℃, and the number of washing cycles is 3 to 5.

[0035] According to an embodiment of the present invention, in step (4), the base used for neutralization is sodium hydroxide, and the pH value after neutralization is 10-13, preferably 11-12.

[0036] According to an embodiment of the present invention, in step (5), the ion exchange resin used has sodium aminophosphate type adsorption groups, the ratio of resin amount to solution volume is 50~100, and the flow rate is 5~20 BV / h.

[0037] According to an embodiment of the present invention, in step (6), the lithium precipitation method is reverse addition of a precipitant, the precipitant is a sodium carbonate solution of 250~300g / L, the molar ratio of the amount of precipitant to the molar amount of lithium is 0.5~0.55, the addition time is 1~2 h, the reaction temperature is 95~100℃, and the aging time is 30~60 min.

[0038] According to an embodiment of the present invention, the container for the experimental reaction is a flat-bottomed container, and the stirring method is vigorous stirring; According to an embodiment of the present invention, in step (6), the lithium carbonate washing liquid-solid ratio is 1:3 to 1:5, the washing temperature is 90 to 95°C, and the number of washing cycles is 3 to 4.

[0039] This invention also provides a method for preparing lithium carbonate, comprising the following steps: (1) Add a eutectic solvent to the lithium precipitation mother liquor to carry out a precipitation reaction, and filter to obtain filtrate and lithium-containing precipitate; (2) The lithium-containing precipitate was washed and then back-extracted with inorganic acid to obtain a eutectic mixture oil phase and a lithium-containing back-extraction solution; (3) The lithium-containing back-extraction solution is neutralized with alkali, and then the neutralized solution is thoroughly purified by ion exchange resin to obtain a refined lithium solution for lithium precipitation. (4) The lithium solution used for lithium precipitation is subjected to lithium precipitation by adding a precipitating agent to prepare lithium carbonate and secondary lithium precipitation mother liquor.

[0040] According to an embodiment of the present invention, the preparation method further includes evaporating and concentrating the filtrate obtained in step (1) to obtain an evaporated lithium precipitation mother liquor.

[0041] According to an embodiment of the present invention, the preparation method further includes mixing the evaporated lithium precipitation mother liquor and the secondary lithium precipitation mother liquor for use in the next cycle of lithium recovery process.

[0042] According to an embodiment of the present invention, in step (1), the molar ratio of tetradecylphosphonic acid to trioctylphosphine oxide in the eutectic solvent is 1:(0.1-2), preferably 1:(0.2-1), and exemplary ratios are 1:0.1, 1:0.2, 1:0.4, 1:0.6, 1:0.8 or 1:1.

[0043] According to an embodiment of the present invention, the molar ratio of tetradecyl phosphoric acid in the eutectic solvent to lithium in the lithium precipitation mother liquor is 0.45~0.525, preferably 0.475~0.5; for example, 0.475, 0.5 or 0.525.

[0044] According to an embodiment of the present invention, in step (1), the lithium concentration in the lithium precipitation mother liquor is greater than 0.5 g / L, the Na concentration is within 30~100 g / L, the calcium and magnesium ion concentrations are within 10 mg / L, and the ratio of carbonate to lithium ions in the lithium precipitation mother liquor is greater than 0.5.

[0045] According to an embodiment of the present invention, in step (1), the reaction temperature during the precipitation process is 60~80℃, for example 60℃, 70℃, 80℃ or 90℃; the reaction time is 30~120 min, for example 30 min, 60 min or 90 min.

[0046] According to an embodiment of the present invention, in step (2), the washing method is rinsing, and the amount of washing water is 0.4 to 1.5 times the volume of the lithium precipitation mother liquor, for example, 0.4 times, 0.6 times, 0.8 times, 1.0 times, 1.2 times or 1.5 times.

[0047] According to an embodiment of the present invention, in step (2), the hydrogen concentration in the back-extracted inorganic acid is 1.5~4 mol / L, the back-extracting liquid-solid ratio is 1:1~1:2, the back-extracting temperature is 40~90℃, and the back-extracting time is 120~240 min; According to an embodiment of the present invention, in step (3), the alkali used for neutralization is sodium hydroxide, and the pH value after neutralization is 10-13, preferably 11-12.

[0048] The beneficial effects of this invention: This invention utilizes a mixture of trioctylphosphine oxide and tetradecyl phosphoric acid to form a eutectic solvent, with trioctylphosphine oxide acting as a hydrogen bond acceptor to modulate the properties of the eutectic solvent extractor-precipitant. Compared to the extractor-precipitant strategy using tetradecyl phosphoric acid alone, this invention significantly increases the particle size of the precipitate by introducing trioctylphosphine oxide, avoiding the use of organic solvents in the back-extraction process while maintaining the high selective precipitation ability of tetradecylphosphonic acid for lithium. Since lithium enrichment can be achieved without the use of isopropyl ether in the back-extraction process, it not only reduces the isopropyl ether evaporation process during the extractor-precipitant cycle and lowers overall energy consumption, but also avoids the performance degradation of the extractor-precipitant caused by isopropyl ether oxidation. Attached Figure Description

[0049] Figure 1 The effect of the amount of trioctylphosphine oxide added in the eutectic solvent on the particle size of the enriched precipitate (1:0~1:1 represents the molar ratio of tetradecylphosphonic acid to trioctylphosphine oxide in the eutectic solvent).

[0050] Figure 2 The upper and middle figures show the infrared spectra of the eutectic solvent (a 1:1 molar ratio of tetradecylphosphonic acid and trioctylphosphine oxide) before and after recycling (the solid line is the infrared spectrum before recycling (without using the extraction precipitant), and the dashed line is the infrared spectrum after recycling). Figure 2 The lower figure shows the infrared spectra of tetradecylphosphonic acid before and after recycling (the solid line is the infrared spectrum before recycling (without using the extraction precipitant), and the dashed line is the infrared spectrum after recycling). Detailed Implementation

[0051] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0052] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0053] Example 1: 0.144 mmol of a eutectic mixture (calculated as tetradecylphosphonic acid, i.e., the molar amount of tetradecylphosphonic acid in the eutectic solvent is 0.144 mmol) was added to 10 mL of simulated lithium-containing wastewater with a pH of 12.46, a Li concentration of 0.2 g / L, a Na concentration of 10 g / L, and a K concentration of 10 g / L; the reaction was carried out at 70 °C for 60 min. The corresponding precipitate particle size is as follows. Figure 1 As shown in the figure, the results indicate that, compared with the extraction-precipitation strategy using only tetradecyl phosphoric acid, the present invention significantly increases the particle size of the precipitate by introducing trioctylphosphine oxide, thus avoiding the use of organic solvents in the back-extraction process.

[0054] Example 2: In a 10 mL lithium precipitation mother liquor with a pH of 10.34 (Li: 2.57 g / L, Na: 60.33 g / L, K: 27.43 mg / L, Ca: 0.76 mg / L, B: 16.389 mg / L, SO42-), 2- A eutectic solvent with a molar ratio of tetradecylphosphonic acid to trioctylphosphine oxide of 1:1 was added to the solution (115.52 g / L); Table 1 summarizes the precipitation rate of lithium ions under different parameters.

[0055] Table 1. Effect of precipitation parameters on lithium precipitation rate

[0056] Example 3: 62.81 g of eutectic solvent (molar ratio of tetradecylphosphonic acid to trioctylphosphine oxide was 1:1) and 0.5 L of lithium precipitation mother liquor (Li: 2.57 g / L, Na: 60.33 g / L, K: 27.43 mg / L, Ca: 0.76 mg / L, B: 16.389 mg / L, SO42-) were mixed. 2- 115.52 g / L, CO32- 0.22 mol / L, HCO3 - The reaction mixture (0.02 mol / L) was reacted at 80 °C for 3 h. The reaction mixture was then hot-filtered using a Buchner funnel to obtain a lithium-containing precipitate filter cake. The filter cake was washed with water, and the wash water was collected every 50 mL to analyze the metal ion concentration. Table 2 shows the metal ion concentrations in different volumes of wash water.

[0057] Table 2. Effect of wash water volume on the concentration of metal ions in wash water

[0058] Example 4: The lithium precipitate obtained in Example 3 after washing with 600 mL of water was dried, and 12.3 g was added to a petri dish with a bottom spout. Then, 10 mL of H2SO4 was added, the beaker was sealed with a rubber stopper, and the mixture was placed in a water bath at 60°C and stirred for 3 hours. After the reaction was complete, the lower aqueous layer was collected as the primary back-extraction solution. Table 3 shows the metal ion concentration and back-extraction rate in the back-extraction solution at different sulfuric acid concentrations.

[0059] Table 3. Effects of H2SO4 concentration on metal stripping rate and metal ion concentration in stripping solution

[0060] The data in the table show that when the Li back-extraction rate is greater than 99%, the lithium concentration in the back-extraction solution exceeds 25 g / L, which meets the concentration requirements for lithium precipitation; while the sodium concentration in the back-extraction solution is less than 1 g / L, which is much lower than the sodium concentration in the lithium precipitation mother liquor, thus achieving selective extraction of lithium.

[0061] Example 5: The back-extraction solution from Example 4 was adjusted to pH 11.98 with alkali and then passed through an adsorption column (inner diameter = 12.8 mm, column volume = 5 mL) packed with Sphelite ACD-500 (Na type) resin (12 BV / h) from top to bottom to remove calcium. The eluent volumes of 0–72 BV were combined, and 100 mL was taken and added dropwise at 0.1 L / h to an adsorption column packed with Sphelite ACD-500 (Na type) resin. The reaction mixture was added to a 250 mL flat-bottomed beaker. During the addition process, the reaction system temperature was maintained at 95℃ using an oil bath, and a 50 mm cylindrical magnetic stirrer was used to ensure uniform mixing. After addition, the mixture was aged for another 30 min under the same conditions, and then filtered while hot to obtain crude Li₂CO₃. The crude Li₂CO₃ was washed three times at 90℃ with a liquid-to-solid ratio of 3:1 and dried to obtain lithium carbonate. After washing, the Li₂CO₃ was vacuum dried at 70℃ for 12 hours to obtain the Li₂CO₃ product. The lithium carbonate content was determined by titration according to standard GB / T 11064.1-2024, and the value was 99.8%. Table 4 shows the changes in the composition of the feed solution during the preparation of lithium carbonate.

[0062] Table 4. Changes in solution composition during lithium carbonate preparation

[0063] This invention describes the technical solution using lithium precipitation mother liquor as a representative application. However, the technical principles and process routes of this invention are not limited to the lithium precipitation mother liquor system. They are also applicable and scalable to the separation and enrichment systems of key metal ions such as rare earth, cobalt, nickel, and copper.

[0064] Example 6: 12.56 g of eutectic solvent (molar ratio of tetradecylphosphonic acid to trioctylphosphine oxide 1:1) was mixed with 100 mL of lithium precipitation mother liquor (Na: 60.33 g / L, K: 27.43 mg / L, Ca: 0.76 mg / L, B: 16.389 mg / L, SO42-). 2- 115.52 g / L, CO3 2- 0.22 mol / L, HCO3 - The reaction mixture (0.02 mol / L) was reacted at 80 °C for 30 min. The reaction mixture was then hot-filtered at room temperature using a Buchner funnel to obtain a lithium-containing precipitate filter cake. The filter cake was washed with water until the wash water was neutral, and then dried to obtain the lithium-containing precipitate. Subsequently, the lithium-containing precipitate, 10 mL of 2.15 mol / L H₂SO₄, and a magnetic stir bar were sequentially added to a Faper beaker, and back-extracted at 60 °C for 3 h to obtain a eutectic mixture oil phase. After the lower back-extraction solution was discharged, the organic phase was back-extracted a second time using 0.5 mol / L H₂SO₄ (back-extracted at 60 °C for 1 h) to remove residual metal ions. After the second back-extraction solution was discharged, the organic phase was washed with 10 mL of water at 60 °C for 10 min, four times, to remove residual acid. Finally, after drying the regenerated eutectic mixture oil phase and replenishing the operating losses, it was recycled for lithium extraction-precipitation in the lithium precipitation mother liquor. The precipitation of lithium in the lithium precipitation mother liquor by the eutectic solvent under different cycles is shown in Table 5.

[0065] Comparative Example 1 Tetradecylphosphonic acid (4.476 g) was mixed with 100 mL of lithium precipitation mother liquor (Na: 55.16 g / L, K: 67.69 mg / L, Ca: 1.29 mg / L, Mg: 1.77 mg / L, B: 24.49 mg / L, SO42-). 2- 107.95 g / L, CO3 2- 0.23 mol / L, HCO3 - The reaction mixture (0.23 mol / L) was reacted at 90 °C for 1 h. The reaction mixture was then hot-filtered at room temperature using a Buchner funnel to obtain a lithium-containing precipitate filter cake. The filter cake was washed with water until the wash water was neutral, and then dried to obtain a lithium-containing precipitate. Subsequently, the lithium-containing precipitate, 50 mL of isopropyl ether, 10 mL of 3 mol / L H₂SO₄, and a magnetic stir bar were sequentially added to a Faper beaker, and back-extracted at 60 °C for 1 h to obtain an organic phase containing monotetradecylphosphonic acid and isopropyl ether. After the lower back-extraction solution was discharged, the organic phase was back-extracted a second time using 2 mol / L H₂SO₄ (back-extracted at 60 °C for 1 h) to remove residual metal ions. After the second back-extraction solution was discharged, the organic phase was washed with 10 mL of water at 60 °C for 10 min, 5 times, to remove residual acid. Finally, the organic phase was transferred to a round-bottom flask and rotary evaporated under negative pressure at 60 °C to obtain regenerated tetradecylphosphonic acid. After replenishing the operating losses of tetradecylphosphonic acid, it was recycled for the extraction-precipitation of lithium in the lithium precipitation mother liquor. The precipitation of lithium in the lithium precipitation mother liquor by tetradecylphosphonic acid at different cycles is shown in Table 5. Table 5. Comparison of cycling performance between tetradecylphosphonic acid, trioctylphosphine oxide, and tetradecylphosphonic acid.

[0066] The data in the table show that the eutectic solvent formed by tetradecylphosphonic acid and trioctylphosphine oxide improves lithium precipitation performance during recycling, while the precipitation rate of lithium by tetradecylphosphonic acid decreases during recycling. This indicates that the eutectic solvent formed by tetradecylphosphonic acid and trioctylphosphine oxide has superior recycling performance compared to tetradecylphosphine.

[0067] The infrared spectra of the eutectic solvent formed by tetradecylphosphonic acid and trioctylphosphine oxide after cycling with tetradecylphosphonic acid are as follows: Figure 2 As shown. At 1370 cm -1 The infrared absorption peak at [location] corresponds to the CH3 angular vibration absorption peak. The CH3 angular vibration absorption peak positions of tetradecylphosphonic acid and trioctylphosphine oxide are completely consistent after recycling, while the angular vibration peak of tetradecylphosphonic acid changes from 1371 cm⁻¹. -1Blue shifted to 1374 cm -1 The shift in the infrared vibration peak indicates a significant change in the chemical environment of methyl groups. This may be due to the degradation of isopropyl ether during the back-extraction process by photocatalytic degradation, producing triacetone peroxide and diacetone dimeroxide byproducts, which leads to a decrease in the performance of the extractant-precipitant.

[0068] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A eutectic solvent, characterized in that, It uses tri-n-octylphosphine oxide (TOPO) as a hydrogen bond acceptor (HBA) and tetradecylphosphonic acid as a hydrogen bond donor (HBD). The molar ratio of HBD to HBA is 1:(0.1-2), preferably 1:(0.6-1).

2. The method for preparing the eutectic solvent according to claim 1, characterized in that, The method includes mixing tri-n-octylphosphine oxide (TOPO) with tetradecylphosphonic acid to prepare the low eutectic solvent.

3. The preparation method according to claim 2, characterized in that, The molar ratio of tetradecylphosphonic acid to tri-n-octylphosphine oxide (TOPO) is 1:(0.1-2), preferably 1:(0.2-1).

4. The application of the eutectic solvent of claim 1 in the precipitation and separation of metal ions such as lithium, cobalt, nickel, copper, and rare earth elements. For example, its application in the extraction and separation of lithium from lithium precipitation mother liquor.

5. A method for separating lithium, characterized in that, This includes mixing the eutectic solvent of claim 1 with a lithium-containing liquid and then performing precipitation separation.

6. A method for treating lithium precipitation mother liquor, characterized in that, The process includes adding the eutectic solvent of claim 1 to the lithium precipitation mother liquor to carry out a precipitation reaction, and filtering to obtain filtrate and lithium-containing precipitate.

7. The processing method as described in claim 6, characterized in that, Includes the following steps: (1) Tetradecylphosphonic acid and trioctylphosphine oxide are heated and stirred to form a liquid; (2) Add eutectic solvent to lithium precipitation mother liquor to carry out precipitation reaction, and filter to obtain filtrate and lithium-containing precipitate filter cake; (3) The lithium-containing precipitate was washed and then an inorganic acid was added for back-extraction to obtain a eutectic mixture oil phase and a lithium-containing back-extraction solution; (4) The oil phase of the eutectic mixture is washed and dried to obtain the regenerated eutectic solvent; (5) The lithium-containing back-extraction solution is neutralized with alkali and then subjected to deep impurity removal through ion exchange resin to obtain a refined lithium solution for lithium precipitation. (6) The lithium solution used for lithium precipitation is prepared by reverse precipitation method to obtain lithium carbonate and secondary lithium precipitation mother liquor.

8. The processing method as described in claim 7, characterized in that, In step (1), the molar ratio of tetradecylphosphonic acid to trioctylphosphine oxide is 1:(0.1-2), preferably 1:(0.2-1). And / or, the ratio of the amount of tetradecyl phosphoric acid in the eutectic solvent to the molar equivalent of lithium in the lithium precipitation mother liquor is 0.475~0.525; And / or, the reaction temperature during the precipitation process is 60~80℃, and the reaction time is 30~120 min; And / or, in step (3), the hydrogen concentration in the back-extracted inorganic acid is 1.5~4 mol / L, the back-extracting liquid-solid ratio is 1:1~1:2, the back-extracting temperature is 40~90 ℃, and the back-extracting time is 120~240 min.

9. The processing method as described in claim 7, characterized in that, In step (4), the base used for neutralization is sodium hydroxide, and the pH value after neutralization is 10-13, preferably 11-12; And / or, in step (5), the ion exchange resin used is an aminophosphate sodium type resin, the ratio of resin volume to solution volume is 50~100, and the flow rate is 5~20 BV / h. And / or, in step (6), the lithium precipitation method is reverse addition of a precipitant, the precipitant is a sodium carbonate solution of 250~300 g / L, the amount of precipitant is 0.5~0.55 of the lithium molar equivalent, the addition time is 1~2 h, the reaction temperature is 95~100 ℃, and the aging time is 30~60 min.

10. A method for preparing lithium carbonate, characterized in that, Includes the following steps: (1) Add the eutectic solvent of claim 1 to the lithium precipitation mother liquor to carry out a precipitation reaction, and filter to obtain filtrate and lithium-containing precipitate; (2) The lithium-containing precipitate was washed and then back-extracted with inorganic acid to obtain a eutectic mixture oil phase and a lithium-containing back-extraction solution; (3) The lithium-containing back-extraction solution is neutralized with alkali, and then the neutralized solution is thoroughly purified by ion exchange resin to obtain a refined lithium solution for lithium precipitation. (4) Lithium carbonate and secondary lithium precipitation mother liquor are prepared by adding a precipitant to the refined lithium solution used for lithium precipitation.

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