Method for producing lithium dihydrogen phosphate by utilizing low-lithium-concentration strong-basicity lithium-containing leaching solution

Abstract

The invention discloses a method for producing lithium dihydrogen phosphate by using a low-lithium-concentration strong-basicity lithium-containing leaching solution, and relates to the technical field of lithium salt production. The method specifically comprises the following steps: adding a sodium phosphate or sodium hydrogen phosphate solution into the lithium-containing leaching solution, reacting to obtain slurry, carrying out solid-liquid separation, washing the obtained filter cake, adding water, slurrying, adding phosphoric acid, completely dissolving to obtain a solution, adding a precipitant into the solution, adjusting the pH value to alkalescence, precipitating, and drying to obtain the lithium-containing leaching solution. And carrying out solid-liquid separation on the obtained precipitate, washing the obtained filter cake, adding water for slurrying, adding phosphoric acid, continuously stirring for reaction, completely dissolving to obtain a clear lithium dihydrogen phosphate solution, and treating to obtain the battery-grade lithium dihydrogen phosphate. According to the method, efficient extraction of lithium is successfully realized, a lithium dihydrogen phosphate product with a high additional value is generated, a large amount of acid consumption in the alkali liquor neutralization process is avoided, the consumption of alkali in the solution is relatively low, and the solution can be returned to the previous procedure for cyclic utilization.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium salt production, and more specifically, to a method for producing lithium dihydrogen phosphate using a strongly alkaline lithium-containing leaching solution with a low lithium concentration. Background Art

[0002] With the continuous development of the new energy industry, the demand for lithium dihydrogen phosphate has been increasing in recent years, and the industry development prospect is very optimistic.

[0003] Alkaline leaching of lepidolite is a relatively common method for preparing lithium dihydrogen phosphate at present, which has the advantage of high lithium leaching rate. However, this method will produce a strongly alkaline lithium-containing leaching solution with a low lithium concentration, and it is impossible to directly form lithium carbonate precipitation. If traditional adsorption or extraction processes are used to extract lithium, it is difficult to find an adsorbent or extractant suitable for strong alkaline conditions. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for producing lithium dihydrogen phosphate using a strongly alkaline lithium-containing leaching solution with a low lithium concentration in view of the above-mentioned prior art deficiencies. The method successfully realizes the efficient extraction of lithium, generates a lithium dihydrogen phosphate product with high added value, avoids a large amount of acid consumption in the alkali liquid neutralization process, consumes less alkali in the solution, and can be recycled to the previous process.

[0005] To achieve the above object, the main technical solution adopted by the present invention is as follows:

[0006] A method for producing lithium dihydrogen phosphate using a strongly alkaline lithium-containing leaching solution with a low lithium concentration, comprising the following steps:

[0007] S1. Add a sodium phosphate or sodium hydrogen phosphate solution to the lithium-containing leaching solution, react to obtain a slurry, and perform solid-liquid separation to obtain a filtrate and a filter cake;

[0008] S2. Wash the filter cake, add water for pulping, then add phosphoric acid, completely dissolve to obtain a solution, add a precipitant to the solution and adjust the pH to weakly alkaline for precipitation, obtain a precipitate and perform solid-liquid separation;

[0009] S3. Wash and filter the filter cake obtained after solid-liquid separation in S2, then add water for pulping, add phosphoric acid and continuously stir for reaction, completely dissolve to obtain a clear lithium dihydrogen phosphate solution, and obtain battery-grade lithium dihydrogen phosphate after treatment.

[0010] Further, in S1, the lithium-containing leaching solution is a strongly alkaline solution, the lithium ion concentration therein is less than 5 g / L, the main solutes are sodium hydroxide and potassium hydroxide, and the sodium hydroxide concentration is higher than 190 g / L.

[0011] The reaction to obtain the slurry is completed under strongly alkaline conditions at a temperature of 50-90 °C.

[0012] The filtrate is a mixed alkali solution, and the filter cake is a lithium-rich phosphate precipitate.

[0013] Furthermore, in the step S2, the precipitate is lithium phosphate or lithium hydrogen phosphate or a mixed precipitate of lithium phosphate and lithium hydrogen phosphate.

[0014] The filter cake is slurried with water at a liquid-solid ratio of 3:1, and after being completely dissolved by adding phosphoric acid, the solutes in the obtained solution are lithium dihydrogen phosphate and sodium dihydrogen phosphate.

[0015] The precipitating agent is sodium phosphate, sodium hydroxide or lithium hydroxide, and the filtrate obtained after solid-liquid separation is a sodium hydrogen phosphate or sodium phosphate solution.

[0016] When adding phosphoric acid for dissolution, adding different amounts of phosphoric acid respectively corresponds to different working conditions: if phosphoric acid is added at a phosphorus-lithium molar ratio of 1:2, no precipitating agent needs to be added to the obtained solution; if phosphoric acid is added at a phosphorus-lithium molar ratio of 1:1, the subsequent precipitating agent added is sodium phosphate, sodium hydroxide or lithium hydroxide.

[0017] Furthermore, in the step S3, the filter cake obtained after solid-liquid separation is slurried with water at a liquid-solid ratio of 1:1, and phosphoric acid is added at a phosphorus-lithium molar ratio of 2:3 or 1:2.

[0018] The treatment of the clarified lithium dihydrogen phosphate solution includes the following steps:

[0019] S3.1 Evaporate the clarified lithium dihydrogen phosphate solution at 110°C - 130°C. After crystallization appears, cool it to below 50°C to precipitate lithium dihydrogen phosphate crystals;

[0020] S3.2 Perform solid-liquid separation on the precipitated lithium dihydrogen phosphate crystals. The liquid is returned to S3.1 for evaporation, and the solid is lithium dihydrogen phosphate;

[0021] S3.3 Dissolve the obtained lithium dihydrogen phosphate in water, repeat the above evaporation, crystallization and cooling process for recrystallization. Wash the solid obtained by recrystallization with a saturated lithium dihydrogen phosphate solution and then dry it. After being crushed, battery-grade lithium dihydrogen phosphate is obtained.

[0022] The present invention has the following beneficial effects and advantages:

[0023] 1. The present invention uses the phosphate precipitation method to extract lithium elements from the alkali solution, which can achieve a lithium leaching rate of more than 90%, and at the same time avoids the organic wastewater generated by the extraction method;

[0024] 2. The final product of the present invention is lithium dihydrogen phosphate, which realizes a high utilization rate of phosphorus elements and conforms to the principle of atom economy. Description of the Drawings

[0025] Figure 1It is the process flow diagram of a method for producing lithium dihydrogen phosphate using a strongly alkaline lithium-containing leaching solution with a low lithium concentration according to the present invention. Detailed implementation manners

[0026] The present invention will be further described below in conjunction with the accompanying drawings of the specification.

[0027] The main components of the alkaline lithium-containing leaching solution are shown in the following table.

[0028] Table 1 Composition table of lithium-containing leaching solution

[0029]

[0030] Example 1:

[0031] S1. Add a sodium phosphate solution to the lithium-containing leaching solution, and react under strong alkaline conditions at 80 °C to obtain a slurry. After solid-liquid separation of the slurry, a filtrate and a filter cake are obtained. Among them, the filtrate can be recycled as a mixed alkali solution to leach lepidolite, and the filter cake is a lithium disodium phosphate precipitate. The reaction is completed under strong alkaline conditions, with less alkali loss in this process, and it can be recycled to the previous alkali leaching process.

[0032] S2. Pulverize the lithium disodium phosphate precipitate with water at a liquid-solid ratio of 3:1, then add phosphoric acid at a phosphorus-lithium molar ratio of 1:1, stir and react at room temperature for a period of time until the precipitate is completely dissolved to obtain a solution. Add a sodium hydroxide solution as a precipitant to the solution and adjust the pH to 8 to precipitate a mixed precipitate of lithium phosphate and lithium hydrogen phosphate. Separate the solid and liquid of the mixed precipitate. The obtained filtrate is a sodium hydrogen phosphate solution, part of which is recycled to S1, and the rest is sold as a by-product.

[0033] S3. After washing and filtering the filter cake obtained by solid-liquid separation in S2, slurry it with water at a liquid-solid ratio of 1:1, then add phosphoric acid at a phosphorus-lithium molar ratio of 2:3, and continuously stir and react until it is completely dissolved to obtain a clear lithium dihydrogen phosphate solution; evaporate the clear lithium dihydrogen phosphate solution at 110 °C, and cool it to 45 °C after crystallization appears. The lithium dihydrogen phosphate crystals are precipitated due to the decrease in solubility; then separate the solid and liquid of the precipitated lithium dihydrogen phosphate crystals, and the liquid is returned to the evaporation and concentration process, and the solid is lithium dihydrogen phosphate; to improve the product purity, dissolve the obtained lithium dihydrogen phosphate in water, repeat the above evaporation, crystallization and cooling process for recrystallization, wash the solid obtained by recrystallization with a saturated lithium dihydrogen phosphate solution and then dry it, and obtain battery-grade lithium dihydrogen phosphate after crushing.

[0034] Example 2:

[0035] S1. Add a sodium hydrogen phosphate solution to the lithium-containing leaching solution, and react under strong alkaline conditions at 80 °C to obtain a slurry. After solid-liquid separation of the slurry, a filtrate and a filter cake are obtained. Among them, the filtrate can be recycled as a mixed alkali solution to leach lepidolite, and the filter cake is a lithium disodium phosphate precipitate. The reaction is completed under strong alkaline conditions, with less alkali loss in this process, and it can be recycled to the previous alkali leaching process.

[0036] S2. Pulverize the lithium disodium phosphate precipitate with water according to a liquid-solid ratio of 3:1, then add phosphoric acid according to a phosphorus-lithium molar ratio of 1:2, stir and react at 70 °C for 2 - 4 h. Part of the lithium disodium phosphate precipitate dissolves. There is no need to add a precipitant to the resulting solution. After sufficient reaction, a lithium hydrogen phosphate precipitate is obtained. After solid-liquid separation of the precipitate, the resulting filtrate is a sodium dihydrogen phosphate solution, and the sodium dihydrogen phosphate solution is all returned to S1 to replace the sodium phosphate solution as a reaction raw material.

[0037] S3. After washing and filtering the filter cake obtained from the solid-liquid separation in S2, slurry it with water according to a liquid-solid ratio of 1:1, then add phosphoric acid according to a phosphorus-lithium molar ratio of 1:2, and continuously stir and react until it is completely dissolved to obtain a clear lithium dihydrogen phosphate solution; evaporate the clear lithium dihydrogen phosphate solution at 120 °C. After crystallization appears, cool it to 48 °C. The lithium dihydrogen phosphate crystals are precipitated due to the decrease in solubility; then perform solid-liquid separation on the precipitated lithium dihydrogen phosphate crystals. The liquid is returned to the evaporation and concentration process, and the solid is lithium dihydrogen phosphate; to improve the product purity, dissolve the obtained lithium dihydrogen phosphate in water, repeat the above evaporation, crystallization, and cooling process for recrystallization, wash the solid obtained from recrystallization with a saturated lithium dihydrogen phosphate solution, and then dry it. After crushing, battery-grade lithium dihydrogen phosphate is obtained.

[0038] In this example, by controlling the amount of phosphoric acid used in S2, sodium can be selectively leached, while the lithium element remains in the solid phase. There is no need to add a precipitant again, which simplifies the lithium-sodium separation step.

[0039] Example 3:

[0040] S1. Add a sodium phosphate solution to the lithium-containing leaching solution, and react under strong alkaline conditions at 80 °C to obtain a slurry. After solid-liquid separation of the slurry, a filtrate and a filter cake are obtained. Among them, the filtrate can be recycled as a mixed alkali solution to leach lepidolite, and the filter cake is a lithium disodium phosphate precipitate. The reaction is completed under strong alkaline conditions, with less alkali loss in this process, and it can be recycled to the previous alkali leaching process.

[0041] S2. Slurry the lithium sodium phosphate precipitate according to a liquid-solid ratio of 3:1 with water, then add phosphoric acid according to a phosphorus-lithium molar ratio of 1:1, stir and react at room temperature for a period of time until the precipitate is completely dissolved to obtain a solution. Add lithium hydroxide solution as a precipitant to the solution and adjust the pH to 8, controlling the molar ratio of lithium ions in the precipitant to lithium ions in the solution to be 1:1. Precipitate lithium phosphate precipitate, separate the solid-liquid of the precipitate slurry, and the obtained filtrate is sodium hydrogen phosphate solution. The sodium hydrogen phosphate solution is all returned to S1 for recycling, replacing the sodium phosphate solution as a reaction raw material.

[0042] S3. After washing and filtering the filter cake obtained from the solid-liquid separation in S2, slurry it with water according to a liquid-solid ratio of 1:1, then add phosphoric acid according to a phosphorus-lithium molar ratio of 2:3, and continuously stir and react until it is completely dissolved to obtain a clear lithium dihydrogen phosphate solution; evaporate the obtained clear lithium dihydrogen phosphate solution at 130 °C, cool it to 45 °C after crystallization appears, and the lithium dihydrogen phosphate crystals are precipitated due to the decrease in solubility; then separate the solid-liquid of the precipitated lithium dihydrogen phosphate crystals, return the liquid to the evaporation and concentration process, and the solid is lithium dihydrogen phosphate; to improve the product purity, dissolve the obtained lithium dihydrogen phosphate in water, repeat the above evaporation, crystallization and cooling process for recrystallization, wash the solid obtained from the recrystallization with saturated lithium dihydrogen phosphate solution and then dry it, and obtain battery-grade lithium dihydrogen phosphate after crushing.

[0043] The above-disclosed are only the preferred embodiments of the present invention. Of course, the scope of the rights of the present invention cannot be limited thereby. Therefore, equivalent changes made according to the claims of the present invention still fall within the scope covered by the present invention.

Claims

1. A method for producing lithium dihydrogen phosphate using a low lithium concentration strong alkaline lithium-containing leachate, characterized in that: The following steps are involved: S1, adding sodium phosphate or sodium hydrogen phosphate solution to the lithium-containing leachate, obtaining slurry after reaction, and obtaining filtrate and filter cake by solid-liquid separation; S2, washing the filter cake and adding water to slurry, then adding phosphoric acid to obtain a solution after complete dissolution, adding a precipitant to the solution and adjusting the pH value to weak alkalinity for precipitation, obtaining a precipitate and performing solid-liquid separation; S3, washing and filtering the filter cake obtained after solid-liquid separation of S2, then adding water to slurry, and then adding phosphoric acid and continuously stirring to react, and obtaining a clear lithium dihydrogen phosphate solution after complete dissolution, and obtaining battery-grade lithium dihydrogen phosphate after treatment.

2. The method for producing lithium dihydrogen phosphate using a low lithium concentration strong alkaline lithium-containing leachate according to claim 1, characterized in that: In S1, the lithium-containing leaching solution is a strongly alkaline solution, in which the lithium ion concentration is less than 5 g / L, the main solutes are sodium hydroxide and potassium hydroxide, and the sodium hydroxide concentration is higher than 190 g / L.

3. The method for producing lithium dihydrogen phosphate using a low lithium concentration strong alkaline lithium-containing leachate according to claim 1, characterized in that: In S1, the reaction to obtain the slurry is completed under a strong alkaline condition at a temperature of 50 to 90°C.

4. The method for producing lithium dihydrogen phosphate using a low lithium concentration strong alkaline lithium-containing leachate according to claim 1, characterized in that: In S1, the filtrate is a mixed alkaline solution, and the filter cake is a lithium-rich phosphate precipitate.

5. The method for producing lithium dihydrogen phosphate using a low lithium concentration strong alkaline lithium-containing leachate according to claim 1, characterized in that: In S2, the precipitate is lithium phosphate or dilithium hydrogen phosphate or a mixed precipitate of lithium phosphate and dilithium hydrogen phosphate.

6. The method for producing lithium dihydrogen phosphate using a low lithium concentration strong alkaline lithium-containing leachate according to claim 1, characterized in that: In S2, the filter cake is slurried with water at a liquid-to-solid ratio of 3:1, and phosphoric acid is added to completely dissolve the filter cake, and the solute components of the obtained solution are lithium dihydrogen phosphate and sodium dihydrogen phosphate.

7. The method for producing lithium dihydrogen phosphate using a low lithium concentration strong alkaline lithium-containing leachate according to claim 1, characterized in that: In S2, the precipitant is sodium phosphate, sodium hydroxide or lithium hydroxide, and the filtrate obtained after solid-liquid separation is sodium hydrogen phosphate or sodium phosphate solution.

8. The method for producing lithium dihydrogen phosphate using a low lithium concentration strong alkaline lithium-containing leachate according to claim 1, characterized in that: In S2, when phosphoric acid is added for dissolution, different amounts of phosphoric acid are added to correspond to different working conditions: if phosphoric acid is added at a phosphorus-to-lithium molar ratio of 1:2, there is no need to add a precipitant to the resulting solution; if phosphoric acid is added at a phosphorus-to-lithium molar ratio of 1:1, the precipitant added subsequently is sodium phosphate, sodium hydroxide or lithium hydroxide.

9. The method for producing lithium dihydrogen phosphate using a low lithium concentration strong alkaline lithium-containing leachate according to claim 1, characterized in that: In S3, the filter cake obtained after solid-liquid separation is slurried with water at a liquid-to-solid ratio of 1:1, and phosphoric acid is added at a phosphorus-to-lithium molar ratio of 2:3 or 1:

2.

10. The method for producing lithium dihydrogen phosphate using a low lithium concentration strong alkaline lithium-containing leachate according to claim 1, characterized in that: In S3, the process of clarifying the lithium dihydrogen phosphate solution comprises the following steps: S3.1 Evaporate the clarified lithium dihydrogen phosphate solution at 110°C-130°C, and cool to below 50°C after crystallization occurs to precipitate lithium dihydrogen phosphate crystals; S3.2 The precipitated lithium dihydrogen phosphate crystals are separated into solid and liquid, and the liquid is returned to S3.1 for evaporation, and the solid is lithium dihydrogen phosphate; S3.3 Dissolve the obtained lithium dihydrogen phosphate in water, repeat the above evaporation, crystallization and cooling process for recrystallization, wash the solid obtained by recrystallization with a saturated lithium dihydrogen phosphate solution and then dry it, and after crushing, obtain battery-grade lithium dihydrogen phosphate.

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