A method for recovering high-purity lithium phosphate from lithium in mother liquor

Abstract

The invention relates to the technical field of lithium salt preparation, and discloses a method for recovering high-purity lithium phosphate from lithium in mother liquor, comprising the following steps: taking mother liquor to determine main components and pH value; when pH≤6, adjusting mother liquor pH value to less than 3 with sulfuric acid, adding Cu2O, stirring and filtering, adding alkali solution to the filtrate to adjust pH value to 12, filtering to obtain filtrate 1; when pH>6, adjusting mother liquor pH value to 12 with alkali solution, filtering, adjusting pH value to less than 3 with sulfuric acid, adding Cu2O, stirring and filtering to obtain filtrate 2; mixing filtrate 1 and filtrate 2, adjusting solution pH value to neutral, obtaining solution 3; treating solution 3 with bipolar membrane to obtain mixed alkali solution 4 and acid solution; stirring and dispersing crystal seeds added to the mixed alkali solution, and then slowly dropping a soluble phosphorus source to obtain slurry; stirring and centrifuging the slurry to obtain wet lithium phosphate, washing and drying to obtain battery-grade lithium phosphate. The purity of lithium phosphate prepared from mother liquor is improved, and the utilization rate of lithium in mother liquor generated in the production process of lithium carbonate and lithium hydroxide is improved.

Description

Technical Field

[0001] The invention relates to the technical field of lithium salt preparation, and in particular to a method for recovering high-purity lithium phosphate from lithium in a mother liquor. Background Art

[0002] A large amount of lithium-containing mother liquor will be generated during the production process of lithium carbonate and lithium hydroxide. These mother liquors contain a large amount of valuable metal ions. If they are directly discharged without effective treatment, it will not only cause waste of resources, but also cause serious pollution to the environment. Traditional lithium phosphate recovery methods mainly include chemical precipitation, solvent extraction, ion exchange, etc., but there are many defects, such as complex operation, high cost, low recovery rate, etc. In recent years, with the continuous advancement of membrane separation technology, lithium phosphate recovery technology based on membrane separation has gradually attracted the attention of researchers. Membrane separation technology is simple to operate, has low energy consumption, does not require the addition of additional reagents, and can achieve continuous operation. It is considered to be a potential new method for lithium phosphate recovery. At present, researchers at home and abroad have done a lot of work on the application of membrane separation technologies such as nanofiltration membranes and reverse osmosis membranes in lithium phosphate recovery, and have made certain research progress.

[0003] However, due to the complexity of the mother liquor source and composition, single membrane separation technology is difficult to meet actual needs and needs to be combined with other technologies to develop a more efficient and economical comprehensive recovery process.

[0004] In the document CN201110190405, a method for preparing battery-grade lithium dihydrogen phosphate using high-purity lithium carbonate lithium precipitation mother liquor is disclosed, which includes the following steps: using phosphoric acid and phosphate to perform preliminary and deep lithium extraction on the lithium carbonate lithium precipitation mother liquor to obtain a mixture of lithium phosphate and dilithium hydrogen phosphate, and then using the mixture to react with phosphoric acid to generate a lithium dihydrogen phosphate solution, and then through concentrated evaporation, cooling crystallization, centrifugal separation, saturated washing, drying, air flow crushing and packaging, to obtain battery-grade lithium dihydrogen phosphate. The method used in this document, when recycling, the purity of lithium phosphate is low, which does not meet the current needs.

[0005] Therefore, a new technical solution is needed to solve the above technical problems. Summary of the invention

[0006] In order to solve the above problems, the present invention discloses a method for recovering high-purity lithium phosphate from lithium in mother liquor. For mother liquors with different pH values, a chemical precipitation method is used to purify the mother liquor. After the purified mother liquor is self-neutralized, a bipolar membrane is used to purify the mother liquor to obtain a mixed alkaline solution, and lithium is further precipitated to obtain high-purity lithium phosphate, thereby improving the utilization rate of lithium in the mother liquor generated in the production process of lithium carbonate and lithium hydroxide.

[0007] The technical solution of the present invention is: a method for recovering high-purity lithium phosphate from lithium in mother liquor, comprising the following steps: Step 1: Take the mother solution to determine the main components and pH value; Step 2: When the pH is less than or equal to 6, the pH value of the mother liquor is adjusted to less than 3 with sulfuric acid, Cu2O is added, the mixture is stirred and filtered, and the pH value of the filtrate is adjusted to 12 with alkali solution, and the mixture is filtered to obtain filtrate 1; when the pH is greater than 6, the pH value of the mother liquor is adjusted to 12 with alkali solution, and the mixture is filtered, the pH value of the filtrate is adjusted to less than 3 with sulfuric acid, Cu2O is added, the mixture is stirred and filtered to obtain filtrate 2; Step 3: Mix filtrate 1 and filtrate 2, and adjust the pH value of the solution to neutral to obtain solution 3; Step 4: Solution 3 is treated by a bipolar membrane to obtain a mixed alkali solution 4 and an acid solution; Step 5: stirring and dispersing the seed crystals added to the mixed alkali solution, and then slowly dropping a soluble phosphorus source to obtain a slurry; Step 6: After stirring the slurry, centrifuge to obtain wet lithium phosphate, wash and dry to obtain battery-grade lithium phosphate.

[0008] Preferably, the mother liquor in step 1 is a lithium-containing solution produced in the production process of lithium carbonate and lithium hydroxide.

[0009] Preferably, in step 2, the amount of Cu2O added is n(Cl):n(Cu2O) is 3-1:1, and during the addition of Cu2O, the solution temperature is controlled at 20-30°C, and the stirring time is 20-40 minutes.

[0010] Preferably, during the bipolar membrane treatment in step 4, the voltage is controlled to be 35V, the current is 4-4.4A, the volume ratio of the stock solution, the acid solution and the alkali solution is 1:0.5:0.5-1:1:1, the conductivity is less than 5 mS / cm, and the treatment is stopped.

[0011] Preferably, the acid solution obtained in step 4 is used to adjust the pH of the mother liquor.

[0012] Preferably, in step 5, the amount of seed crystals added is 0.5 g to 1 g / 1L, the phosphorus source is a soluble phosphorus source such as phosphoric acid, sodium phosphate, ammonium phosphate, or sodium dihydrogen phosphate, and the addition time is 30 to 120 min.

[0013] Preferably, the slurry stirring time in step 6 is 20-40 minutes.

[0014] The benefits of the present invention are as follows: 1. The present invention adopts a chemical precipitation method to purify mother liquors with different pH values. After the purified mother liquors are self-neutralized, a bipolar membrane is used to purify the mother liquors to obtain a mixed alkaline solution, and lithium is further precipitated to obtain high-purity lithium phosphate, thereby improving the utilization rate of lithium in the mother liquors generated in the production process of lithium carbonate and lithium hydroxide.

[0015] 2. The present invention solves the technical problem that the mother liquor has different sources and complex components, and a single technology is difficult to meet the recovery requirements, and improves the purity of lithium phosphate prepared from the mother liquor 3. In the lithium recovery process of the present invention, impurity ions are removed by precipitation, and the recovered lithium is more environmentally friendly and will not pollute the environment, thus effectively reducing environmental pressure. DETAILED DESCRIPTION

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Example

[0017] The mother liquor was tested for its main components, and the data are as follows

[0018] Take 1L of mother liquor and add a small amount of caustic soda to adjust the pH value to 12. After filtering, add sulfuric acid to the filtrate to adjust the pH value to 2.6. Add 41.78g of Cu2O, stir for 20 minutes and then centrifuge. Add 856ml of the treated alkaline filtrate to the filtrate and the solution becomes neutral.

[0019] The liquid was tested for its main components and the data are as follows.

[0020]

[0021] After bipolar membrane electrodialysis, 1.5L of liquid was subjected to 1L mixed alkali solution and 1L acid solution, with a voltage of 35V, a current of 4A, and a conductivity of 4.75 mS / cm, and the treatment was stopped.

[0022] The concentration of lithium oxide was tested by mixed alkali solution, and the data are as follows.

[0023]

[0024] Take 800mL of mixed alkali solution, add 0.5g of lithium phosphate seed, add 15.55g of phosphoric acid while stirring, and add for 60min. After the feeding is completed, stir for half an hour and centrifuge to obtain 13.61g of wet lithium phosphate. After washing and drying, test the chemical indicators. Example

[0025] The mother liquor was tested for its main components, and the data are as follows

[0026] Take 1L of mother liquor and add a small amount of sulfuric acid to adjust the pH value to 2, add 29.2 g Cu2O, stir for 30 minutes and filter, add caustic soda to the filtrate to adjust the pH value to 12.4, stir for 5 minutes and centrifuge, add 1100 ml of the treated acidic filtrate to the filtrate, and the solution is neutral.

[0027] The liquid was tested for its main components and the data are as follows.

[0028]

[0029] After bipolar membrane electrodialysis, 2L of the neutralized liquid was subjected to 1.5L of mixed alkali solution and 1.5L of acid solution, with a voltage of 35V, a current of 4.4A, and a conductivity of 4.9 mS / cm, and the treatment was stopped.

[0030] The concentration of lithium oxide was tested by mixed alkali solution, and the data are as follows.

[0031]

[0032] Take 1000mL of mixed alkali solution, add 0.8g of lithium phosphate seed, add sodium phosphate solution (27.23g of sodium phosphate) while stirring, the addition time is 90min, after the feeding is completed, stir for half an hour, centrifuge to obtain 16.25g of wet lithium phosphate, wash and dry, and test the chemical indicators. Example

[0033] The mother liquor was tested for its main components, and the data are as follows.

[0034]

[0035] Take 1L of mother liquor and filter the filtrate. Add sulfuric acid to adjust the pH value to 2, add 27.99 g Cu2O, stir for 20 minutes and centrifuge. Add 980 ml of treated alkaline filtrate to the filtrate. The solution is neutral. The liquid is tested for its main components, and the data are as follows.

[0036]

[0037] After bipolar membrane electrodialysis, 1.5L of liquid was subjected to 800mL of mixed alkali solution and 800mL of acid solution, with a voltage of 35V, a current of 4.2A, and a conductivity of 4.9 mS / cm, and the treatment was stopped.

[0038] The concentration of lithium oxide was tested by mixed alkali solution, and the data are as follows.

[0039]

[0040] Take 700mL of mixed alkali solution, add 0.4g of lithium phosphate seed crystals, add sodium dihydrogen phosphate solution (18.1g of sodium dihydrogen phosphate) while stirring, the addition time is 90min, after the feeding is completed, stir for half an hour, centrifuge to obtain 17.5g of wet lithium phosphate, wash and dry, and test the chemical indicators. Example

[0041] The mother liquor was tested for its main components, and the data are as follows.

[0042]

[0043] Take 1L of mother liquor and add 23.2 g of Cu2O, stir for 30 minutes and filter, add caustic soda to adjust the pH value to 12, stir for 5 minutes and centrifuge, add 1050 ml of treated acidic filtrate to the filtrate, the solution is neutral. The liquid is tested for its main components, and the data are as follows.

[0044]

[0045] After bipolar membrane electrodialysis, 1.8 L of the neutralized liquid was subjected to 1.5 L of mixed alkali solution and 1.5 L of acid solution, with a voltage of 35 V, a current of 4.4 A, and a conductivity of 4.95 mS / cm, and the treatment was stopped.

[0046] The concentration of lithium oxide was tested by mixed alkali solution, and the data are as follows.

[0047]

[0048] Take 1000mL of mixed alkali solution, add 1g of lithium phosphate seed crystals, add 19.95g of phosphoric acid while stirring, and the addition time is 120min. After the feeding is completed, stir for half an hour and centrifuge to obtain 16.64g of wet lithium phosphate. After washing and drying, test the chemical indicators.

[0049] The lithium phosphate products obtained in Examples 1-4 were sampled and analyzed, and the contents of the components in the samples were as follows:

[0050] As can be seen from the above table, the lithium phosphate prepared by the method for recovering high-purity lithium phosphate from lithium in a mother liquor in the preparation method of the present invention has a higher purity, and some indicators are better than fluorescent agent lithium phosphate.

[0051] It should be understood by those skilled in the art that the embodiments of the present invention described above are only examples and do not limit the present invention, and the purpose of the present invention has been fully and effectively achieved. The functional and structural principles of the present invention have been demonstrated and explained in the embodiments, and the embodiments of the present invention may be deformed or modified in any way without departing from the principles.

Claims

1. A method for recovering high-purity lithium phosphate from lithium in mother liquor, characterized in that: The following steps are involved: Step 1: Take the mother solution to determine the main components and pH value; Step 2: When the pH is less than or equal to 6, the pH value of the mother liquor is adjusted to less than 3 with sulfuric acid, Cu2O is added, the mixture is stirred and filtered, and the pH value of the filtrate is adjusted to 12 with alkali solution, and the mixture is filtered to obtain filtrate 1; when the pH is greater than 6, the pH value of the mother liquor is adjusted to 12 with alkali solution, and the mixture is filtered, the pH value of the filtrate is adjusted to less than 3 with sulfuric acid, Cu2O is added, the mixture is stirred and filtered to obtain filtrate 2; Step 3: Mix filtrate 1 and filtrate 2, and adjust the pH value of the solution to neutral to obtain solution 3; Step 4: Solution 3 is treated by a bipolar membrane to obtain a mixed alkali solution 4 and an acid solution; Step 5: stirring and dispersing the seed crystals added to the mixed alkali solution, and then slowly dropping a soluble phosphorus source to obtain a slurry; Step 6: After stirring the slurry, centrifuge to obtain wet lithium phosphate, wash and dry to obtain battery-grade lithium phosphate.

2. The method for recovering high-purity lithium phosphate from lithium in a mother liquor according to claim 1, characterized in that: The mother liquor in step 1 is a lithium-containing solution produced during the production process of lithium carbonate and lithium hydroxide.

3. The method for recovering high-purity lithium phosphate from lithium in a mother liquor according to claim 1, characterized in that: In the step 2, the amount of Cu2O added is n(Cl):n(Cu2O) is 3-1:1, and the solution temperature is controlled at 20-30°C during the Cu2O addition process, and the stirring time is 20-40 minutes.

4. The method for recovering high-purity lithium phosphate from lithium in a mother liquor according to claim 1, characterized in that: During the bipolar membrane treatment in step 4, the voltage is controlled to be 35V, the current is 4-4.4A, the volume ratio of the stock solution, the acid solution and the alkali solution is 1:0.5:0.5-1:1:1, and the conductivity is less than 5 mS / cm, and the treatment is stopped.

5. The method for recovering high-purity lithium phosphate from lithium in mother liquor according to claim 1, characterized in that: The acid solution obtained in step 4 is used to adjust the pH value of the mother liquor.

6. The method for recovering high-purity lithium phosphate from lithium in mother liquor according to claim 1, characterized in that: In step 5, the amount of seed crystal added is 0.5 g to 1 g / 1 L, the phosphorus source is a soluble phosphorus source such as phosphoric acid, sodium phosphate or ammonium phosphate or sodium dihydrogen phosphate, and the addition time is 30 to 120 min.

7. The method for recovering high-purity lithium phosphate from lithium in mother liquor according to claim 1, characterized in that: The slurry stirring time in step 6 is 20-40 minutes.

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