Method for recycling and preparing lithium carbonate from waste lithium iron phosphate battery

Abstract

This invention discloses a method for recycling waste lithium iron phosphate batteries to prepare lithium carbonate, comprising: mixing waste lithium iron phosphate battery powder with water, an oxidant, an acidic solution, and a surfactant, reacting, and separating the solid and liquid phases to obtain a first leachate with a pH of 2-2.5; mixing the first leachate with waste lithium iron phosphate battery powder, an oxidant, an acidic solution, and a surfactant, reacting, and separating the solid and liquid phases to obtain a second leachate with a pH of 1.5-2; mixing the second leachate with waste lithium iron phosphate battery powder, an oxidant, an acidic solution, and a surfactant, reacting, and separating the solid and liquid phases to obtain a third leachate with a pH of 1-1.5; removing impurities from the third leachate to obtain a lithium chloride solution; adding water-soluble carbonate to the lithium chloride solution, reacting, and separating the solid and liquid phases to obtain lithium carbonate and a chloride solution. This invention can improve the efficiency of lithium carbonate production. + Leaching rate.

Description

Technical Field

[0001] This invention relates to the field of battery recycling technology, and in particular to a method for recycling waste lithium iron phosphate batteries to prepare lithium carbonate. Background Technology

[0002] Due to their lower production costs, higher safety, and longer lifespan, lithium iron phosphate (LFP) batteries have seen a significant increase in production volume in recent years. Therefore, considering resource recycling, the recovery of retired LFP batteries will become a top priority. Currently, the main method for recycling retired LFP battery powder is the wet process. This involves dissolving and crushing the battery powder with strong acid, allowing lithium ions and other metal ions to leach into the solution. Then, through processes such as precipitation purification, evaporation crystallization, and drying, lithium carbonate or lithium hydroxide materials required for battery production are prepared.

[0003] Research has revealed the following technical problems with existing waste battery recycling processes: After the acid leaching process, the lithium-containing leachate is not recycled, resulting in a low lithium content and generating a large amount of wastewater. This increases the pressure on subsequent lithium liquid evaporation and wastewater treatment. Furthermore, adding excessive amounts of hydrochloric acid, liquid alkali, and lithium source will further increase costs. Summary of the Invention

[0004] Based on the technical problems existing in the background technology, this invention proposes a method for recycling waste lithium iron phosphate batteries to prepare lithium carbonate. This invention can increase the Li content in waste lithium iron phosphate battery powder. + It has a high leaching rate, increases yield, has fewer impurities, and is low in cost.

[0005] This invention proposes a method for recycling spent lithium iron phosphate batteries to prepare lithium carbonate, comprising the following steps:

[0006] S1. The waste lithium iron phosphate battery powder is mixed with water, oxidant, acidic solution and surfactant, reacted and separated into solid and liquid components to obtain the first leachate with pH=2-2.5.

[0007] S2. The first leachate is mixed with waste lithium iron phosphate battery powder, oxidant, acidic solution and surfactant, and reacted. Solid-liquid separation is performed to obtain a second leachate with pH=1.5-2.

[0008] S3. The second leachate is mixed with waste lithium iron phosphate battery powder, oxidant, acidic solution and surfactant, and reacted. Solid-liquid separation is performed to obtain a third leachate with pH=1-1.5.

[0009] S4. The third leachate is treated to remove impurities to obtain a lithium chloride solution; water-soluble carbonate is added to the lithium chloride solution to react and separate the solid and liquid phases to obtain lithium carbonate and chloride solutions; the chloride solution is electrolyzed by ion exchange to obtain hydroxide and hydrogen chloride. Hydrogen chloride is recycled as an acidic substance in S1-S3, and hydroxide is recycled for the impurity removal treatment in S4.

[0010] This invention involves adding waste lithium iron phosphate battery powder in three steps, and sequentially adjusting the pH values ​​of the first, second, and third leachates to a stepped pattern (pH values ​​decreasing sequentially), which can increase the Li content in the waste lithium iron phosphate battery powder. + This method improves leaching efficiency and avoids the problem of directly adding strong acid for leaching in a low pH environment, where other metallic impurities (such as Cu) are easily leached out, increasing the difficulty of impurity removal and reducing the purity of lithium chloride. Furthermore, multiple additions of waste lithium iron phosphate battery powder can achieve a lithium content of 12-20 g / L in the third leaching solution, eliminating the need for additional lithium sources to adjust the lithium content and reducing costs. After impurity removal, the third leaching solution can directly react with carbonates; the high lithium concentration significantly reduces the cost of lithium source usage and evaporation concentration; and the hydroxide and hydrogen chloride obtained from the chloride solution through ion exchange electrolysis can be recycled, further reducing costs.

[0011] Preferably, the oxidant is at least one of hydrogen peroxide and hypochlorous acid.

[0012] Preferably, the surfactant is at least one of potassium monododecyl phosphate and disodium fatty alcohol polyoxyethylene ether-3-sulfosuccinate monoester.

[0013] The present invention uses a suitable surfactant to appropriately increase the lithium leaching rate.

[0014] Preferably, the acidic solution is at least one of hydrochloric acid aqueous solution and sulfuric acid aqueous solution.

[0015] Preferably, the hydrochloric acid aqueous solution has a mass fraction of 20-30 wt%.

[0016] Preferably, in S1, the reaction temperature is 60-90℃ and the time is 1.5-2.5h.

[0017] Preferably, in S1, the weight ratio of water to waste lithium iron phosphate battery powder is 3-6:1.

[0018] Preferably, in S1, the oxidant reacts with Fe in the waste lithium iron phosphate battery powder. 2+ The molar ratio is 0.5-1.5:1.

[0019] Preferably, in S1, the amount of surfactant used is 0.1-0.5 times the weight of the waste lithium iron phosphate battery powder.

[0020] Preferably, in S2, the reaction temperature is 60-90℃ and the time is 1.5-2.5h.

[0021] Preferably, in S2, the weight ratio of the first leachate to the waste lithium iron phosphate battery powder is 3-6:1.

[0022] Preferably, in S2, the oxidant reacts with Fe in the waste lithium iron phosphate battery powder. 2+ The molar ratio is 0.5-1.5:1.

[0023] Preferably, in S2, the amount of surfactant used is 0.1-0.5 times the weight of the waste lithium iron phosphate battery powder.

[0024] Preferably, in S3, the reaction temperature is 60-90℃ and the time is 1.5-2.5h.

[0025] Preferably, in S3, the weight ratio of the second leachate to the waste lithium iron phosphate battery powder is 3-6:1.

[0026] Preferably, in S3, the oxidant reacts with Fe in the waste lithium iron phosphate battery powder. 2+ The molar ratio is 0.5-1.5:1.

[0027] Preferably, in S3, the amount of surfactant used is 0.1-0.5 times the weight of the waste lithium iron phosphate battery powder.

[0028] By adjusting the amounts of waste lithium iron phosphate battery powder, surfactants, and oxidants, the leaching of Li can be maximized. + Meanwhile, adjusting the pH of the acid leaching solution to a gradient can reduce the leaching of impurities and improve the purity of lithium chloride.

[0029] Preferably, in step S4, the impurity removal process includes the following steps: adjusting the pH of the third leachate to 11-13, adding a purifying agent, performing solid-liquid separation, removing impurities from the liquid with resin, and obtaining a lithium chloride solution.

[0030] The above-mentioned resin impurity removal method can be as follows: pass the liquid through a resin chromatography column, collect the liquid, and obtain a lithium chloride solution.

[0031] Preferably, the purifying agent is at least one of sodium carbonate, ferric chloride, ammonium dihydrogen phosphate, and calcium oxide.

[0032] Preferably, the weight ratio of the third leachate to the purifying agent is 1:0.05-0.2.

[0033] Choosing a suitable impurity removal method can remove impurities while avoiding Li + The loss.

[0034] Preferably, in S4, the water-soluble carbonate is at least one of sodium carbonate, potassium carbonate, and ammonium bicarbonate.

[0035] In step S4, a water-soluble carbonate is added to the lithium chloride solution, and the reaction continues until no precipitate is formed, at which point the solid and liquid are separated. The amount of water-soluble carbonate used is not limited, as long as the lithium chloride reacts completely.

[0036] Preferably, in step S4, the solution after solid-liquid separation is subjected to ion exchange electrolysis to prepare hydrochloric acid and water-soluble hydroxide.

[0037] In S4, the solution after solid-liquid separation is a water-soluble chloride solution. Taking sodium chloride solution as an example, it enters the ion exchange electrolysis system (the system is divided into an anode chamber, a cathode chamber, and a salt chamber; the anode chamber membrane only allows large Cl molecules). - Through the cathode chamber membrane, OH - Electrolysis is performed, producing chlorine gas at the anode and hydrogen gas at the cathode, which reacts with water to form hydrochloric acid. OH- is then produced at the cathode. - Entering the salt chamber with Na + It combines to form NaOH.

[0038] The hydrochloric acid produced by ion exchange electrolysis can be recycled in steps S1-S3. Only a small amount of hydrochloric acid needs to be added in each step to adjust to the required pH value. The NaOH produced by ion exchange electrolysis can be used in the impurity removal step in S4, which can reduce the amount of strong acid and NaOH used and save costs. Furthermore, ion exchange electrolysis of sodium chloride solution can reduce waste and avoid environmental pollution.

[0039] Beneficial effects:

[0040] 1. This invention involves adding waste lithium iron phosphate battery powder in three steps and adjusting the pH values ​​of the first, second, and third leachates in a stepped manner. This not only increases the Li content in the waste lithium iron phosphate battery powder, but also... + It has a high leaching rate (up to 99% or more) and can reduce the amount of acid used; it can also avoid the problem of directly adding strong acid to leach in a low pH environment, where other metal impurities such as Cu are easily leached out, increasing the difficulty of impurity removal and reducing the purity of lithium chloride.

[0041] 2. Adding waste lithium iron phosphate battery powder multiple times can make the lithium content in the third leachate as high as 12-20g / L, eliminating the need to add lithium source to adjust the lithium content. After impurity removal treatment, the third leachate can react directly with carbonates. The high lithium concentration can significantly reduce the cost of lithium source use and evaporation concentration.

[0042] 3. Ion exchange electrolysis of sodium chloride solution can reduce waste and avoid environmental pollution caused by sodium chloride solution; the hydrochloric acid and water-soluble hydroxide produced by ion exchange electrolysis can be recycled in S1-S4, reducing the amount of hydrochloric acid and water-soluble hydroxide used and lowering costs. Attached Figure Description

[0043] Figure 1 This is a process flow diagram of the method for preparing lithium carbonate from waste lithium iron phosphate batteries according to the present invention. Detailed Implementation

[0044] The technical solution of the present invention will now be described in detail through specific embodiments.

[0045] Example 1

[0046] A method for recycling spent lithium iron phosphate batteries to prepare lithium carbonate includes the following steps:

[0047] S1. Mix 10g of waste lithium iron phosphate battery powder with 30g of water, hydrogen peroxide aqueous solution, 25wt% hydrochloric acid aqueous solution, and 1g of potassium monododecyl phosphate. React at 75℃ for 2h, filter, and obtain a first leachate with pH=2.0. The hydrogen peroxide reacts with the Fe in the waste lithium iron phosphate battery powder. 2+ The molar ratio is 1:1;

[0048] S2. Mix 30g of the first leachate with 10g of waste lithium iron phosphate battery powder, hydrogen peroxide aqueous solution, 25wt% hydrochloric acid aqueous solution, and 1g of potassium monododecyl phosphate. React at 75℃ for 2 hours, filter, and obtain a second leachate with pH=1.5. The hydrogen peroxide reacts with the Fe in the waste lithium iron phosphate battery powder. 2+ The molar ratio is 1:1;

[0049] S3. Mix 30g of the second leachate with 10g of waste lithium iron phosphate battery powder, hydrogen peroxide aqueous solution, 25wt% hydrochloric acid aqueous solution, and 1g of potassium monododecyl phosphate. React at 75℃ for 2 hours, filter, and obtain a third leachate with pH=1.0. The hydrogen peroxide reacts with the Fe in the waste lithium iron phosphate battery powder. 2+ The molar ratio is 1:1;

[0050] S4. Adjust the pH of 30g of the third leachate to 12 with a 25wt% NaOH aqueous solution. Add 2g of purifying agent (a mixture of sodium carbonate, ferric chloride, and ammonium dihydrogen phosphate). Filter, pass the filtrate through a resin chromatography column, collect the liquid, and obtain Li. +A lithium chloride solution with a concentration of 20 g / L was prepared. 0.024 mol of sodium carbonate was added to 100 ml of the lithium chloride solution and the reaction was carried out until no precipitate was formed. The solution was filtered, and the filter cake was dried to obtain lithium carbonate. The filtrate was subjected to ion exchange electrolysis to prepare hydrochloric acid and NaOH. The hydrochloric acid was recycled for S1-S3, and the NaOH was recycled for S4.

[0051] Example 2

[0052] A method for recycling spent lithium iron phosphate batteries to prepare lithium carbonate includes the following steps:

[0053] S1. Mix 10g of waste lithium iron phosphate battery powder with 30g of water, hydrogen peroxide aqueous solution, 20wt% hydrochloric acid aqueous solution, and 1g of potassium monododecyl phosphate. React at 60℃ for 2.5h, filter, and obtain a first leachate with pH=2.25. The hydrogen peroxide reacts with the Fe in the waste lithium iron phosphate battery powder. 2+ The molar ratio is 0.5:1;

[0054] S2. Mix 30g of the first leachate with 10g of waste lithium iron phosphate battery powder, hydrogen peroxide aqueous solution, 20wt% hydrochloric acid aqueous solution, and 1g of potassium monododecyl phosphate. React at 60℃ for 2.5h, filter, and obtain a second leachate with pH=1.75. The hydrogen peroxide reacts with the Fe in the waste lithium iron phosphate battery powder. 2+ The molar ratio is 0.5:1;

[0055] S3. Mix 30g of the second leachate with 10g of waste lithium iron phosphate battery powder, hydrogen peroxide aqueous solution, 20wt% hydrochloric acid aqueous solution, and 1g of potassium monododecyl phosphate. React at 60℃ for 2.5h, filter, and obtain a third leachate with pH=1.25. The hydrogen peroxide reacts with the Fe in the waste lithium iron phosphate battery powder. 2+ The molar ratio is 0.5:1;

[0056] S4. Adjust the pH of 30g of the third leachate to 11 with a 20wt% KOH aqueous solution, add 1.5g of purifying agent (a mixture of sodium carbonate, ferric chloride, and ammonium dihydrogen phosphate), filter, pass the filtrate through a resin chromatography column, collect the liquid, and obtain Li. + A lithium chloride solution with a concentration of 16 g / L was prepared. 0.019 mol of potassium carbonate was added to 100 ml of the lithium chloride solution and the reaction was carried out until no precipitate was formed. The solution was filtered, and the filter cake was dried to obtain lithium carbonate. The filtrate was subjected to ion exchange electrolysis to prepare hydrochloric acid and KOH. The hydrochloric acid was recycled for S1-S3, and the KOH was recycled for S4.

[0057] Example 3

[0058] A method for recycling spent lithium iron phosphate batteries to prepare lithium carbonate includes the following steps:

[0059] S1. Mix 10g of waste lithium iron phosphate battery powder with 60g of water, hydrogen peroxide aqueous solution, 30wt% hydrochloric acid aqueous solution, and 5g of disodium fatty alcohol polyoxyethylene ether-3-sulfosuccinate monoester. React at 90℃ for 1.5h, filter, and obtain a first leachate with pH=2.5. The hydrogen peroxide reacts with the Fe in the waste lithium iron phosphate battery powder. 2+ The molar ratio is 1.5:1;

[0060] S2. Mix 60g of the first leachate with 10g of waste lithium iron phosphate battery powder, hydrogen peroxide aqueous solution, 30wt% hydrochloric acid aqueous solution, and 5g of disodium fatty alcohol polyoxyethylene ether-3-sulfosuccinate monoester. React at 90℃ for 1.5h, filter, and obtain a second leachate with pH=2. The hydrogen peroxide reacts with the Fe in the waste lithium iron phosphate battery powder. 2+ The molar ratio is 1.5:1;

[0061] S3. Mix 60g of the second leachate with 10g of waste lithium iron phosphate battery powder, hydrogen peroxide aqueous solution, 30wt% hydrochloric acid aqueous solution, and 5g of disodium fatty alcohol polyoxyethylene ether-3-sulfosuccinate monoester. React at 90℃ for 1.5h, filter, and obtain a third leachate with pH=1.5. The hydrogen peroxide reacts with the Fe in the waste lithium iron phosphate battery powder. 2+ The molar ratio is 1.5:1;

[0062] S4. Adjust the pH of 60g of the third leachate to 13 with a 30wt% NaOH aqueous solution, add 3g of purifying agent (a mixture of sodium carbonate, ferric chloride, and ammonium dihydrogen phosphate), filter, pass the filtrate through a resin chromatography column, collect the liquid, and obtain Li. + A lithium chloride solution with a concentration of 12 g / L was prepared. 0.014 mol of sodium carbonate was added to 100 ml of the lithium chloride solution and the reaction was carried out until no precipitate was formed. The solution was filtered, and the filter cake was dried to obtain lithium carbonate. The filtrate was subjected to ion exchange electrolysis to prepare hydrochloric acid and NaOH. The hydrochloric acid was recycled for S1-S3, and the NaOH was recycled for S4.

[0063] Comparative Example 1

[0064] Take 30g of waste lithium iron phosphate battery powder, mix it with 90g of water, hydrogen peroxide aqueous solution, 25wt% hydrochloric acid aqueous solution, and 3g of potassium monododecyl phosphate, react at 75℃ for 2h, filter, and obtain a leachate with pH=1.0. The hydrogen peroxide reacts with the Fe in the waste lithium iron phosphate battery powder. 2+ The molar ratio was 1:1; lithium carbonate was prepared from the leachate according to step S4 of Example 1.

[0065] Comparative Example 2

[0066] The pH of the first leachate is 3, the pH of the second leachate is 2.5, and the pH of the third leachate is 2. Other conditions are the same as in Example 1.

[0067] Comparative Example 3

[0068] The pH of the first leachate is 1.5, the pH of the second leachate is 1, and the pH of the third leachate is 0.5. The other conditions are the same as in Example 1.

[0069] The waste lithium iron phosphate battery powder used in Examples 1-3 and Comparative Examples 1-3 was the same.

[0070] The purity of lithium carbonate and the Li content of lithium chloride solutions obtained in Examples 1-3 and Comparative Examples 1-3 were determined. + Concentration and lithium carbonate yield were statistically analyzed, and the results are shown in Table 1.

[0071] Table 1 Test Results

[0072] Testing items <![CDATA[Li concentration of lithium chloride solution + g / L]]> Lithium carbonate purity % Lithium carbonate yield % Example 1 20 99.91 99.0 Example 2 16 99.81 98.9 Example 3 12 99.52 98.3 Comparative Example 1 13 97.05 96.1 Comparative Example 2 8 99.39 82.9 Comparative Example 3 19 95.12 98.8

[0073] As can be seen from Table 1, the lithium carbonate recovered by this invention has higher purity and higher yield.

[0074] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for recycling spent lithium iron phosphate battery to prepare lithium carbonate, characterized in that, The application relates to a method for preparing lithium carbonate from waste lithium iron phosphate batteries. The method comprises the following steps: S1, mixing waste lithium iron phosphate batteries powder, water, an oxidizing agent, an acidic solution and a surfactant, and then performing reaction, solid-liquid separation, to obtain a first leaching solution with pH=2-2.5; S2, mixing the first leaching solution, waste lithium iron phosphate batteries powder, an oxidizing agent, an acidic solution and a surfactant, and then performing reaction, solid-liquid separation, to obtain a second leaching solution with pH=1.5-2; S3, mixing the second leaching solution, waste lithium iron phosphate batteries powder, an oxidizing agent, an acidic solution and a surfactant, and then performing reaction, solid-liquid separation, to obtain a third leaching solution with pH=1-1.5; S4, performing impurity removal treatment on the third leaching solution to obtain a lithium chloride solution; adding a water-soluble carbonate into the lithium chloride solution, performing reaction, solid-liquid separation, to obtain lithium carbonate and a chloride solution; the chloride solution is subjected to ion exchange electrolysis to obtain hydroxide and hydrochloric acid, the hydrochloric acid is recycled as an acidic substance for use in S1-S3, and the hydroxide is recycled for use in the impurity removal treatment in S4; 2. The method for recycling waste lithium iron phosphate batteries to prepare lithium carbonate according to claim 1, characterized in that, the acidic solution is hydrochloric acid aqueous solution.

3. The method for preparing lithium carbonate from waste lithium iron phosphate battery according to claim 1 or 2, characterized in that, The oxidizing agent is at least one of hydrogen peroxide and hypochlorous acid.

4. The method for preparing lithium carbonate from waste lithium iron phosphate battery according to claim 1 or 2, characterized in that, The surfactant is at least one of potassium monododecyl phosphate and disodium fatty alcohol polyoxyethylene ether-3-sulfosuccinate monoester.

5. The method for preparing lithium carbonate from waste lithium iron phosphate battery according to claim 1 or 2, characterized in that, The mass fraction of the hydrochloric acid aqueous solution is 20-30wt%.

6. The method of claim 1 or 2, wherein the spent lithium iron phosphate battery is recovered to produce lithium carbonate. In S1, the reaction temperature is 60-90 DEG C, and the time is 1.5-2.5h.

7. The method of claim 1 or 2, wherein the spent lithium iron phosphate battery is recovered to produce lithium carbonate. In S1, the oxidant reacts with Fe in the waste lithium iron phosphate battery powder. 2+ The molar ratio is 0.5-1.5:

1.

8. The method for preparing lithium carbonate from waste lithium iron phosphate battery according to claim 1 or 2, characterized in that, In S1, the weight ratio of water to waste lithium iron phosphate batteries powder is 3-6:

1.

9. The method of claim 1 or 2, wherein the spent lithium iron phosphate battery is recovered to produce lithium carbonate. In S1, the amount of the surfactant is 0.1-0.5 times the weight of the waste lithium iron phosphate batteries powder.

10. The method of claim 1 or 2, wherein the spent lithium iron phosphate battery is recovered to produce lithium carbonate. In S2, the reaction temperature is 60-90 DEG C, and the time is 1.5-2.5h.

11. The method of claim 1 or 2, wherein the spent lithium iron phosphate battery is recovered to produce lithium carbonate. In S2, the oxidant reacts with Fe in the waste lithium iron phosphate battery powder. 2+ The molar ratio is 0.5-1.5:

1.

12. The method of claim 1 or 2, wherein the spent lithium iron phosphate battery is recovered to produce lithium carbonate. In S2, the weight ratio of the first leaching solution to waste lithium iron phosphate batteries powder is 3-6:

1.

13. The method of claim 1 or 2, wherein the spent lithium iron phosphate battery is recovered to produce lithium carbonate. In S2, the amount of the surfactant is 0.1-0.5 times the weight of the waste lithium iron phosphate batteries powder.

14. The method of claim 1 or 2, wherein the spent lithium iron phosphate battery is recovered to produce lithium carbonate. In S3, the reaction temperature is 60-90 DEG C, and the time is 1.5-2.5h.

15. The method of claim 1 or 2, wherein the spent lithium iron phosphate battery is recovered to produce lithium carbonate. In S3, the oxidant reacts with Fe in the waste lithium iron phosphate battery powder. 2+ The molar ratio is 0.5-1.5:

1.

16. The method of claim 1 or 2, wherein the spent lithium iron phosphate battery is recovered to produce lithium carbonate. In S3, the weight ratio of the second leaching solution to waste lithium iron phosphate batteries powder is 3-6:

1.

17. The method of claim 1 or 2, wherein the spent lithium iron phosphate battery is recovered to produce lithium carbonate. In S3, the amount of the surfactant is 0.1-0.5 times the weight of the waste lithium iron phosphate batteries powder.

18. The method of claim 17, wherein the spent lithium iron phosphate battery is recovered to produce lithium carbonate. In S4, the impurity removal treatment comprises the following steps: adjusting the pH of the third leaching solution to 11-13, adding a purification agent, performing solid-liquid separation, taking the liquid to remove impurities by using a resin, and obtaining the lithium chloride solution.

19. The method for recycling waste lithium iron phosphate batteries to prepare lithium carbonate according to claim 17, characterized in that, The purification agent is at least one of sodium carbonate, ferric chloride, ammonium dihydrogen phosphate and calcium oxide.

20. The method of claim 1 or 2, wherein the spent lithium iron phosphate battery is recovered to produce lithium carbonate. The weight ratio of the third leaching solution to the purification agent is 1:0.05-0.

2. In S4, the water-soluble carbonate is at least one of sodium carbonate, potassium carbonate and ammonium bicarbonate.

Images