Recycling method for short extraction process of battery powder of waste power battery

Abstract

The invention belongs to the technical field of resource recovery, and discloses a recovery method of a battery powder short extraction process of a waste power battery, which comprises the following steps: (1) leaching; (2) impurity removal: removing copper, iron and aluminum from the leaching solution to obtain an impurity-removed solution; (3) manganese extraction: extracting manganese from the impurity-removed liquid by using a Cyanex272 extraction agent to obtain an extract liquid 1 and a raffinate 1; (4) nickel-cobalt co-extraction: carrying out nickel-cobalt co-extraction on the raffinate 1 by using a BC196 extracting agent to obtain an extracting solution 2 and a raffinate 2; (5) removing calcium and magnesium: removing calcium and magnesium from the raffinate 2 through resin to obtain a lithium-containing solution; and (6) lithium extraction: extracting and enriching the lithium-containing solution to obtain extract liquor 3 and raffinate 3. According to the method, in the extraction and recovery process of nickel, cobalt and manganese, the number of traditionally needed five or more extraction lines is reduced to two, in the lithium recovery process, lithium extraction is adopted, lithium in raffinate can be reduced to be within 10 ppm, and the concentration of lithium in strip liquor reaches 20 g / L or above.

Description

Technical Field

[0001] The invention belongs to the technical field of resource recovery, and in particular relates to the recovery of waste power batteries. Background Art

[0002] As the popularity of new energy vehicles continues to increase, "electric vehicles" have become a trend of the times that can be seen everywhere in daily life. As the industry gradually matures, the recycling link at the end of the industrial chain has gradually become the focus of market attention. At present, the recycling of waste power batteries has become an urgent problem that needs to be solved.

[0003] The recycling of used power batteries includes processes such as battery disassembly and wet extraction of battery powder. Battery powder is recycled through the wet extraction process to recover nickel, cobalt, manganese and lithium.

[0004] For lithium recovery, there are two main process routes: priority lithium extraction and raffinate lithium extraction. Priority lithium extraction uses a roasting-water leaching process to first extract lithium to separate it from nickel, cobalt and manganese. After the water leaching solution is purified, lithium carbonate is obtained by lithium precipitation using sodium carbonate. Raffinate lithium extraction uses a leaching-purification-extraction separation process to first extract nickel, cobalt and manganese, and then lithium is extracted from the raffinate. Priority lithium extraction, because the battery powder contains fluorine, high equipment anti-corrosion requirements are high under high-temperature roasting conditions, equipment investment is large, and the equipment life cycle is limited; in addition, the battery powder after priority lithium extraction still contains about 0.5% lithium, which enters the wet extraction process with nickel, cobalt and manganese and is difficult to recover, reducing the economic benefits. When using raffinate lithium extraction, the lithium concentration is continuously diluted with the nickel, cobalt and manganese extraction process. Low-concentration lithium can only be prepared into lithium carbonate by concentration or low-value lithium phosphate by trisodium phosphate precipitation, and the lithium recovery rate is low.

[0005] Solvent extraction is usually used to recover nickel, cobalt, and manganese. P204 is used to extract and separate Ca, Zn, Mn, and Cu. After stripping, the extract is further stripped by chemical impurities and extraction separation to prepare manganese sulfate. The raffinate is separated by P507 to separate cobalt, enrich nickel and magnesium, etc. The traditional solvent extraction method requires five or more extraction lines, and the extraction process is long. In the process of P204 extracting calcium, hydrochloric acid is usually used for stripping to reduce the precipitation of calcium sulfate during stripping, which leads to the introduction of Cl - , which has high requirements on equipment and needs to handle Cl - Wastewater.

[0006] In general, the conventional extraction process for battery powder is long, has low economic benefits, and faces problems such as difficult equipment maintenance and high wastewater treatment costs. Summary of the invention

[0007] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for recovering battery powder of waste power batteries by a short extraction process.

[0008] To achieve the above objectives, the present invention adopts the following specific technical solutions.

[0009] A method for recovering battery powder of waste power batteries by a short extraction process comprises the following steps: (1) Leaching: Sulfuric acid and a reducing agent are used to jointly leach the battery powder to obtain a leachate and leaching residue; (2) Impurity removal: copper, iron and aluminum are removed from the leaching solution to obtain an impurity-removing solution; (3) Extracting manganese: extracting manganese from the impurity removal liquid with Cyanex272 (di(2,4,4-trimethylpentyl)phosphinic acid) extractant to obtain extract 1 and raffinate 1; (4) Nickel-cobalt co-extraction: The raffinate 1 is subjected to nickel-cobalt co-extraction using BC196 extractant to obtain extract 2 and raffinate 2; (5) Removal of calcium and magnesium: The raffinate 2 is treated with a resin to remove calcium and magnesium to obtain a lithium-containing solution; (6) Lithium extraction: The lithium-containing solution is enriched by extraction to obtain extract 3 and raffinate 3.

[0010] In a further preferred embodiment, the reducing agent is one or more of hydrogen peroxide, sodium thiosulfate, and sodium metabisulfite.

[0011] In a further preferred embodiment, one or both of iron powder and sodium thiosulfate are added to the leaching solution to remove copper; one or both of sodium hydroxide and sodium carbonate are used to remove iron and aluminum.

[0012] In a further preferred embodiment, the mass fraction of Cyanex272 extractant in the organic phase for manganese extraction is 10% to 15%, the diluent is sulfonated kerosene, and the saponification rate is 30% to 50%.

[0013] In a further preferred embodiment, the phase ratio during manganese extraction is O:A=2~11:1.

[0014] In a further preferred embodiment, the extract 1 is stripped with a sulfuric acid solution to obtain a manganese sulfate solution. The concentration of the sulfuric acid solution is further preferably 2-2.5 mol / L.

[0015] In a further preferred embodiment, the phase ratio of the extract 1 when stripped with sulfuric acid solution is O:A=20~50:1.

[0016] In a further preferred embodiment, the mass fraction of BC196 extractant in the organic phase of nickel-cobalt co-extraction is 20%-25%, the diluent is sulfonated kerosene, and the saponification rate is 40-50%.

[0017] In a further preferred embodiment, the phase ratio of nickel and cobalt during co-extraction is O:A=4~6:1.

[0018] In a further preferred embodiment, the extract 2 is stripped with a sulfuric acid solution to obtain a mixed solution of nickel sulfate and cobalt sulfate. The concentration of the sulfuric acid solution is further preferably 2-2.5 mol / L.

[0019] More preferably, the mixed solution of manganese sulfate solution, nickel sulfate and cobalt sulfate is directly used to prepare the nickel-cobalt-manganese precursor.

[0020] In a further preferred embodiment, the phase ratio of the extract 2 when stripped with sulfuric acid solution is O:A=10-20:1.

[0021] In a further preferred embodiment, the resin used for removing calcium and magnesium is HP4010.

[0022] In a further preferred embodiment, the extractant for extracting lithium comprises a main extractant and a co-extractant; Preferably, the main extractant is one or more of 1-butyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium fluoride, 1-ethyl-3-methylimidazolium chloride, 1-propyl-3-methylimidazolium tetrafluoroborate, 1-alkenyl-3-methylpyridinium salt, and ammonium tetrafluoroborate; Preferably, the co-extractant is one or more of tributyl phosphate, dioctyl phosphate, trioctyl phosphate, triethylamine, trioctylamine, 2-ethylhexyl phosphate mono-2-ethylhexyl ester, and di(2-ethylhexyl) phosphate; Preferably, the mass ratio of the main extractant to the co-extractant is 1:0.75-1.5; Preferably, the mass content of the diluent in the organic phase for extracting lithium is 50%-80%; Preferably, the diluent is one or more of sulfonated kerosene, n-hexane, isohexane, isomeric decanol, isomeric undecanol, and isomeric dodecanol; Preferably, the phase ratio during lithium extraction is O:A=2-3:1.

[0023] In a further preferred embodiment, the extract 3 is stripped with a sulfuric acid solution to obtain a lithium sulfate solution. The concentration of the sulfuric acid solution is further preferably 2-2.5 mol / L.

[0024] In a further preferred embodiment, the phase ratio of the extract 3 when stripped with sulfuric acid solution is O:A=10~20:1.

[0025] In a further preferred embodiment, the mother liquor after lithium precipitation in the lithium sulfate solution is returned to the lithium extraction process.

[0026] Compared with the prior art, the above one or more technical solutions of the present invention can achieve at least one of the following beneficial effects: In the extraction and recovery process of nickel, cobalt and manganese, the traditional five or more extraction lines are reduced to two, which greatly shortens the process flow, reduces investment costs, and reduces the amount of wastewater output. In the lithium recovery process, the lithium in the raffinate can be reduced to less than 10ppm by using extraction, and the lithium concentration in the stripping solution reaches more than 20g / L, which can directly prepare lithium carbonate, solving the problems of low lithium yield and low added value of lithium products.

[0027] The present invention provides an extraction process and extraction route that are completely different from the prior art, broadens the industry's vision, and promotes technological changes in the field of battery recycling.

[0028] The recovery method provided by the invention has high recovery rate of valuable metals and high added value of products. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0030] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings and preferred embodiments of the present invention, but the protection scope of the present invention is not limited to the following specific embodiments.

[0031] Unless otherwise defined, all the professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0032] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0033] The specific process flow adopted in the following specific embodiments is shown in Figure 1 .

[0034] Example 1 The contents of major metals in the impurity-removing liquid obtained after the battery powder is leached with reducing acid and copper, iron and aluminum are removed from the leaching liquid are shown in Table 1-1.

[0035] Table 1-1 (1) Manganese Extraction The extractant in the organic phase of manganese extraction is Cyanex 272. In the organic phase, the mass fraction of Cyanex 272 is 10%, and the rest is sulfonated kerosene, and the saponification rate is 50%.

[0036] The extraction phase ratio is O:A=6.5:1.

[0037] After the extraction is completed, extract 1 and raffinate 1 are obtained.

[0038] The extract 1 was back-extracted with a 2.5 mol / L sulfuric acid solution, and the back-extraction phase ratio O:A=46.7:1.

[0039] The contents of main metals in stripping solution 1 are shown in Table 1-2.

[0040] Table 1-2 (2) Nickel-cobalt co-extraction The extractant in the nickel-cobalt co-extraction organic phase is BC196. In the organic phase, the mass fraction of BC196 is 25%, and the rest is sulfonated kerosene with a saponification rate of 50%.

[0041] The extraction phase ratio is O:A=4.7:1.

[0042] After the extraction is completed, extract 2 and raffinate 2 are obtained.

[0043] The extract 2 was back-extracted with a 2 mol / L sulfuric acid solution, and the back-extraction phase ratio O:A=10.5:1.

[0044] The contents of major metals in the stripping solution 2 are shown in Table 1-3.

[0045] Table 1-3 (3) Removal of calcium and magnesium The raffinate 2 was passed through a HP4010 resin column at a flow rate of 1 BV / h to obtain a lithium-containing solution. The contents of the main metals in the lithium-containing solution are shown in Table 1-4.

[0046] Table 1-4 (4) Lithium Extraction The lithium-containing solution and the sodium hydroxide solution are prepared at a molar ratio of NaOH:Li=1.4:1, the main extractant is 1-ethyl-3-methylimidazolium tetrafluoroborate, the co-extractant is dioctyl phosphate, the mass ratio of the main extractant to the co-extractant is 1:0.8, the mass content of the diluent in the organic phase is 50%, the diluent is sulfonated kerosene, and the extraction phase ratio O:A=2.1:1.

[0047] After the extraction is completed, extract 3 and raffinate 3 are obtained.

[0048] The extract 3 was back-extracted with a 2 mol / L sulfuric acid solution, and the back-extraction phase ratio O:A=10:1.

[0049] The contents of various elements in the stripping solution 3 are shown in Table 1-5; the stripping solution 3 is precipitated with sodium carbonate to obtain a lithium carbonate product.

[0050] Table 1-5 Example 2 The contents of major metals in the impurity-removing liquid obtained after the battery powder is leached with reducing acid and copper, iron and aluminum are removed from the leaching liquid are shown in Table 2-1.

[0051] Table 2-1 (1) Manganese Extraction The extractant in the organic phase of manganese extraction is Cyanex 272. In the organic phase, the mass fraction of Cyanex 272 is 15%, and the rest is sulfonated kerosene, and the saponification rate is 45%.

[0052] The extraction phase ratio is O:A=4.6:1.

[0053] After the extraction is completed, extract 1 and raffinate 1 are obtained.

[0054] The extract 1 was back-extracted with a 2 mol / L sulfuric acid solution, and the back-extraction phase ratio O:A=27.9:1.

[0055] The contents of main metals in stripping solution 1 are shown in Table 2-2.

[0056] Table 2-2 (2) Nickel-cobalt co-extraction The extractant in the nickel-cobalt co-extraction organic phase is BC196. In the organic phase, the mass fraction of BC196 is 20%, and the rest is sulfonated kerosene with a saponification rate of 50%.

[0057] The extraction phase ratio is O:A=5.9:1.

[0058] After the extraction is completed, extract 2 and raffinate 2 are obtained.

[0059] The extract 2 was back-extracted with a 2 mol / L sulfuric acid solution, and the back-extraction phase ratio O:A=13.2:1.

[0060] The contents of main metals in stripping solution 2 are shown in Table 2-3.

[0061] Table 2-3 (3) Removal of calcium and magnesium The raffinate 2 was passed through a HP4010 resin column at a flow rate of 1 BV / h to obtain a lithium-containing solution. The contents of the main metals in the lithium-containing solution are shown in Table 2-4.

[0062] Table 2-4 (4) Lithium Extraction The lithium-containing solution is subjected to lithium extraction process, the molar ratio of sodium hydroxide: Li=1.5, the main extractant is 1-butyl-3-methylimidazolium chloride, the co-extractant is tributyl phosphate, the mass ratio of the main extractant and the co-extractant is 1:0.75, the mass content of the diluent in the organic phase is 60%, the diluent is n-hexane, and the extraction phase ratio O:A=2.4:1. After the extraction is completed, extract 3 and raffinate 3 are obtained.

[0063] The extract 3 was back-extracted with a sulfuric acid solution having a concentration of 2.5 mol / L, and the back-extraction phase ratio O:A=15.9:1.

[0064] The content of each element in the stripping solution 3 is shown in Table 2-5; the stripping solution 3 is precipitated with sodium carbonate to obtain a lithium carbonate product.

[0065] Table 2-5 Example 3 The contents of major metals in the impurity-removing liquid obtained after the battery powder is leached with reducing acid and copper, iron and aluminum are removed from the leaching liquid are shown in Table 3-1.

[0066] Table 3-1 (1) Manganese Extraction The extractant in the organic phase of manganese extraction is Cyanex 272. In the organic phase, the mass fraction of Cyanex 272 is 13%, and the rest is sulfonated kerosene, and the saponification rate is 40%.

[0067] The extraction phase ratio is O:A=5.6:1.

[0068] After the extraction is completed, extract 1 and raffinate 1 are obtained.

[0069] The extract 1 was back-extracted with a sulfuric acid solution having a concentration of 2.2 mol / L, and the back-extraction phase ratio O:A=39.8:1.

[0070] The contents of main metals in stripping solution 1 are shown in Table 3-2.

[0071] Table 3-2 (2) Nickel-cobalt co-extraction The extractant in the nickel-cobalt co-extraction organic phase is BC196. In the organic phase, the mass fraction of BC196 is 23%, and the rest is sulfonated kerosene with a saponification rate of 45%.

[0072] The extraction phase ratio is O:A=5.6:1.

[0073] After the extraction is completed, extract 2 and raffinate 2 are obtained.

[0074] The extract 2 was back-extracted with a 2 mol / L sulfuric acid solution, and the back-extraction phase ratio O:A=12:1.

[0075] The contents of main metals in stripping solution 2 are shown in Table 3-3.

[0076] Table 3-3 (3) Removal of calcium and magnesium The raffinate 2 was passed through an HP4010 resin column at a flow rate of 1 BV / h to obtain a lithium-containing solution. The contents of the main metals in the lithium-containing solution are shown in Table 3-4.

[0077] Table 3-4 (4) Lithium Extraction The lithium-containing solution is subjected to a lithium extraction process, the molar ratio of sodium hydroxide: Li=1.3, the main extractant is 1-propyl-3-methylimidazolium tetrafluoroborate, the co-extractant is trioctylamine, the mass relationship ratio of the main extractant and the co-extractant is 1:1, the mass content of the diluent in the organic phase is 70%, the diluent is isohexane, and the extraction phase ratio O:A=2.7:1. After the extraction is completed, extract 3 and raffinate 3 are obtained.

[0078] The extract 3 was back-extracted with a sulfuric acid solution having a concentration of 2.2 mol / L, and the back-extraction phase ratio O:A=13:1.

[0079] The content of each element in the stripping solution 3 is shown in Table 3-5; the stripping solution 3 is precipitated with sodium carbonate to obtain a lithium carbonate product.

[0080] Table 3-5 Example 4 The contents of major metals in the impurity-removing liquid obtained after the battery powder is leached with reducing acid and copper, iron and aluminum are removed from the leaching liquid are shown in Table 4-1.

[0081] Table 4-1 (1) Manganese Extraction The extractant in the organic phase of manganese extraction is Cyanex 272. In the organic phase, the mass fraction of Cyanex 272 is 15%, and the rest is sulfonated kerosene, and the saponification rate is 38%.

[0082] The extraction phase ratio is O:A=5.1:1.

[0083] After the extraction is completed, extract 1 and raffinate 1 are obtained.

[0084] The extract 1 was back-extracted with a sulfuric acid solution having a concentration of 2.1 mol / L, and the back-extraction phase ratio O:A=34.5:1.

[0085] The contents of main metals in stripping solution 1 are shown in Table 4-2.

[0086] Table 4-2 (2) Nickel-cobalt co-extraction The extractant in the nickel-cobalt co-extraction organic phase is BC196. In the organic phase, the mass fraction of BC196 is 25%, and the rest is sulfonated kerosene, and the saponification rate is 41%.

[0087] The extraction phase ratio is O:A=5.8:1.

[0088] After the extraction is completed, extract 2 and raffinate 2 are obtained.

[0089] The extract 2 was stripped with a 2.2 mol / L sulfuric acid solution, and the stripping phase ratio O:A=13.2:1.

[0090] The contents of main metals in stripping solution 2 are shown in Table 4-3.

[0091] Table 4-3 (3) Removal of calcium and magnesium The raffinate 2 was passed through an HP4010 resin column at a flow rate of 1 BV / h to obtain a lithium-containing solution. The contents of major metals in the lithium-containing solution are shown in Table 4-4.

[0092] Table 4-4 (4) Lithium Extraction The lithium-containing solution is subjected to lithium extraction process, the molar ratio of sodium hydroxide:Li=1.4, the main extractant is 1-alkenyl-3-methylpyridinium salt, the co-extractant is 2-ethylhexyl phosphate mono-2-ethylhexyl ester, the mass relationship ratio of the main extractant and the co-extractant is 1:0.9, the mass content of the diluent in the organic phase is 60%, the diluent is isomeric decanol, and the extraction phase ratio O:A=2.6:1.

[0093] After the extraction is completed, extract 3 and raffinate 3 are obtained.

[0094] The extract 3 was back-extracted with a 2 mol / L sulfuric acid solution, and the back-extraction phase ratio O:A=11.5:1.

[0095] The content of each element in the stripping solution 3 is shown in Table 4-5; the stripping solution 3 is precipitated with sodium carbonate to obtain a lithium carbonate product.

[0096] Table 4-5 The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for recycling battery powder from waste power batteries by a short extraction process. It is characterized in that The following steps are involved: (1) Leaching: Sulfuric acid and a reducing agent are used to jointly leach the battery powder to obtain a leachate and leaching residue; (2) Impurity removal: copper, iron and aluminum are removed from the leaching solution to obtain an impurity-removing solution; (3) Extraction of manganese: extract manganese from the impurity removal liquid using Cyanex272 extractant to obtain extract 1 and raffinate 1; (4) Nickel-cobalt co-extraction: The raffinate 1 is subjected to nickel-cobalt co-extraction using BC196 extractant to obtain extract 2 and raffinate 2; (5) Removal of calcium and magnesium: The raffinate 2 is treated with a resin to remove calcium and magnesium to obtain a lithium-containing solution; (6) Lithium extraction: The lithium-containing solution is enriched by extraction to obtain extract 3 and raffinate 3.

2. The recycling method according to claim 1, It is characterized in that The reducing agent is one or more of hydrogen peroxide, sodium thiosulfate, and sodium metabisulfite; Preferably, one or both of iron powder and sodium thiosulfate are added to the leaching solution to remove copper; Preferably, one or both of sodium hydroxide and sodium carbonate are used to remove iron and aluminum.

3. The recovery method according to claim 1 or 2, It is characterized in that The mass fraction of Cyanex272 extractant in the organic phase of manganese extraction is 10%~15%, the diluent is sulfonated kerosene, and the saponification rate is 30%~50%; Preferably, the phase ratio during manganese extraction is O:A=2~11:

1.

4. The recovery method according to any one of claims 1 to 3, It is characterized in that The extract 1 is stripped with sulfuric acid solution to obtain a manganese sulfate solution; Preferably, the concentration of the sulfuric acid solution is 2 to 2.5 mol / L; Preferably, when the extract 1 is stripped with sulfuric acid solution, the phase ratio O:A=20~50:

1.

5. The recovery method according to any one of claims 1 to 4, It is characterized in that The mass fraction of BC196 extractant in the organic phase of nickel-cobalt co-extraction is 20%-25%, the diluent is sulfonated kerosene, and the saponification rate is 40-50%; Preferably, the phase ratio of nickel and cobalt during co-extraction is O:A=4~6:

1.

6. The recovery method according to any one of claims 1 to 5, It is characterized in that The extract 2 is stripped with a sulfuric acid solution to obtain a mixed solution of nickel sulfate and cobalt sulfate; Preferably, the concentration of the sulfuric acid solution is 2-2.5 mol / L; Preferably, when the extract 2 is stripped with sulfuric acid solution, the phase ratio O:A=10-20:

1.

7. The recovery method according to claim 4 or 6, It is characterized in that A mixed solution of manganese sulfate solution, nickel sulfate and cobalt sulfate is used to prepare a nickel-cobalt-manganese precursor.

8. The recovery method according to any one of claims 1 to 7, It is characterized in that The resin used for removing calcium and magnesium is HP4010.

9. The recovery method according to any one of claims 1 to 8, It is characterized in that The extracting agents for lithium extraction include main extracting agents and co-extracting agents; Preferably, the main extractant is one or more of 1-butyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium fluoride, 1-ethyl-3-methylimidazolium chloride, 1-propyl-3-methylimidazolium tetrafluoroborate, 1-alkenyl-3-methylpyridinium salt, and ammonium tetrafluoroborate; Preferably, the co-extractant is one or more of tributyl phosphate, dioctyl phosphate, trioctyl phosphate, triethylamine, trioctylamine, 2-ethylhexyl phosphate mono-2-ethylhexyl ester, and di(2-ethylhexyl) phosphate; Preferably, the mass ratio of the main extractant to the co-extractant is 1:0.75-1.5; Preferably, the mass content of the diluent in the organic phase for extracting lithium is 50%-80%; Preferably, the diluent is one or more of sulfonated kerosene, n-hexane, isohexane, isomeric decanol, isomeric undecanol, and isomeric dodecanol; Preferably, the phase ratio during lithium extraction is O:A=2-3:

1.

10. The recycling method according to any one of claims 1 to 9, It is characterized in that The extract 3 is stripped with a sulfuric acid solution to obtain a lithium sulfate solution; Preferably, the concentration of the sulfuric acid solution is 2-2.5 mol / L; Preferably, the ratio of the extract 3 to the sulfuric acid solution during back extraction is O:A=10-20:1; Preferably, the mother liquor after lithium precipitation in the lithium sulfate solution is returned to the lithium extraction process.

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