Method for improving lithium recovery rate

Abstract

The invention discloses a method for improving lithium recovery rate, which comprises the following steps: S1, removing impurities from a lithium source solution, and carrying out solid-liquid separation to obtain waste residue and lithium-containing filtrate; s2, concentrating the lithium-containing filtrate to obtain lithium precipitation mother liquor; s3, treating the lithium precipitation mother liquor by using saturated sodium carbonate, and carrying out solid-liquid separation to obtain a crude lithium carbonate product and primary residual liquid; s4, carrying out carbonization pyrolysis treatment on the primary residual liquid, and carrying out solid-liquid separation to obtain battery-grade lithium carbonate and secondary residual liquid; s5, carrying out phosphoric acid lithium precipitation treatment on the secondary residual liquid, and carrying out solid-liquid separation to obtain solid lithium phosphate; according to the present invention, the sodium carbonate lithium precipitation, the carbonization pyrolysis and the phosphoric acid lithium precipitation are combined to form the three-stage precipitation process, such that the gradient recovery of the lithium is achieved, the comprehensive recovery rate of the lithium is improved, the staged precipitation avoids the inhibition of the impurities (Ca < 2 + > and SO4 < 2->) on the subsequent reaction, and the circulation energy consumption and the lithium loss are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of battery recycling, and in particular to a method for improving lithium recovery rate. Background Art

[0002] In the industrialized processes of lithium extraction from salt lakes, lithium ore processing, waste liquid recovery, and battery black powder leaching, precipitation is the current mainstream lithium carbonate production process. Specifically, lithium-containing raw materials undergo pretreatment to form a lithium carbonate mother liquor (lithium precipitation mother liquor), which contains lithium ions and impurity ions such as Na⁺, K⁺, CO₃²⁻, Cl⁻, and SO₄²⁻. Existing technologies generally use saturated sodium carbonate solution as a precipitant, which reacts to precipitate lithium as lithium carbonate, thereby achieving initial lithium recovery. This process has become a standard procedure in the battery recycling industry due to its ease of operation and manageable costs.

[0003] Despite widespread use, the sodium carbonate precipitation method faces significant bottlenecks in lithium recovery efficiency, with the primary precipitation rate for lithium reaching only 70-80%, though this rate has been increased to 85-90%. The residual mother liquor still contains a high concentration of Li⁺, necessitating recycling to the front-end process for secondary purification. However, impurities such as Na⁺ and SO₄²⁻ in the mother liquor continue to accumulate over multiple cycles, not only inhibiting the efficiency of subsequent lithium precipitation but also leading to lithium entrainment and loss with the waste residue during solid-liquid separation. Furthermore, repeated purification requires the addition of additional precipitants, increases energy consumption for evaporation and concentration, and drives up waste residue treatment costs and the product's carbon footprint. These deficiencies make it difficult for existing technologies to achieve a comprehensive lithium recovery rate exceeding 90%, resulting in waste of resources and reduced economic efficiency.

[0004] Therefore, a technical solution needs to be provided to improve the recovery rate of lithium extraction from battery black powder. Summary of the Invention

[0005] In view of this, the present application provides a method for improving the lithium recovery rate, which is used to solve the problem of how to improve the recovery rate of lithium extracted from battery black powder.

[0006] In order to achieve the above technical objectives, this application adopts the following technical solutions: The present application provides a method for improving lithium recovery rate, comprising the following steps: S1. After removing impurities from the lithium source solution, solid-liquid separation is performed to obtain waste residue and a lithium-containing filtrate; S2. The lithium-containing filtrate is concentrated to obtain a lithium-precipitated mother liquor; S3. The mother liquor of lithium precipitate was treated with saturated sodium carbonate, solid-liquid separation was performed to obtain crude lithium carbonate and a residual liquid; S4. The primary residual liquid is subjected to carbonization and pyrolysis treatment, solid-liquid separation, to obtain battery-grade lithium carbonate and a secondary residual liquid; S5. The secondary residual liquid is subjected to lithium phosphate precipitation treatment and solid-liquid separation to obtain solid lithium phosphate.

[0007] Preferably, the lithium source solution is a liquid phase obtained by solid-liquid separation after acid leaching and / or alkaline leaching of battery black powder.

[0008] Preferably, the steps of carbonization and pyrolysis are: introducing CO2 into the primary residual liquid to carry out a carbonization reaction to obtain a solution containing LiHCO3; adjusting the pH value of the solution containing LiHCO3 to alkaline to obtain battery-grade lithium carbonate and a secondary residual liquid; the purity of the battery-grade lithium carbonate is greater than or equal to 99.5%.

[0009] Preferably, the step of lithium phosphate precipitation is to add unsaturated phosphoric acid to the secondary residual liquid to carry out precipitation reaction, and obtain solid lithium phosphate and tertiary residual liquid after solid-liquid separation.

[0010] Preferably, the molar ratio of lithium in the secondary residual solution to phosphorus in the unsaturated phosphoric acid is 3:1-2.

[0011] Preferably, the process further comprises detecting the Li concentration in the tertiary residual liquid. When the Li concentration in the tertiary residual liquid is ≤50 mg / L, the tertiary residual liquid is discharged; when the Li concentration in the tertiary residual liquid is ≥1 g / L, the tertiary residual liquid is reused in the impurity removal process.

[0012] Preferably, the lithium source solution Li + The concentration is 3.3-5.5g / L, Ca 2+ Concentration is 0.01-100mg / L, SO4 2- The concentration is 30-85g / L.

[0013] Preferably, the Li in the lithium precipitation mother solution + Concentration ≥10g / L.

[0014] Preferably, the Li in the primary residual solution + The concentration is 1-1.5g / L.

[0015] Preferably, the solid-liquid separation method is centrifugal separation.

[0016] The beneficial effects of this application are as follows: This application forms a three-stage precipitation process by combining sodium carbonate lithium precipitation, carbonization pyrolysis, and phosphate lithium precipitation to achieve gradient recovery of lithium, improve the comprehensive recovery rate of lithium, and at the same time, staged precipitation avoids impurities (Ca 2 + 、SO4 2- ) inhibit subsequent reactions, reduce cycle energy consumption and lithium loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is the process flow chart of this application. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0019] like Figure 1 As shown, the present application provides a method for improving lithium recovery rate, comprising the following steps: S1. After removing impurities from the lithium source solution, solid-liquid separation is performed to obtain waste residue and a lithium-containing filtrate; S2. The lithium-containing filtrate is concentrated to obtain a lithium-precipitated mother liquor; S3. The mother liquor of lithium precipitate was treated with saturated sodium carbonate, solid-liquid separation was performed to obtain crude lithium carbonate and a residual liquid; S4. The primary residual liquid is subjected to carbonization and pyrolysis treatment, solid-liquid separation, to obtain battery-grade lithium carbonate and a secondary residual liquid; S5. The secondary residual liquid is subjected to lithium phosphate precipitation treatment and solid-liquid separation to obtain solid lithium phosphate.

[0020] This application forms a three-stage precipitation process by combining sodium carbonate lithium precipitation, carbonization pyrolysis, and phosphate lithium precipitation to achieve gradient recovery of lithium, improve the comprehensive recovery rate of lithium, and simultaneously avoid impurities (Ca 2+ 、SO4 2- ) inhibit subsequent reactions, reduce cycle energy consumption and lithium loss.

[0021] Among them, sodium carbonate lithium precipitation uses the low solubility product of lithium carbonate (Ksp≈1.7×10-³) to preferentially precipitate most of the lithium. Due to the low Ksp of lithium carbonate, it can be precipitated better than other metal carbonates (such as calcium carbonate and magnesium carbonate) to obtain crude lithium carbonate. The remaining residual lithium enters the primary residual liquid. Depending on the pre-treatment procedure of battery black powder, sodium carbonate lithium precipitation may involve the following process: 2LiCl+Na2CO3→Li2CO3↓+2NaCl, Li2SO4+Na2CO3→Li2CO3↓+Na2SO4; The primary residual liquid is then subjected to a carbonization reaction with CO2 and alkali adjustment to further recover lithium while removing calcium and sulfate. The carbonization reaction involves the following processes: LiOH + CO2 → LiHCO3 Li2SO4+ 2CO2+ 2H2O→2LiHCO3+ H2SO4 After obtaining lithium bicarbonate, the pH is adjusted to alkaline to precipitate lithium carbonate. The lithium carbonate obtained at this time is battery-grade lithium carbonate with few impurities and a purity of more than 99.5%. The process is as follows: 2LiHCO3→ Li2CO3↓+ CO2↑+ H2O Although the carbonization method can produce battery-grade lithium carbonate with low impurity content, it can also remove Ca and SO4 2- , but Li, Ca and SO4 still remain in the solution 2- (The content is lower than before impurity removal, lithium, calcium, and sodium sulfate coexist), which will inevitably cause lithium loss and blockage of related subsequent equipment. Therefore, the phosphoric acid method is introduced to prepare crude lithium phosphate to reduce lithium loss (accompanied by the precipitation of part of calcium, without the introduction of Na and sulfate), and Na and sulfate are discharged from the system with wastewater; the mechanism of lithium phosphate precipitation is to utilize the extremely low solubility product of lithium phosphate (Ksp≈3.2×10⁻ 9 ) Deep recovery of residual lithium. Depending on the pre-treatment procedures of battery black powder, the reaction process involved is: 3Li2SO4+ 2H3PO4→ 2Li3PO4+ 3H2SO4 3LiOH + H3PO4→ Li3PO4↓+ 3H2O In some embodiments, the lithium source solution is a liquid phase obtained by solid-liquid separation after acid leaching and / or alkaline leaching of battery black powder.

[0022] In this embodiment, the lithium source is widely available, and the liquid phase obtained after acid leaching or alkaline leaching of battery black powder can be used as the lithium source of this application. The method of improving the lithium recovery rate of this application has a wide range of applications.

[0023] In some embodiments, the steps of carbonization and pyrolysis are: introducing CO2 into the primary residual liquid to carry out a carbonization reaction to obtain a solution containing LiHCO3; adjusting the pH value of the solution containing LiHCO3 to alkaline to obtain battery-grade lithium carbonate and a secondary residual liquid; the purity of the battery-grade lithium carbonate is greater than or equal to 99.5%.

[0024] In this embodiment, battery-grade lithium carbonate (≥99.5%) is prepared by carbonization pyrolysis to reduce lithium loss caused by impurity entrainment.

[0025] In some embodiments, the step of lithium phosphate precipitation is to add unsaturated phosphoric acid to the secondary residual liquid to carry out a precipitation reaction, and obtain solid lithium phosphate and a tertiary residual liquid after solid-liquid separation.

[0026] In this embodiment, lithium phosphate precipitation is used to deeply recover lithium from the secondary residual solution.

[0027] In some embodiments, the molar ratio of lithium in the secondary raffinate to phosphorus in the unsaturated phosphoric acid is 3:1-2.

[0028] In this embodiment, by optimizing the phosphoric acid addition ratio, the lithium recovery rate and the risk of excessive phosphorus in wastewater are balanced to ensure that the lithium is completely precipitated. However, excessive use of phosphoric acid will cause excessive phosphorus in the wastewater and fail to meet the discharge standard. The process involved is: 3Li + + H3PO4 → Li3PO4 + 3H +, Ksp≈3.2×10 -9 ; Li is less than or equal to (0.05g / L), the H3PO4 excess coefficient is 1.0-1.2 (fine-tuned according to the residual Li content of the solution), and the water is discharged to the back-end wastewater treatment facility to treat the excess phosphorus in the solution.

[0029] In some embodiments, the process further includes detecting the Li concentration in the tertiary residual liquid. When the Li concentration in the tertiary residual liquid is ≤50 mg / L, the tertiary residual liquid is discharged; when the Li concentration in the tertiary residual liquid is ≥1 g / L, the tertiary residual liquid is reused in the impurity removal process.

[0030] In the prior art, the full circulation of mother liquor will lead to impurities (Na + 、SO4 2- ) enrichment and suppression of lithium precipitation. This embodiment avoids the accumulation of impurities and reduces the circulation load through selective reuse, while also maximizing the recovery of lithium and reducing external discharge losses.

[0031] In some embodiments, the lithium source solution contains Li + The concentration is 3.3-5.5g / L, Ca 2+ Concentration is 0.01-100mg / L, SO4 2- The concentration is 30-85g / L.

[0032] In this embodiment, if the initial Li concentration is too low, the concentration energy consumption will be too high; if the initial Li concentration is too high, the impurities will be simultaneously concentrated and inhibit precipitation.

[0033] In some embodiments, the Li in the lithium precipitation mother solution + Concentration ≥10g / L.

[0034] In this embodiment, the lithium precipitation efficiency is improved by concentration, and the precipitant consumption is reduced.

[0035] In some embodiments, the Li + The concentration is 1-1.5g / L.

[0036] In some embodiments, the solid-liquid separation method is centrifugal separation.

[0037] The present invention is further described below through specific examples.

[0038] Example 1 A method for improving lithium recovery comprises the following steps: S1. After the battery black powder is leached with sulfuric acid, the solid-liquid separation is performed to obtain the lithium source solution. + The concentration is 3.38g / L, Ca 2+ The concentration is 2.19mg / L, SO4 2-The concentration is 81.82g / L, F - The concentration is 58.43 g / L, and the lithium source solution is treated with saturated calcium hydroxide to remove impurities, and then centrifuged to obtain waste residue and lithium-containing filtrate; S2. The lithium-containing filtrate is concentrated, sulfuric acid is added for acidification, and the pH is adjusted to 6-8 to obtain a lithium precipitation mother liquor. The Li in the lithium precipitation mother liquor is + The concentration is 16.74 g / L, Ca 2+ Concentration is 0.01mg / L, SO4 2- The concentration is 188.68 g / L; S3. Treat the lithium precipitation mother liquor with saturated sodium carbonate (Li: CO3 2- Molar ratio = 2:1, excess coefficient 1.3), solid-liquid separation, to obtain 98% purity lithium carbonate crude product and a residual liquid, the Li in the residual liquid + The concentration is 1.01g / L, Ca 2+ The concentration is 0.44mg / L, SO4 2- The concentration is 31.84 g / L; S4. CO2 is introduced into the primary residual liquid for carbonization reaction to obtain a solution containing LiHCO3; the temperature of the LiHCO3 solution is adjusted, and the decomposition system equipment adopts a continuous decomposition tower. The lithium bicarbonate solution and steam are indirectly heat-exchanged to thermally decompose the lithium bicarbonate at a certain temperature to obtain battery-grade lithium carbonate with a purity of 99.8% and a secondary residual liquid. The Li in the secondary residual liquid is + The concentration is 1.01g / L, Ca 2+ The concentration is 0.44mg / L, SO4 2- The concentration is 31.84 g / L; S5. Unsaturated phosphoric acid was added to the secondary residual solution to carry out a precipitation reaction, wherein the molar ratio of lithium in the secondary residual solution to phosphorus in the unsaturated phosphoric acid was 3:1, and solid-liquid separation was performed to obtain 97% pure solid lithium phosphate and a tertiary residual solution. The Li concentration in the tertiary residual solution was detected. The Li + The concentration is 60.86 mg / L, Ca 2+ The concentration is 0.22mg / L, SO4 2- The concentration is 49.9 g / L, and the tertiary residual liquid is discharged as wastewater.

[0039] Example 2 A method for improving lithium recovery comprises the following steps: S1. After the battery black powder is leached with sulfuric acid, the solid-liquid separation is performed to obtain the lithium source solution. + The concentration is 5.49g / L, Ca 2+ The concentration is 1.33mg / L, SO4 2-The concentration is 49.84 g / L, F - The concentration is 72.84 g / L, and the lithium source solution is treated with saturated calcium hydroxide to remove impurities, and then centrifuged to obtain waste residue and lithium-containing filtrate; S2. The lithium-containing filtrate is concentrated to obtain a lithium precipitation mother liquor. The Li + The concentration is 19.24 g / L, Ca 2+ The concentration is 10.65mg / L, SO4 2- The concentration is 210.09 g / L; S3. The lithium precipitate mother liquor was treated with saturated sodium carbonate and solid-liquid separation was performed to obtain a crude lithium carbonate product with a purity of 98% and a residual liquid. + The concentration is 3g / L, Ca 2+ The concentration is 8mg / L, SO4 2- The concentration is 180g / L; S4. CO2 is introduced into the primary residual liquid for carbonization reaction to obtain a solution containing LiHCO3; the temperature of the solution containing LiHCO3 is adjusted, and the decomposition system equipment adopts a continuous decomposition tower. The lithium bicarbonate solution and steam are indirectly heat-exchanged to thermally decompose the lithium bicarbonate at a certain temperature to obtain battery-grade lithium carbonate and a secondary residual liquid. The Li in the secondary residual liquid is + The concentration is 0.9 g / L, Ca 2+ The concentration is 0.2mg / L, SO4 2- The concentration is 10g / L; S5. Unsaturated phosphoric acid is added to the secondary residual liquid to carry out a precipitation reaction, wherein the molar ratio of lithium in the secondary residual liquid to phosphorus in the unsaturated phosphoric acid is 3:1, solid lithium phosphate and a tertiary residual liquid are obtained after solid-liquid separation, and the Li concentration in the tertiary residual liquid is detected. + The concentration is 20.31 mg / L, Ca 2+ The concentration is 0.01mg / L, SO4 2- The concentration is 27.07 g / L, the P (phosphorus content only, not converted into phosphate content) concentration is 648 mg / L, and the tertiary residual liquid is discharged as wastewater.

[0040] Comparative Example 1 A method for improving lithium recovery rate, wherein the other steps are the same as those in Example 1, except that the lithium phosphate precipitation step is not included.

[0041] Comparative Example 2 A method for improving lithium recovery rate, wherein the other steps are the same as those in Example 1, except that the steps of lithium phosphate precipitation and carbonization pyrolysis are not included.

[0042] Testing and Evaluation The solid lithium salt products obtained in different embodiments and comparative examples were collected respectively, and the recovery rates were calculated. The results are shown in Table 1.

[0043] Table 1 Test results

[0044] The above results show that the present invention forms a three-stage precipitation process by combining sodium carbonate precipitation, carbonization pyrolysis and phosphate precipitation to achieve gradient recovery of lithium, improve the comprehensive recovery rate of lithium, and simultaneously avoid impurities (Ca 2+ 、SO4 2- ) inhibit subsequent reactions, reduce cycle energy consumption and lithium loss.

[0045] The above are only preferred specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or replacements that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for improving lithium recovery, characterized in that, The following steps are involved: After removing impurities from the lithium source solution, solid-liquid separation is performed to obtain waste residue and lithium-containing filtrate; Concentrating the lithium-containing filtrate to obtain a lithium precipitation mother liquor; Treating the lithium precipitation mother liquor with saturated sodium carbonate to separate the solid and liquid to obtain a crude lithium carbonate product and a primary residual liquid; Carrying out carbonization and pyrolysis treatment on the primary residual liquid, and separating the solid and liquid to obtain battery-grade lithium carbonate and secondary residual liquid; The secondary residual liquid is subjected to lithium phosphate precipitation treatment and solid-liquid separation to obtain solid lithium phosphate.

2. The method for improving lithium recovery according to claim 1, wherein The lithium source solution is a liquid phase obtained by acid leaching and / or alkaline leaching of battery black powder and solid-liquid separation.

3. The method for improving lithium recovery according to claim 1, wherein The carbonization and pyrolysis steps are as follows: introducing CO2 into the primary residual liquid for carbonization reaction to obtain a solution containing LiHCO3; adjusting the pH value of the LiHCO3-containing solution to alkaline to obtain battery-grade lithium carbonate and a secondary residual liquid; the purity of the battery-grade lithium carbonate is greater than or equal to 99.5%.

4. The method for improving lithium recovery according to claim 1, wherein The steps of lithium phosphate precipitation are as follows: adding unsaturated phosphoric acid to the secondary residual liquid to carry out precipitation reaction, and obtaining solid lithium phosphate and tertiary residual liquid after solid-liquid separation.

5. The method for improving lithium recovery according to claim 4, wherein The molar ratio of lithium in the secondary residual solution to phosphorus in the unsaturated phosphoric acid is 3:1-2.

6. The method for improving lithium recovery according to claim 4, wherein The method further includes detecting the Li concentration in the tertiary residual liquid. When the Li concentration in the tertiary residual liquid is ≤50 mg / L, the tertiary residual liquid is discharged; when the Li concentration in the tertiary residual liquid is ≥1 g / L, the tertiary residual liquid is reused in the impurity removal process.

7. The method for improving lithium recovery according to claim 1, wherein The lithium source solution contains Li + The concentration is 3.3-5.5g / L, Ca 2+ Concentration is 0.01-100mg / L, SO4 2- The concentration is 30-85g / L.

8. The method for improving lithium recovery according to claim 1, wherein The Li in the lithium precipitation mother solution + Concentration ≥10g / L.

9. The method for improving lithium recovery according to claim 1, wherein Li in the primary residual liquid + The concentration is 1-1.5g / L.

10. The method for improving lithium recovery according to claim 1, wherein: The solid-liquid separation method is centrifugal separation.

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