A process for preparing high-purity lithium metal from lithium iron phosphate recycled material
By combining a specific acid leaching system and a two-stage extraction system with evaporation concentration and refining steps, the problems of impurities and organic solvents in lithium iron phosphate recycled materials are solved, and high-purity metallic lithium is produced, meeting the purity and recovery rate requirements of high-end fields and improving the stability and economy of the process.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JIANGXI LONGKAI CYCLE TECHNOLOGY CO LTD
- Filing Date
- 2026-05-12
- Publication Date
- 2026-06-12
AI Technical Summary
In existing technologies, when preparing high-purity lithium metal using recycled retired lithium iron phosphate materials, the lithium chloride solution contains high levels of impurities and organic solvents, resulting in low purity of lithium salt refining, low lithium resource utilization, and incomplete removal of impurities, which affects the purity of lithium metal products and makes it difficult to meet the requirements of high-end fields.
High-purity lithium metal is prepared by using a specific acid leaching system and a two-stage extraction system, combined with evaporation concentration and refining steps, followed by melt electrolysis. Through multi-stage countercurrent extraction and optimized electrolysis parameters, impurities and organic solvents are removed.
It achieves deep removal of metallic impurities such as Ni, Ca, Mg, Fe, and Al, with an impurity removal rate of ≥99.5%, a lithium metal purity of 99.95%, a lithium resource recovery rate of ≥99.0%, an extended electrolytic cell operating cycle, and a reduced equipment failure rate, meeting the requirements of green chemical industry.
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Figure CN122189381A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium battery resource recycling technology, and in particular to a process for preparing high-purity metallic lithium using recycled lithium iron phosphate as raw material. Background Technology
[0002] High-purity lithium metal is a lightweight, high negative potential, and high specific energy metallic material, which is widely used in new battery energy materials, alloy materials in aircraft, and coolants in nuclear fusion reactors.
[0003] Currently, the process of preparing lithium chloride from recycled lithium iron phosphate materials and further electrolyzing it to produce high-purity lithium metal is the mainstream direction for lithium resource recycling. However, existing processes still have many technical problems: First, the lithium chloride solution obtained after acid leaching of recycled lithium iron phosphate materials has a complex composition, containing various metallic impurity ions such as nickel, calcium, magnesium, iron, and aluminum. Traditional impurity removal processes use a single precipitation method, which is incomplete in removing impurities, and residual impurities will seriously affect the purity of subsequent lithium salts and electrolysis efficiency. Second, the solution obtained after acid leaching of recycled materials is mixed with organic solvents, resulting in low purity of subsequent lithium salt crystals and even causing side reactions in the electrolysis process, reducing the quality of lithium metal products. Third, the overall process has poor synergy between impurity removal and lithium recovery, and some impurity removal processes can cause lithium element loss, reducing the comprehensive utilization rate of lithium resources. These problems make it difficult to achieve a purity of 99.95% for the prepared high-purity lithium metal, which cannot meet the needs of high-end applications. Summary of the Invention
[0004] The purpose of this invention is to provide a process for preparing high-purity lithium metal from recycled lithium iron phosphate material, in order to solve the technical problems of high impurities and organic solvents in the lithium chloride solution, low purity of lithium salt refining, low lithium resource utilization, and ultimately substandard purity of lithium metal products in the current process for preparing high-purity lithium metal from recycled lithium iron phosphate material.
[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a process for preparing high-purity lithium metal from recycled lithium iron phosphate material, comprising the following steps: 1) Add water and hydrochloric acid to the lithium iron phosphate recycled material, adjust the pH of the system, add oxidant, stir the reaction and then filter; 2) The filtrate obtained from filtration is then subjected to a two-stage extraction system for deep purification. 3) The purified lithium chloride solution was sequentially evaporated, concentrated, and refined to obtain anhydrous lithium chloride crystals; 4) Anhydrous lithium chloride crystals are mixed with potassium chloride and placed in an electrolytic cell for molten electrolysis. The metallic lithium produced by electrolysis is deposited and aggregated on the surface of liquid lead at the cathode, and high-purity metallic lithium is collected.
[0006] Furthermore, the mass ratio of the lithium iron phosphate recycled material, water, and hydrochloric acid is 1:4~6:0.5~1.5, and the pH of the system is adjusted to 1.3~1.5.
[0007] Furthermore, the oxidant is NaClO3, and the amount of oxidant added is 1-2% of the mass of the lithium iron phosphate recycled material; the stirring reaction time is 2-4 hours.
[0008] Furthermore, the two-stage extraction system is as follows: the first-stage extraction uses di(2-ethylhexyl) phosphate as the extractant and sulfonated kerosene as the diluent, with an O / A ratio of 1:1~3 and a pH value of 2.0~3.0, and employs multi-stage countercurrent extraction; The secondary extraction uses tributyl phosphate as the extractant, with an O / A ratio of 1:1~2.
[0009] Furthermore, the mass concentration of the lithium chloride solution is controlled to be 40-50% during the evaporation and concentration process.
[0010] Furthermore, the purification process involves crystallizing at 0-5°C for 12-16 hours, followed by centrifugation to obtain anhydrous lithium chloride crystals.
[0011] Furthermore, the mass ratio of the anhydrous lithium chloride crystals to potassium chloride is 1:0.9~1.2.
[0012] Furthermore, in the melt electrolysis: the melting temperature is 400~500℃, and the electrolysis parameters are: the cathode current density is controlled at 15~25A / dm³. 2 The anode current density is controlled at 8~12A / dm². 2 The tank voltage is controlled between 6.0 and 8.0V.
[0013] The beneficial effects of this invention are: 1. Extremely high impurity removal rate and product purity This invention utilizes a two-stage extraction system (P204+TBP) to achieve not only deep removal of metallic impurities such as Ni, Ca, Mg, Fe, and Al, but also simultaneous removal of organic residues. Experimental data shows that this invention achieves a total removal rate of ≥99.5% for major impurity ions, and the final prepared lithium metal has a purity of 99.95%~99.99%, fully meeting the stringent requirements of high-end fields such as nuclear fusion coolants and aerospace alloy materials, breaking through the bottleneck of traditional processes that struggle to achieve a purity exceeding 99.9%.
[0014] 2. Excellent lithium resource recovery rate
[0015] This invention optimizes the acid leaching oxidation system and extraction conditions, avoiding lithium loss caused by co-precipitation in traditional precipitation methods. Through full-process material balance, the total recovery rate of lithium resources is increased to ≥99.0%, significantly higher than the industry average (usually below 95%), greatly improving the efficiency of comprehensive resource utilization.
[0016] 3. Improved process stability and economic efficiency
[0017] This invention completely eliminates organic solvents, preventing electrode passivation and electrolyte contamination caused by organic decomposition during electrolysis. This results in an electrolytic cell operating cycle extended by more than 30% and a significant reduction in equipment failure rate. Simultaneously, the recycling of the extractant reduces the consumption of fresh reagents, lowering overall energy consumption by approximately 20% compared to traditional processes.
[0018] 4. Environmental friendliness
[0019] The entire process of this invention is operated at normal temperature and pressure (except for electrolysis), with no toxic gas emissions; the waste liquid is mainly recyclable extraction residue, which is easy to treat and meets the standards, and meets the requirements of green chemical industry and circular economy. Attached Figure Description
[0020] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation
[0021] This invention provides a process for preparing high-purity lithium metal from recycled lithium iron phosphate material, comprising the following steps: 1) Add water and hydrochloric acid to the lithium iron phosphate recycled material, adjust the pH of the system, add oxidant, stir the reaction and then filter; 2) The filtrate obtained from filtration is then subjected to a two-stage extraction system for deep purification. 3) The purified lithium chloride solution was sequentially evaporated, concentrated, and refined to obtain anhydrous lithium chloride crystals; 4) Anhydrous lithium chloride crystals are mixed with potassium chloride and placed in an electrolytic cell for molten electrolysis. The metallic lithium produced by electrolysis is deposited and aggregated on the surface of liquid lead at the cathode, and high-purity metallic lithium is collected.
[0022] In this invention, the mass ratio of the lithium iron phosphate recycled material, water and hydrochloric acid is 1:4~6:0.5~1.5, preferably 1:5:0.9; the pH of the system is adjusted to 1.3~1.5, preferably 1.4.
[0023] In this invention, the oxidant is NaClO3, and the amount of oxidant added is 1-2% of the mass of the lithium iron phosphate recycled material, preferably 1-1.5%; the stirring reaction time is 2-4 hours, preferably 3 hours.
[0024] In this invention, the two-stage extraction system is as follows: the first-stage extraction uses di(2-ethylhexyl) phosphate as the extractant and sulfonated kerosene as the diluent, with an O / A ratio of 1:1 to 3, preferably 1:2; the pH value is 2.0 to 3.0, preferably 2.2 to 2.8; and multi-stage countercurrent extraction is employed. The secondary extraction uses tributyl phosphate as the extractant, with an O / A ratio of 1:1~2, preferably 1:1.2~1.8.
[0025] In this invention, the mass concentration of the lithium chloride solution controlled by evaporation and concentration is 40-50%, preferably 42-48%, and more preferably 45%.
[0026] In this invention, the refining process involves crystallizing at 0-5°C for 12-16 hours, followed by centrifugation to obtain anhydrous lithium chloride crystals; preferably, the process involves crystallizing at 1-4°C for 13-15 hours.
[0027] In this invention, the mass ratio of anhydrous lithium chloride crystals to potassium chloride is 1:0.9~1.2, preferably 1:1.
[0028] In this invention, during the melt electrolysis: the melting temperature is 400~500℃, preferably 420~480℃, and more preferably 440~460℃; the electrolysis parameters are: the cathode current density is controlled at 15~25A / dm³. 2 Preferably 18~22 A / dm 2 Further preferred is 20A / dm 2 Anode current density is controlled at 8~12 A / dm³ 2 Preferably 10A / dm 2 The tank voltage is controlled between 6.0 and 8.0V, preferably between 6.5 and 7.5V.
[0029] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.
[0030] Example 1
[0031] High-purity metallic lithium was prepared using cathode powder from a retired lithium iron phosphate battery as raw material.
[0032] 1) Raw material pretreatment and hydrochloric acid leaching oxidation: Take 1 kg of decommissioned lithium iron phosphate recycled material, crush it through a universal pulverizer and then pass it through a 200-mesh standard sieve. Place the sieved powder in an electric constant temperature oven and dry it at 80℃ for 3 hours to remove moisture and surface adsorbed impurities, thus obtaining pretreated lithium iron phosphate powder. According to the mass ratio of slag:water:acid of 1:5:0.9, put 5L of bottom water and 0.9 kg of concentrated hydrochloric acid into a reaction vessel, add 1 kg of pretreated powder, and add 0.01 kg of sodium chlorate at 1% of the raw material mass. Start stirring and control the stirring speed at 300 r / min. React at a constant temperature for 3 hours to complete the acid leaching oxidation. After acid leaching, the liquid is separated into solid and liquid by a plate and frame filter press to remove the filter residue and obtain a crude lithium chloride solution. The lithium leaching rate is 99.0% according to ICP-OES test.
[0033] 2) Deep extraction for impurity removal: The crude lithium chloride solution was subjected to primary extraction and secondary extraction with di(2-ethylhexyl) phosphate and tributyl phosphate, respectively. The O / A ratio of the primary extraction and secondary extraction was 1:2. The temperature was controlled at 25℃, pH 2.5, and the extraction reaction was carried out for 30 min. Then, the mixture was allowed to stand for 20 min to separate the phases, so as to achieve the separation of impurities from the lithium chloride solution.
[0034] 3) Purification of raffinate and refining of lithium salt: The aqueous raffinate after phase separation was transferred to a vacuum stripping kettle and stripped under vacuum of -0.07 MPa and 40°C for 1 hour. At the same time, 5 L of deionized water was added for washing and analysis to obtain a purified lithium chloride solution. The residual organic solvent content was found to be 0.0008%. The purified lithium chloride solution was concentrated by vacuum evaporation to control the endpoint to achieve a lithium chloride solution mass concentration of 45%. Subsequently, it was crystallized at 2°C for 12 hours. Anhydrous lithium chloride crystals were obtained by centrifugation, and the purity was found to be 99.3%.
[0035] 4) Molten salt electrolysis: Anhydrous lithium chloride crystals and potassium chloride are mixed at a mass ratio of 1:1 and placed in an electrolytic cell and heated to 400℃ to form an electrolyte. Graphite is used as the anode and stainless steel as the cathode. The cathode current density is controlled at 20A / dm², the anode current density is 10A / dm², and the cell voltage is maintained at 7.0V for constant current electrolysis. During the electrolysis process, metallic lithium is deposited on the cathode (stainless steel material) and floats to the surface of the electrolyte in liquid beads. It is periodically scooped out with a strainer and poured into a mold to cool and solidify.
[0036] Product testing results: According to the testing of a third-party testing agency, the purity of this high-purity lithium metal product is 99.95%, with Ca content of 0.004%, Mg content of 0.002%, Fe content of 0.001%, Al content of 0.001%, and no organic solvent residue was detected. All indicators meet the requirements for high-end lithium battery applications.
[0037] Example 2
[0038] Same as Example 1, except that in step 4), the melting temperature is 480°C and the cathode current density is 25A / dm².
[0039] Product testing results: Electrolysis efficiency has improved, but potassium content in the product has increased slightly. After secondary purification, the final purity of metallic lithium can still reach 99.96%, verifying the wide applicability of the process parameters of this invention.
[0040] Example 3
[0041] Same as Example 1, except that in step 3), the lithium chloride solution is evaporated and concentrated to a mass concentration of 50%, the crystallization temperature is 0°C, and the crystallization time is 15 hours.
[0042] Product testing results: The precipitation rate and single batch yield of lithium chloride crystals have improved, but the test found that the purity of anhydrous lithium chloride is 99.2%, with trace amounts of sodium chloride and potassium chloride eutectic precipitation. After subsequent molten salt electrolysis, the final purity of metallic lithium can still reach 99.95%.
[0043] Example 4
[0044] Same as Example 1, except that in step 2), the O / A ratio for primary extraction is adjusted to 1:1, and the O / A ratio for secondary extraction is adjusted to 1:2.
[0045] Product testing results: Testing showed that primary extraction at a lower phase ratio slightly reduced the removal rate of high-valence metal impurities such as Fe and Al. However, secondary extraction at a higher phase ratio effectively retained residual Ni and Ca ions and further removed organic phase entrainment. The final purity of the lithium metal product was 99.94%.
[0046] Example 5
[0047] Same as Example 1, except that in step 1), the amount of hydrochloric acid added is 1.1 times the mass of the iron phosphate recovery material, and the amount of sodium chlorate added as oxidant is 2% of the mass of the recovery material.
[0048] Product test results: Lithium leaching rate 99.1%, electrolytic cell operation stable, lithium metal purity 99.96%, no organic solvent residue.
[0049] Comparative Example 1
[0050] Similar to Example 1, except that in step 2), only di(2-ethylhexyl) phosphate (P204) is used as the extractant, sulfonated kerosene is used as the diluent, the O / A ratio is 1:2, the pH value is 2.5, and multi-stage countercurrent extraction is adopted, eliminating the subsequent secondary extraction (TBP extraction) step.
[0051] Product testing results: After this process, trace amounts of residual organic solvents and trace amounts of metal impurity ions can still be detected in the purified lithium chloride solution. Subsequent refining and electrolysis under the same conditions yielded a finished lithium metal product with a purity of only 99.82%, failing to meet high-purity standards, and the electrolytic cell is prone to passivation.
[0052] Comparative Example 2
[0053] Same as Example 1, except that in step 4), the mass ratio of anhydrous lithium chloride to potassium chloride is still 1:1, and the melting temperature is 350°C.
[0054] Product test results: The electrolyte was not completely melted, electrolysis could not proceed stably, and lithium metal deposition was difficult.
[0055] As can be seen from the above embodiments, the present invention provides a process for preparing high-purity lithium metal from lithium iron phosphate recycled materials. Through the specific embodiments described above, it can be seen that the process provided by the present invention can effectively process lithium iron phosphate recycled materials. By using a specific acid leaching system and extractant combination, the problem of impurity and organic residue is solved, ultimately achieving an impurity removal rate ≥99.5% and preparing high-purity lithium metal with a purity ≥99.95%. Furthermore, the lithium recovery rate is high, demonstrating strong potential for industrial application.
[0056] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A process for preparing high-purity lithium metal from recycled lithium iron phosphate material, characterized in that, Includes the following steps: 1) Add water and hydrochloric acid to the lithium iron phosphate recycled material, adjust the pH of the system, add oxidant, stir the reaction and then filter; 2) The filtrate obtained from filtration is then subjected to a two-stage extraction system for deep purification. 3) The purified lithium chloride solution was sequentially evaporated, concentrated, and refined to obtain anhydrous lithium chloride crystals; 4) Anhydrous lithium chloride crystals are mixed with potassium chloride and placed in an electrolytic cell for molten electrolysis. The metallic lithium produced by electrolysis is deposited and aggregated on the surface of liquid lead at the cathode, and high-purity metallic lithium is collected.
2. The process method according to claim 1, characterized in that, The mass ratio of the lithium iron phosphate recycled material, water, and hydrochloric acid is 1:4~6:0.5~1.5, and the pH of the system is adjusted to 1.3~1.
5.
3. The process method according to claim 1 or 2, characterized in that, The oxidant is NaClO3, and the amount of oxidant added is 1-2% of the mass of the lithium iron phosphate recycled material; the stirring reaction time is 2-4 hours.
4. The process method according to claim 3, characterized in that, The two-stage extraction system is as follows: the first stage extraction uses di(2-ethylhexyl) phosphate as the extractant and sulfonated kerosene as the diluent, with an O / A ratio of 1:1~3 and a pH value of 2.0~3.0, and adopts multi-stage countercurrent extraction; The secondary extraction uses tributyl phosphate as the extractant, with an O / A ratio of 1:1~2.
5. The process method according to claim 1, 2, or 4, characterized in that, The evaporation and concentration process controls the mass concentration of the lithium chloride solution to be 40-50%.
6. The process method according to claim 5, characterized in that, The purification process involves crystallizing at 0-5°C for 12-16 hours, followed by centrifugation to obtain anhydrous lithium chloride crystals.
7. The process method according to claim 1 or 6, characterized in that, The mass ratio of anhydrous lithium chloride crystals to potassium chloride is 1:0.9~1.
2.
8. The process method according to claim 7, characterized in that, In the aforementioned melt electrolysis: the melting temperature is 400~500℃, and the electrolysis parameters are: the cathode current density is controlled at 15~25A / dm³. 2 The anode current density is controlled at 8~12A / dm². 2 The tank voltage is controlled between 6.0 and 8.0V.