Method for preparing lithium fluoride by using waste electrolyte

Abstract

The application provides a method for preparing lithium fluoride by using waste electrolyte, which can comprise: performing distillation treatment on the waste electrolyte to obtain distillation residue from which organic solvents are removed; adding a first extraction system to extract lithium, and obtaining an organic phase containing lithium ions and a raffinate aqueous phase containing fluorophosphate after the extraction is completed; performing washing and back extraction on the organic phase containing lithium ions to obtain a lithium ion-containing solution; performing acid-catalyzed hydrolysis on the raffinate aqueous phase containing fluorophosphate to obtain a hydrolysis liquid containing phosphate ions and fluorine ions; adding a pre-acidified second extraction system, extracting fluorine ions, and then back extracting to obtain a fluorine ion-containing solution; and mixing the lithium ion-containing solution and the fluorine ion-containing solution, heating to the end of the reaction, and obtaining lithium fluoride. The method has high lithium and fluorine recovery rates and high product purity.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion batteries, and more specifically, relates to a method for preparing lithium fluoride using waste electrolyte. Background Technology

[0002] Lithium-ion battery electrolytes are mainly composed of carbonate organic solvents and lithium salts such as lithium hexafluorophosphate (LiPF6). With the rapid development of new energy vehicles and energy storage industries, the number of retired lithium-ion batteries has surged. Their waste electrolytes are rich in high-value elements such as lithium and fluorine, making green and efficient recycling a pressing issue for the industry. Currently, the treatment and resource utilization of fluorine-containing waste is an international research hotspot, but mainstream technologies both domestically and internationally still rely on strong acid leaching and traditional chemical precipitation methods, which generally suffer from problems such as large quantities of fluorine-containing sludge and low added value of resource-based products. my country has not yet developed a systematic solution for "full-process resource utilization" in this field, especially lacking in-depth research on the synergistic resource utilization mechanism of fluorine and lithium in multi-pollutant coexisting systems.

[0003] The existing recovery processes, such as strong acid leaching and traditional chemical precipitation, mainly face the following technical bottlenecks: (1) The hydrolysis process of lithium hexafluorophosphate is difficult to control: Under acidic conditions, LiPF6 undergoes rapid irreversible hydrolysis upon contact with water. Traditional processes often cause it to decompose prematurely in an acidic environment, resulting in complex solution composition and incomplete recovery of lithium and fluorine, especially causing serious loss of fluorine resources. (2) Low selectivity and efficiency of fluoride ion extraction: In complex systems with high acidity or high salinity, conventional extractants have low selectivity and extraction rate for fluoride ions, making it difficult to meet the requirements of efficient separation in industrial applications. (3) Difficulty in separating lithium and fluorine: Existing technologies make it difficult to recover high-purity lithium and fluorine, resulting in difficulty in separating lithium and fluorine and low recovery rate of fluorine resources.

[0004] In summary, existing technologies cannot simultaneously achieve efficient recovery of lithium and fluorine from waste electrolytes. The dual constraints of uncontrolled hydrolysis of lithium hexafluorophosphate and low selective extraction efficiency of fluoride ions lead to a large loss of fluorine resources and insufficient purity of recovered products, thus limiting the economic value of resource-based products. Summary of the Invention

[0005] In view of the shortcomings of the prior art, one of the objectives of this invention is to solve one or more problems existing in the prior art. For example, one objective of this invention is to provide a method for preparing high-purity lithium fluoride that can be greenly and efficiently extracted and recovered preferentially from lithium ions, then efficiently and selectively recovered from fluoride ions after hydrolysis of hexafluorophosphate, and then resynthesizing the recovered lithium and fluoride.

[0006] This invention provides a method for preparing lithium fluoride using waste electrolyte, which may include the following steps: distilling the waste electrolyte to obtain a distillation residue with organic solvent removed; adding a first extraction system to extract lithium, and after extraction, obtaining an organic phase containing lithium ions and a raffinate aqueous phase containing fluoride phosphate; washing and back-extracting the organic phase containing lithium ions to obtain a lithium ion solution; acid-catalyzing hydrolysis of the raffinate aqueous phase containing fluoride ions to obtain a hydrolysate containing phosphate ions and fluoride ions; adding a pre-acidified second extraction system to extract fluoride ions and then back-extracting to obtain a fluoride ion solution; mixing the lithium ion solution and the fluoride ion solution and heating until the reaction is complete to obtain lithium fluoride.

[0007] Furthermore, the second extraction system may include, by volume fraction, 20%–40% extractant, 2%–20% modifier, and 40%–78% diluent; wherein the extractant may be selected from one or more of tributyl phosphate, organic amines, and trialkylphosphine oxide, the diluent may be selected from sulfonated kerosene or kerosene, and the modifier may be selected from one or more of isooctanol, n-butanol, and tributyl phosphate.

[0008] Furthermore, the pre-acidification of the second extraction system may include mixing the second extractant system with an acidifying agent and acidifying at a temperature of 10°C to 40°C for 10 to 25 minutes. The acidifying agent may be at least one of sulfuric acid, nitric acid, and hydrochloric acid, and the concentration of the acidifying agent may be 1 mol / L to 2.5 mol / L. The volume ratio of the second extractant system to the acidifying agent may be 1:(1 to 2.5).

[0009] Furthermore, in the step of obtaining the fluoride ion solution, the extraction of fluoride ions includes controlling the volume ratio of the extraction phase to the aqueous phase to be (1.5~2.5):1, the extraction temperature to be 10℃~40℃, and the extraction time to be 10 minutes~25 minutes; the back-extraction agent used is an ammonia solution or sodium hydroxide solution with a concentration of 1mol / L~5mol / L.

[0010] Furthermore, the distillation temperature can be 40℃~80℃, and the pressure can be -0.08Mpa~-0.095Mpa.

[0011] Furthermore, the first extraction system may include an extractant, a co-extractant, and a diluent, wherein the extractant may be one or more of tributyl phosphate, trioctyl phosphate, and trialkylphosphine oxide, and its volume fraction in the first extraction system may be 20% to 50%; the co-extractant may be ferric chloride, and its concentration in the first extraction system may be expressed as Fe. 3+ The concentration can be 0.1 mol / L to 0.5 mol / L; the diluent can be selected from one or more of sulfonated kerosene, kerosene and dichloroethane.

[0012] Furthermore, after adding the first extraction system, the distillation residue can be subjected to 2 to 6 stages of countercurrent extraction. The extraction temperature can be 10℃ to 40℃, and the volume ratio of the extract phase to the aqueous phase can be (1 to 4):1.

[0013] Furthermore, in the step of obtaining the lithium-ion-containing solution, the stripping agent used for stripping can be a hydrochloric acid solution or a sulfuric acid solution with a concentration of 1.0 mol / L to 3.0 mol / L.

[0014] Furthermore, acid-catalyzed hydrolysis may include adding an inorganic acid to the raffinate aqueous phase to adjust the acidity, and hydrolyzing at a temperature of 20℃ to 50℃ for 3 to 6 hours. The inorganic acid may be at least one of hydrochloric acid, sulfuric acid, and nitric acid, and the acidity may be 4 mol / L to 7 mol / L.

[0015] Furthermore, in the step of obtaining lithium fluoride, the lithium-ion solution and the fluorine-ion solution can be mixed at a Li to F molar ratio of 1:(1~1.2), heated to 40℃~80℃, and reacted for 1 hour to 4 hours.

[0016] Furthermore, it also includes the addition of a Lewis acid catalyst during the acid-catalyzed hydrolysis process, wherein the Lewis acid catalyst is selected from at least one of aluminum chloride and iron chloride with a concentration of 0.05 mol / L to 0.3 mol / L.

[0017] Furthermore, it also includes pretreatment of the waste electrolyte before distillation. Pretreatment includes filtering the waste electrolyte followed by low-temperature settling. This low-temperature settling can be done at -15℃ to -5℃ for 10 to 14 hours. For example, settling at -10℃ for 12 hours.

[0018] Compared with the prior art, the beneficial effects of the present invention include at least the following: The method of the present invention adopts a stepwise recovery process, which "disassembles" the complex waste electrolyte into single-component solutions containing lithium and fluorine step by step, which significantly improves the recovery rate of lithium and fluorine and the purity of the product. The total recovery rate of lithium can reach more than 99%, the total recovery rate of fluorine can reach more than 90%, and the purity of lithium fluoride products can reach more than 99%. Detailed Implementation

[0019] The method for preparing lithium fluoride from waste electrolyte according to the present invention will be described in detail below with reference to exemplary embodiments.

[0020] Specifically, this invention employs a stepwise recovery process, prioritizing the recovery of lithium from the electrolyte, followed by the recovery of fluorine. Each step targets only specific ions for separation and purification, gradually reducing system complexity and efficiently recovering fluorine and lithium resources. When recovering fluoride ions from the hydrolysate, to avoid interference from competing anions such as sulfate and phosphate, the extraction organic phase (second extraction system) is pre-acidified. This pre-acidifies the phosphoyl groups of the extractant (e.g., Cyanex 923), forming positively charged active sites R3P. + -O-H. This protonation site preferentially attracts negatively charged fluoride ions through electrostatic attraction, while sulfate and phosphate ions, due to their lower charge density and larger hydration radius, have a weaker binding affinity to the protonation site. Therefore, even under conditions of high concentrations of competing anions, the pre-acidified second extraction system can still achieve highly selective extraction of fluoride ions. Thus, this invention fundamentally solves the problems of fluoride resource loss and low product purity caused by uncontrollable hydrolysis of lithium hexafluorophosphate, achieving efficient synergistic recovery of fluoride and lithium resources and high product purification from complex waste electrolytes.

[0021] This invention provides a method for preparing lithium fluoride using waste electrolyte. In some embodiments, the method may include the following steps: S01, the waste electrolyte is distilled to obtain a distillation residue with organic solvents removed; SO2 is added to the first extraction system to extract lithium. After extraction, an organic phase containing lithium ions and a raffinate aqueous phase containing fluorinated phosphate are obtained. SO3 is used to wash the lithium-ion-containing organic phase and back-extract it to obtain a lithium-ion-containing solution. S04 is used to perform acid-catalyzed hydrolysis of the raffinate containing fluoride phosphate to obtain a hydrolysate containing phosphate ions and fluoride ions. S05 is added to a pre-acidified second extraction system to extract fluoride ions, followed by back-extraction to obtain a fluoride ion-containing solution. S06, a lithium ion solution and a fluoride ion solution are mixed and heated until the reaction is complete to obtain lithium fluoride.

[0022] In some implementation schemes, the waste electrolyte can be lithium-ion battery waste electrolyte, mainly composed of organic solvents and electrolyte lithium salts such as lithium hexafluorophosphate (LiF6). Before distillation, the waste electrolyte can be pretreated by filtration and low-temperature settling. Filtration removes suspended particulate matter, and low-temperature settling precipitates high-melting-boiling-point organic esters that are difficult to distill, such as ethylene carbonate and propyne carbonate. These precipitates are then removed by filtration, completing the waste electrolyte pretreatment. Low-temperature settling can be performed at -15℃ to -5℃ for 10 to 14 hours. For example, it can be performed at -10℃ for 12 hours.

[0023] In some implementations, the purpose of distillation in step S01 is to remove low-boiling-point organic solvents, such as dimethyl carbonate, from the waste electrolyte. The distillation temperature can be 40°C to 80°C, and the pressure can be -0.08 MPa to -0.095 MPa. For example, the distillation temperature can be 45°C to 75°C, and the pressure can be -0.085 MPa to -0.09 MPa. Yet another example is that the distillation temperature can be 50°C to 70°C, and the pressure can be -0.086 MPa to -0.088 MPa.

[0024] In some implementations, step S02, by adding a first extraction system, preferentially extracts and separates lithium ions from the distillation residue, obtaining a lithium-ion-containing organic phase; fluorophosphate (mainly hexafluorophosphate) remains in the raffinate aqueous phase. The first extraction system can be a neutral organophosphorus extraction system. The first extraction system may include an extractant, a co-extractant, and a diluent. The extractant can be one or more of tributyl phosphate, trioctyl phosphate, and trialkylphosphine oxide. The volume fraction of the extractant in the first extraction system can be 20%–50%. If the extractant percentage is less than 20%, the lithium ion extraction rate will decrease; if the extractant percentage is greater than 50%, the extraction efficiency will not increase with the extractant percentage, and increasing the extractant percentage will result in raw material waste. For example, the volume fraction of the extractant in the first extraction system can be a combination of 22%–47%, 29%–40%, 33%–36%, or higher. The co-extractant can be ferric chloride. When the co-extractant is ferric chloride, Fe... 3+ The concentration meter can be a combination of 0.1 mol / L to 0.5 mol / L, 0.2 mol / L to 0.4 mol / L, or higher. The diluent can be selected from one or more of sulfonated kerosene, kerosene, and dichloroethane.

[0025] In some implementations, after adding the first extraction system, step S02 can involve 2-6 stages of countercurrent extraction on the distillation residue. This multi-stage countercurrent extraction can achieve a total lithium-ion extraction rate of no less than 95%. For example, 3, 4, or 5 stages of countercurrent extraction can be performed. The extraction temperature can be 10℃~40℃, and the volume ratio of the extract phase (first extraction system) to the aqueous phase can be (1~4):1. If the volume ratio of the extract phase to the aqueous phase is less than 1:1, the lithium-ion extraction rate will decrease; if the volume ratio is greater than 4:1, increasing the volume ratio will not further improve the lithium-ion extraction rate. Therefore, the volume ratio of the extract phase to the aqueous phase is set to (1~4):1. For example, the extraction temperature can be 18℃~32℃, and the volume ratio of the extract phase to the aqueous phase can be (2~3):1. Another example is an extraction temperature of 25℃, where the volume ratio of the extract phase to the aqueous phase can be 2.5:1. In multi-stage countercurrent extraction, the time for each stage of countercurrent extraction can be 10 min~20 min. For example, the time for each stage of countercurrent extraction can be 15 minutes.

[0026] In some embodiments, after lithium ions are extracted in step S02, the lithium-ion-containing organic phase can be washed first, and then back-extracted to obtain a lithium-ion-containing solution. Preferably, lithium ion extraction can avoid premature hydrolysis of lithium hexafluorophosphate, which would make separation of lithium fluoride difficult and lead to fluorine resource loss. The back-extraction agent used can be a hydrochloric acid solution with a concentration of 1.0 mol / L to 3.0 mol / L or a sulfuric acid solution with a concentration of 1.0 mol / L to 3.0 mol / L. For example, a 2.0 mol / L hydrochloric acid solution can be used, in which case a lithium chloride solution is obtained after back-extraction.

[0027] In some embodiments, in step S04, utilizing the kinetic characteristics of acid-catalyzed hydrolysis of hexafluorophosphate, the hydrolysis of hexafluorophosphate is carried out under acidified conditions. This overcomes the technical bottleneck of extremely slow hydrolysis of hexafluorophosphate at room temperature, achieving full release and efficient recovery of fluorine. Acid-catalyzed hydrolysis may include adding an inorganic acid to the raffinate aqueous phase to adjust the acidity, and hydrolyzing at a temperature of 20°C to 50°C for 3 to 6 hours. The inorganic acid can be at least one of hydrochloric acid, sulfuric acid, and nitric acid, with an acidity of 4 mol / L to 7 mol / L. For example, hydrolysis can be carried out at an acidity of 5 mol / L to 6 mol / L and a temperature of 25°C to 43°C for 4 to 5 hours. Another example is hydrolysis at an acidity of 5.5 mol / L and a temperature of 32°C for 4.5 hours. After acid-catalyzed hydrolysis, fluorophosphate can be fully hydrolyzed into phosphate and fluoride ions. In some embodiments, preferably, a Lewis acid catalyst can be added during the acid-catalyzed hydrolysis process. Adding a Lewis acid catalyst can further lower the hydrolysis energy barrier, improve hydrolysis efficiency, and achieve full release of fluorine. The Lewis acid catalyst can be at least one of aluminum chloride and iron chloride. For example, the Lewis acid catalyst can be AlCl3 with a concentration of 0.05 mol / L to 0.3 mol / L or FeCl3 with a concentration of 0.05 mol / L to 0.3 mol / L.

[0028] In some embodiments, after adding the pre-acidified second extraction system in step S05, fluoride ions can be extracted and separated in the hydrolysate. The pre-acidification treatment allows the organic phase of the extractant in the second extraction system to carry protons, enhancing the electrostatic attraction between the extraction system and fluoride ions, thereby achieving selective extraction of fluoride ions under conditions where sulfate and phosphate coexist. In some embodiments, multi-stage countercurrent extraction can be used; for example, 2 to 6 stages of countercurrent extraction can be performed, with a single-stage extraction rate of not less than 85%. Compared to the 54% extraction rate of direct fluoride extraction without pre-acidification, this significantly exceeds the extraction rate and purity of fluoride, effectively improving the extraction rate and selectivity of fluoride ions. In some embodiments, the second extraction system may include, by volume fraction, 20%–40% extractant, 2%–20% modifier, and 40%–78% diluent. For example, the second extraction system may include 22%–36% extractant, 5%–15% modifier, and 44%–70% diluent. For example, the second extraction system may include 28%–33% extractant, 9%–12% modifier, and 50%–62% diluent. In some embodiments, the extractant may be selected from one or more of tributyl phosphate, organic amines, and trialkylphosphine oxide. The diluent may be selected from sulfonated kerosene or kerosene. The modifier may be selected from one or more of isooctanol, n-butanol, and tributyl phosphate.

[0029] In some embodiments, pre-acidification of the second extraction system may include mixing the second extractant system with an acidifying agent and acidifying at a temperature of 10°C to 40°C for 10 to 25 minutes. For example, acidification may be performed at a temperature of 13°C to 36°C for 14 to 22 minutes. Another example is acidification at a temperature of 21°C to 30°C for 17 to 20 minutes. The acidifying agent may be at least one of sulfuric acid, nitric acid, and hydrochloric acid. The concentration of the acidifying agent may be 1 mol / L to 2.5 mol / L. The concentration of the acidifying agent affects the extraction rate of fluoride ions. When the concentration of the acidifying agent is below 1 mol / L, the extraction rate of fluoride ions decreases significantly; when the concentration of the acidifying agent is above 2.5 mol / L, the surface tension of the organic phase decreases significantly due to the excessively high concentration of reverse micelles, resulting in a significant decrease in the extraction rate of fluoride ions and a significant extension of the separation time. For example, the concentration of the acidifying agent may be 1.5 mol / L to 2.0 mol / L. The volume ratio of the second extractant system to the acidifier can be 1:(1~2.5). For example, the volume ratio of the second extractant system to the acidifier can be a combination of 1:1.2, 1:1.5, 1:1.8, 1:2.2 or above.

[0030] In some embodiments, in step S05, obtaining the fluoride ion solution, the extraction of fluoride ions includes controlling the volume ratio of the extraction phase (second extraction system) to the aqueous phase to be (1.5~2.5):1, the extraction temperature to be 10℃~40℃, and the extraction time to be 10 minutes~25 minutes. For example, the volume ratio of the extraction phase to the aqueous phase can be (1.7~2.2):1, the extraction temperature can be 15℃~36℃, and the extraction time can be 12 minutes~22 minutes. As another example, the volume ratio of the extraction phase to the aqueous phase can be (1.9~2.1):1, the extraction temperature can be 20℃~30℃, and the extraction time can be 18 minutes~20 minutes.

[0031] In some embodiments, in step S05, where a fluoride ion solution is obtained, the stripping agent used for stripping can be an aqueous ammonia solution with a concentration of 1 mol / L to 5 mol / L or a sodium hydroxide solution with a concentration of 1 mol / L to 5 mol / L. For example, the stripping agent can be an aqueous ammonia solution with a concentration of 2 mol / L, 3 mol / L, or 4 mol / L.

[0032] In some embodiments, in step S06, the lithium-ion solution and the fluoride-ion solution are mixed in a predetermined ratio and heated to undergo a metathesis reaction to precipitate high-purity lithium fluoride. For example, the lithium-ion solution and the fluoride-ion solution are mixed at a Li to F molar ratio of 1:(1~1.2), heated to 40°C to 80°C, and reacted for 1 to 4 hours. Another example is that the lithium-ion solution and the fluoride-ion solution are mixed at a Li to F molar ratio of 1:1.1, heated to 60°C, and reacted for 3 hours. In some embodiments, the lithium fluoride obtained after the metathesis reaction precipitation can be washed and dried. Washing can be performed 2 to 5 times with hot pure water at 50°C to 60°C, and drying can be performed at 80 to 120°C for 12 to 24 hours.

[0033] In some implementations, the first and second extraction systems can be recycled after back-extraction in steps S03 and S05, respectively. Before each recycling, 5% to 10% of the lost extraction system can be added.

[0034] In this invention, lithium is preferentially extracted in step S03, which not only yields a high-purity lithium-ion solution but, more importantly, prevents premature hydrolysis of lithium hexafluorophosphate in subsequent steps, thus avoiding fluorine dispersion. This is a prerequisite for controlled hydrolysis in step S04. Simultaneously, the hydrolysis in step S04 allows fluorine to exist in a free state, providing conditions for subsequent fluoride ion extraction. The pre-acidification second extraction system in step S05 is specifically designed for the high acidity and high salinity environment generated in step S04, achieving highly selective separation of fluoride ions. Through these interconnected steps, the recovery rate of lithium or fluorine can be significantly improved. The preferential extraction and separation of lithium ions using the first extraction system achieves a single-stage extraction rate of over 75%, approximately 10 percentage points higher than the recovery rate of direct hydrolysis without prior lithium separation. After four stages of countercurrent extraction, the total lithium extraction rate can reach over 99%, with good separation effects for impurity ions such as Ni²⁺, Co²⁺, and Mn²⁺, resulting in high-purity lithium recovery and simplifying the composition of the raffinate.

[0035] To better understand the present invention, specific examples are provided below to further illustrate the content of the present invention, but the content of the present invention is not limited to the examples below. Example

[0036] 1.0 L of waste electrolyte obtained from the dismantling of a retired ternary lithium battery was analyzed by ICP-OES. The concentration of Li⁺ was 0.85 mol / L, and the PF6 concentration was [not specified]. - The concentration of (hexafluorophosphate) is 0.82 mol / L, and it also contains Ni. 2+ Co 2+ Mn 2+The total concentration of impurity ions is approximately 0.05 mol / L. The steps for preparing lithium fluoride using this waste electrolyte as a raw material may include: Step 1, Pretreatment: Filter the waste electrolyte to remove suspended particulate matter, let it stand at -10℃ for 12 h, and filter the precipitated part.

[0037] Step 2, vacuum distillation: The pretreated filtrate is subjected to vacuum distillation at 60℃ and -0.095 MPa to recover low-boiling-point organic solvents (such as dimethyl carbonate), yielding approximately 180 mL of distillation residue.

[0038] Step 3, lithium preferential extraction: Prepare the extraction organic phase (first extraction system): 30% TBP (tributyl phosphate), 0.3 mol / L FeCl3 (calculated as Fe³⁺), and sulfonated kerosene as diluent. Perform four-stage countercurrent extraction at a ratio O / A (extraction organic phase / aqueous phase) of 2:1 and 25°C, with each stage lasting 15 min. The single-stage extraction rate of lithium was 75.2%, and the total extraction rate across the four countercurrent stages reached 99.2%.

[0039] Step 4: The lithium-ion-loaded organic phase is back-extracted with 2.0 mol / L hydrochloric acid solution to obtain a lithium chloride solution (Li⁺ concentration 2.1 mol / L). The main component of the raffinate aqueous phase is hexafluorophosphate.

[0040] Step 5, Acid-catalyzed hydrolysis: Concentrated sulfuric acid is added to the raffinate obtained in Step 4 to adjust the H⁺ concentration to 7 mol / L, and AlCl₃ is added as a Lewis acid catalyst. 3+ The concentration was 0.1 mol / L. Hydrolysis at 40℃ for 4.5 hours resulted in the complete hydrolysis of hexafluorophosphate into phosphate and fluoride ions.

[0041] Step 6, Pre-acidification and fluorine extraction: The organic phase for extraction (second extraction system) consisted of 30% trialkylphosphine oxide (Cyanex 923) and 8% isooctanol, with sulfonated kerosene as the diluent. Before use, it was pre-acidified with 2 mol / L sulfuric acid at a ratio of 1:1.5 at 25°C for 15 min. Extraction conditions: O / A ratio = 2:1, extraction at 25°C for 20 min, two-stage countercurrent extraction. The single-stage extraction rate of fluorine reached 86.3%, and the total two-stage countercurrent extraction rate was 98.7%. The fluoride-loaded organic phase was back-extracted with 2 mol / L ammonia to obtain a fluoride-containing solution (F⁻ concentration 1.95 mol / L).

[0042] Step 7, Synthesis of Lithium Fluoride: The lithium chloride solution obtained in Step 4 and the fluoride-containing ion solution obtained in Step 6 are mixed at a Li:F molar ratio of 1:1.05 and reacted at 60°C for 2 hours to form lithium fluoride precipitate. After filtration, it is washed three times with hot pure water at 50°C and dried at 100°C for 12 hours to obtain approximately 21.8g of high-purity lithium fluoride product. The product purity was tested to be 99.95%. Example

[0043] 1.0 L of waste electrolyte obtained from the dismantling of a retired ternary lithium battery was analyzed by ICP-OES. The concentration of Li⁺ was 0.92 mol / L, and the PF6 concentration was [not specified]. - The concentration was 0.88 mol / L. In this example, lithium fluoride was prepared using the aforementioned waste electrolyte as a raw material.

[0044] Compared with Example 1, the main differences in the preparation process are as follows: In step 3 of this example, the TBP volume fraction in the extracted organic phase is increased to 40%, the FeCl3 concentration is 0.4 mol / L, the O / A ratio is 3:1, the extraction temperature is 35℃, and the total lithium-ion extraction rate is 99.5% after 4 stages of countercurrent extraction. In step 5, the H⁺ concentration is 6 mol / L, the AlCl3 concentration is 0.05 mol / L, the hydrolysis temperature is 45℃, and the hydrolysis time is 4 hours. In step 6, the Cyanex 923 volume fraction is 35%, isooctanol is 10%, and it is pre-acidified with 3 mol / L sulfuric acid, with an O / A ratio of 1:1.8, an extraction temperature of 30℃, 2 stages of countercurrent extraction, and a total fluoride ion extraction rate of 99.1%. In step 7, the Li:F molar ratio is 1:1.1, the reaction temperature is 50℃, the reaction time is 1.5 hours, and the sample is washed 5 times.

[0045] The prepared lithium fluoride product weighed 23.6g and had a purity of 99.96%. Example

[0046] Take 1.0 L of the same batch of waste battery electrolyte as in Example 1. The difference from Example 1 is that the Lewis acid catalyst AlCl3 is not added in step 5; otherwise, it is the same as Example 1.

[0047] Comparative Example 1 Take 1.0 L of waste electrolyte with the same composition as in Example 1, add concentrated sulfuric acid directly to adjust the acidity to 7 mol / L, hydrolyze at 40℃ for 4.5 h, then add sodium hydroxide to neutralize to pH 8~9, and precipitate to obtain crude lithium fluoride.

[0048] The recovery rates of lithium and fluorine were tested. The lithium recovery rate was only 65%, the fluorine recovery rate was 45%, the product purity was 97.5%, and a large amount of fluorine-containing sludge was generated.

[0049] Comparative Example 2 Compared with Example 1, the pre-acidification treatment of the extraction organic phase is omitted in step 6 of this comparative example, and the unacidified extraction organic phase is used directly to extract fluorine.

[0050] The test results showed that the single-stage fluorine extraction rate was only 54%, the total extraction rate of the two stages was 81%, the final lithium fluoride purity was 98.2%, and the fluorine recovery rate was significantly lower than that of the extraction process after pre-acidification treatment.

[0051] Comparative Example 3 Compared to Example 1, this comparative example omits the preferential lithium extraction processes in steps 3 and 4. Instead, the waste electrolyte after vacuum distillation is directly subjected to acid-catalyzed hydrolysis, followed by simultaneous extraction of lithium and fluorine from the hydrolysate. The extraction of lithium and fluorine from the hydrolysate includes the following steps: Pre-acidification extraction of fluoride: The organic phase for extraction (second extraction system) consisted of 30% trialkylphosphine oxide (Cyanex 923) and 8% isooctanol, diluted with sulfonated kerosene. Before use, it was pre-acidified with 2 mol / L sulfuric acid at a ratio of 1:1.5 at 25°C for 15 min. Extraction conditions: O / A ratio = 2:1, extraction at 25°C for 20 min, two-stage countercurrent extraction. The fluoride-loaded organic phase was back-extracted with 2 mol / L ammonia to obtain a fluoride-containing solution.

[0052] Lithium extraction: Using the lithium-ion raffinate after fluorine extraction as raw material, an extraction organic phase (first extraction system) was prepared: 30% TBP (tributyl phosphate) volume fraction, 0.3 mol / L FeCl3 concentration (calculated as Fe³⁺), and sulfonated kerosene as diluent. Four-stage countercurrent extraction was performed at a ratio O / A (extraction organic phase / aqueous phase) of 2:1 and 25℃, with each stage lasting 15 min.

[0053] Test results show that, due to the formation of complex complexes between lithium ions and fluorine during hydrolysis, the fluorine extraction rate drops to 55%, the lithium extraction rate drops to 58%, and the lithium fluoride product has a purity of only 95.0% due to the presence of entrained lithium salts. This indicates that the preferential lithium extraction of the present invention can significantly improve the recovery rate of lithium and fluorine, as well as the purity of lithium fluoride.

[0054] The lithium and fluorine recovery effects and product purity of Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0055] Table 1 Comparison of Lithium and Fluorine Recovery Efficiency and Product Purity

[0056] As shown in Table 1, the present invention achieves a total recovery rate of over 90% for both lithium and fluorine through a synergistic process of "prioritized lithium extraction + acid-catalyzed hydrolysis + pre-acidification selective fluorine extraction," and the purity of the lithium fluoride product can reach over 99%. Comparing Example 1 and Example 3, in Example 3, without the addition of a Lewis acid catalyst, the hydrolysis efficiency of hexafluorophosphate decreased, and the concentration of free fluoride ions after hydrolysis was only 82% of the theoretically calculated value, leading to a decrease in the subsequent total fluorine extraction rate. However, after adding 0.1 mol / L AlCl3 (Example 1), the fluoride ion recovery rate reached over 99% under the same hydrolysis conditions. Therefore, it is preferable to add a Lewis acid catalyst during the acid catalysis process to achieve a total recovery rate of over 99% for both lithium and fluorine.

[0057] Comparing Examples 1-3 with Comparative Example 1, the traditional direct hydrolysis precipitation method in Comparative Example 1 not only resulted in low lithium and fluorine recovery rates (approximately 65% ​​and 45%, respectively), with a product purity of only about 97.5%, but also generated a large amount of fluorine-containing sludge. In contrast, Comparative Example 2, which used a direct fluorine extraction method without pre-acidification, achieved a single-stage fluorine extraction rate of only 54%, which is insufficient for industrial applications. Comparative Example 3, which did not preferentially extract lithium, resulted in a decrease in fluorine ion concentration and extraction efficiency during subsequent extractions due to the formation of complex complexes between lithium ions and fluorine during hydrolysis. Furthermore, the final product had low purity due to the presence of entrained lithium salts.

[0058] Although the invention has been described above in conjunction with exemplary embodiments, those skilled in the art will understand that various modifications and changes can be made to the exemplary embodiments of the invention without departing from the spirit and scope defined by the claims.

Claims

1. A method for preparing lithium fluoride using waste electrolyte, characterized in that, Includes the following steps: The waste electrolyte is distilled to obtain a distillation residue from which organic solvents have been removed; Lithium was extracted by adding it to the first extraction system. After extraction, an organic phase containing lithium ions and a raffinate aqueous phase containing fluorinated phosphate were obtained. The lithium-ion-containing organic phase is washed and back-extracted to obtain a lithium-ion-containing solution. The raffinate containing fluoride phosphate was subjected to acid-catalyzed hydrolysis to obtain a hydrolysate containing phosphate ions and fluoride ions. Add a pre-acidified second extraction system to extract fluoride ions, then back-extract to obtain a fluoride ion-containing solution; A lithium ion-containing solution and a fluoride ion-containing solution are mixed and heated until the reaction is complete to obtain lithium fluoride.

2. The method for preparing lithium fluoride from waste electrolyte according to claim 1, characterized in that, The second extraction system comprises, by volume fraction, 20%–40% extractant, 2%–20% modifier, and 40%–78% diluent; wherein the extractant is selected from one or more of tributyl phosphate, organic amines, and trialkylphosphine oxide, the diluent is selected from sulfonated kerosene or kerosene, and the modifier is selected from one or more of isooctanol, n-butanol, and tributyl phosphate.

3. The method for preparing lithium fluoride from waste electrolyte according to claim 1 or 2, characterized in that, The pre-acidification of the second extraction system includes mixing the second extractant system with an acidifying agent and acidifying at a temperature of 10℃~40℃ for 10 minutes to 25 minutes. The acidifying agent is at least one of sulfuric acid, nitric acid and hydrochloric acid, and the concentration of the acidifying agent is 1 mol / L to 2.5 mol / L. The volume ratio of the second extractant system to the acidifying agent is 1:(1~2.5).

4. The method for preparing lithium fluoride from waste electrolyte according to claim 1 or 2, characterized in that, In the step of obtaining the fluoride ion solution, the extraction of fluoride ions includes controlling the volume ratio of the extractant phase to the aqueous phase to be (1.5~2.5):1, the extraction temperature to be 10℃~40℃, and the extraction time to be 10 minutes~25 minutes; the back-extraction agent used is an ammonia solution or sodium hydroxide solution with a concentration of 1mol / L~5mol / L.

5. The method for preparing lithium fluoride from waste electrolyte according to claim 1 or 2, characterized in that, The distillation process is carried out at temperatures ranging from 40℃ to 80℃ and pressures ranging from -0.08 MPa to -0.095 MPa.

6. The method for preparing lithium fluoride from waste electrolyte according to claim 1, characterized in that, The first extraction system includes an extractant, a co-extractant, and a diluent. The extractant is one or more of tributyl phosphate, trioctyl phosphate, and trialkyl phosphorus oxide, accounting for 20%–50% of the volume of the first extraction system. The co-extractant is ferric chloride, and its concentration in the first extraction system is expressed as Fe. 3+ The concentration is 0.1 mol / L to 0.5 mol / L; the diluent is selected from one or more of sulfonated kerosene, kerosene and dichloroethane.

7. The method for preparing lithium fluoride from waste electrolyte according to claim 1 or 6, characterized in that, After adding the first extraction system, the distillation residue is subjected to 2 to 6 stages of countercurrent extraction at an extraction temperature of 10℃ to 40℃ and a volume ratio of extract phase to aqueous phase of (1 to 4):

1.

8. The method for preparing lithium fluoride from waste electrolyte according to claim 1, characterized in that, In the step of obtaining the lithium-ion-containing solution, the stripping agent used for stripping is a hydrochloric acid solution or sulfuric acid solution with a concentration of 1.0 mol / L to 3.0 mol / L.

9. The method for preparing lithium fluoride from waste electrolyte according to claim 1, characterized in that, Acid-catalyzed hydrolysis involves adding an inorganic acid to the raffinate aqueous phase to adjust the acidity, and hydrolyzing at a temperature of 20℃ to 50℃ for 3 to 6 hours. The inorganic acid is at least one of hydrochloric acid, sulfuric acid, and nitric acid, and the acidity is 4 mol / L to 7 mol / L.

10. The method for preparing lithium fluoride from waste electrolyte according to claim 9, characterized in that, Acid-catalyzed hydrolysis also includes adding a Lewis acid catalyst to the raffinate aqueous phase, wherein the Lewis acid catalyst is selected from at least one of aluminum chloride and iron chloride.

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