Method for recovering lithium phosphate from lithium iron phosphate positive electrode material

Abstract

The invention provides a method for recovering lithium phosphate from a lithium iron phosphate positive electrode material, which comprises the following steps: carrying out oxidation leaching on the lithium iron phosphate positive electrode material by using an acid solution and an oxidizing agent to obtain a first leaching solution and a first leaching residue; after water is added into the first leaching residues for size mixing, alkali leaching is conducted through sodium hydroxide, second leaching liquid and iron / carbon insoluble residues are obtained, and sodium phosphate crystals are obtained after the second leaching liquid is condensed; carrying out lithium precipitation reaction on the first leaching solution by using the sodium phosphate crystal to obtain lithium phosphate and lithium precipitation residual liquid; the lithium precipitation residual liquid is subjected to concentration and impurity removal, and then is subjected to a bipolar membrane electrodialysis process to obtain an acid solution and sodium hydroxide for reutilization. The invention aims to provide a method for mutually separating lithium, iron and phosphorus aiming at the waste lithium iron phosphate positive electrode material, the method can almost completely recover lithium, iron and phosphorus in the lithium iron phosphate positive electrode material, and the lithium is high in recovery rate and high in purity.

Description

Technical Field

[0001] This invention belongs to the field of waste lithium battery recycling technology, and particularly relates to a method for recovering lithium phosphate from lithium iron phosphate cathode materials. Background Technology

[0002] Lithium iron phosphate (LFP) batteries boast advantages such as high operating voltage, high energy density, long cycle life, and good safety performance. These superior properties have led to a rapid increase in their market share, currently accounting for over 70% of the power lithium-ion battery market. However, after prolonged use, side reactions can occur within lithium-ion batteries, such as the dissolution of active materials, blockage of separator pores, and electrolyte aging. These problems can all affect the normal operation of power lithium-ion batteries. Therefore, recycling retired lithium-ion batteries will be a crucial issue that needs to be addressed for future development.

[0003] The recycling of phosphate cathode materials (such as lithium iron phosphate, LiFePO4) is not only a key link in resource recycling, but also the core of the regeneration of strategic resources such as lithium, iron, and phosphorus. Patent CN116240384A proposes a scheme for selective lithium extraction from waste lithium iron phosphate cathode powder through synergistic oxidation leaching. This scheme oxidizes iron to trivalent form in situ without damaging the olivine structure of the lithium iron phosphate material, allowing it to occupy some of the lithium lattice sites and thus enabling lithium intercalation. While this scheme achieves efficient recovery of lithium from waste lithium iron phosphate, it lacks the treatment of iron and phosphorus. Patent CN112499609A proposes dissolving lithium iron phosphate powder residue under acidic conditions, heating it, and adding a precipitation aid to react. After separation, iron phosphate is obtained. However, due to large fluctuations in copper and aluminum impurities, the impurity content in the recycled iron phosphate material is unstable, resulting in low product purity and low added value.

[0004] In summary, current methods for recovering lithium, iron, and phosphorus from lithium iron phosphate batteries suffer from problems such as low purity of recycled products, low product value, and high losses. Summary of the Invention

[0005] Based on the above-mentioned technical problems, this invention provides a method for recovering lithium phosphate from lithium iron phosphate cathode materials. The aim is to provide a method for separating lithium, iron, and phosphorus from waste lithium iron phosphate cathode materials. This method can recover almost all lithium, iron, and phosphorus from lithium iron phosphate cathode materials, with high lithium recovery rate and high purity. This solves the problems of low purity, low product value, and high loss in current lithium, iron, and phosphorus recovery schemes for lithium, iron, and phosphorus in lithium iron phosphate.

[0006] This invention proposes a method for recovering lithium phosphate from lithium iron phosphate cathode materials, comprising the following steps:

[0007] S1. After oxidizing and leaching the lithium iron phosphate cathode material with an acid solution and an oxidant, a first leachate and a first leachate residue are obtained.

[0008] S2. After adding water to the first leaching residue to make a slurry, it is leached with sodium hydroxide to obtain a second leaching solution and an iron / carbon insoluble residue. The second leaching solution is then condensed to obtain sodium phosphate crystals.

[0009] S3. After the first leachate is subjected to lithium precipitation reaction with the above-mentioned sodium phosphate crystals, lithium phosphate and lithium precipitation residue are obtained.

[0010] S4. After concentrating and removing impurities, the remaining lithium precipitation solution is subjected to bipolar membrane electrodialysis to obtain an acid solution and sodium hydroxide, which are then returned to steps S1 and S2 for reuse.

[0011] In this invention, a complete continuous process is used to simultaneously recover lithium and reuse phosphorus from waste lithium iron phosphate batteries, ultimately recovering lithium phosphate. This improves the economic benefits of the recycled products, simplifies the recycling process, and reduces recycling costs.

[0012] Preferably, in step S1, the acid solution is at least one of sulfuric acid, hydrochloric acid, or nitric acid solution; and the oxidant is at least one of hydrogen peroxide, chlorine, ozone, or hypochlorous acid.

[0013] Preferably, the concentration of the acid solution is 5wt%-20wt%;

[0014] Preferably, when the oxidant is hydrogen peroxide, the concentration of hydrogen peroxide is 5wt%-50wt%, and the molar ratio of hydrogen peroxide in hydrogen peroxide to iron in lithium iron phosphate is 0.8-1.2:1.

[0015] Preferably, the oxidative leaching temperature is 25℃-70℃ and the time is 20min-120min.

[0016] In this invention, by adding an acid solution to lithium iron phosphate, hydrogen ions can be provided, placing the lithium iron phosphate waste slurry in an acidic environment, thereby increasing the reactivity of lithium iron phosphate. In conjunction with an oxidant, a redox reaction occurs, causing the iron element to increase from divalent iron to trivalent iron, resulting in iron phosphate and lithium ions, thus achieving lithium leaching and facilitating subsequent lithium recovery and extraction.

[0017] Preferably, in step S2, the pH of the alkali leaching is controlled to be 5-10, and the molar ratio of sodium ions to phosphorus is 2-5:1;

[0018] Preferably, the condensation temperature is 0℃-30℃ and the time is 0.5h-10h.

[0019] In this invention, by adjusting the pH to 5-10 with sodium hydroxide and the molar ratio of sodium ions to phosphorus to 2-5:1, the iron / carbon insoluble residue can be separated from the solution system. Sodium phosphate crystals are then obtained by condensation, which can be used for subsequent lithium precipitation reaction to obtain lithium phosphate product.

[0020] Preferably, in step S3, before the first leachate is subjected to the lithium precipitation reaction with the sodium phosphate crystals described above, the first leachate is further subjected to impurity removal.

[0021] Preferably, the impurity removal includes: first adjusting the pH of the solution to 4-7 with an alkaline solution of 5wt%-30wt%, and then adjusting the pH of the solution to 10-12 with an alkaline solution of 5wt%-30wt%.

[0022] Preferably, the alkaline solution is at least one of sodium hydroxide, calcium hydroxide, ammonia, or sodium carbonate solution.

[0023] In this invention, the first leachate inevitably contains a small amount of cations such as iron ions, magnesium phosphate, aluminum, and copper. The solution pH is first adjusted to 4-7 to provide hydroxide ions to remove iron and aluminum, and then the solution pH is adjusted to 10-12 to continue to provide hydroxide ions to remove copper. This is beneficial for obtaining high-purity lithium phosphate in the subsequent process, thereby achieving high-value lithium recovery.

[0024] Preferably, in step S3, before the first leachate is subjected to the lithium precipitation reaction with the sodium phosphate crystals described above, the sodium phosphate crystals are first prepared into a solution.

[0025] Preferably, the concentration of the solution is 0.1 mol / L to 2 mol / L.

[0026] Preferably, in step S3, the temperature of the lithium precipitation reaction is 25℃-90℃, more preferably 40℃-80℃, the pH is controlled at 7-12, more preferably 8-10, and the reaction time is 1h-3h;

[0027] Preferably, the sodium phosphate crystals are added with an excess of 5 mol% to 30 mol% of phosphate ions, more preferably an excess of 5 mol% to 20 mol%, based on a theoretical molar ratio of phosphate ions to lithium ions of 1:3.

[0028] In this invention, by adding sodium phosphate, it can react with lithium ions in the first leachate to generate lithium phosphate precipitate, thereby achieving the extraction and recovery of lithium. The prepared lithium phosphate has high purity and high recovery rate.

[0029] Preferably, in step S4, the residual lithium precipitate is concentrated to a sodium salt concentration of 2wt%-30wt%, more preferably 5wt%-15wt%.

[0030] In this invention, when the sodium salt concentration is too low, the ion migration efficiency is low and the energy consumption ratio increases; when the concentration is too high, crystallization easily blocks the flow channel. Therefore, controlling the sodium salt concentration in the lithium precipitation residue helps to carry out the bipolar membrane electrodialysis process in order to obtain recyclable sulfuric acid solution and sodium hydroxide solution.

[0031] Preferably, in step S4, the impurity removal is performed by selectively adsorbing impurity ions other than sodium ions using a cation exchange resin or a chelating resin.

[0032] Preferably, the functional group of the cation exchange resin is at least one of sulfonic acid group -SO3H, carboxylic acid group -COOH, or phosphate group -PO3H2, and the functional group of the chelating resin is at least one of iminodiacetic acid group -CH2-N(CH2COOH)2, aminophosphonic acid group -N(CH2PO3H2)2, or geminal aminooxime group -C(=NOH)-NH2.

[0033] In this invention, cation exchange resin or chelating resin is used to selectively adsorb impurity ions such as calcium ions or magnesium ions, thereby achieving deep impurity removal.

[0034] Preferably, the resin used for impurity removal is an ion exchange resin containing both sulfonic acid groups -SO3H and aminophosphonic acid groups -NHCH2PO3H2.

[0035] Preferably, the ion exchange resin is obtained by amination reaction of chloromethylated chlorospheres with ethylenediamine and p-aminobenzenesulfonic acid, followed by condensation addition reaction with formaldehyde and phosphorous acid.

[0036] In this invention, the ion exchange resin containing both sulfonic acid group -SO3H and aminophosphonic acid group -NHCH2PO3H2 can more comprehensively adsorb impurity ions compared to simple cation exchange resins or chelating resins, thereby achieving a deeper impurity removal effect.

[0037] The structural diagram of the above-mentioned ion exchange resin is shown below:

[0038]

[0039] In step S4, the temperature of the bipolar membrane electrodialysis process is 10℃-80℃, preferably 20℃-45℃, and the current density is 60mA / cm². 2 -150mA / cm 2 ;

[0040] Preferably, the equipment used in the bipolar membrane electrodialysis process consists of multiple compartments composed of alternating cation membranes, anion membranes, and bipolar membranes, with anode and cathode electrodes at both ends.

[0041] In this invention, in the bipolar membrane electrodialysis process, excessively high current density can easily lead to membrane heating, intensified water decomposition, and increased energy consumption; excessively low temperature will reduce ion migration rate, while excessively high temperature will cause a sharp increase in operating costs.

[0042] Compared with the prior art, the present invention has the following technical effects:

[0043] (1) This invention utilizes oxidative leaching and alkaline leaching processes to achieve efficient extraction of lithium, phosphorus and iron from lithium iron phosphate cathode materials, avoiding the problems of high impurity content and large losses in direct regeneration of iron phosphate from phosphorus slag;

[0044] (2) This invention utilizes alkaline leaching process to achieve efficient treatment of iron-phosphorus slag oxidized by leaching, and cleverly utilizes its product sodium phosphate to extract lithium from the oxidized leaching product, thereby obtaining high-purity lithium phosphate product.

[0045] (3) The present invention utilizes the bipolar membrane electrodialysis process to properly treat the residual liquid of lithium phosphate precipitation, and obtains acid and sodium hydroxide solution for process recycling.

[0046] (4) The overall lithium iron phosphate cathode material recycling process of the present invention realizes the efficient recovery of high-value elements (lithium and sodium), greatly improving the product value of the overall recycling process. In addition, the bipolar membrane electrodialysis process is used to treat the sodium salt in the lithium phosphate precipitation residue, and the resulting product acid and sodium hydroxide solution can be recycled, realizing the closed loop of acid and alkali process. Attached Figure Description

[0047] Figure 1 This is a flowchart of the method for recovering lithium phosphate from lithium iron phosphate cathode material according to an embodiment of the present invention. Detailed Implementation

[0048] The present invention will now be described in detail through specific embodiments. However, these embodiments are clearly provided for illustrative purposes and are not intended to limit the scope of the present invention.

[0049] Example 1

[0050] A method for recovering lithium iron phosphate from lithium iron phosphate cathode materials includes the following steps:

[0051] (1) 100g of lithium iron phosphate cathode material was mixed with water at a solid-liquid ratio of 1:3, and then 10g of sulfuric acid solution with a concentration of 15wt% and 70g of hydrogen peroxide with a concentration of 30wt% were added for oxidation leaching. The oxidation leaching temperature was 50℃ and the time was 1.5h. After filtration, the first leaching solution and the first leaching residue were obtained.

[0052] (2) After adding water to the first leaching residue at a solid-liquid ratio of 1:3 to make slurry, sodium hydroxide is added to adjust the pH value to the range of 5-10 for alkaline leaching, and the molar ratio of sodium ions to phosphorus elements is 3:1. After filtration, the second leaching solution and iron / carbon insoluble residue are obtained.

[0053] (3) Cool the second leachate at 10°C for 5 hours, filter the resulting cooled and crystallized solution to obtain sodium phosphate crystals;

[0054] (4) Add a 15wt% sodium hydroxide solution to the first leachate to adjust the pH to 5.5. After filtering to remove insoluble impurities, add a 20wt% sodium hydroxide solution to adjust the pH to 11. After filtering to remove insoluble impurities, the first impurity-removed solution is obtained. The obtained insoluble impurities are also iron / carbon insoluble residues.

[0055] (5) The sodium phosphate crystals were prepared into a solution with a concentration of 1 mol / L and added to the first impurity removal solution to carry out the lithium precipitation reaction. The lithium precipitation reaction temperature was 60℃, the pH was 9, and the reaction time was 2h. The sodium phosphate crystals were added in excess of 15 mol% based on the theoretical molar ratio of phosphate ions to lithium ions of 1:3. After solid-liquid separation, lithium phosphate product and lithium precipitation residue were obtained.

[0056] (6) The sodium sulfate in the lithium precipitation residue is concentrated to 10 wt%, and after impurity removal by 732 cation exchange resin, a second impurity-removed solution is obtained. This solution is then subjected to bipolar membrane electrodialysis at a temperature of 30°C and a current density of 100 mA / cm². 2 The resulting recyclable sulfuric acid solution and sodium hydroxide solution are returned to steps (1), (2), and (4) for reuse, and 200g of lithium iron phosphate cathode material is further processed.

[0057] Example 2

[0058] A method for recovering lithium iron phosphate from lithium iron phosphate cathode materials includes the following steps:

[0059] (1) 100g of lithium iron phosphate cathode material was mixed with water at a solid-liquid ratio of 1:3, and then 30g of sulfuric acid solution with a concentration of 5wt% and 85g of hydrogen peroxide with a concentration of 30wt% were added for oxidation leaching. The oxidation leaching temperature was 25℃ and the time was 2h. After filtration, the first leaching solution and the first leaching residue were obtained.

[0060] (2) After adding water to the first leaching residue at a solid-liquid ratio of 1:3 to make slurry, sodium hydroxide is added to adjust the pH value to the range of 5-10 for alkaline leaching, and the molar ratio of sodium ions to phosphorus elements is 2:1. After filtration, the second leaching solution and iron / carbon insoluble residue are obtained.

[0061] (3) Cool the second leachate at 0°C for 0.5 h, filter the resulting cooled and crystallized solution to obtain sodium phosphate crystals;

[0062] (4) Add a 5 wt% sodium hydroxide solution to the first leachate to adjust the pH value to 4. After filtering to remove insoluble impurities, add a 30 wt% sodium hydroxide solution to adjust the pH value to 12. After filtering to remove insoluble impurities, the first impurity-removed solution is obtained. The obtained insoluble impurities are also iron / carbon insoluble residues.

[0063] (5) The sodium phosphate crystals are prepared into a solution with a concentration of 0.1 mol / L and added to the first impurity removal solution to carry out the lithium precipitation reaction. The lithium precipitation reaction temperature is 90℃, the pH is 8, and the reaction time is 1h. The sodium phosphate crystals are added in excess of 5 mol% based on the theoretical molar ratio of phosphate ions to lithium ions of 1:3. After solid-liquid separation, lithium phosphate product and lithium precipitation residue are obtained.

[0064] (6) The sodium sulfate in the lithium precipitation residue is concentrated to 5 wt%, and after impurity removal by 732 cation exchange resin, a second impurity-removed solution is obtained. This solution is then subjected to bipolar membrane electrodialysis at a temperature of 45°C and a current density of 60 mA / cm². 2 The resulting recyclable sulfuric acid solution and sodium hydroxide solution are returned to steps (1), (2), and (4) for reuse, and 200g of lithium iron phosphate cathode material is further processed.

[0065] Example 3

[0066] A method for recovering lithium iron phosphate from lithium iron phosphate cathode materials includes the following steps:

[0067] (1) 100g of lithium iron phosphate cathode material was mixed with water at a solid-liquid ratio of 1:3, and then 7.5g of sulfuric acid solution with a concentration of 15wt% and 65g of hydrogen peroxide with a concentration of 30wt% were added for oxidation leaching. The oxidation leaching temperature was 70℃ and the time was 20min. After filtration, the first leaching solution and the first leaching residue were obtained.

[0068] (2) After adding water to the first leaching residue at a solid-liquid ratio of 1:3 to make slurry, sodium hydroxide is added to adjust the pH value to the range of 5-10 for alkaline leaching, and the molar ratio of sodium ions to phosphorus elements is 5:1. After filtration, the second leaching solution and iron / carbon insoluble residue are obtained.

[0069] (3) Cool the second leachate at 20°C for 10 hours, filter the resulting cooled and crystallized solution to obtain sodium phosphate crystals;

[0070] (4) Add a 10wt% sodium hydroxide solution to the first leachate to adjust the pH value to 7, filter to remove insoluble impurities, add a 20wt% sodium hydroxide solution to adjust the pH value to 10, filter to remove insoluble impurities, and obtain the first impurity-removed solution. The obtained insoluble impurities are also iron / carbon insoluble residues.

[0071] (5) The sodium phosphate crystals were prepared into a solution with a concentration of 2 mol / L and added to the first impurity removal solution for lithium precipitation reaction. The lithium precipitation reaction temperature was 40℃, the pH was 10, and the reaction time was 3h. The sodium phosphate crystals were added in excess of 30 mol% based on the theoretical molar ratio of phosphate ions to lithium ions of 1:3. After solid-liquid separation, lithium phosphate product and lithium precipitation residue were obtained.

[0072] (6) The sodium sulfate in the lithium precipitation residue is concentrated to 15 wt%, and after impurity removal by 732 cation exchange resin, a second impurity-removed solution is obtained. This solution is then subjected to bipolar membrane electrodialysis at a temperature of 20°C and a current density of 150 mA / cm². 2 The resulting recyclable sulfuric acid solution and sodium hydroxide solution are returned to steps (1), (2), and (4) for reuse, and 200g of lithium iron phosphate cathode material is further processed.

[0073] Example 4

[0074] A method for recovering lithium iron phosphate from lithium iron phosphate cathode materials includes the following steps:

[0075] (1) 100g of lithium iron phosphate cathode material was mixed with water at a solid-liquid ratio of 1:3, and then 10g of sulfuric acid solution with a concentration of 15wt% and 70g of hydrogen peroxide with a concentration of 30wt% were added for oxidation leaching. The oxidation leaching temperature was 50℃ and the time was 1.5h. After filtration, the first leaching solution and the first leaching residue were obtained.

[0076] (2) After adding water to the first leaching residue at a solid-liquid ratio of 1:3 to make slurry, sodium hydroxide is added to adjust the pH value to the range of 5-10 for alkaline leaching, and the molar ratio of sodium ions to phosphorus elements is 3:1. After filtration, the second leaching solution and iron / carbon insoluble residue are obtained.

[0077] (3) Cool the second leachate at 10°C for 5 hours, filter the resulting cooled and crystallized solution to obtain sodium phosphate crystals;

[0078] (4) Add a 15wt% sodium hydroxide solution to the first leachate to adjust the pH to 5.5. After filtering to remove insoluble impurities, add a 20wt% sodium hydroxide solution to adjust the pH to 11. After filtering to remove insoluble impurities, the first impurity-removed solution is obtained. The obtained insoluble impurities are also iron / carbon insoluble residues.

[0079] (5) The sodium phosphate crystals were prepared into a solution with a concentration of 1 mol / L and added to the first impurity removal solution to carry out the lithium precipitation reaction. The lithium precipitation reaction temperature was 60℃, the pH was 9, and the reaction time was 2h. The sodium phosphate crystals were added in excess of 15 mol% based on the theoretical molar ratio of phosphate ions to lithium ions of 1:3. After solid-liquid separation, lithium phosphate product and lithium precipitation residue were obtained.

[0080] (6) The sodium sulfate in the lithium precipitation residue is concentrated to 10 wt%, and after impurity removal by Sryrene-DV phosphoric acid cation chelating resin, a second impurity-removed solution is obtained. This solution is then subjected to bipolar membrane electrodialysis at a temperature of 30°C and a current density of 100 mA / cm². 2 The resulting recyclable sulfuric acid solution and sodium hydroxide solution are returned to steps (1), (2), and (4) for reuse, and 200g of lithium iron phosphate cathode material is further processed.

[0081] Example 5

[0082] A method for recovering lithium iron phosphate from lithium iron phosphate cathode materials includes the following steps:

[0083] (1) 100g of lithium iron phosphate cathode material was mixed with water at a solid-liquid ratio of 1:3, and then 10g of sulfuric acid solution with a concentration of 15wt% and 70g of hydrogen peroxide with a concentration of 30wt% were added for oxidation leaching. The oxidation leaching temperature was 50℃ and the time was 1.5h. After filtration, the first leaching solution and the first leaching residue were obtained.

[0084] (2) After adding water to the first leaching residue at a solid-liquid ratio of 1:3 to make slurry, sodium hydroxide is added to adjust the pH value to the range of 5-10 for alkaline leaching, and the molar ratio of sodium ions to phosphorus elements is 3:1. After filtration, the second leaching solution and iron / carbon insoluble residue are obtained.

[0085] (3) Cool the second leachate at 10°C for 5 hours, filter the resulting cooled and crystallized solution to obtain sodium phosphate crystals;

[0086] (4) Add a 15wt% sodium hydroxide solution to the first leachate to adjust the pH to 5.5. After filtering to remove insoluble impurities, add a 20wt% sodium hydroxide solution to adjust the pH to 11. After filtering to remove insoluble impurities, the first impurity-removed solution is obtained. The obtained insoluble impurities are also iron / carbon insoluble residues.

[0087] (5) The sodium phosphate crystals were prepared into a solution with a concentration of 1 mol / L and added to the first impurity removal solution to carry out the lithium precipitation reaction. The lithium precipitation reaction temperature was 60℃, the pH was 9, and the reaction time was 2h. The sodium phosphate crystals were added in excess of 15 mol% based on the theoretical molar ratio of phosphate ions to lithium ions of 1:3. After solid-liquid separation, lithium phosphate product and lithium precipitation residue were obtained.

[0088] (6) The sodium sulfate in the lithium precipitation residue is concentrated to 10 wt%, and after impurity removal by ion exchange resin, a second impurity-removed solution is obtained. This solution is then subjected to bipolar membrane electrodialysis at a temperature of 30°C and a current density of 100 mA / cm². 2 The resulting recyclable sulfuric acid solution and sodium hydroxide solution are returned to steps (1), (2), and (4) for reuse, and 200g of lithium iron phosphate cathode material is further processed.

[0089] The ion exchange resin was prepared by the following method: chloromethylated chlorine beads (macroporous chloromethylated polystyrene-divinylbenzene copolymer beads with a chlorine content of 20.5%) were added to N,N-dimethylformamide and swollen for 2 hours. Then, 20 wt% diethylenetriamine and 10 wt% p-aminobenzenesulfonic acid were added. The mixture was heated to 80°C and stirred for 24 hours. After filtration, a hydrochloric acid solution (50 wt%) containing 50 wt% phosphorous acid of the chloromethylated chlorine beads was added. The mixture was heated to 90°C and an aqueous solution containing 50 wt% formaldehyde of the chloromethylated chlorine beads was added. The mixture was stirred and refluxed for 24 hours. After filtration, the mixture was washed with ethanol and deionized water sequentially and dried to obtain the ion exchange resin.

[0090] The lithium recovery rate and the content of some components of the lithium phosphate products obtained in each embodiment were tested, and the results are shown in Table 1.

[0091] Table 1. Performance comparison of the silicon-carbon anode materials described in the examples and comparative examples.

[0092]

[0093]

[0094] As can be seen from the table above, the lithium phosphate prepared in the embodiments of the present invention has a high recovery rate and extremely low impurity content, enabling high-value recovery of lithium, iron, and phosphorus. Among them, the lithium phosphate product obtained in Example 5 has the highest purity. It can be seen that compared with simple cation exchange resins or chelating resins, the ion exchange resin containing both sulfonic acid groups (-SO3H) and aminophosphonic acid groups (-NHCH2PO3H2) performs more comprehensive adsorption of impurity ions, thereby achieving a deeper impurity removal effect.

[0095] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for recovering lithium phosphate from a lithium iron phosphate cathode material, characterized by, The method comprises the following steps: S1, after the lithium iron phosphate positive electrode material is subjected to oxidative leaching with an acid solution and an oxidizing agent, a first leaching solution and a first leaching residue are obtained; S2, after the first leaching residue is slurried with water, the slurry is subjected to alkaline leaching with sodium hydroxide, a second leaching solution and an iron / carbon insoluble residue are obtained, and the second leaching solution is condensed to obtain sodium phosphate crystals; S3, after the first leaching solution is subjected to lithium precipitation with the sodium phosphate crystals, lithium phosphate and a lithium precipitation residual solution are obtained; S4, after the lithium precipitation residual solution is concentrated and impurities are removed, a bipolar membrane electrodialysis process is performed to obtain an acid solution and sodium hydroxide, which are returned to steps S1 and S2 for reuse.

2. The method of recovering lithium phosphate from a lithium iron phosphate cathode material according to claim 1, wherein In step S1, the acid solution is at least one of sulfuric acid, hydrochloric acid or nitric acid solution; and the oxidizing agent is at least one of hydrogen peroxide, chlorine, ozone or hypochlorous acid. Preferably, the concentration of the acid solution is 5wt%-20wt%. Preferably, when the oxidizing agent is hydrogen peroxide, the concentration of the hydrogen peroxide is 5wt%-50wt%, and the molar ratio of hydrogen peroxide to iron in the hydrogen peroxide is 0.8-1.2:

1. Preferably, the oxidative leaching temperature is 25℃-70℃, and the time is 20min-120min.

3. The method of recovering lithium phosphate from a lithium iron phosphate cathode material according to claim 1 or 2, characterized in that, In step S2, the pH of the alkaline leaching is controlled to be 5-10, and the molar ratio of sodium ions to phosphorus elements is 2-5:

1. Preferably, the condensation temperature is 0℃-30℃, and the time is 0.5h-10h.

4. The method of recovering lithium phosphate from lithium iron phosphate cathode material according to any one of claims 1 to 3, characterized in that, In step S3, before the first leaching solution is subjected to lithium precipitation with the sodium phosphate crystals, the first leaching solution is also subjected to impurity removal. Preferably, the impurity removal comprises: first adjusting the pH to 4-7 with an alkaline solution having a concentration of 5wt%-30wt%, and then adjusting the pH of the solution to 10-12 with an alkaline solution having a concentration of 5wt%-30wt%. Preferably, the alkaline solution is at least one of sodium hydroxide, calcium hydroxide, ammonia water or sodium carbonate solution.

5. The method of recovering lithium phosphate from lithium iron phosphate cathode material according to any one of claims 1 to 4, characterized in that, In step S3, before the first leaching solution is subjected to lithium precipitation with the sodium phosphate crystals, the sodium phosphate crystals are first configured into a solution. Preferably, the concentration of the solution is 0.1mol / L-2mol / L.

6. The method of recovering lithium phosphate from lithium iron phosphate cathode material according to any one of claims 1 to 5, characterized in that, In step S3, the temperature of the lithium precipitation reaction is 25℃-90℃, preferably 40℃-80℃, the pH is controlled to be 7-12, preferably 8-10, and the reaction time is 1h-3h. Preferably, the sodium phosphate crystals are added in excess of 5mol%-30mol% of phosphate ions based on a theoretical molar ratio of 1:3 of phosphate ions to lithium ions, preferably in excess of 5mol%-20mol%.

7. The method of recovering lithium phosphate from lithium iron phosphate cathode material according to any one of claims 1 to 6, characterized in that, In step S4, the lithium precipitation residual solution is concentrated to a sodium salt concentration of 2wt%-30wt%, preferably 5wt%-15wt%.

8. The method of recovering lithium phosphate from lithium iron phosphate cathode material according to any one of claims 1 to 7, characterized in that, In step S4, the impurity removal is selective adsorption and removal of impurity ions other than sodium ions with a cation exchange resin or a chelating resin. Preferably, the functional group of the cation exchange resin is at least one of sulfonic acid group -SO3H, carboxylic acid group -COOH or phosphoric acid group -PO3H2, and the functional group of the chelating resin is at least one of imido diacetic acid -CH2-N(CH2COOH)2, amino phosphonic acid group -N(CH2PO3H2)2 or amidoxime group -C(=NOH)-NH2.

9. The method of recovering iron, lithium and phosphorous from lithium iron phosphate cathode material according to claim 8, wherein, The resin used for the impurity removal is an ion exchange resin containing both sulfonic acid group -SO3H and amino phosphonic acid group -NHCH2PO3H2; Preferably, the ion exchange resin is obtained by amine reaction of chloromethylated chloromacrosphere with ethylenediamine, p-aminobenzenesulfonic acid, and then condensation addition reaction with formaldehyde and phosphorous acid.

10. The method of recovering iron, lithium and phosphorous from lithium iron phosphate cathode material according to any one of claims 1-9, characterized in that, In step S4, the temperature of the bipolar membrane electrodialysis process is from 10°C to 80°C, preferably from 20°C to 45°C, and the current density is from 60 mA / cm 2 -150 mA / cm 2 ; Preferably, the equipment used in the bipolar membrane electrodialysis process is composed of multiple compartments with alternating arrangement of anode membrane, cathode membrane and bipolar membrane, and anode and cathode electrodes are arranged at both ends.

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