Method for preparing phosphate from lithium extraction residue of waste lithium iron phosphate positive electrode material

Abstract

This invention discloses a method for preparing phosphate from lithium extraction residue of waste lithium iron phosphate cathode material, comprising the following steps: S1, taking the lithium extraction residue, adding water to slurry, adding a phosphorus leaching agent to adjust the pH to 9.5-11.5, reacting, and separating the solid and liquid to obtain iron-containing filter residue 1 and phosphorus-containing leachate 1; S2, adding a defluorinating agent to the phosphorus-containing leachate 1, reacting, and separating the solid and liquid to obtain defluorinated liquid 2; S3, adjusting the pH of defluorinated liquid 2 to < 8.5, adding a flocculant for flocculation treatment, and separating the solid and liquid to obtain phosphorus-containing finished liquid 3; S4, taking phosphorus-containing finished liquid 3, adjusting the pH to 10.8-12.5, separating the solid and liquid, and crystallizing the liquid to obtain phosphate. The method of this invention can improve the phosphorus leaching rate and the purity and quality of phosphate, and reduce costs; the method of this invention can prepare various high-purity phosphates.

Description

Technical Field

[0001] This invention relates to the field of battery material recycling technology, and in particular to a method for preparing phosphate from the residue after lithium extraction from waste lithium iron phosphate cathode material. Background Technology

[0002] Lithium iron phosphate (LFP) batteries are currently the most widely installed type of battery in both automotive and energy storage applications. It is estimated that their final disposal volume will reach millions of tons in the future, making their resource recovery and harmless disposal crucial. The recyclable components of retired LFP batteries include the casing, electrodes, separator, electrolyte, and positive and negative electrode materials. Comparatively, the recycling value of the positive electrode material far exceeds that of the other components.

[0003] Currently, the extraction of lithium from spent lithium iron phosphate (LFP) cathode materials is of paramount concern to both industry and academia. However, with the gradual decline in lithium carbonate prices, the revenue from solely recovering lithium has been significantly reduced, resulting in low overall profits, which is detrimental to the long-term development of the industry. After lithium extraction through oxidation leaching, spent LFP cathode materials leave behind a waste residue primarily composed of iron phosphate, known as lithium extraction residue. This residue typically contains high levels of impurities such as carbon, lithium, aluminum, fluorine, and sulfate, making it unsuitable as a precursor for refurbished LFP. Although patents provide methods for converting lithium extraction residue into relatively pure iron phosphate, it lacks advantages in performance, cost, and price compared to commercially available refurbished iron phosphate. Therefore, the resource utilization of lithium extraction residue requires new solutions.

[0004] Lithium extraction residue is rich in phosphorus and can be used as a phosphate rock to prepare phosphates of a certain purity, such as sodium phosphate, potassium phosphate, and diammonium hydrogen phosphate. These have wide applications in food, feed, fertilizer, and water treatment, with a broad market. Furthermore, lithium extraction residue typically does not contain heavy metals or other harmful substances, giving it an inherent advantage in preparing these substances. Existing methods for preparing hydrated sodium phosphate from lithium extraction residue result in low purity, low recovery rates, and a limited product range. Therefore, there is a need to develop a method for preparing high-purity phosphates. Summary of the Invention

[0005] Based on the technical problems existing in the background technology, this invention proposes a method for preparing phosphate from the lithium extraction residue of waste lithium iron phosphate cathode material. The method of this invention can improve the phosphorus leaching rate and the purity and quality of phosphate, reduce costs, and make the P content in the iron-containing filter residue 1 meet the landfill requirements of general solid waste; it can also be used as an iron-containing raw material; the method of this invention can prepare a variety of high-purity phosphates, expanding the market for the obtained products.

[0006] This invention proposes a method for preparing phosphate from the residue after lithium extraction from waste lithium iron phosphate cathode materials, comprising the following steps:

[0007] S1. Take the lithium extraction residue, add water to slurry, add phosphorus leaching agent to adjust pH to 9.5-11.5, carry out the reaction, and separate the solid and liquid to obtain iron-containing filter residue 1 and phosphorus-containing leachate 1;

[0008] S2. Add a defluorinating agent to phosphorus-containing leachate 1, react, separate the solid and liquid, and obtain defluorinated liquid 2.

[0009] S3. Adjust the pH of the defluorinated liquid 2 to < 8.5, add flocculant for flocculation treatment, and separate solid and liquid to obtain phosphorus finished liquid 3;

[0010] S4. Take 3g of the finished phosphorus solution, adjust the pH to 10.8-12.5, separate the solid and liquid, and crystallize the liquid to obtain phosphate.

[0011] Preferably, in S1, the phosphorus leaching agent is one of sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, or ammonia water.

[0012] Preferably, when the phosphorus leaching agent is sodium hydroxide, sodium carbonate, potassium hydroxide, or potassium carbonate, the pH is 10.5-11.5.

[0013] Preferably, when the phosphorus leaching agent is ammonia, the pH is 9.5-10.5.

[0014] The aforementioned lithium extraction residue refers to the waste residue generated after the lithium element is extracted from waste lithium iron phosphate cathode materials through oxidation leaching. Its main component is iron phosphate, but it also contains a certain amount of other impurities such as carbon, lithium, aluminum, fluorine, and sulfate.

[0015] In S1, the reaction principle between iron phosphate and phosphorus leaching agent in the lithium extraction residue is as follows:

[0016] FePO4+2OH-+H2O→Fe(OH)3(s) +HPO4 2- (1)

[0017]

[0018] When the phosphorus leaching agent is sodium hydroxide, potassium hydroxide, or ammonia, OH- is directly provided.

[0019] When the phosphorus leaching agent is sodium carbonate or potassium carbonate, it first hydrolyzes to obtain OH-, and then proceeds with the reaction of formula (1)-(2); while CO3 2- It will react with the cations in the lithium extraction residue to form a precipitate, and will not be introduced into the phosphorus leaching solution 1.

[0020] The inventors discovered that by adding a phosphorus leaching agent, PO4 can be obtained. 3- It forms phosphates with cations in the solution, and its solubility is low, resulting in PO4 in phosphorus-containing leachate 1. 3-The concentration is not high, and due to its low solubility, the phosphate in phosphate leachate 1 is close to saturation. During filtration and impurity removal, the temperature is not easy to control, and a lot of phosphate crystals will precipitate out and remain in the filter residue, reducing the yield of P.

[0021] Therefore, through numerous experiments, the inventors discovered that adding a phosphate leaching agent and adjusting the pH to 9.5-11.5 allows the ferric phosphate in the lithium extraction residue to react with the OH- provided by the phosphate leaching agent. - Only the reaction of formula (1) is carried out, producing Fe(OH)3 precipitate and HPO4. 2- HPO4 2- It forms monohydrogen phosphate with cations, which has a much higher solubility than phosphate and is less prone to crystallization, thus significantly increasing the leaching rate of P in phosphate leachate 1 and improving the yield of phosphate; and compared to complete conversion to PO4. 3- This method can also reduce the consumption of phosphate leaching agent, thereby greatly reducing costs;

[0022] In addition, the residue after lithium extraction also contains Al(OH)3, which reacts with OH-, and the reaction principle is as follows:

[0023] Al(OH)3(s) + OH - →AlO2 - (aq) + 2H₂O (3);

[0024] By controlling the appropriate pH, the inventors reduced the reaction in formula (3), thereby reducing the amount of Al dissolved and thus reducing the burden of impurity removal.

[0025] In S1 above, the phosphorus leaching agent is added in the form of an aqueous solution, the mass fraction of which is 10-50 wt%; more preferably 20-50 wt%; the phosphorus leaching agent is added dropwise.

[0026] The dropwise addition method makes it easy to control pH stability, and the slow addition of alkali facilitates continuous operation and industrial application.

[0027] Preferably, in S1, the reaction temperature is 40-70°C; more preferably, the leaching temperature is 60°C.

[0028] Preferably, in S1, the reaction time is 1-8 hours; more preferably, the reaction time is 2-3 hours.

[0029] Preferably, in S1, the molar ratio of P to phosphorus leaching agent in the lithium extraction residue is 1:1.5-2.0; more preferably, it is 1:1.8-2.0.

[0030] Preferably, in S1, during the slurry addition, the weight ratio of water to lithium extraction residue is 1.5-10:1; more preferably, it is 1.5-3:1.

[0031] Preferably, in S1, the lithium extraction residue is pretreated and then slurried with water.

[0032] Preferably, the pretreatment steps include: taking the lithium extraction residue, adding water to form a slurry, adjusting the pH to 4.5-5.5, stirring and washing, separating the solid and liquid, and taking the solid to obtain the pretreated lithium extraction residue.

[0033] During the above pretreatment, the lithium extraction residue can be crushed and then water can be added to form a slurry. Preferably, the residue is crushed to a particle size that passes through an 80-mesh sieve.

[0034] During the above pretreatment, the solid can be rinsed with water; preferably, the solid is rinsed with water at 40-60℃ 1-3 times, and the weight ratio of water to solid is 0.5-1.0:1 each time; the rinsed water can be recycled.

[0035] After lithium extraction, the residue undergoes pretreatment to remove soluble impurities such as SO4. 2- Li + Na + K + Separation and removal reduce the burden on subsequent impurity removal processes.

[0036] Preferably, during pretreatment, the pH is adjusted using one of sodium hydroxide, potassium hydroxide, or ammonia.

[0037] Preferably, during pretreatment, the weight ratio of water to lithium extraction residue is 1-4:1.

[0038] Preferably, during pretreatment, the temperature for stirring and washing is 40-60℃, and the time for stirring and washing is 30-90 minutes.

[0039] In the above S1, the iron-containing filter residue 1 is purified; the purification process includes: soaking the iron-containing filter residue 1 in dilute alkaline solution to remove residual P, then separating the solid and liquid, washing the solid, and drying to obtain ferric hydroxide.

[0040] During the above purification process, the solid is rinsed with water 1-4 times, with the ratio of water volume to solid weight being 0.5-2:1 each time. Rinsing ensures that soluble phosphorus is completely washed away, and the rinsed water can be recycled for soaking iron-containing filter residue 1.

[0041] During the above purification process, soaking the iron-containing filter residue 1 in dilute alkaline solution can deeply leach out the P (content of about 1-5 wt%) remaining in the iron-containing filter residue 1, so that the P content in the ferric hydroxide is less than 1.0%, which meets the requirements for landfill treatment as general solid waste; the Fe content of the above ferric hydroxide is >50 wt%, so it can also be used as an iron-containing raw material.

[0042] The dilute alkaline solution is one of sodium hydroxide aqueous solution, potassium hydroxide aqueous solution or ammonia solution, and its mass fraction is preferably 0.5-5 wt%; the weight ratio of the dilute alkaline solution to the iron-containing filter residue 1 is preferably 2-10:1; the soaking time of the dilute alkaline solution is preferably 2-4 hours.

[0043] After soaking the iron-containing filter residue 1 in the above-mentioned dilute alkaline solution, it can be recycled for soaking the next batch of iron-containing filter residue 1. The mass fraction of the dilute alkaline solution can be made up to meet the soaking requirements by adding alkali. The alkali is added according to the molar ratio of P to alkali in the lithium-extraction residue of 1:1-2.

[0044] When the phosphorus concentration in the dilute alkali solution reaches 35 g / L, it can be added to phosphorus-containing leachate 1 for further processing, thereby improving the utilization rate of the dilute alkali solution and reducing phosphorus loss.

[0045] Preferably, in S2, the defluorinating agent is at least one of calcium oxide, calcium hydroxide, and calcium chloride.

[0046] Preferably, in S2, the molar ratio of F to defluorinating agent in the phosphorus-containing leachate 1 is 1:2-8.

[0047] Preferably, in S2, the reaction temperature is 40-70℃ and the reaction time is 30-60 min.

[0048] Preferably, in S3, the pH is adjusted with phosphoric acid or carbon dioxide.

[0049] The inventors adjusted the pH of the defluorinated solution 2 to <8.5, which can precipitate high-valence impurity metal ions. Taking Al as an example, the reaction equation is: AlO2 - (aq)+H + (aq) + H2O → Al(OH)3(s), thereby effectively removing high-valence impurity metal ions.

[0050] In addition, after the pH of the defluorinated liquid 2 is adjusted, small particles of aluminum hydroxide are produced, and a small amount of ferric hydroxide colloid is also present. By adding a specific type of flocculant, the inventors can flocculate various small particles, making their particle size larger and easier to filter out.

[0051] Preferably, in S3, the flocculant is an anionic flocculant or a nonionic flocculant.

[0052] Preferably, the anionic flocculant is anionic polyacrylamide.

[0053] Preferably, the nonionic flocculant is nonionic polyacrylamide.

[0054] Preferably, in S3, the ratio of flocculant to defluorinated liquid 2 is 1-25 mg: 1 L; more preferably, it is 1-10 mg: 1 L.

[0055] Preferably, in S4, the pH is adjusted using a mixed solution of sodium hydroxide and ammonia, a mixed solution of potassium hydroxide and ammonia, sodium hydroxide, or potassium hydroxide.

[0056] Preferably, when adjusting the pH with sodium hydroxide or potassium hydroxide, the pH is adjusted to 11.5-12.5.

[0057] Preferably, when adjusting the pH of a mixed solution of sodium hydroxide and ammonia or a mixed solution of potassium hydroxide and ammonia, the pH is adjusted to 10.8-11.2.

[0058] Preferably, in step S4, an organic solvent is added to the liquid, followed by crystallization.

[0059] Preferably, the organic solvent is at least one of ethanol and methanol.

[0060] Preferably, after solid-liquid separation, the volume ratio of liquid to organic solvent is 1:0.1-2.

[0061] In the above S4, the addition of an organic solvent can increase the amount of phosphate crystals and make it less likely for impurities to be mixed into the crystals, thereby improving the purity and quality of the phosphate.

[0062] In S4 above, adjusting the pH to 10.8-12.5 allows for solid-liquid separation, which can further remove iron from the solution.

[0063] During the crystallization process of S4 described above, seed crystals can be added to induce crystallization, with a seed crystal to liquid weight ratio of 0.1-0.5:100. The seed crystal is one of trisodium dodecahydrate, tripotassium dodecahydrate, or triammonium trihydrate.

[0064] During the crystallization process of S4 described above, cooling crystallization is performed. The specific steps are as follows: the liquid temperature is cooled to 40°C, seed crystals are added to induce crystallization, and crystallization is completed by cooling to 20°C. The crystals are then rinsed with a saturated orthophosphate aqueous solution and dried to obtain the phosphate. The saturated orthophosphate aqueous solution can be recycled for crystal rinsing.

[0065] In step S4 above, cooling and crystallization are carried out at a rate of 5℃ / h. Maintaining low-speed stirring during cooling can further improve the crystallization effect. The mother liquor after crystallization can be reused.

[0066] The aforementioned phosphate is one of trisodium phosphate or its crystalline hydrate, tripotassium phosphate or its crystalline hydrate, or triammonium phosphate or its crystalline hydrate.

[0067] When the phosphate is trisodium phosphate or its hydrated form, the phosphorus leaching agent is sodium hydroxide or sodium carbonate. The pH adjuster in the pretreatment, the solute in the dilute alkaline solution, and the pH adjuster in S4 are all sodium hydroxide.

[0068] When the phosphate is tripotassium phosphate or its crystalline hydrate, the phosphorus leaching agent is potassium hydroxide or potassium carbonate. The pH adjuster in the pretreatment, the solute in the dilute alkaline solution, and the pH adjuster in S4 are all potassium hydroxide.

[0069] When the phosphate is triammonium phosphate or its hydrated form, the solutes of the pretreatment pH adjuster, phosphorus leaching agent, and dilute alkaline solution are all ammonia water. The pH adjuster in S4 is a mixed solution of sodium hydroxide and ammonia water or a mixed solution of potassium hydroxide and ammonia water.

[0070] The water mentioned above can be deionized water, pure water, reverse osmosis water, etc.

[0071] Beneficial effects:

[0072] This invention optimizes each step and coordinates the steps to improve the phosphorus leaching rate in the lithium extraction residue, reduce the amount of phosphorus leaching agent used, reduce costs, and improve the purity and quality of phosphates. It also reduces the P content in the iron-containing filter residue 1 to meet the landfill requirements of general solid waste and can also be used as an iron-containing raw material.

[0073] The method described in this invention can recycle and render harmless the phosphorus-rich lithium extraction residue, producing a variety of high-purity phosphates. This can further increase the profit margin of lithium iron phosphate recycling, expand the sales channels of the obtained products, and has broad market potential and good industrial application prospects. It solves the problems of single product and insufficient purity in the resource utilization process of lithium extraction residue in the existing lithium iron phosphate recycling industry, and provides a new method for the comprehensive recycling and utilization of spent lithium iron phosphate. Detailed Implementation

[0074] The technical solution of the present invention will now be described in detail through specific embodiments.

[0075] Example 1

[0076] A method for preparing phosphate from lithium extraction residue of waste lithium iron phosphate cathode material includes the following steps:

[0077] S1. Take 100g of lithium extraction residue, grind and crush it to pass through an 80-mesh sieve, add 300mL of pure water to make a slurry, adjust the pH to 5.0 with sodium hydroxide aqueous solution, stir and wash at 50℃ for 60min, filter, and rinse the filter cake twice with 50mL of pure water at 50℃ to obtain the pretreated lithium extraction residue.

[0078] The concentrations of each element leached from the above-mentioned leaching solution are as follows: Ca 0.3943 g / L, Na 0.1586 g / L, Cu 0.0005 g / L, K 0.0004 g / L, Mg 0.0024 g / L, Al 0.0090 g / L, Fe 0.0004 g / L, Li 0.0860 g / L, F 0.0162 g / L, SO42- 2- 4.728 g / L, PO4 3- The concentration of SO4 in the lithium extraction residue was 0.5929 g / L, indicating that after pretreatment, the soluble impurity SO4 in the residue was significantly reduced. 2- Li + Na + K + Large quantities of these substances can be separated and removed, especially SO4. 2- The removal volume is large, thus avoiding its impact on subsequent steps;

[0079] Take the pretreated lithium extraction residue, add pure water to slurry at a weight ratio of water to lithium extraction residue of 1.5:1, slowly add 50 mL of 50 wt% sodium hydroxide aqueous solution, adjust the initial pH to 10.5-11.0, react at 60℃ for 3 h, filter, and obtain filter cake containing iron 1 and filtrate containing phosphorus 1.

[0080] The elemental contents of phosphorus-containing leachate 1 are as follows: Ca 0.1622 g / L, Cu 0.0051 g / L, K 0.5110 g / L, Mg 0.0081 g / L, Al 1.302 g / L, Fe 3.016 g / L, Li 0.0621 g / L, F 1.614 g / L, SO42- 2- 12.35 g / L, PO4 3- 122.1 g / L, with a phosphorus leaching rate of 53.6%;

[0081] A 3.8 wt% sodium hydroxide aqueous solution was used to soak iron-containing filter cake 1 at a liquid-to-solid ratio of 5:1 for 3 hours at 60℃ to remove residual phosphorus. The solution was filtered, and the filter cake was rinsed three times with pure water to completely remove soluble phosphorus. The ratio of pure water to filter cake weight was 0.5:1 for each rinse (the rinse water could be recycled for soaking iron-containing filter cake 1). The solution was dried to obtain ferric hydroxide (the elemental contents of ferric hydroxide are: Li 0.1399%, Ca 1.724%, Mg 0.0209%, K 0.0603%, Cu 0.1259%, Al 0.2510%, Fe 0.53%, P 0.12%, C 16.89%. Its P content is less than 0.5%, meeting the requirements for landfill treatment as general solid waste; its Fe content is >50 wt%, also suitable for use as an iron-containing raw material).

[0082] The remaining filtrate can be recycled for the next batch of iron-containing filter residue 1. The mass fraction of the dilute alkali solution can be replenished to meet the leaching requirements. The alkali replenishment is carried out according to the molar ratio of P to alkali in the lithium-extraction residue of 1:1-2. When the P concentration in the filtrate reaches 35 g / L, it can be added to the phosphorus-containing leachate 1 for the next step of treatment, thereby improving the utilization rate of the dilute alkali solution and reducing the loss of P.

[0083] The concentrations of each element in the filtrate were as follows: Ca 0.0014 g / L, Cu 0.0001 g / L, K 0.1830 g / L, Mg 0.0006 g / L, Al 1.277 g / L, Fe 0.0188 g / L, Li 0.0343 g / L, F 0.5010 g / L, SO42- 2- 2.205 g / L, PO4 3- 43.05 g / L; After two leaching operations in step S1, namely soaking in phosphorus-containing leachate 1 and iron-containing filter residue 1, 99.2% of the phosphorus in the lithium-extracting residue was extracted.

[0084] S2. Add quicklime (i.e. calcium oxide) to phosphorus-containing leachate 1 to make the molar ratio of F to defluorinating agent in phosphorus-containing leachate 1 1:4. React at 60℃ for 60 min, filter, and take the filtrate to obtain defluorinated liquid 2.

[0085] The content of each element in the defluorinated solution 2 is as follows: Ca 0.0602 g / L, Cu 0.0001 g / L, K 0.1280 g / L, Mg 0.0003 g / L, Al 1.050 g / L, Fe 2.568 g / L, Li 0.0312 g / L, F 0.079 g / L, SO42- 2- 10.46 g / L, PO4 3- 119.7 g / L; More than 95% of the F was removed in this step, meeting the F requirements for subsequent product purification;

[0086] S3. Adjust the pH of the defluorinated solution 2 to < 8.5 with phosphoric acid, then add 10 mg of anionic polyacrylamide to each 1 L of defluorinated solution 2, stir slowly at 60 °C for 30 min, then flocculate and precipitate to remove Al and some Fe, filter, and take the filtrate to obtain phosphoric acid finished solution 3.

[0087] The elemental contents of phosphorus solution 3 are as follows: Ca 0.0462 g / L, Cu 0.0001 g / L, K 0.1040 g / L, Mg 0.0002 g / L, Al 0.0032 g / L, Fe 0.2060 g / L, Li 0.0298 g / L, F 0.071 g / L, SO42- 2- 10.29 g / L, PO4 3-131.2 g / L; In this step, over 99% of Al and some Fe are removed, meeting the Al requirements for subsequent product purification;

[0088] S4. Take 3g of phosphorus product solution, adjust the pH to 11.5-12.0 with 50wt% sodium hydroxide aqueous solution, filter to remove iron, take the filtrate, and then add ethanol at a volume ratio of 1:1 between the filtrate and ethanol. Cool at a rate of 5℃ / h. When the temperature drops to 40℃, add 2g of trisodium dodecahydrate as a seed crystal to induce crystallization. Continue cooling to 20℃ until crystallization is complete. Filter and rinse the filter cake twice with saturated trisodium phosphate aqueous solution, each time using 25mL. Then air dry at room temperature for 10h to obtain trisodium dodecahydrate.

[0089] The composition of trisodium phosphate dodecahydrate is as follows: trisodium phosphate (calculated as Na3PO4·12H2O) 99.7%, Ca 0.0016%, Mg 0.0003%, Cu <0.0001%, K 0.0006%, Al 0.0054%, Fe 0.0080%, Li 0.0538%, As 0.0001%, Cl - 0.0002%, SO4 2- 0.0019%, F 0.0018%, insoluble matter <0.0001%, pH=11.90; the obtained trisodium dodecahydrate has met the product requirements for food grade.

[0090] Example 2

[0091] A method for preparing phosphate from lithium extraction residue of waste lithium iron phosphate cathode material includes the following steps:

[0092] S1. Take 100g of lithium extraction residue, grind and crush it to pass through an 80-mesh sieve, add 100mL of pure water to make a slurry, adjust the pH to 5.5 with potassium hydroxide solution, stir and wash at 40℃ for 90min, filter, and rinse the filter cake 3 times with 100mL of pure water at 40℃ to obtain the pretreated lithium extraction residue.

[0093] Take the pretreated lithium extraction residue, add pure water to slurry at a weight ratio of water to lithium extraction residue of 2.0:1, slowly add 50wt% potassium hydroxide aqueous solution, adjust pH to 11.0-11.5, react at 40℃ for 8h, filter, and obtain filter cake containing iron filter residue 1 and filtrate containing phosphorus leachate 1.

[0094] The elemental contents of phosphorus-containing leachate 1 are as follows: Ca 0.0085 g / L, Cu 0.0001 g / L, Mg 0.0171 g / L, Al 1.542 g / L, Fe 2.2456 g / L, Li 0.0441 g / L, F 1.454 g / L, SO42-2- 16.35 g / L, PO4 3- 108.60 g / L, with a phosphorus leaching rate of 63.30%;

[0095] Take a 5 wt% potassium hydroxide aqueous solution and soak iron-containing filter cake 1 in it at a liquid-to-solid ratio of 2:1 for 4 hours at 60℃ to remove residual phosphorus. Filter the solution and rinse the filter cake 4 times with pure water to completely remove soluble phosphorus. The ratio of pure water to filter cake weight for each rinse is 0.5:1 (the rinse water can be recycled for soaking iron-containing filter cake 1). Dry the solution to obtain ferric hydroxide (the elemental contents of ferric hydroxide are: Li 0.06544%, Ca 1.356%, Mg 0.0335%, K 1.2122%, Cu 0.0824%, Al 0.4520%, Fe 52.50%, P 0.88%, C 12.28%. Its P content is less than 1.0%, which meets the requirements for landfill treatment as general solid waste; its Fe content is >50 wt%, which can also be used as an iron-containing raw material).

[0096] The remaining filtrate can be recycled for soaking the next batch of iron-containing filter residue 1; wherein the concentrations of each element in the above filtrate are: Ca 0.0064 g / L, Cu 0.0001 g / L, Mg 0.0001 g / L, Al 0.647 g / L, Fe 0.0028 g / L, Li 0.0123 g / L, F 0.1410 g / L, SO42- 2- 1.745 g / L, PO4 3- 40.05 g / L; After two leaching operations, namely soaking in phosphorus-containing leachate 1 and iron-containing filter residue 1 in step S1, 98.6% of the phosphorus in the lithium extraction residue is extracted.

[0097] The filtrate was used to soak iron-containing filter residue 1 three times. During each soak, the same molar amount of flake potassium hydroxide was added to the filtrate. After the third soak, the elemental contents of the filtrate were: Ca 0.0032 g / L, Cu 0.0001 g / L, Mg 0.0001 g / L, Al 1.847 g / L, Fe 0.0012 g / L, Li 0.0325 g / L, F 0.5620 g / L, SO42- 2- 6.088 g / L, PO4 3- 102.36 g / L; The filtrate obtained after the third soaking was added to phosphorus-containing leachate 1 and the S2 step was performed;

[0098] S2. Add calcium hydroxide, a defluorinating agent, to phosphorus-containing leachate 1 so that the molar ratio of F to defluorinating agent in phosphorus-containing leachate 1 is 1:2. React at 40℃ for 60 min, filter, and take the filtrate to obtain defluorinated liquid 2.

[0099] The content of each element in the defluorinated solution 2 is as follows: Ca 0.0540 g / L, Cu 0.0001 g / L, Mg 0.0001 g / L, Al 1.755 g / L, Fe 0.8202 g / L, Li 0.0285 g / L, F 0.0320 g / L, SO42- 2- 10.88 g / L, PO4 3- 104.89 g / L; More than 95% of the F was removed in this step, meeting the F requirements for subsequent product purification;

[0100] S3. Adjust the pH of the defluorinated solution 2 to < 8.5 with phosphoric acid, then add 25 mg of anionic polyacrylamide to each 1 L of defluorinated solution 2, stir slowly at 60℃ for 30 min, then flocculate and precipitate to remove Al and some Fe, filter, and take the filtrate to obtain phosphoric acid finished solution 3.

[0101] The elemental contents of phosphorus solution 3 are as follows: Ca 0.0440 g / L, Cu 0.0001 g / L, Mg 0.0001 g / L, Al 0.0041 g / L, Fe 0.3012 g / L, Li 0.0280 g / L, F 0.0300 g / L, SO42- 2- 10.54 g / L, PO4 3- 115.52 g / L; In this step, over 99% of Al and some Fe are removed, meeting the Al requirements for subsequent product purification;

[0102] S4. Take 3g of the phosphorus product solution, adjust the pH to 12.0-12.5 with 50wt% potassium hydroxide aqueous solution, filter to remove iron, take the filtrate, and then add ethanol at a volume ratio of 1:0.5 between the filtrate and ethanol, cool at a rate of 5℃ / h, and when the temperature reaches 40℃, add tripotassium dodecahydrate as a seed crystal to induce crystallization. Continue cooling to 25℃ until crystallization is complete, filter, and rinse the filter cake twice with saturated tripotassium phosphate aqueous solution, each time using 25mL, and then air dry at room temperature for 10h to obtain tripotassium dodecahydrate.

[0103] The composition of tripotassium phosphate dodecahydrate is as follows: tripotassium phosphate (calculated as K3PO4·12H2O) 99.1%, Ca 0.0046%, Mg 0.0002%, Cu <0.0001%, Al 0.0078%, Fe 0.0064%, Li 0.0068%, As 0.0001%, Cl - 0.0052%, SO4 2- 0.0989%, F 0.0554%, insoluble matter <0.0001%, pH=12.10; the obtained tripotassium dodecahydrate fully meets the requirements of industrial grade.

[0104] Example 3

[0105] A method for preparing phosphate from lithium extraction residue of waste lithium iron phosphate cathode material includes the following steps:

[0106] S1. Take 100g of lithium extraction residue, grind and crush it to pass through an 80-mesh sieve, add 400mL of pure water to make a slurry, adjust the pH to 4.5 with ammonia water, stir and wash at 60℃ for 30min, filter, rinse the filter cake once with 80mL of pure water at 60℃ to obtain the pretreated lithium extraction residue.

[0107] Take the pretreated lithium extraction residue, add pure water to slurry at a weight ratio of water to lithium extraction residue of 1.5:1, slowly add 25wt% ammonia water, adjust the pH to 10.0, react at 70℃ for 1h, filter, and obtain filter cake containing iron filter residue 1 and filtrate containing phosphorus leachate 1.

[0108] The elemental concentrations of phosphorus-containing leachate 1 are as follows: Ca 0.0428 g / L, Cu 0.0001 g / L, Mg 0.0015 g / L, Al 0.8845 g / L, Fe 2.6554 g / L, Li 0.0086 g / L, F 1.2712 g / L, SO42- 2- 9.753 g / L, PO4 3- 90.43 g / L;

[0109] Take 2 wt% ammonia water and soak iron-containing filter cake 1 in a liquid-to-solid ratio of 10:1 at 60℃ for 2 hours to remove residual phosphorus. Filter, rinse the filter cake twice with pure water to completely remove soluble phosphorus. The ratio of pure water to filter cake weight for each rinse is 2:1 (the rinse water can be recycled for soaking iron-containing filter cake 1). Dry to obtain ferric hydroxide (the element content of ferric hydroxide is: Li 0.04624%, Ca 1.726%, Mg 0.0225%, K 0.8112%, Cu 0.0174%, Al 0.9510%, Fe 53.19%, P 0.98%, C 14.17%. Its P content is less than 1.0%, which meets the requirements for landfill treatment as general solid waste; its Fe content is >50wt%, which can also be used as an iron-containing raw material; through the two-stage leaching operation of soaking in phosphorus-containing leachate 1 and iron-containing filter residue 1 in step S1, 94% of the phosphorus in the lithium extraction residue is extracted.

[0110] The remaining filtrate can be recycled for soaking the next batch of iron-containing filter residue 1; after a total of 3 cycles of soaking, the concentrations of each element in the filtrate obtained after the third soaking are enriched as follows: Ca 0.0025 g / L, Cu 0.0001 g / L, Mg 0.0001 g / L, Al 1.243 g / L, Fe 0.0005 g / L, Li 0.0049 g / L, F 0.6712 g / L, SO42- 2- 7.168 g / L, PO4 3- 101.33 g / L; The filtrate obtained after the third soaking was added to phosphorus-containing leachate 1 and the S2 step was performed;

[0111] S2. Add calcium oxide, a defluorinating agent, to phosphorus-containing leachate 1 so that the molar ratio of F to defluorinating agent in phosphorus-containing leachate 1 is 1:8. React at 70℃ for 30 min, filter, and take the filtrate to obtain defluorinated liquid 2.

[0112] The content of each element in the defluorinated solution 2 is as follows: Ca 0.0215 g / L, Cu 0.0001 g / L, Mg 0.0001 g / L, Al 0.9214 g / L, Fe 0.3045 g / L, Li 0.0072 g / L, F 0.018 g / L, SO42- 2- 8.229 g / L, PO4 3- 96.42 g / L; More than 90% of the F was removed in this step, meeting the F requirements for subsequent product purification;

[0113] S3. Adjust the pH of the defluorinated liquid 2 to < 8.5 by introducing carbon dioxide. Then add 5 mg of anionic polyacrylamide to each 1 L of defluorinated liquid 2, stir slowly at 60℃ for 30 min, then flocculate and precipitate to remove Al and some Fe, filter, and take the filtrate to obtain phosphorus finished liquid 3.

[0114] The elemental contents of phosphorus solution 3 are as follows: Ca 0.0204 g / L, Cu 0.0001 g / L, Mg 0.0001 g / L, Al 0.0014 g / L, Fe 0.1933 g / L, Li 0.0154 g / L, F 0.0172 g / L, SO42- 2- 8.004 g / L, PO4 3- 95.94 g / L; In this step, over 90% of Al and some Fe are removed, meeting the requirements for Fe and Al in subsequent product purification;

[0115] S4. Take 3 phosphate product solution, mix 25 wt% ammonia water and 50 wt% sodium hydroxide aqueous solution at a volume ratio of 1:1, adjust pH=11.2, filter to remove iron, take the filtrate, then add ethanol at a volume ratio of 1:2, cool at a rate of 5℃ / h, when cooled to 40℃, add triammonium phosphate trihydrate as seed crystal to induce crystallization, continue cooling to 25℃ to complete crystallization, filter, wash the filter cake twice with saturated triammonium phosphate aqueous solution, each time with a washing volume of 25 mL, then air dry at room temperature for 10 h to obtain triammonium phosphate trihydrate;

[0116] The composition of triammonium phosphate trihydrate is as follows: triammonium phosphate (calculated as (NH4)3PO4·3H2O) 98.6%, Ca 0.0072%, Mg 0.0004%, Cu <0.0001%, Al 0.012%, Fe 0.0093%, Li 0.0077%, As 0.0001%, Cl - 0.0048%, SO4 2- 0.1425%, F 0.1124%, insoluble matter <0.0001%, pH=11.14; the obtained triammonium phosphate trihydrate has met the requirements of industrial-grade products.

[0117] Comparative Example 1

[0118] Phosphorus-containing leachate 1 was prepared according to S1 of Example 1. The pH was adjusted to 12.0 using a 50 wt% sodium hydroxide aqueous solution, and other steps were the same as in S1 of Example 1. The content of each element in the resulting phosphorus-containing leachate 1 was as follows: Ca 0.3641 g / L, Cu 0.0031 g / L, K 0.6210 g / L, Mg 0.0091 g / L, Al 2.682 g / L, Fe 0.062 g / L, Li 0.0582 g / L, F 2.759 g / L, SO42- 2- 18.92 g / L, PO4 3- 100.15g / L.

[0119] It can be seen that the phosphorus leaching rate of Comparative Example 1 is not only lower than that of Example 1, but also contains more impurities. Although the concentration of Fe impurity is lower, the concentration of other impurities such as Al, F and sulfate ions is significantly increased. The amount of reagents required for subsequent impurity removal will increase significantly. Moreover, the consumption of sodium hydroxide phosphate leaching agent is more than 50% higher than that of Example 1, which is unreasonable in terms of cost. Furthermore, the solubility of trisodium phosphate is low under this pH condition, close to saturation. During filtration, even slight pre-cooling can easily result in a large amount of trisodium dodecahydrate crystals remaining in the residue, reducing the yield of trisodium dodecahydrate.

[0120] Comparative Example 2

[0121] Phosphorus-containing leachate 1 was prepared according to S1 of Example 1, with the pH adjusted to 10.0, and all other steps being the same as S1 of Example 1; the resulting phosphorus-containing leachate 1 contained PO4. 3- The concentration was 42.63 g / L, and its phosphorus leaching rate was much lower than that in Example 1.

[0122] Comparative Example 3

[0123] Phosphorus solution 3 was prepared according to S1-S3 of Example 1. The pH of the defluorinated solution 2 was adjusted to 9.0 with phosphoric acid. Other steps were the same as S1-S3 of Example 1. The resulting phosphorus solution 3 had an Al concentration of 1.1853 g / L and an Fe concentration of 0.2556 g / L, which were much higher than those in Example 1. Al and Fe could not be effectively removed.

[0124] Comparative Example 4

[0125] Phosphorus solution 3 was prepared according to S1-S3 of Example 1, without the addition of anionic polyacrylamide, and otherwise the same as S1-S3 of Example 1; the aluminum hydroxide precipitate particles in the resulting phosphorus solution 3 were too fine, and direct filtration would penetrate the filter paper, so Al could not be effectively removed.

[0126] The lithium extraction residue used in Example 1 and Comparative Examples 1-4 was from the same batch.

[0127] Comparative Example 5

[0128] Phosphorus-containing leachate 1 was prepared according to S1 of Example 3, with the pH adjusted to 9.0, and the rest being the same as S1 of Example 3; the resulting phosphorus-containing leachate 1 contained PO4. 3- The concentration was 36.44 g / L, and the phosphorus leaching rate was much lower than that in Example 3.

[0129] The lithium extraction residue used in Example 3 and Comparative Example 5 was from the same batch.

[0130] 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 preparing phosphate from the lithium extraction residue of waste lithium iron phosphate cathode material, characterized in that, Includes the following steps: S1. Take the lithium extraction residue, add water to slurry, add phosphorus leaching agent to adjust pH=9.5-11.5, carry out the reaction, and separate the solid and liquid to obtain iron-containing filter residue 1 and phosphorus-containing leachate 1. S2. Add a defluorinating agent to phosphorus-containing leachate 1, react, separate the solid and liquid, and obtain defluorinated liquid 2. S3. Adjust the pH of the defluorinated liquid 2 to < 8.5, add flocculant for flocculation treatment, and separate solid and liquid to obtain phosphorus finished liquid 3; S4. Take 3g of the finished phosphorus solution, adjust the pH to 10.8-12.5, separate the solid and liquid, and crystallize the liquid to obtain phosphate. In S1, during the slurry addition, the weight ratio of water to lithium extraction residue is 1.5-10:

1. In S2, the defluorinating agent is at least one of calcium oxide, calcium hydroxide, and calcium chloride; In S2, the molar ratio of F to defluorinating agent in phosphorus-containing leachate 1 is 1:2-8; In S3, the pH is adjusted using phosphoric acid or carbon dioxide; In S3, the flocculant is anionic polyacrylamide or nonionic polyacrylamide; In S3, the ratio of flocculant to defluorinated liquid 2 is 1-25 mg: 1 L.

2. The method for preparing phosphate from the lithium extraction residue of waste lithium iron phosphate cathode material according to claim 1, characterized in that, In S1, the phosphorus leaching agent is one of sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, or ammonia water.

3. The method for preparing phosphate from the lithium extraction residue of waste lithium iron phosphate cathode material according to claim 2, characterized in that, When the phosphorus leaching agent is sodium hydroxide, sodium carbonate, potassium hydroxide, or potassium carbonate, the pH is 10.5-11.

5.

4. The method for preparing phosphate from the lithium extraction residue of waste lithium iron phosphate cathode material according to claim 2, characterized in that, When the phosphorus leaching agent is ammonia, the pH is 9.5-10.

5.

5. The method for preparing phosphate from the lithium extraction residue of waste lithium iron phosphate cathode material according to claim 1 or 2, characterized in that, In S1, the reaction temperature is 40-70℃.

6. The method for preparing phosphate from the lithium extraction residue of waste lithium iron phosphate cathode material according to claim 1 or 2, characterized in that, In S1, the reaction time is 1-8 hours.

7. The method for preparing phosphate from the lithium extraction residue of waste lithium iron phosphate cathode material according to claim 1 or 2, characterized in that, In S1, the molar ratio of P to phosphorus leaching agent in the lithium extraction residue is 1:1.5-2.

0.

8. The method for preparing phosphate from the lithium extraction residue of waste lithium iron phosphate cathode material according to claim 1 or 2, characterized in that, In S1, the lithium extraction residue is pretreated and then slurried with water.

9. The method for preparing phosphate from the lithium extraction residue of waste lithium iron phosphate cathode material according to claim 8, characterized in that, The pretreatment steps include: taking the lithium extraction residue, adding water to form a slurry, adjusting the pH to 4.5-5.5, stirring and washing, separating the solid and liquid, and taking the solid to obtain the pretreated lithium extraction residue.

10. The method for preparing phosphate from the lithium extraction residue of waste lithium iron phosphate cathode material according to claim 9, characterized in that, During pretreatment, the pH is adjusted using one of sodium hydroxide, potassium hydroxide, or ammonia.

11. The method for preparing phosphate from the lithium extraction residue of waste lithium iron phosphate cathode material according to claim 9, characterized in that, During pretreatment, the weight ratio of water to lithium extraction residue is 1-4:

1.

12. The method for preparing phosphate from the lithium extraction residue of waste lithium iron phosphate cathode material according to claim 9, characterized in that, During pretreatment, the temperature for stirring and washing is 40-60℃, and the time for stirring and washing is 30-90 minutes.

13. The method for preparing phosphate from the lithium extraction residue of waste lithium iron phosphate cathode material according to claim 1 or 2, characterized in that, In S2, the reaction temperature is 40-70℃ and the reaction time is 30-60min.

14. The method for preparing phosphate from the lithium extraction residue of waste lithium iron phosphate cathode material according to claim 1 or 2, characterized in that, In S4, the pH is adjusted using a mixed solution of sodium hydroxide and ammonia, a mixed solution of potassium hydroxide and ammonia, sodium hydroxide, or potassium hydroxide.

15. The method for preparing phosphate from the lithium extraction residue of waste lithium iron phosphate cathode material according to claim 14, characterized in that, When adjusting the pH with sodium hydroxide or potassium hydroxide, adjust the pH to 11.5-12.

5.

16. The method for preparing phosphate from the lithium extraction residue of waste lithium iron phosphate cathode material according to claim 14, characterized in that, When adjusting the pH of a mixed solution of sodium hydroxide and ammonia or a mixed solution of potassium hydroxide and ammonia, adjust the pH to 10.8-11.

2.

17. The method for preparing phosphate from the lithium extraction residue of waste lithium iron phosphate cathode material according to claim 1 or 2, characterized in that, In S4, an organic solvent is added to the liquid, followed by crystallization.

18. The method for preparing phosphate from the lithium extraction residue of waste lithium iron phosphate cathode material according to claim 17, characterized in that, The organic solvent is at least one of ethanol and methanol.

19. The method for preparing phosphate from the lithium extraction residue of waste lithium iron phosphate cathode material according to claim 17, characterized in that, After solid-liquid separation, the volume ratio of liquid to organic solvent is 1:0.1-2.

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