A method for recovering iron phosphate and lithium carbonate from lithium iron phosphate waste

Abstract

The present invention provides a method for recovering ferric phosphate and lithium carbonate from lithium iron phosphate waste, comprising the following steps: (1) pretreatment; (2) acid leaching; (3) impurity removal treatment; (4) lithium precipitation; (5) iron recovery. The process of this method is simple, can effectively shorten the leaching time when using microorganisms for treatment, and effectively improves the purity of ferric phosphate and lithium carbonate.

Description

Technical Field

[0001] The present invention belongs to the technical field of recycling of lithium iron phosphate waste, and particularly relates to a method for recovering iron phosphate and lithium carbonate from lithium iron phosphate waste. Background Art

[0002] With the rapid development of the new energy industry, lithium iron phosphate (LiFePO4) batteries have been widely used in fields such as electric vehicles and energy storage systems due to their high safety, long cycle life, and environmental protection characteristics. However, with the large-scale use of lithium iron phosphate batteries, their scrap volume is increasing year by year.

[0003] Lithium iron phosphate waste contains a large amount of valuable metal elements such as lithium, iron, and phosphorus. By recycling these valuable metal elements for the preparation of important raw materials (iron phosphate and lithium carbonate) for lithium iron phosphate batteries, it is not only possible to solve the problems of resource waste and environmental pollution caused by lithium iron phosphate waste, but also effectively reduce the production cost of lithium iron phosphate batteries.

[0004] Currently, common methods for recovering iron phosphate and lithium carbonate from lithium iron phosphate waste mainly include hydrometallurgy and biohydrometallurgy. Hydrometallurgy dissolves the valuable metal elements in the waste by acid leaching or alkali leaching, and then separates and recovers the target substances by methods such as precipitation and extraction. However, the use of high-concentration strong acids (such as sulfuric acid and hydrochloric acid) in the acid leaching process seriously corrodes the equipment, and the treatment cost of the generated waste liquid is high. Secondly, there are many impurity ions in the solution after acid leaching, and the separation and purification process is complex, with a low recovery rate.

[0005] Biohydrometallurgy uses the metabolic action of microorganisms to dissolve or enrich the metal elements in the waste and then recovers them. CN202210298042.2 discloses a method for selectively leaching and recovering lithium in waste lithium iron phosphate power battery black powder using Acidithiobacillus ferrooxidans, including the following steps: adding lithium iron phosphate battery black powder and Acidithiobacillus ferrooxidans bacterial liquid cultured to the logarithmic phase into a conical flask containing an improved 9K medium without FeSO4·7H2O for leaching reaction, performing solid-liquid separation after the reaction to obtain a leaching solution and a filter residue, and then dropping NaOH solution into the leaching solution to adjust the pH to make Fe 3+ generate Fe(OH)3 precipitation, filtering the precipitation, and adding saturated Na2CO3 solution to the filtrate to precipitate Li2CO3 to achieve the recovery of lithium in the lithium ion battery black powder. This method uses a single Acidithiobacillus ferrooxidans to treat lithium iron phosphate waste. Although this method can increase the leaching rate of lithium to 97.5%, its leaching time is long (5 - 8 days), and the purity of the recovered lithium carbonate and iron phosphate has not been studied.

[0006] Therefore, it is urgent to develop a method for effectively recovering valuable metals from lithium iron phosphate waste for the preparation of iron phosphate and lithium carbonate to solve the above problems existing in the prior art and achieve efficient and low-cost resource recovery. Summary of the Invention

[0007] The object of the present invention is to provide a method for recovering iron phosphate and lithium carbonate from lithium iron phosphate waste. The process of this method is simple, which can effectively shorten the leaching time during microbial treatment and effectively improve the purity of iron phosphate and lithium carbonate.

[0008] To achieve the above object, the present invention provides the following technical solution: A method for recovering iron phosphate and lithium carbonate from lithium iron phosphate waste, comprising the following steps:

[0009] (1) Pretreatment: Crush the lithium iron phosphate waste, mix it with a composite bacterial solution at a solid-liquid ratio of 1:(3 - 5), and leach for 2 - 3 days at 30 - 45°C and pH 1.5 - 2.5 to obtain a mixed material; the composite bacterial solution contains a Thiobacillus ferrooxidans bacterial suspension, an Acidiphilium acidophilum bacterial suspension, and an Aspergillus niger bacterial suspension, and the volume ratio of the three bacterial suspensions is (1 - 3):(0.5 - 2):(0.3 - 1); (2) Acid leaching: Add dilute sulfuric acid to the mixed material, introduce oxygen and react for 1 - 2 hours, then filter to obtain an acid leaching solution and an iron-containing filter residue; (3) Impurity removal treatment: Add a composite impurity removal agent composed of polyacrylamide, sodium silicate, and lignosulfonate to the acid leaching solution, stir and react, and then filter to obtain a purified solution; (4) Lithium precipitation: Heat the purified solution to 60°C, slowly add sodium carbonate until the pH is 10 - 11, cool down in three stages, the first stage is from 60°C to 50°C, the second stage is from 50°C to 40°C, and the third stage is from 40°C to 25°C, and centrifuge to obtain lithium carbonate; (5) Iron recovery: Wash the iron-containing filter residue with an oxalic acid solution, and dry it to obtain iron phosphate.

[0010] Further, the concentration of the Thiobacillus ferrooxidans bacterial suspension is 10 6 -10 7 CFU / mL, the concentration of the Acidiphilium acidophilum bacterial suspension is 5×10 5 -2×10 6 CFU / mL, and the concentration of the Aspergillus niger bacterial suspension is 1×10 5 -5×10 5 CFU / mL.

[0011] In the method for recovering iron phosphate and lithium carbonate from lithium iron phosphate waste of the present invention, first, Thiobacillus ferrooxidans, Acidiphilium acidophilum, and Aspergillus niger are used to synergistically treat the lithium iron phosphate waste. Thiobacillus ferrooxidans can oxidize Fe 2+ to Fe 3+, it destroys the lattice structure of LiFePO4 to release lithium ions. With the cooperation of Aspergillus niger, it can further dissolve part of the lithium by using the organic acids secreted by Aspergillus niger. Moreover, Acidithiobacillus can acidify the environment to keep the whole reaction in an acidic environment, which can effectively promote the release of metal ions and reduce the release burden of lithium ions during subsequent acid leaching, thereby effectively reducing the concentration and dosage of acid during subsequent acid leaching;

[0012] The pretreated mixture is added with dilute sulfuric acid for acid leaching. During the acid leaching process, dilute sulfuric acid reacts with the remaining LiFePO4 to completely dissociate lithium, iron, and phosphorus, generating soluble lithium sulfate, ferric sulfate, and phosphoric acid; and Fe in the generated ferric sulfate 2 + is further oxidized to Fe under the action of oxygen 3+ , and this part of Fe 3+ reacts with the Fe obtained in the pretreatment 3+ to react with phosphoric acid to form ferric phosphate precipitate;

[0013] Then a composite impurity remover is used to remove impurities from the acid-base solution. Sodium silicate forms aluminosilicate precipitate with Al 3+ ; polyacrylamide agglomerates colloidal impurities through adsorption bridging; lignosulfonate disperses microcrystals and inhibits the coprecipitation of a small part of the remaining Fe 3+ and PO4 3- in the acid leaching solution to improve the purity of lithium carbonate;

[0014] Then sodium carbonate is used to combine with lithium ions in the purified solution to form lithium carbonate precipitate. In this process, a three-stage cooling mode is used to make Li2CO3 crystallize in a gradient manner, which can effectively reduce the large generation of a large number of small nuclei of Li2CO3, thereby effectively avoiding the phenomenon that due to the large specific surface area of small nuclei, they are easy to adsorb Na + , reducing the entrainment of Na + and improving the purity of lithium carbonate;

[0015] Finally, oxalic acid is used to wash the iron-containing filter residue (ferric phosphate precipitate), which can further remove sulfate ions in the filter residue and improve the purity of ferric phosphate.

[0016] Preferably, in the pretreatment, the solid-liquid ratio of the crushed lithium iron phosphate waste to the composite bacterial solution is 1:4, and the volume ratio of the Acidithiobacillus ferrooxidans suspension, Acidiphilium sp. suspension, and Aspergillus niger suspension is 2:1:0.5.

[0017] Furthermore, in the step (1), 0.1 - 0.5 g of ammonium sulfate is added per liter of the composite bacterial solution, and oxygen is introduced during the reaction, and the oxygen flow rate is 0.1 - 0.3 L / min·L of the composite bacterial solution.

[0018] Furthermore, in step (2), the weight volume ratio of the mixture to the dilute sulfuric acid is 1:(8-12), the concentration of the dilute sulfuric acid is 2-4%, and the reaction temperature during acid leaching is 50-70°C.

[0019] Furthermore, the mass ratio of the polyacrylamide, sodium silicate and lignin sulfonate is 1:(1-3):(0.3-1), and the addition amount of the composite impurity remover is 0.5%-1.5% of the mass of the acid leaching solution;

[0020] Sodium silicate is also modified by a modifying liquid. The specific modification method is:

[0021] S1: The bentonite is first heat treated at 150-160°C for 1 hour, then treated at 230-240°C for 30 minutes, and then air-cooled to room temperature after the treatment.

[0022] S2: 3-5 parts of the product of S1, 4-7 parts of a 5% by mass chitosan solution, 2-3 parts of carbon nanotubes and 1-3 parts of alumina are mixed and stirred to obtain a modified solution;

[0023] S3: Sodium silicate and modified liquid are stirred at a weight ratio of 3:7, with a stirring speed of 350-400 r / min for 1 hour. After the stirring is completed, the mixture is filtered and dried to obtain modified sodium silicate.

[0024] The modified liquid obtained by the specific method of the present invention is improved and optimized, and the performance effect of the product tends to be optimized. The bentonite in the modified liquid is thermally improved by the present invention, and the interlamellar spacing of the bentonite is increased. At the same time, the modified liquid obtained by the specific method of carbon nanotubes, alumina, etc. is improved and optimized, so that the obtained sodium silicate is coordinated into the system, and the performance of the product tends to be optimized and improved.

[0025] Furthermore, in step (3), the stirring reaction time is 30-60 minutes, and the stirring speed is 300-500 rpm.

[0026] Furthermore, in step (4), the rate of adding sodium carbonate is 2-5 g / min, and the cooling time of each stage is 30 min when the cooling is divided into three stages.

[0027] Furthermore, in step (5), the iron-containing filter residue is washed 2-3 times, and the concentration of the oxalic acid solution is 0.5 mol / L.

[0028] Furthermore, the drying temperature in step (5) is 80-100° C., and the drying time is 2-4 hours.

[0029] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0030] 1. Through the synergistic effect of Acidithiobacillus ferrooxidans, Bacillus acidophilus and Aspergillus niger, Acidithiobacillus ferrooxidans oxidizes Fe 2+ to Fe 3+ to destroy the LiFePO4 lattice and release lithium ions; organic acids such as citric acid and acetic acid secreted by Aspergillus niger and Bacillus acidophilus can effectively promote the dissolution of lithium, significantly reducing the sulfuric acid concentration requirement for subsequent acid leaching. The synergistic effect of the three realizes the efficient pretreatment of lithium iron phosphate waste, not only increasing the lithium leaching rate to over 98.5%, but also shortening the microbial treatment leaching time to 2 - 3 days, greatly shortening the recovery time and improving the recovery efficiency;

[0031] 2. The present invention uses a composite impurity removal agent composed of polyacrylamide - sodium silicate - lignosulfonate to treat the acid leaching solution. Based on the principle of dual adsorption - complexation, it selectively removes impurities such as Al 3+ in the acid leaching solution, making the purity of lithium carbonate reach over 99.4%, greatly improving the purity of the recovered lithium carbonate;

[0032] 3. In the reaction of sodium carbonate combining with lithium ions to form lithium carbonate precipitate, the present invention uses a method of cooling in three stages, which can effectively avoid the entrainment of Na + and reduce the residue of Na + and contribute to subsequent filtration operations, improving the purity and recovery efficiency of lithium carbonate;

[0033] 4. The present invention uses oxalic acid to wash the iron - containing filter residue, which can further remove sulfate ions in the iron phosphate precipitate, making the purity of iron phosphate reach over 98.5%, greatly improving the purity of the recovered iron phosphate. Specific Embodiments

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0035] Example 1

[0036] This example provides a method for recovering iron phosphate and lithium carbonate from lithium iron phosphate waste, including the following steps:

[0037] (1) Pretreatment: The lithium iron phosphate waste is crushed to a particle size of 0.5 mm, mixed with the composite bacterial solution at a solid-liquid ratio of 1:4, 0.3 g of ammonium sulfate is added per liter of the composite bacterial solution, and leaching is carried out at 40 °C and pH 2.0 for 2.5 days. Oxygen is introduced during the reaction, and the oxygen flow rate is 0.2 L / min·L of the composite bacterial solution to obtain a mixed material; the composite bacterial solution contains a Thiobacillus ferrooxidans bacterial suspension, an Acidiphilium acidophilum bacterial suspension, and an Aspergillus niger bacterial suspension, and the volume ratio of the three bacterial suspensions is 2:1:0.5; the concentration of the Thiobacillus ferrooxidans bacterial suspension is 10 6 CFU / mL, the concentration of the Acidiphilium acidophilum bacterial suspension is 5×10 5 CFU / mL, and the concentration of the Aspergillus niger bacterial suspension is 1×10 5 CFU / mL;

[0038] The preparation method of the Thiobacillus ferrooxidans bacterial suspension is: inoculating Thiobacillus ferrooxidans into 9K basal medium ((NH4)2SO4 3.0 g / L, KCl 0.1 g / L, K2HPO4 0.5 g / L, MgSO4·7H2O 0.5 g / L, Ca(NO3)2 0.01 g / L, and FeSO4·7H2O 44.7 g / L, prepared with distilled water, pH 1.8 - 2.2, sterilized at 121 °C for 20 min) at an inoculation amount of 10%, culturing with shaking at 30 °C and 150 rpm for 5 - 7 days; then centrifuging the culture solution at 4 °C and 8000 rpm for 10 min, discarding the supernatant, and washing the thalli twice with a pH 2.0 dilute sulfuric acid solution, and finally resuspending to a concentration of 10 6 CFU / mL;

[0039] The preparation method of the Acidiphilium acidophilum bacterial suspension is: inoculating Acidiphilium acidophilum into the modified acidophilic medium (glucose 10 g / L, yeast extract 0.5 g / L, (NH4)2SO4 2.0 g / L, MgSO4·7H2O 0.5 g / L, and KH2PO4 3.0 g / L, prepared with distilled water, pH 3.0, sterilized at 121 °C for 20 min) at an inoculation amount of 10%, culturing statically at 35 °C for 48 hours until the OD is equal to 1.0, centrifuging at 6000 rpm for 10 minutes, discarding the supernatant, and resuspending with a pH 2.5 citrate buffer to a concentration of 5×10 5 CFU / mL;

[0040] The preparation method of Aspergillus niger suspension is as follows: inoculate Aspergillus niger onto a PDA solid slant and culture at 28°C for 5 days until the spores mature (black-brown); scrape the spores and suspend them in sterile physiological saline, filter to remove the hyphae, and then inoculate them into PDA liquid culture medium (potato extract powder 200 g / L, glucose 20 g / L, KH2PO4 3 g / L, MgSO4·7H2O 1.5 g / L, prepared with distilled water, sterilized at 121°C for 20 min) at a 1% inoculum rate, and culture at 28°C and 200 rpm for 72 hours; filter through double-layer sterile gauze and centrifuge at 4000 rpm for 10 minutes, discard the supernatant and resuspend with sterile water to a concentration of 1×10 5 CFU / mL.

[0041] (2) Acid leaching: add 3% dilute sulfuric acid to the mixture at a weight volume ratio of 1:10, introduce oxygen, react at 60°C for 1.5 hours, filter, and obtain an acid leaching solution and iron-containing filter residue;

[0042] (3) impurity removal treatment: adding a composite impurity remover consisting of polyacrylamide, sodium silicate and lignin sulfonate to the acid leaching solution at a rate of 1% by mass of the acid leaching solution, stirring the mixture at a speed of 400 rpm for 45 minutes, and then filtering to obtain a purified solution; the mass ratio of the polyacrylamide, sodium silicate and lignin sulfonate is 1:2:0.5;

[0043] Sodium silicate is also modified by a modifying liquid. The specific modification method is:

[0044] S1: The bentonite was first heat treated at 155°C for 1 hour, then at 235°C for 30 minutes, and then air-cooled to room temperature;

[0045] S2: 4 parts of the product of S1, 5.5 parts of a 5% by mass chitosan solution, 2.5 parts of carbon nanotubes and 2 parts of alumina are mixed and stirred to obtain a modified solution;

[0046] S3: stirring the sodium silicate and the modified liquid at a weight ratio of 3:7, at a stirring speed of 370 r / min, for 1 h. After the stirring is completed, filtering and drying are performed to obtain modified sodium silicate;

[0047] (4) Lithium precipitation: Heat the purified solution to 60°C, slowly add sodium carbonate at a rate of 3 g / min to a pH of 10.5, cool it in three stages, the first stage from 60°C to 50°C, the second stage from 50°C to 40°C, and the third stage from 40°C to 25°C. The cooling time for each stage is 30 min, and centrifuge to obtain lithium carbonate.

[0048] (5) Iron recovery: The iron-containing filter residue was washed twice with an oxalic acid solution with a concentration of 0.5 mol / L, and then dried at 90 °C for 3 h to obtain iron phosphate.

[0049] Example 2

[0050] This embodiment provides a method for recovering iron phosphate and lithium carbonate from lithium iron phosphate waste, comprising the following steps:

[0051] (1) Pretreatment: The lithium iron phosphate waste is crushed to a particle size of 1 mm, mixed with a composite bacterial solution at a solid-liquid ratio of 1:3, 0.1 g of ammonium sulfate is added per liter of the composite bacterial solution, and leached at 30°C and pH 1.5 for 2 days. Oxygen is introduced during the reaction, and the oxygen flow rate is 0.1 L / min·L composite bacterial solution; a mixture is obtained; the composite bacterial solution comprises a suspension of Thiobacillus ferrooxidans, a suspension of Bacillus acidophilus, and a suspension of Aspergillus niger, and the volume ratio of the three suspensions is 1:0.5:0.3; the concentration of the suspension of Thiobacillus ferrooxidans is 10 6 CFU / mL, the concentration of the acidophilic Bacillus suspension was 5×10 5 CFU / mL, the concentration of Aspergillus niger suspension is 1×10 5 CFU / mL;

[0052] (2) Acid leaching: add 2% dilute sulfuric acid to the mixture at a weight volume ratio of 1:8, introduce oxygen, react at 50°C for 1 hour, filter, and obtain an acid leaching solution and iron-containing filter residue;

[0053] (3) Impurity removal treatment: adding a composite impurity remover consisting of polyacrylamide, sodium silicate and lignin sulfonate at 0.5% of the mass of the acid leaching solution, stirring at a speed of 300 rpm for 30 minutes, and then filtering to obtain a purified solution; the mass ratio of the polyacrylamide, sodium silicate and lignin sulfonate is 1:1:0.3;

[0054] Sodium silicate is also modified by a modifying liquid. The specific modification method is:

[0055] S1: The bentonite was first heat treated at 155°C for 1 hour, then at 235°C for 30 minutes, and then air-cooled to room temperature;

[0056] S2: 4 parts of the product of S1, 5.5 parts of a 5% by mass chitosan solution, 2.5 parts of carbon nanotubes and 2 parts of alumina are mixed and stirred to obtain a modified solution;

[0057] S3: stirring the sodium silicate and the modified liquid at a weight ratio of 3:7, at a stirring speed of 370 r / min, for 1 h. After the stirring is completed, filtering and drying are performed to obtain modified sodium silicate;

[0058] (4) Lithium precipitation: Heat the purified liquid to 60 °C, slowly add sodium carbonate at a rate of 2 g / min until the pH reaches 10, cool down in three stages. The first stage is from 60 °C to 50 °C, the second stage is from 50 °C to 40 °C, and the third stage is from 40 °C to 25 °C. The cooling time for each stage is 30 min, and then centrifuge to obtain lithium carbonate;

[0059] (5) Iron recovery: Wash the iron-containing filter residue with oxalic acid solution with a concentration of 0.5 mol / L twice, dry it at 80 °C for 2 h, and then obtain iron phosphate.

[0060] Example 3

[0061] This example provides a method for recovering iron phosphate and lithium carbonate from lithium iron phosphate waste, which includes the following steps:

[0062] (1) Pretreatment: Crush the lithium iron phosphate waste to a particle size of 0.1 mm, mix it with the composite bacterial solution at a solid-liquid ratio of 1:5, add 0.5 g of ammonium sulfate per liter of the composite bacterial solution, and leach at 45 °C and pH 2.5 for 3 days. Oxygen is introduced during the reaction, and the oxygen flow rate is 0.3 L / min·L of the composite bacterial solution; obtain a mixture; the composite bacterial solution contains a suspension of Acidithiobacillus ferrooxidans, a suspension of Acidiphilium acidophilum, and a suspension of Aspergillus niger, and the volume ratio of the three bacterial suspensions is 3:2:1; the concentration of the suspension of Acidithiobacillus ferrooxidans is 10 7 CFU / mL, the concentration of the suspension of Acidiphilium acidophilum is 2×10 6 CFU / mL, and the concentration of the suspension of Aspergillus niger is 5×10 5 CFU / mL;

[0063] (2) Acid leaching: Add dilute sulfuric acid with a concentration of 4% to the mixture at a weight-volume ratio of the mixture to dilute sulfuric acid of 1:12, introduce oxygen and react at 70 °C for 2 hours, then filter to obtain an acid leaching solution and an iron-containing filter residue;

[0064] (3) Impurity removal treatment: Add a composite impurity removal agent composed of polyacrylamide, sodium silicate, and lignosulfonate to the acid leaching solution at 1.5% of the mass of the acid leaching solution, stir and react at a speed of 500 rpm for 60 minutes, and then filter to obtain a purified liquid; the mass ratio of polyacrylamide, sodium silicate, and lignosulfonate is 1:3:1;

[0065] Sodium silicate also undergoes modification treatment with a modification solution. The specific modification method is:

[0066] S1: Heat the bentonite at 155 °C for 1 h first, and then treat it at 235 °C for 30 min. After the treatment, air-cool it to room temperature;

[0067] S2: 4 parts of the product of S1, 5.5 parts of a 5% by mass chitosan solution, 2.5 parts of carbon nanotubes and 2 parts of alumina are mixed and stirred to obtain a modified solution;

[0068] S3: stirring the sodium silicate and the modified liquid at a weight ratio of 3:7, at a stirring speed of 370 r / min, for 1 h. After the stirring is completed, filtering and drying are performed to obtain modified sodium silicate;

[0069] (4) Lithium precipitation: Heat the purified solution to 60°C, slowly add sodium carbonate at a rate of 5 g / min to pH 11, cool it in three stages, the first stage from 60°C to 50°C, the second stage from 50°C to 40°C, and the third stage from 40°C to 25°C. The cooling time for each stage is 30 min. Centrifuge to obtain lithium carbonate.

[0070] (5) Iron recovery: The iron-containing filter residue was washed three times with an oxalic acid solution with a concentration of 0.5 mol / L and dried at 100 °C for 4 h to obtain iron phosphate.

[0071] Comparative Example 1

[0072] The difference between this comparative example and Example 1 is that the crushed lithium iron phosphate waste is directly subjected to acid leaching treatment, and the weight volume ratio of the lithium iron phosphate waste to the dilute sulfuric acid is 1:12.

[0073] Comparative Example 2

[0074] The difference between this comparative example and Example 1 is that the impurity removal treatment in step (3) is not included, and the acid leaching solution is directly used for lithium precipitation.

[0075] Comparative Example 3

[0076] The difference between this comparative example and Example 1 is that in step (4), the purified liquid is heated to 60° C. and then the temperature is lowered to 25° C. within 30 min.

[0077] Comparative Example 4

[0078] The difference between this comparative example and Example 1 is that step (5) is not included, and the obtained iron-containing filter residue is directly washed with water and then dried.

[0079] Comparative Example 5

[0080] The difference between this comparative example and Example 1 is that only Thiobacillus ferrooxidans is used for leaching treatment, that is, the operation of step (1) is: the lithium iron phosphate waste is crushed to a particle size of 0.5 mm, mixed with a Thiobacillus ferrooxidans bacterial suspension at a solid-liquid ratio of 1:4, 0.3 g of ammonium sulfate is added per liter of bacterial suspension, and leaching is carried out at 40° C. and pH 2.0 for 2.5 days. Oxygen is introduced during the reaction at an oxygen flow rate of 0.2 L / min·L composite bacterial liquid to obtain a mixed material; the concentration of the Thiobacillus ferrooxidans bacterial suspension is 106 CFU / mL.

[0081] Comparative Example 6

[0082] The difference between this comparative example and Example 1 is that only Thiobacillus ferrooxidans and Bacillus acidophilus are used for leaching treatment, that is, the operation in step (1) is: crushing the lithium iron phosphate waste to a particle size of 0.5 mm, mixing it with the composite bacterial solution at a solid-liquid ratio of 1:4, adding 0.3 g of ammonium sulfate per liter of the composite bacterial solution, leaching for 2.5 days at 40 °C and pH 2.0, introducing oxygen during the reaction, with an oxygen flow rate of 0.2 L / min·L of the composite bacterial solution to obtain a mixture; the composite bacterial solution contains a Thiobacillus ferrooxidans bacterial suspension and a Bacillus acidophilus bacterial suspension, and the volume ratio of the two bacterial suspensions is 2:1; the concentration of the Thiobacillus ferrooxidans bacterial suspension is 10 6 CFU / mL, and the concentration of the Bacillus acidophilus bacterial suspension is 5×10 5 CFU / mL.

[0083] Comparative Example 7

[0084] The difference between this comparative example and Example 1 is that only Thiobacillus ferrooxidans and Aspergillus niger are used for leaching treatment, that is, the operation in step (1) is: crushing the lithium iron phosphate waste to a particle size of 0.5 mm, mixing it with the composite bacterial solution at a solid-liquid ratio of 1:4, adding 0.3 g of ammonium sulfate per liter of the composite bacterial solution, leaching for 2.5 days at 40 °C and pH 2.0, introducing oxygen during the reaction, with an oxygen flow rate of 0.2 L / min·L of the composite bacterial solution to obtain a mixture; the composite bacterial solution contains a Thiobacillus ferrooxidans bacterial suspension and an Aspergillus niger bacterial suspension, and the volume ratio of the two bacterial suspensions is 2:1:0.5; the concentration of the Thiobacillus ferrooxidans bacterial suspension is 10 6 CFU / mL, and the concentration of the Aspergillus niger bacterial suspension is 1×10 5 CFU / mL.

[0085] The present invention measured the purity of lithium carbonate, the Li leaching rate, the purity of iron phosphate, and the Na⁺ residue prepared in Examples 1-3 and Comparative Examples 1-6. The results are shown in Table 1:

[0086] Table 1 Test results of the purity of lithium carbonate, the Li leaching rate, the purity of iron phosphate, and the Na⁺ residue in lithium carbonate:

[0087]

[0088] From the above performance test results, it can be seen that the lithium leaching rates (98.7% - 93.1%), lithium carbonate purities (99.4% - 99.7%), and iron phosphate purities (98.5% - 98.9%) of Examples 1 - 3 are all significantly better than those of Comparative Examples 1 - 7, and the Na⁺ residue amounts (0.012% - 0.019%) are all lower than those of Comparative Examples 1 - 7. The comprehensive performance of Example 3 is the most prominent. This is mainly because the present invention adopts a four - step collaborative process of composite strain pretreatment - low - acid leaching - composite impurity removal agent impurity removal - gradient crystallization - oxalic acid washing activation, which can effectively promote the leaching rate of lithium ions in lithium iron phosphate waste, shorten the time of microbial leaching, reduce sodium ion residue, and improve the purities of lithium carbonate and iron phosphate.

[0089] In Comparative Example 1, the pretreatment step was changed (without pretreatment with composite bacterial solution). It can be seen that the lithium leaching rate decreased from 98.7% to 76.4%, and the purities of lithium carbonate and iron phosphate and the effect of sodium ion residue are all inferior to those of Example 1, proving that using composite strains to treat waste during pretreatment has an important impact on improving the lithium leaching rate and purity and reducing sodium ion residue.

[0090] In Comparative Example 2, the composite impurity removal agent was not used. It can be seen that the lithium carbonate purity decreased from 99.6% to 95.8% and the sodium ion residue increased from 0.017% to 0.042%, proving that the composite impurity removal agent has an important impact on removing impurities such as 3+ Al and inhibiting sodium ion entrainment. The reason is that the adsorption effect of polyacrylamide, the complexation effect of sodium silicate, and the dispersion synergy of lignosulfonate in Example 1 can selectively remove impurity ions.

[0091] In Comparative Example 3, the cooling step was changed (single - stage cooling). It can be seen that the purity of lithium carbonate decreased from 99.6% to 92.3% and the sodium ion residue increased from 0.017% to 0.04%, proving that the segmented temperature control scheme plays a key role in the directional growth of crystals and reducing impurity entrainment.

[0092] In Comparative Example 4, oxalic acid activation was not used. It can be seen that the purity of iron phosphate decreased from 98.7% to 93.4%, proving that the oxalic acid activation scheme has an important impact on removing sulfate residue and improving the purity of iron phosphate.

[0093] In Comparative Example 5, only Thiobacillus ferrooxidans was used. It can be seen that the lithium leaching rate decreased from 98.7% to 80.0%, proving that the technology using Thiobacillus ferrooxidans treatment has a limited effect on improving the lithium leaching rate and it cannot leach out most of the lithium ions in lithium iron phosphate waste.

[0094] In Comparative Example 6, Aspergillus niger was not used. It can be seen that the lithium leaching rate dropped from 98.7% to 83.7%, proving that the technology of using Thiobacillus ferrooxidans and Bacillus acidophilus for treatment cannot effectively increase the lithium leaching rate to more than 92%, and cannot leach most of the lithium ions in the lithium iron phosphate waste.

[0095] In Comparative Example 7, Bacillus acidophilus was not used. It can be seen that the lithium leaching rate dropped from 98.7% to 83.9%, proving that the technology using Thiobacillus ferrooxidans and Aspergillus niger cannot effectively make the lithium leaching rate reach more than 92%, and most of the lithium ions in the lithium iron phosphate waste cannot be leached. Only under the synergistic effect of Thiobacillus ferrooxidans, Aspergillus niger and Bacillus acidophilus can the lithium leaching rate be effectively improved to more than 92%, and the leaching time can be controlled to 2-3 days, shortening the leaching time.

[0096] Based on the above performance tests, the present invention further explores the modification of sodium silicate:

[0097] Sodium silicate is also modified by a modifying liquid. The specific modification method is:

[0098] S1: The bentonite was first heat treated at 155°C for 1 hour, then at 235°C for 30 minutes, and then air-cooled to room temperature;

[0099] S2: 4 parts of the product of S1, 5.5 parts of a 5% by mass chitosan solution, 2.5 parts of carbon nanotubes and 2 parts of alumina are mixed and stirred to obtain a modified solution;

[0100] S3: Sodium silicate and modified liquid are stirred at a weight ratio of 3:7 at a stirring speed of 370 r / min for 1 hour. After the stirring is completed, the mixture is filtered and dried to obtain modified sodium silicate.

[0101] Optimization Example 1

[0102] The difference between this comparative example and Example 1 is that the S1 product is not added to the modified liquid.

[0103] Optimization Example 2

[0104] The difference between this comparative example and Example 1 is that no aluminum oxide and carbon nanotubes are added to the modified liquid.

[0105] Optimization Example 3

[0106] The difference between this comparative example and Example 1 is that the chitosan solution is replaced by water.

[0107] Table 2 shows the effect of sodium silicate modification methods on product performance test:

[0108]

[0109] It can be seen from Optimization Examples 1-3 that when the S1 product is not added to the modification solution, alumina, carbon nanotubes are not added, and the chitosan solution is replaced with water, the Li leaching rate of the product shows a trend of varying degrees of deterioration. At the same time, the purity of lithium carbonate, the purity of iron phosphate, and the Na⁺ residue also show a deteriorating trend compared to Example 1. Only when the sodium silicate modified by the modification solution obtained by the specific method of the present invention is used, the performance effect of the product is the most significant.

[0110] The above are the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for recovering iron phosphate and lithium carbonate from lithium iron phosphate waste, characterized in that, The following steps are involved: (1) Pretreatment: crush the lithium iron phosphate waste, mix it with the composite bacterial solution at a solid-liquid ratio of 1: (3-5), and leach it at 30-45°C and pH 1.5-2.5 for 2-3 days to obtain a mixture; the composite bacterial solution contains a suspension of Thiobacillus ferrooxidans, a suspension of Bacillus acidophilus and a suspension of Aspergillus niger, and the volume ratio of the three suspensions is (1-3): (0.5-2): (0.3-1); (2) Acid leaching: add dilute sulfuric acid to the mixture, introduce oxygen, react for 1-2 hours, and then filter to obtain an acid leaching solution and iron-containing filter residue; (3) Impurity removal treatment: add a composite impurity remover composed of polyacrylamide, sodium silicate and lignin sulfonate to the acid leaching solution, stir the reaction, and then filter to obtain a purified solution; (4) Lithium precipitation: heat the purified solution to 60°C, slowly add sodium carbonate to a pH of 10-11, cooling in three stages, the first stage from 60°C to 50°C, the second stage from 50°C to 40°C, and the third stage from 40°C to 25°C, and centrifugation to obtain lithium carbonate; (5) Iron recovery: washing the iron-containing filter residue with oxalic acid solution, and drying to obtain iron phosphate.

2. The method for recovering ferric phosphate and lithium carbonate from lithium iron phosphate waste according to claim 1, characterized in that, The concentration of the Thiobacillus ferrooxidans bacterial suspension is 10 6 -10 7 CFU / mL, the concentration of the Bacillus acidophilus bacterial suspension is 5×10 5 -2×10 6 CFU / mL, and the concentration of the Aspergillus niger bacterial suspension is 1×10 5 -5×10 5 CFU / mL.

3. The method for recovering ferric phosphate and lithium carbonate from lithium iron phosphate waste according to claim 2, characterized in that, In the pretreatment, the solid-liquid ratio of the crushed lithium iron phosphate waste and the composite bacterial solution is 1:4, and the volume ratio of the Thiobacillus ferrooxidans suspension, the Bacillus acidophilus suspension and the Aspergillus niger suspension is 2:1:0.

5.

4. A method for recovering ferric phosphate and lithium carbonate from lithium iron phosphate waste according to claim 1, characterized in that, In the step (1), 0.1-0.5 g of ammonium sulfate is added per liter of the composite bacterial liquid, and oxygen is introduced during the reaction, with an oxygen flow rate of 0.1-0.3 L / min·L composite bacterial liquid.

5. A method for recovering ferric phosphate and lithium carbonate from lithium iron phosphate waste according to claim 1, characterized in that, In step (2), the weight volume ratio of the mixture to the dilute sulfuric acid is 1:(8-12), the concentration of the dilute sulfuric acid is 2-4%, and the reaction temperature during acid leaching is 50-70°C.

6. A method for recovering iron phosphate and lithium carbonate from lithium iron phosphate waste according to claim 1, characterized in that, The mass ratio of the polyacrylamide, sodium silicate and lignin sulfonate is 1:(1-3):(0.3-1), and the addition amount of the composite impurity remover is 0.5%-1.5% of the mass of the acid leaching solution; Sodium silicate is also modified by a modifying liquid. The specific modification method is: S1: The bentonite is first heat treated at 150-160°C for 1 hour, then treated at 230-240°C for 30 minutes, and then air-cooled to room temperature after the treatment; S2: 3-5 parts of the product of S1, 4-7 parts of a 5% by mass chitosan solution, 2-3 parts of carbon nanotubes and 1-3 parts of alumina are mixed and stirred to obtain a modified solution; S3: Sodium silicate and modified liquid are stirred at a weight ratio of 3:7, with a stirring speed of 350-400 r / min for 1 hour. After the stirring is completed, the mixture is filtered and dried to obtain modified sodium silicate.

7. A method for recovering iron phosphate and lithium carbonate from lithium iron phosphate waste according to claim 1, characterized in that, The stirring reaction time in step (3) is 30-60 minutes, and the stirring speed is 300-500 rpm.

8. A method for recovering iron phosphate and lithium carbonate from lithium iron phosphate waste according to claim 1, characterized in that, In step (4), the rate of adding sodium carbonate is 2-5 g / min, and the cooling time of each stage is 30 min when the temperature is cooled in three stages.

9. A method for recovering iron phosphate and lithium carbonate from lithium iron phosphate waste according to claim 1, characterized in that, In the step (5), the iron-containing filter residue is washed 2-3 times, and the concentration of the oxalic acid solution is 0.5 mol / L.

10. A method for recovering iron phosphate and lithium carbonate from lithium iron phosphate waste according to claim 1, characterized in that, The drying temperature in step (5) is 80-100°C and the drying time is 2-4h.

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