A method for wet recycling of retired lithium iron phosphate battery powder to extract lithium and prepare lithium carbonate

Abstract

The present invention provides a method for preparing lithium carbonate by extracting lithium from retired lithium iron phosphate battery powder by wet recovery, comprising the following steps: step one, adding retired LiFePO4 and an oxidant to a container, adding water, and forming a mixed solution; step two, heating the temperature of the mixed solution to 40-80°C, adding acid solution for acid leaching and dissolving, stopping heating after insulation reaction, filtering to obtain lithium-containing filtrate and iron phosphate filter residue; step three, adding calcium salt or magnesium salt at 50-70°C of lithium-containing filtrate, adding alkali solution to adjust pH to neutral, filtering and removing impurities, and obtaining a first filtrate; step four, at room temperature, adding alkali solution dropwise to the first filtrate, adjusting the pH of the liquid to 11-13, filtering and removing impurities, and obtaining a second filtrate; step five, adding carbonate to the second filtrate, filtering after stirring, and obtaining lithium carbonate after the filter residue is dried. The method of the present invention can effectively improve the recovery rate of lithium, reduce the loss of iron and phosphorus elements, and the purity of the product lithium carbonate is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste lithium battery resource recovery, and specifically relates to a method for wet-process recovery of retired lithium iron phosphate battery powder to extract lithium and prepare lithium carbonate. Background Art

[0002] To prevent the depletion of traditional chemical energy, new energy is being continuously developed and utilized. Under this trend, traditional fuel vehicles will gradually be replaced by new energy vehicles, and the power batteries of new energy vehicles are mostly lithium-ion batteries. As a type of lithium-ion battery, the production volume of lithium iron phosphate batteries will increase significantly. In order to achieve the recycling of resources, the recycling of retired lithium iron phosphate batteries will become a top priority after the battery is used up.

[0003] At present, the wet recovery of retired lithium iron phosphate battery powder is mainly to dissolve the metal ions including lithium ions in the retired lithium iron phosphate battery powder with acid solution, and then extract the lithium ions in the form of lithium salt through impurity removal, precipitation, washing, drying and other processes. The goal of wet recovery is to extract the Li element in the retired lithium iron phosphate battery positive electrode material into lithium salt, and re-prepare the Fe and P elements into the precursor FePO4 of the positive electrode material to achieve the recovery of Li, Fe and P. Therefore, in the process of dissolving retired lithium iron phosphate battery powder, the leaching rate of the three elements Li, Fe and P is the main indicator for evaluating the recovery effect. We hope that the leaching rate of Li is as high as possible during dissolution, and most of the Fe and P elements can be retained in solid form. The key to dissolution is the ratio between the dissolution process and the raw materials. Under different lithium leaching conditions, the leaching rates of the three elements are different, so it is important to choose the appropriate lithium leaching conditions; at the same time, the purity of lithium carbonate is expected to be as high as possible to ensure stable performance.

[0004] The method for recycling retired lithium iron phosphate batteries disclosed in patent document CN110752415A is to add lithium source, iron source and phosphorus source to the treated lithium iron phosphate roasted material for ball milling, drying, reduction regeneration and air flow crushing to obtain lithium iron phosphate powder, and finally screen and remove iron to obtain lithium iron phosphate products. However, the disadvantage of this recycling method is that the obtained lithium iron phosphate products have high impurity content and unstable properties.

[0005] The method for recycling retired lithium iron phosphate batteries disclosed in patent document CN113912036A is to acid-leach the treated battery powder, add surfactants and antioxidants, then add lithium source, phosphorus source and iron source for reaction, and then wash, dry, sinter and crush to obtain lithium iron phosphate. However, the defect of the recycling method in the prior art is that it does not go through the impurity removal process, and the obtained lithium iron phosphate product has a high impurity content and unstable properties.

[0006] Therefore, it is necessary to provide an improved technical solution to address the above-mentioned deficiencies in the prior art. Summary of the invention

[0007] The purpose of the present invention is to provide a method for wet recycling of retired lithium iron phosphate battery powder to extract lithium and prepare lithium carbonate, so as to solve the problem faced by the current recycling of lithium iron phosphate battery powder that the extraction of lithium causes the simultaneous leaching of Fe and P, resulting in resource loss and high impurity content in the prepared lithium carbonate.

[0008] In order to achieve the above object, the present invention provides the following technical solutions:

[0009] A method for preparing lithium carbonate by wet recycling of retired lithium iron phosphate battery powder, characterized in that the method comprises the following steps:

[0010] Step 1: Add the recycled retired lithium iron phosphate battery powder LiFePO4 and an oxidant into a container, and then add water into the container to form a mixed solution;

[0011] Step 2, heating the container to make the temperature of the mixed solution reach 40-80° C., pouring acid solution into the container for acid leaching and dissolving, keeping the temperature for 2-4 hours and then stopping heating, filtering to obtain lithium-containing filtrate and iron phosphate residue;

[0012] Step 3, adding calcium salt or magnesium salt to the lithium-containing filtrate at 50-70° C., stirring evenly, adding alkali solution to adjust the pH to neutral, and then filtering to remove impurities to obtain a first filtrate;

[0013] Step 4, at room temperature, adding alkali solution dropwise to the first filtrate to adjust the pH of the liquid to 11-13, then stopping the dropwise addition, filtering and removing impurities to obtain a second filtrate;

[0014] Step 5, adding carbonate to the second filtrate, stirring and filtering, and drying the filter residue to obtain lithium carbonate.

[0015] In the method for wet recovery of retired lithium iron phosphate battery powder to extract lithium and prepare lithium carbonate as described above, preferably, in step one, the sum of the lithium iron phosphate battery powder and the oxidant and the water satisfy a solid-liquid mass ratio of 1:(2-4).

[0016] In the method for preparing lithium carbonate by extracting lithium from retired lithium iron phosphate battery powder by wet method as described above, preferably, in step 2, the acid solution is one or a mixture of HCl solution and H2SO4 solution;

[0017] The concentration of the HCl solution is 10-15 mol / L;

[0018] The concentration of the H2SO4 solution is 15-20 mol / L.

[0019] In the method for preparing lithium carbonate by extracting lithium from retired lithium iron phosphate battery powder by wet method as described above, preferably, when the acid solution is HCl solution, the molar ratio of LiFePO4 to HCl is 1:(1-2);

[0020] When the acid solution is a H2SO4 solution, the molar ratio of LiFePO4 to H2SO4 is (1-2):1;

[0021] When the acid solution is a mixed acid formed by mixing an HCl solution and an H2SO4 solution, the molar ratio of HCl to H2SO4 in the mixed acid is 3:2; and the molar ratio of LiFePO4 to the mixed acid is 1:(1.2-1.5).

[0022] In the method for wet recovery of retired lithium iron phosphate battery powder to extract lithium and prepare lithium carbonate as described above, preferably, in step five, after adding carbonate to the second filtrate, the second filtrate is also heated to 80-95°C, and then stirred and filtered.

[0023] In the method for wet recovery of retired lithium iron phosphate battery powder to extract lithium to prepare lithium carbonate as described above, preferably, in step five, constant temperature filtration is adopted during the filtration process, and the constant temperature is 80-95°C.

[0024] In the method for wet recovery of retired lithium iron phosphate battery powder to prepare lithium carbonate, preferably, in step three, the amount of calcium salt and magnesium salt added is 2-5% more than the theoretical calculated amount, and the theoretical calculated amount is the mass of calcium salt and magnesium salt required for complete precipitation of phosphate ions in the lithium-containing filtrate.

[0025] In the method for preparing lithium carbonate by extracting lithium from retired lithium iron phosphate battery powder by wet method as described above, preferably, the oxidant is one or a mixture of H2O2 and NaClO3;

[0026] When the oxidant is H2O2, the molar ratio of LiFePO4 to H2O2 is (3-5):2;

[0027] When the oxidant is NaClO3, the molar ratio of LiFePO4 to NaClO3 is (5-7):1;

[0028] When the oxidant is a mixed oxidant formed by mixing H2O2 and NaClO3, the molar ratio of NaClO3 to H2O2 in the mixed oxidant is 2:3, and the molar ratio of LiFePO4 to the mixed oxidant is (5-6):1.

[0029] In the method for wet recovery of retired lithium iron phosphate battery powder to extract lithium to prepare lithium carbonate as described above, preferably, the alkali solution is one or more of sodium hydroxide, potassium hydroxide, ammonia water, calcium hydroxide, calcium oxide, potassium oxide and sodium oxide.

[0030] In the method for wet recovery of retired lithium iron phosphate battery powder to extract lithium to prepare lithium carbonate as described above, preferably, in step three and step four, the pH is adjusted and then reacted for 0.5-1h before filtering.

[0031] Beneficial effects:

[0032] The method for preparing lithium carbonate by extracting lithium from retired lithium iron phosphate battery powder by wet method of the present invention can effectively improve the recovery rate of lithium and reduce the loss of Fe and P elements; on the one hand, by specifically controlling the dissolution conditions: the amount of acid solution and oxidant, the reaction temperature, the reaction time and the solid-liquid ratio, the leaching rate of Li element during acid leaching is improved and the leaching rates of Fe and P elements are reduced; by quantitatively controlling the pH of the leachate, the generation of hydroxide colloid is reduced, the efficiency of leachate filtration is improved, and the loss of lithium ions caused by being adsorbed on the colloid and filtered out is reduced; on the other hand, by removing impurities from the filtrate obtained after filtration, the content of impurity elements in the filtrate is reduced, and the purity of the product lithium carbonate is improved; by controlling the ambient temperature during lithium precipitation, the precipitation rate of lithium salt is improved, thereby improving the recovery rate of retired lithium iron phosphate battery powder as a whole. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0034] The present invention will be described in detail below in conjunction with embodiments. It should be noted that the embodiments and features in the embodiments of the present invention can be combined with each other without conflict.

[0035] The present invention provides a method for wet-process recycling of retired lithium iron phosphate battery powder to extract lithium and prepare lithium carbonate, the method comprising the following steps:

[0036] Step 1: Add the recycled retired lithium iron phosphate battery powder LiFePO4 and an oxidant into a container, and then add water into the container to form a mixed solution;

[0037] In a specific embodiment of the present invention, the sum of the lithium iron phosphate battery powder and the oxidant and water satisfy a solid-liquid mass ratio of 1:(2-4) (such as 1:2, 1:2.5, 1:3, 1:3.5).

[0038] In a specific embodiment of the present invention, the oxidant is one or a mixture of H2O2 and NaClO3;

[0039] When the oxidant is H2O2, the molar ratio of LiFePO4 to H2O2 is (3-5):2 (e.g. 3:2, 3.5:2, 4:2, 4.5:2);

[0040] When the oxidant is NaClO3, the molar ratio of LiFePO4 to NaClO3 is (5-7):1 (e.g., 5:1, 5.5:1, 6:1, 6.5:1).

[0041] When the oxidant is a mixed oxidant formed by mixing H2O2 and NaClO3, the molar ratio of NaClO3 to H2O2 in the mixed oxidant is 2:3, and the molar ratio of LiFePO4 to the mixed oxidant is (5-6):1 (such as 5.2:1, 5.4:1, 5.5:1, 5.8:1). During the use of retired lithium iron phosphate battery powder, part of the trivalent iron will be reduced to divalent iron. The use of oxidants can oxidize the divalent iron to trivalent iron. If the oxidant content is too low, the divalent iron cannot be fully oxidized. If the content is too high, it will cause a waste of oxidant. Therefore, the use of oxidants needs to be controlled within a certain range.

[0042] Step 2, heating the container to make the temperature of the mixed solution reach 40-80°C (such as 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C), pouring acid solution into the container for acid leaching and dissolution, controlling the pH at 1-2, and stopping heating after the insulation reaction for 2-4h (such as 2.5h, 3h, 3.5h), filtering to obtain a lithium-containing filtrate and an iron phosphate filter residue;

[0043] In a specific embodiment of the present invention, in step 2, the acid solution is one or a mixture of HCl solution and H2SO4 solution;

[0044] The concentration of HCl solution is 10-15mol / L (such as 11mol / L, 12mol / L, 13mol / L, 14mol / L); the concentration of H2SO4 solution is 15-20mol / L (such as 16mol / L, 17mol / L, 18mol / L, 19mol / L, 20mol / L).

[0045] In a specific embodiment of the present invention, when the acid solution is HCl solution, the molar ratio of LiFePO4 to HCl is 1:(1-2) (e.g., 1:1.5, 1:1.8); when the acid solution is H2SO4 solution, the molar ratio of LiFePO4 to H2SO4 is (1-2):1 (e.g., 1.5:1, 1.8:1). When the acid solution is a mixed acid formed by mixing HCl solution and H2SO4 solution, the molar ratio of HCl to H2SO4 in the mixed acid is 3:2; the molar ratio of LiFePO4 to the mixed acid is 1:(1.2-1.5) (e.g., 1:1.3, 1:1.4, 1:1.5).

[0046] The molar ratio of acid to lithium iron phosphate enables retired lithium iron phosphate battery powder to react completely in the acid, thereby increasing the lithium leaching rate while avoiding excessive leaching of iron and phosphorus elements.

[0047] Step three, adding calcium salt or magnesium salt to the lithium-containing filtrate at 50-70°C, stirring evenly, adding alkali solution to adjust the pH to neutral, reacting for 0.5-1h (such as 0.6h, 0.7h, 0.8h, 0.9h), and then filtering and removing impurities to obtain a first filtrate; adding calcium salt and magnesium salt at 50-70°C to the lithium-containing filtrate is conducive to the impurity removal reaction, and calcium phosphate or magnesium phosphate can be quickly formed under neutral conditions after adding alkali solution.

[0048] In a specific embodiment of the present invention, in step 3, the amount of calcium salt and magnesium salt added is 2-5% more than the theoretically calculated amount, and the theoretically calculated amount is the mass of calcium salt and magnesium salt required for complete precipitation of phosphate ions in the lithium-containing filtrate, ensuring that the amount of calcium salt and magnesium salt added meets the amount required for precipitation of all phosphate ions, and at the same time, the amount of calcium salt and magnesium salt added is not too much, causing inconvenience in subsequent impurity removal.

[0049] When performing theoretical calculations on the phosphate ions in the lithium-containing filtrate in the present invention, the theoretical value of the phosphate dissolved in the lithium-containing filtrate can be calculated by calculating the amount of iron phosphate in the filter residue in step 2, or the phosphorus content in the lithium-containing filtrate can be directly measured by ICP to understand the phosphate ion content, and then calculate the required calcium salt and magnesium salt content.

[0050] During acid leaching, a small amount of phosphorus and iron will be leached out in the form of phosphate and iron ions and dissolved in the lithium-containing filtrate, so a removal process is required to ensure that the phosphorus and iron leached out in the lithium-containing filtrate are precipitated and filtered out in the form of calcium phosphate or magnesium phosphate. The iron ions are subsequently added to form an alkaline environment and are precipitated and filtered out in the form of iron hydroxide.

[0051] Step 4, at room temperature, add alkali solution dropwise to the first filtrate, adjust the pH of the liquid to 11-13, then stop adding, react for 0.5-1h (such as 0.6h, 0.7h, 0.8h, 0.9h), and then filter and remove impurities to obtain a second filtrate; adding alkali solution dropwise in this step can accurately control the pH of the liquid and prevent waste caused by excessive addition of alkali solution.

[0052] In a specific embodiment of the present invention, the alkali solution is one or more of sodium hydroxide, potassium hydroxide, ammonia water, calcium hydroxide, calcium oxide, potassium oxide and sodium oxide.

[0053] In a specific embodiment of the present invention, the secondary impurity removal is mainly to remove the excess calcium ions and magnesium ions added in step 3 and the trace aluminum ions contained in the retired battery powder itself, and to precipitate them in the form of hydroxide by adjusting the pH. After adjusting the pH, the reaction is allowed to proceed for 0.5-1h to completely precipitate the ions.

[0054] After two impurity removals, the types and contents of ions in the lithium-containing filtrate are reduced to a minimum, greatly improving the purity of the final product, lithium carbonate.

[0055] Step 5, adding carbonate to the second filtrate, stirring and filtering, and drying the filter residue to obtain lithium carbonate.

[0056] In a specific embodiment of the present invention, after adding carbonate to the second filtrate, the second filtrate is heated to 80-95°C (e.g., 82°C, 85°C, 88°C, 90°C, 92°C, 95°C), and then stirred and filtered. Constant temperature filtration is used during the filtration process, and the constant temperature is 80-95°C (e.g., 82°C, 85°C, 88°C, 90°C, 92°C, 95°C).

[0057] The amount of carbonate added is a theoretical calculated value, which is the amount that can completely precipitate lithium ions in the form of lithium carbonate, that is, all the lithium elements in retired lithium iron phosphate battery powder.

[0058] In the present invention, after adding carbonate, the second filtrate is heated to 80-95°C, and constant temperature filtration is adopted during filtration. At this temperature, the solubility of lithium carbonate can be minimized (the solubility of lithium carbonate decreases with increasing temperature, and the higher the temperature, the more conducive to precipitation), and at this temperature, the maximum precipitation of lithium carbonate can be achieved in the liquid state, thereby maximizing the leaching rate and utilization rate of lithium element.

[0059] The leaching rates of lithium, iron and phosphorus in the following embodiments of the present invention are calculated based on the total amount of Li, Fe and P in the retired lithium iron phosphate battery powder LiFePO4 added in the experiment, which is 100%. The lithium, phosphorus and iron contents in the filtrate are calculated by performing ICP test on the lithium-containing filtrate in step 2, and the dissolution rates of Li, Fe and P in the wet process for recovering lithium from retired lithium iron phosphate battery powder are obtained.

[0060] Example 1

[0061] This embodiment provides a method for wet recycling of retired lithium iron phosphate battery powder to extract lithium to prepare lithium carbonate, the method comprising the following steps:

[0062] a. Weigh the recycled retired lithium iron phosphate battery powder LiFePO4 with HCl and NaClO3 in a molar ratio of 6:6:1. The concentration of the HCl solution is 12 mol / L.

[0063] b. Add the weighed LiFePO4 and NaClO3 into a container, and add water until the solid-liquid ratio is controlled at 1:2 to form a mixed liquid.

[0064] c. Heat the container, and when the temperature of the mixed solution rises to 40°C, pour the weighed HCl solution into the container for acid leaching and dissolution, and control the pH at 1. After reacting for 2 hours, stop heating and filter to obtain lithium-containing filtrate and iron phosphate-containing filter residue.

[0065] d. Add calcium chloride to the lithium-containing filtrate at 50-70°C, stir evenly, then add sodium hydroxide to adjust the pH to neutral, react for 0.5h, then filter and remove impurities to obtain the first filtrate. The amount of calcium chloride added is 2% more than the theoretical amount (molar ratio of Ca 2- :PO4 3- =3:2).

[0066] e. At room temperature, add sodium hydroxide dropwise to the first filtrate to adjust the pH of the liquid to 11-13, then stop adding, react for 0.5h, filter and remove impurities to obtain a second filtrate.

[0067] f. Add sodium carbonate to the second filtrate, heat the solution to 90°C, stir and filter at a constant temperature of 90°C, dry the residue and obtain lithium carbonate. The amount of sodium carbonate added is the theoretical calculated value (molar ratio Li + :CO3 2- =2:1).

[0068] The lithium-containing filtrate in step c of the embodiment of the present invention is subjected to an ICP test, and the ratio of the content of lithium, phosphorus and iron in the filtrate to the respective content in the retired lithium iron phosphate battery powder is calculated, that is, the dissolution rate is obtained, as shown in Table 1 below; at the same time, the recovery rate of lithium carbonate is calculated (the recovery rate of lithium carbonate is based on the lithium content in the retired lithium iron phosphate powder as 100%) and the purity of lithium carbonate is measured.

[0069] Example 2

[0070] This embodiment provides a method for wet recycling of retired lithium iron phosphate battery powder to extract lithium to prepare lithium carbonate, the method comprising the following steps:

[0071] a. Weigh the recycled retired lithium iron phosphate battery powder LiFePO4 with H2SO4 and H2O2 in a molar ratio of 2:1:1. The concentration of the H2SO4 solution is 18 mol / L.

[0072] b. Add the weighed LiFePO4 and H2O2 into a container, and add water until the solid-liquid ratio is controlled at 2:5 to form a mixed liquid.

[0073] c. Heat the container until the temperature of the mixed solution rises to 45°C, then pour weighed H2SO4 into the container for acid leaching and dissolution, and control the pH at 1.5. After reacting for 2.5 hours, stop heating and filter to obtain lithium-containing filtrate and iron phosphate-containing filter residue.

[0074] d. Add magnesium chloride to the lithium-containing filtrate at 50-70°C, stir evenly, add potassium hydroxide to adjust the pH to neutral, react for 2 hours, and then filter to remove impurities to obtain the first filtrate. The amount of magnesium chloride added is 3% more than the theoretical amount (molar ratio Mg 2- :PO4 3- =3:2).

[0075] e. At room temperature, add potassium hydroxide dropwise to the first filtrate to adjust the pH of the liquid to 11-13, then stop adding, react for 2 hours, filter and remove impurities to obtain a second filtrate.

[0076] f. Add sodium carbonate to the second filtrate, heat the solution to 90°C, stir and filter at a constant temperature of 90°C, dry the residue and obtain lithium carbonate. The amount of potassium carbonate added is the theoretical calculated value (molar ratio Li + :CO3 2- =2:1).

[0077] The lithium-containing filtrate in step c of the embodiment of the present invention is subjected to ICP test to calculate the contents of lithium, phosphorus and iron in the filtrate, i.e., the dissolution rate, as shown in Table 1. At the same time, the yield of lithium carbonate is calculated and the purity of lithium carbonate is measured.

[0078] Example 3

[0079] This embodiment provides a method for wet recycling of retired lithium iron phosphate battery powder to extract lithium to prepare lithium carbonate, the method comprising the following steps:

[0080] a. Weigh the recycled retired lithium iron phosphate battery powder LiFePO4 with HCl and H2O2 in a molar ratio of 10:12:5. The concentration of the HCl solution is 10 mol / L.

[0081] b. Add the weighed LiFePO4 and H2O2 into a container, and add water until the solid-liquid ratio is controlled at 1:4 to form a mixed liquid.

[0082] c. Heat the container, and when the temperature of the mixed solution rises to 50°C, pour weighed HCl into the container for acid leaching and dissolution, and control the pH at 2. After reacting for 3 hours, stop heating and filter to obtain lithium-containing filtrate and iron phosphate-containing filter residue.

[0083] d. Add calcium chloride to the lithium-containing filtrate at 50-70°C, stir evenly, then add sodium hydroxide to adjust the pH to neutral, react for 1 hour, and then filter to remove impurities to obtain the first filtrate. The amount of calcium chloride added is 5% more than the theoretical amount (molar ratio of Ca 2- :PO4 3- =3:2).

[0084] e. At room temperature, add sodium hydroxide dropwise to the first filtrate to adjust the pH of the liquid to 11-13, then stop adding, react for 1 hour, filter and remove impurities to obtain a second filtrate.

[0085] f. Add sodium carbonate to the second filtrate, heat the solution to 95°C, stir and filter at a constant temperature of 95°C, dry the residue and obtain lithium carbonate. The amount of sodium carbonate added is the theoretical calculated value (molar ratio Li + :CO3 2- =2:1).

[0086] The lithium-containing filtrate in step c of the embodiment of the present invention is subjected to ICP test to calculate the contents of lithium, phosphorus and iron in the filtrate, i.e., the dissolution rate, as shown in Table 1. At the same time, the yield of lithium carbonate is calculated and the purity of lithium carbonate is measured.

[0087] Example 4

[0088] This embodiment provides a method for wet recycling of retired lithium iron phosphate battery powder to extract lithium to prepare lithium carbonate, the method comprising the following steps:

[0089] a. Weigh the recycled retired lithium iron phosphate battery powder LiFePO4, mixed acid and mixed oxidant at a molar ratio of 5:7:1, where the molar ratio of HCl to H2SO4 in the mixed acid is 3:2; the molar ratio of NaClO3 to H2O2 in the mixed oxidant is 2:3. The concentration of the HCl solution is 12 mol / L; the concentration of the H2SO4 solution is 18 mol / L.

[0090] b. Add the weighed LiFePO4 and mixed oxidant into a container, add water until the solid-liquid ratio is controlled at 1:3 to form a mixed liquid.

[0091] c. Heat the container until the temperature of the mixed solution rises to 60°C, then pour the weighed mixed acid into the container for acid leaching and dissolution, and control the pH at 1.5. After reacting for 3.5 hours, stop heating and filter to obtain lithium-containing filtrate and iron phosphate-containing filter residue.

[0092] d. Add magnesium chloride to the lithium-containing filtrate at 50-70°C, stir evenly, add potassium hydroxide to adjust the pH to neutral, react for 1 hour, and then filter to remove impurities to obtain the first filtrate. The amount of magnesium chloride added is 3% more than the theoretical amount (molar ratio Mg 2- :PO4 3- =3:2).

[0093] e. At room temperature, add potassium hydroxide dropwise to the first filtrate to adjust the pH of the liquid to 11-13, then stop adding, react for 1 hour, filter and remove impurities to obtain a second filtrate.

[0094] f. Add sodium carbonate to the second filtrate, heat the solution to 90°C, stir and filter at a constant temperature of 90°C, dry the residue and obtain lithium carbonate. The amount of potassium carbonate added is the theoretical calculated value (molar ratio Li + :CO3 2- =2:1).

[0095] The lithium-containing filtrate in step c of the embodiment of the present invention is subjected to ICP test to calculate the contents of lithium, phosphorus and iron in the filtrate, i.e., the dissolution rate, as shown in Table 1. At the same time, the yield of lithium carbonate is calculated and the purity of lithium carbonate is measured.

[0096] Example 5

[0097] This embodiment provides a method for wet recycling of retired lithium iron phosphate battery powder to extract lithium to prepare lithium carbonate, the method comprising the following steps:

[0098] a. Weigh the recycled retired lithium iron phosphate battery powder LiFePO4 with H2SO4 and H2O2 in a molar ratio of 2:2:1. The concentration of the H2SO4 solution is 20 mol / L.

[0099] b. Add the weighed LiFePO4 and H2O2 into a container, and add water until the solid-liquid ratio is controlled at 1:4 to form a mixed liquid.

[0100] c. Heat the container, and when the temperature of the mixed solution rises to 70°C, pour weighed H2SO4 into the container for acid leaching and dissolution, and control the pH at 1. After reacting for 4 hours, stop heating and filter to obtain lithium-containing filtrate and iron phosphate-containing filter residue.

[0101] d. Add calcium chloride to the lithium-containing filtrate at 50-70°C, stir evenly, then add sodium hydroxide to adjust the pH to neutral, react for 1 hour, and then filter to remove impurities to obtain the first filtrate. The amount of calcium chloride added is 5% more than the theoretical amount (molar ratio of Ca 2- :PO4 3- =3:2).

[0102] e. At room temperature, add sodium hydroxide dropwise to the first filtrate to adjust the pH of the liquid to 11-13, then stop adding, react for 1 hour, filter and remove impurities to obtain a second filtrate.

[0103] f. Add sodium carbonate to the second filtrate, heat the solution to 80°C, stir and filter at a constant temperature of 80°C, dry the residue and obtain lithium carbonate. The amount of sodium carbonate added is the theoretical calculated value (molar ratio Li + :CO3 2- =2:1).

[0104] The lithium-containing filtrate in step c of the embodiment of the present invention is subjected to ICP test to calculate the contents of lithium, phosphorus and iron in the filtrate, i.e., the dissolution rate, as shown in Table 1. At the same time, the yield of lithium carbonate is calculated and the purity of lithium carbonate is measured.

[0105] Example 6

[0106] This embodiment provides a method for wet recycling of retired lithium iron phosphate battery powder to extract lithium to prepare lithium carbonate, the method comprising the following steps:

[0107] a. Weigh the recycled retired lithium iron phosphate battery powder LiFePO4 with HCl and NaClO3 in a molar ratio of 6:12:1. The concentration of the HCl solution is 15 mol / L.

[0108] b. Add the weighed LiFePO4 and NaClO3 into a container, and add water until the solid-liquid ratio is controlled at 1:4 to form a mixed liquid.

[0109] c. Heat the container, and when the temperature of the mixed solution rises to 80°C, pour weighed HCl into the container for acid leaching and dissolution, and control the pH at 1. After reacting for 4 hours, stop heating and filter to obtain lithium-containing filtrate and iron phosphate-containing filter residue.

[0110] d. Add magnesium chloride to the lithium-containing filtrate at 50-70°C, stir evenly, add potassium hydroxide to adjust the pH to neutral, react for 1 hour, and then filter to remove impurities to obtain the first filtrate. The amount of magnesium chloride added is 3% more than the theoretical amount (molar ratio Mg 2- :PO4 3- =3:2).

[0111] e. At room temperature, add potassium hydroxide dropwise to the first filtrate to adjust the pH of the liquid to 11-13, then stop adding, react for 1 hour, filter and remove impurities to obtain a second filtrate.

[0112] f. Add sodium carbonate to the second filtrate, heat the solution to 90°C, stir and filter at a constant temperature of 90°C, dry the residue and obtain lithium carbonate. The amount of potassium carbonate added is the theoretical calculated value (molar ratio Li + :CO3 2- =2:1).

[0113] The lithium-containing filtrate in step c of the embodiment of the present invention is subjected to ICP test to calculate the contents of lithium, phosphorus and iron in the filtrate, i.e., the dissolution rate, as shown in Table 1. At the same time, the yield of lithium carbonate is calculated and the purity of lithium carbonate is measured.

[0114] Comparative Example 1

[0115] The control example provides a method for wet recovery of retired lithium iron phosphate battery powder to extract lithium and prepare lithium carbonate. The difference from Example 4 is that in step c, the temperature of the mixed solution is changed to 30°C, and the other steps and methods are the same as Example 4.

[0116] The lithium-containing filtrate obtained in this comparative example was subjected to ICP testing to calculate the contents of lithium, phosphorus and iron in the filtrate, i.e., the dissolution rate, as shown in Table 1. At the same time, the yield of lithium carbonate was calculated and the purity of lithium carbonate was measured.

[0117] Comparative Example 2

[0118] The method for preparing lithium carbonate by extracting lithium from retired lithium iron phosphate battery powder by wet method provided in this comparative example is different from that in Example 4 in that the molar ratio of LiFePO4 to H2SO4 and H2O2 in step a is changed, and the molar ratio of LiFePO4 to H2SO4 and H2O2 is weighed according to 3:1:1, and the other steps and methods are the same as those in Example 4. At the same time, the yield of lithium carbonate is calculated and the purity of lithium carbonate is measured.

[0119] The lithium-containing filtrate obtained in this comparative example was subjected to ICP test, and the contents of lithium, phosphorus and iron in the filtrate, i.e., the dissolution rate, were calculated, as shown in Table 1 below.

[0120] Comparative Example 3

[0121] The method for preparing lithium carbonate by extracting lithium from retired lithium iron phosphate battery powder by wet method provided in this comparative example is different from that in Example 4 in that after adding carbonate in step f, the solution is heated to 60°C, filtered and impurities are removed at 60°C to obtain lithium carbonate. The other steps and methods are the same as those in Example 4. At the same time, the yield of lithium carbonate is calculated and the purity of lithium carbonate is measured.

[0122] The yield of lithium carbonate obtained in this comparative example is low.

[0123] Table 1 Element dissolution rate in lithium-containing filtrate of the embodiments of the present invention and the comparative examples

[0124]

[0125] It can be seen from the above table that the method for extracting lithium from retired lithium iron phosphate battery powder to prepare lithium carbonate in Example 4 can achieve good results. While the lithium element leaching rate is high, the dissolution rates of iron and phosphorus elements in the lithium-containing filtrate are low, and the yield of the prepared lithium carbonate is high, and the purity of the lithium carbonate reaches 99.5%.

[0126] In summary: the method for wet recovery of retired lithium iron phosphate battery powder to extract lithium and prepare lithium carbonate of the present invention can effectively improve the recovery rate of lithium and reduce the loss of Fe and P elements; on the one hand, by specifically controlling the dissolution conditions: the amount of acid and oxidant, the reaction temperature, the reaction time and the solid-liquid ratio, the leaching rate of Li element during acid leaching is improved and the leaching rate of Fe and P elements is reduced; by quantitatively controlling the pH of the leachate, the production of hydroxide colloid is reduced, the efficiency of leachate filtration is improved, and the loss of lithium ions caused by being adsorbed on the colloid and filtered out is reduced; on the other hand, by removing impurities from the filtrate obtained after filtration, the content of impurity elements in the filtrate is reduced, and the purity of the product lithium carbonate is improved; by controlling the ambient temperature during lithium precipitation, the precipitation rate of lithium salt is improved, thereby improving the overall recovery rate of retired lithium iron phosphate battery powder.

[0127] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing lithium carbonate by wet recycling of retired lithium iron phosphate battery powder, characterized in that: The method comprises the following steps: Step 1: Add the recycled retired lithium iron phosphate battery powder LiFePO4 and an oxidant into a container, and then add water into the container until the solid-liquid ratio is 1:3 to form a mixed solution; Step 2: heating the container to make the temperature of the mixed solution reach 60° C., pouring acid solution into the container for acid leaching and dissolution, controlling the pH value at 1.5, and stopping heating after keeping the reaction for 3.5 hours, filtering to obtain a lithium-containing filtrate and an iron phosphate residue; Step 3, adding calcium salt or magnesium salt to the lithium-containing filtrate at 50-70° C., stirring evenly, adding alkali solution to adjust the pH to neutral, reacting for 1 h, and then filtering to remove impurities to obtain a first filtrate; Step 4: at room temperature, add alkali solution dropwise to the first filtrate to adjust the pH of the liquid to 11-13, then stop adding, react for 1 hour, filter and remove impurities to obtain a second filtrate; Step 5, adding carbonate to the second filtrate, stirring and filtering, and drying the filter residue to obtain lithium carbonate; In step 2, the acid solution is a mixed acid of HCl solution and H2SO4 solution, the molar ratio of HCl to H2SO4 in the mixed acid is 3:2, the concentration of the HCl solution is 12 mol / L, and the concentration of the H2SO4 solution is 18 mol / L; the oxidant is a mixed oxidant formed by mixing H2O2 and NaClO3, the molar ratio of NaClO3 to H2O2 in the mixed oxidant is 2:3, and the molar ratio of LiFePO4 to the mixed acid and the mixed oxidant is 5:7:1; In step five, after adding carbonate to the second filtrate, the second filtrate is heated to 90°C, and then the second filtrate is stirred and filtered. In step five, constant temperature filtration is used during the filtration process, and the constant temperature is 90°C.

2. The method for preparing lithium carbonate by wet recovery of retired lithium iron phosphate battery powder according to claim 1, characterized in that: In step 3, the amount of calcium salt and magnesium salt added exceeds the theoretical amount by 2-5%, and the theoretical amount is the mass of calcium salt and magnesium salt required for complete precipitation of phosphate ions in the lithium-containing filtrate.

3. The method for preparing lithium carbonate by wet recovery of retired lithium iron phosphate battery powder according to claim 1, characterized in that: The alkali solution is one or more of sodium hydroxide, potassium hydroxide, ammonia water, calcium hydroxide, calcium oxide, potassium oxide and sodium oxide.

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