Method for preparing battery-grade lithium carbonate by regenerating waste lithium iron phosphate battery

Abstract

The invention belongs to the field of recycling of waste lithium iron phosphate batteries, and provides a method for preparing battery-grade lithium carbonate by regenerating the waste lithium iron phosphate batteries, which comprises the following steps: performing oxidation acid leaching on positive electrode powder of the waste lithium iron phosphate batteries, performing solid-liquid separation and filtration, adding ion exchange resin into a separated liquid-phase solution, and performing solid-liquid separation to obtain lithium carbonate; after adsorption saturation, dropwise adding a sodium chloride solution, stirring and filtering out solid particles to obtain a coarse lithium carbonate solution; introducing H2 into the crude lithium carbonate solution for hydrotreating and filtering to obtain a liquid-phase lithium bicarbonate solution; a solution A prepared by dissolving ammonium nitrate in nitric acid and a solution B prepared by adding isopropanol into tetraisopropyl titanate are heated, mixed and reacted to prepare modified titanium dioxide particles; adding the modified titanium dioxide particles into the lithium bicarbonate solution to obtain a deeply defluorinated lithium bicarbonate solution; and carrying out thermal decomposition, solid-liquid separation and filtration to obtain the battery-grade wet lithium carbonate. According to the invention, primary fluorine removal is carried out and then deep fluorine removal is carried out by using modified titanium dioxide, so that the fluorine removal effect is good.

Description

Technical Field

[0001] The invention relates to the technical field of recycling waste lithium iron phosphate batteries, and in particular to a method for preparing battery-grade lithium carbonate by recycling waste lithium iron phosphate batteries. Background Art

[0002] In recent years, the rapid development of new energy vehicles has led to a great deal of attention to lithium resources due to the demand for lithium iron phosphate batteries. At present, the raw materials of lithium carbonate, an important component of lithium iron phosphate batteries, mainly come from the extraction of ore resources and salt lake brine resources, as well as the recycling of waste lithium batteries. With the continuous advancement of recycling technology for waste lithium iron phosphate batteries, the recycling cost has gradually decreased, while the market price of materials such as battery-grade lithium carbonate has risen. Therefore, the recycling of waste batteries can not only reduce the production cost of new batteries, but also bring economic benefits to enterprises. However, the high fluorine content in the lithium carbonate raw materials produced by the current recycling technology will not only affect the quality of the product and the performance of lithium iron phosphate batteries, but also seriously corrode production equipment and pipelines, pollute the surrounding environment and cause harm to people's health. Therefore, defluorination is inevitable in the process of recycling waste batteries.

[0003] At present, there are two common ways to reduce the fluorine content in the process of regenerating waste lithium iron phosphate batteries to prepare battery-grade lithium carbonate. One is to keep the fluorine in the mother liquor and not input it into the downstream products during the lithium precipitation process. The second is to remove it directly through precipitation or adsorption by adsorbents. The second method has been used more frequently in recent years. The more mature fluorine removal methods include chemical precipitation, coagulation adsorption precipitation, electrodialysis and ion exchange resin. However, there are still problems such as complex preparation methods, high costs, easy introduction of by-products during the reaction process, and inability to efficiently remove the fluorine content. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing battery-grade lithium carbonate by efficiently removing fluorine in the regeneration process of waste lithium iron phosphate batteries. By combining chemical precipitation method and adsorption method, aluminum hydroxide is first reacted with the liquid lithium bicarbonate solution obtained after oxidative acid leaching and hydrogenation treatment, so that aluminum hydroxide reacts with fluorine ions in the water body to generate a precipitate that is insoluble in water, thereby separating it from the water body to achieve preliminary fluorine removal, and then the adsorption method is adopted, and nano titanium dioxide with a high specific surface area is used as an inorganic ion exchanger to achieve deep fluorine removal. The method has the advantages of simple preparation method, low cost, no introduction of by-products, and efficient fluorine removal.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] The method for regenerating waste lithium iron phosphate batteries to prepare battery-grade lithium carbonate comprises the following steps:

[0007] Step S1, pretreatment of raw materials

[0008] The waste lithium iron phosphate battery positive electrode powder is subjected to oxidation acid leaching and then solid-liquid separation and filtration, an ion exchange resin is added to the separated liquid phase solution, a sodium chloride solution is added dropwise after adsorption saturation, and a crude lithium carbonate solution is obtained after sufficient stirring and filtering out solid particles;

[0009] Step S2, hydrogenation treatment

[0010] The crude lithium carbonate solution is introduced with H2 for hydrogenation treatment to obtain a lithium bicarbonate hydrogenated liquid, and the lithium bicarbonate hydrogenated liquid is filtered to obtain a liquid lithium bicarbonate solution;

[0011] Step S3, maintaining the pH of the liquid phase lithium bicarbonate solution in the range of 6 to 7, and adding a certain amount of aluminum hydroxide therein, and after the reaction is completed, filtering to obtain a preliminarily defluorinated lithium bicarbonate solution;

[0012] Step S4, dissolving ammonium nitrate in nitric acid to obtain liquid A, adding isopropyl alcohol to tetraisopropyl titanate to obtain liquid B, mixing liquid A and liquid B under heating conditions for reaction, and after the reaction is completed, filtering and drying the mixed solution to obtain modified titanium dioxide particles;

[0013] Step S5, adding the modified carbon dioxide particles of step S4 to the lithium bicarbonate solution preliminarily defluorinated in step S3 to obtain a lithium bicarbonate solution with deep defluorination;

[0014] Step S6, subjecting the lithium bicarbonate solution from step S5 to deep defluorination to thermal decomposition and solid-liquid separation and filtration to obtain battery-grade wet lithium carbonate.

[0015] As the preferred technical solution:

[0016] Optionally, in step S1, the oxidative acid leaching refers to slurrying the waste lithium iron phosphate battery positive electrode powder with pure water in a solid-liquid ratio of 1:20 to 1:25, and then adding concentrated sulfuric acid and hydrogen peroxide to carry out heating leaching reaction to obtain an oxidative acid leaching slurry; the solid-liquid separation refers to being carried out in a disc or tubular centrifuge, and controlling the temperature in the range of room temperature to 40°C and the rotation speed in the range of 400 to 600 r / min; the ion exchange resin is a strong alkaline anion exchange resin.

[0017] Optionally, the waste lithium iron phosphate battery positive electrode powder and the pure water are slurried in a solid-liquid ratio of 1:20; the molar ratio of lithium, sulfuric acid and hydrogen peroxide during oxidative acid leaching should satisfy: Li: H2SO4: H2O2 = 1: (0.5-0.8): (0.6-0.9); the ion exchange resin is an acrylic acid-based strong alkaline anion exchange resin.

[0018] Optionally, in step S2, the hydrogenation treatment is to preheat the crude lithium carbonate solution in a reactor to 40°C, keep it warm for 5-10 min, introduce H2 gas into the reactor and gradually increase the temperature to 60-70°C at a rate of 1-3°C / min and keep it warm for 5-10 min, then gradually increase the temperature to 100-130°C at a rate of 5-10°C / min and keep it warm for 5-10 min, finally gradually increase the temperature to 150-180°C at a rate of 5-10°C / min and keep it warm until the solution becomes clear, stop introducing H2 and end the insulation, and cool the reactor to room temperature after the reaction is completed; the filtration method is pressure filtration.

[0019] Optionally, in step S3, according to n (Al 2+ ):n(F - ) is added with aluminum hydroxide at a ratio of 0.2 to 0.5, and the reaction time is 20 to 30 minutes. Compared with the prior art, the present invention uses a trace amount of aluminum to achieve the adsorption of fluoride ions, providing a basis for subsequent deep defluorination.

[0020] Optionally, in step S4, the concentration of the nitric acid is 0.2-0.5 mol / L, and the amount of ammonium nitrate added to the liquid A accounts for 20-40% by mass of the liquid A;

[0021] The volume ratio of isopropyl alcohol to tetraisopropyl titanate in the B solution is 3:5, and the mixture is stirred at room temperature for 10 to 15 minutes;

[0022] The conditions of the mixed reaction are: the ammonium nitrate solution is heated and kept at 50°C, then dissolved in nitric acid, and the mixture is stirred according to n(NH4 + The B solution was added dropwise therein at a ratio of ):n(Ti)=1:1, stirred for 2 hours, cooled to room temperature, and filtered to dry.

[0023] Optionally, in step S4, the prepared modified titanium dioxide is further mixed with hydrated titanium dioxide in a certain ratio to prepare a mixture, and the mixture is added to the lithium bicarbonate solution preliminarily defluorinated in step S3 to obtain a deeply defluorinated lithium bicarbonate solution.

[0024] Optionally, the certain ratio is (8-10):1, and the amount of the mixture added is 1-1.5 kg / L.

[0025] Optionally, in step S6, the decomposition temperature of the thermal decomposition is 80-100°C.

[0026] Optionally, the fluorine content in the lithium bicarbonate solution for preliminary defluorination is 10-20 ppm, the fluorine content in the lithium bicarbonate solution for deep defluorination is <5 ppm, and the remaining contents are all below the standard (calcium content <50 ppm, sulfate content <800 ppm, chlorine content <30 ppm, sodium content <250 ppm, potassium content <10 ppm, magnesium content <80 ppm).

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The existing technology usually uses a combination of defluorination agents and chemical precipitation methods to achieve the defluorination of raw materials in the process of regenerating waste lithium iron phosphate batteries to prepare battery-grade lithium carbonate. Although this method has the advantages of simple method, convenient treatment, low operating cost, etc., and is particularly common in the treatment of high-concentration fluoride-containing water, it is less effective in treating low-fluoride water. This is because the crystal nuclei formed by the precipitation induced by low-fluoride water are difficult to generate.

[0029] The present invention pre-treats the raw material by first using oxidative acid leaching to leach out metal and other impurities and extract lithium ions. Then, the leached large particles of metal impurities are removed by centrifugal separation and filtration, and then a specific ion exchange resin is used to further remove impurity ions such as calcium and magnesium in the raw material. Hydrogenation treatment is then used to improve the purity of the solution, so as to prepare for removing fluoride ions in the solution. Then, a small amount of aluminum hydroxide solution is added to the fluoride-containing water to react with the fluoride ions to generate a precipitate that is insoluble in water, and the precipitate is separated from the water body to achieve preliminary fluoride removal. Then, an adsorption method is used for deep fluoride removal. The adsorption method has the advantages of high efficiency, low cost, simple operation and maintenance, etc., and an adsorbent with excellent performance is the key to the adsorption method. The present invention uses ammonium to modify titanium dioxide, and ammonium is loaded on titanium dioxide as a cation, so that the specific surface area of ​​titanium dioxide is greatly increased, and at the same time, the anion F - The adsorption effect is enhanced, thereby achieving deep fluoride removal. In addition, the modified nano titanium dioxide (TiO2) is also mixed with hydrated titanium dioxide (TiO2·nH2O) as a mixed adsorbent, which has a high specific surface area and has a very friendly selective adsorption capacity for some ions as an inorganic ion exchanger. It also has excellent physical and chemical properties and environmental friendliness. Titanium dioxide can also be compounded with silicon dioxide to increase its adsorption capacity for fluoride ions in water. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 is a flow chart of the method of the present invention;

[0032] Figure 2 This is a SEM image of the surface of the modified titanium dioxide particles prepared in the present invention. DETAILED DESCRIPTION

[0033] In the following, only some exemplary embodiments are briefly described. As those skilled in the art will appreciate, the described embodiments may be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and descriptions are considered to be exemplary and non-restrictive in nature.

[0034] The disclosure below provides many different embodiments or examples for implementing different processes of the present invention. In order to simplify the disclosure of the present invention, the components and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present invention. In addition, the present invention can repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplicity and clarity, which itself does not indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides various specific examples of processes and materials, but those of ordinary skill in the art can appreciate the application of other processes and / or the use of other materials.

[0035] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0036] Example 1

[0037] A method for regenerating waste lithium iron phosphate batteries to prepare battery-grade lithium carbonate, the embodiment comprising the following steps:

[0038] Step S1, pretreatment of raw materials

[0039] The waste lithium iron phosphate battery positive electrode powder and pure water are slurried according to a solid-liquid ratio of 1:20, and then concentrated sulfuric acid and hydrogen peroxide are added for heating and leaching reaction to obtain an oxidative acid leaching slurry, wherein the molar ratio of lithium, sulfuric acid and hydrogen peroxide in the oxidative acid leaching process should satisfy the following: Li:H2SO4:H2O2=1:0.5:0.7; the oxidative acid leaching slurry is then placed in a disc centrifuge, and the temperature is controlled within the range of room temperature to 40°C, and the speed is within the range of 400-600r / min. Under the action of centrifugal force, the solid phase particles are pushed to the drum wall to form sediment, and the liquid phase solution is discharged and collected through a drain pipe, and an acrylic acid-based strong alkaline anion exchange resin is added to the separated liquid phase solution, and after adsorption saturation, a sodium chloride solution with a concentration of 8-10% is added dropwise, and the solid particles are filtered out after sufficient stirring to obtain a crude lithium carbonate solution;

[0040] Step S2, hydrogenation treatment

[0041] High-purity H2 is introduced into the crude lithium carbonate solution for hydrogenation treatment, and the specific process is: the crude lithium carbonate solution is placed in a reactor and preheated to 40°C, and kept warm for 5 minutes, H2 is introduced into the reactor and the temperature is gradually increased to 70°C at a rate of 1°C / min and kept warm for 10 minutes, then the temperature is gradually increased to 110°C at a rate of 8°C / min and kept warm for 5 minutes, and finally the temperature is gradually increased to 175°C at a rate of 6°C / min and kept warm until the solution becomes clear, and the H2 introduction is stopped. After the reaction is completed, the reactor is cooled to room temperature to obtain lithium bicarbonate hydrogenated liquid, and the lithium bicarbonate hydrogenated liquid is filtered to obtain a liquid lithium bicarbonate solution;

[0042] Step S3, maintaining the pH of the liquid phase lithium bicarbonate solution at 6-7 and mixing the solution according to n(Al 2+ ):n(F - )=0.2, aluminum hydroxide was added, stirred and reacted for 30 minutes, and then filtered to obtain a lithium bicarbonate solution with preliminary defluorination;

[0043] Step S4, dissolving 0.3 mol / L ammonium nitrate in 0.3 mol / L nitric acid to obtain liquid A, wherein the amount of ammonium nitrate added accounts for 20% by mass of liquid A; adding 1 mol / L isopropanol to 1 mol / L tetraisopropyl titanate (the volume ratio of isopropanol to tetraisopropyl titanate is 3:5) and stirring at room temperature for 15 min to obtain liquid B; heating liquid A and keeping it warm at 50°C, and then heating liquid B according to n(NH4 + ):n(Ti)=1:1, liquid B was added dropwise therein, stirred for 2 hours, cooled to room temperature, filtered and dried to obtain modified titanium dioxide particles. The SEM image of the modified titanium dioxide is shown in Figure 2 As shown in the figure, it can be seen that a plurality of fine particles are formed on the surface of the modified titanium dioxide particles prepared by the present invention. The specific surface area of ​​the modified titanium dioxide particles detected by the BET method is 131 m 2 / g, compared with 57m before modification 2 / g, and the specific surface area increased significantly, which indicates that the modification process increased the surface activity of TiO2, thereby enhancing the adsorption capacity of TiO2 for F.

[0044] Step S5, adding 1.5 kg of modified titanium dioxide particles to the 1 m 3 Stirring in a lithium bicarbonate solution to obtain a lithium bicarbonate solution with deep defluorination;

[0045] Step S6, after solid-liquid separation, the lithium bicarbonate solution with deep defluorination is thermally decomposed at 80° C. and filtered to obtain battery-grade lithium carbonate.

[0046] After testing, the fluorine content in the lithium bicarbonate solution after preliminary defluorination and the fluorine content in the lithium bicarbonate solution after deep defluorination (i.e., lithium carbonate solid product) before and after defluorination are compared as shown in Table 1 below.

[0047] Table 1 Comparison of fluorine content before and after preliminary defluorination and deep defluorination of lithium carbonate in Example 1

[0048] Before fluoride removal (ppm) After fluoride removal (ppm) Lithium bicarbonate solution 20 4.2 Lithium carbonate solid products 400 83

[0049] Example 2

[0050] A method for regenerating waste lithium iron phosphate batteries to prepare battery-grade lithium carbonate, the embodiment comprising the following steps:

[0051] Step S1, pretreatment of raw materials

[0052] The waste lithium iron phosphate battery positive electrode powder and pure water are slurried according to a solid-liquid ratio of 1:22, and then concentrated sulfuric acid and hydrogen peroxide are added to perform a heating leaching reaction to obtain an oxidative acid leaching slurry, wherein the molar ratio of lithium, sulfuric acid and hydrogen peroxide in the oxidative acid leaching process should satisfy the following: Li:H2SO4:H2O2=1:0.5:0.6; the oxidative acid leaching slurry is then placed in a disc centrifuge, and the temperature is controlled within a range of room temperature to 40°C, and the speed is within a range of 400-600r / min. Under the action of centrifugal force, the solid phase particles are pushed to the drum wall to form sediment, and the liquid phase solution is discharged and collected through a drain pipe, and an acrylic acid-based strong alkaline anion exchange resin is added to the liquid phase solution, and after adsorption saturation, a sodium chloride solution with a concentration of 8-10% is added dropwise, and the solid particles are filtered out after sufficient stirring to obtain a crude lithium carbonate solution;

[0053] Step S2, hydrogenation treatment

[0054] The crude lithium carbonate solution is introduced with high-purity H2 for hydrogenation treatment, and the specific process is as follows: the crude lithium carbonate solution is placed in a reactor and preheated to 40°C, and kept warm for 6 minutes, H2 is introduced into the reactor and the temperature is gradually increased to 70°C at a rate of 3°C / min and kept warm for 9 minutes, and then the temperature is gradually increased to 100°C at a rate of 5°C / min and kept warm for 10 minutes, and finally the temperature is gradually increased to 180°C at a rate of 10°C / min and kept warm until the solution becomes clear, and the introduction of H2 is stopped. After the reaction is completed, the reactor is cooled to room temperature to obtain lithium bicarbonate hydrogenated liquid, and the lithium bicarbonate hydrogenated liquid is filtered to obtain a liquid lithium bicarbonate solution;

[0055] Step S3, maintaining the pH of the liquid phase lithium bicarbonate solution at 6-7 and mixing the solution according to n(Al 2+ ):n(F - )=0.2, aluminum hydroxide was added, stirred and reacted for 30 minutes, and then filtered to obtain a lithium bicarbonate solution with preliminary defluorination;

[0056] Step S4, dissolving 0.6 mol / L ammonium nitrate in 0.3 mol / L nitric acid to obtain liquid A, wherein the amount of ammonium nitrate added accounts for 40% by mass of liquid A, adding 2 mol / L isopropanol to 2 mol / L tetraisopropyl titanate (the volume ratio of isopropanol to tetraisopropyl titanate is 3:5) and stirring at room temperature for 12 min to obtain liquid B, heating liquid A and keeping it warm at 50°C, and then heating according to n(NH4 + Liquid B was added dropwise in a ratio of 1:1 and the mixture was stirred for 2 h, cooled to room temperature and filtered to dry to obtain modified titanium dioxide particles.

[0057] Step S5, adding 3.0 kg of modified titanium dioxide particles to the 2 m 3 Stirring in a lithium bicarbonate solution to obtain a lithium bicarbonate solution with deep defluorination;

[0058] Step S6, after solid-liquid separation, the deeply defluorinated lithium bicarbonate solution is thermally decomposed at 90° C. and filtered to obtain battery-grade wet lithium carbonate.

[0059] After testing, the fluorine content in the lithium bicarbonate solution after preliminary defluorination and the fluorine content in the lithium bicarbonate solution after deep defluorination (i.e., lithium carbonate solid product) before and after defluorination are compared as shown in Table 2 below.

[0060] Table 2 Comparison of fluorine content before and after preliminary defluorination and deep defluorination of lithium carbonate in Example 2

[0061] Before fluoride removal (ppm) After fluoride removal (ppm) Lithium bicarbonate solution 20 4.5 Lithium carbonate solid products 600 94

[0062] Example 3

[0063] A method for regenerating waste lithium iron phosphate batteries to prepare battery-grade lithium carbonate, the embodiment comprising the following steps:

[0064] Step S1, pretreatment of raw materials

[0065] The waste lithium iron phosphate battery positive electrode powder and pure water are slurried according to a solid-liquid ratio of 1:25, and then concentrated sulfuric acid and hydrogen peroxide are added for heating and leaching reaction to obtain an oxidative acid leaching slurry, wherein the molar ratio of lithium, sulfuric acid and hydrogen peroxide in the oxidative acid leaching process should satisfy the following: Li:H2SO4:H2O2=1:0.8:0.6; the oxidative acid leaching slurry is then placed in a disc centrifuge, and the temperature is controlled within the range of room temperature to 40°C, and the speed is within the range of 400-600r / min. Under the action of centrifugal force, the solid phase particles are pushed to the drum wall to form sediment, and the liquid phase solution is discharged and collected through a drain pipe, and an acrylic acid-based strong alkaline anion exchange resin is added to the liquid phase solution, and after adsorption saturation, a sodium chloride solution with a concentration of 8-10% is added dropwise, and the solid particles are filtered out after sufficient stirring to obtain a crude lithium carbonate solution;

[0066] Step S2, hydrogenation treatment

[0067] High-purity H2 is introduced into the crude lithium carbonate solution for hydrogenation treatment, and the specific process is: the crude lithium carbonate solution is placed in a reactor and preheated to 40°C, and kept warm for 10 minutes, H2 is introduced into the reactor and the temperature is gradually increased to 60°C at a rate of 2°C / min and kept warm for 5 minutes, then the temperature is gradually increased to 100°C at a rate of 10°C / min and kept warm for 10 minutes, and finally the temperature is gradually increased to 180°C at a rate of 5°C / min and kept warm until the solution becomes clear, and the H2 introduction is stopped. After the reaction is completed, the reactor is cooled to room temperature to obtain lithium bicarbonate hydrogenated liquid, and the lithium bicarbonate hydrogenated liquid is filtered to obtain a liquid lithium bicarbonate solution;

[0068] Step S3, maintaining the pH of the liquid phase lithium bicarbonate solution at 6-7 and mixing the solution according to n(Al 2+ ):n(F - )=0.4, aluminum hydroxide was added, stirred and reacted for 20 minutes, and then filtered to obtain a lithium bicarbonate solution with preliminary defluorination;

[0069] Step S4, dissolving 0.3 mol / L ammonium nitrate in 0.3 mol / L nitric acid to obtain liquid A, wherein the amount of ammonium nitrate added accounts for 30% by mass of liquid A, adding 1 mol / L isopropanol to 1 mol / L tetraisopropyl titanate (the volume ratio of isopropanol to tetraisopropyl titanate is 3:5) and stirring at room temperature for 11 minutes to obtain liquid B, heating liquid A and keeping it warm at 50°C, and then heating according to n(NH4 + The B solution is added dropwise therein at a ratio of ) : n (Ti) = 1: 1, stirred for 2 hours, cooled to room temperature, and filtered and dried to obtain modified titanium dioxide particles.

[0070] Step S5: 2.0 kg of modified titanium dioxide particles are placed in a 1.7 m 3 Stirring in a lithium bicarbonate solution to obtain a lithium bicarbonate solution with deep defluorination;

[0071] Step S6, after solid-liquid separation, the lithium bicarbonate solution with deep defluorination is thermally decomposed at 85° C. and filtered to obtain battery-grade wet lithium carbonate.

[0072] After testing, the fluorine content in the lithium bicarbonate solution after preliminary defluorination and the fluorine content in the lithium bicarbonate solution after deep defluorination (i.e., lithium carbonate solid product) before and after defluorination are compared as shown in Table 3 below.

[0073] Table 3 Comparison of fluorine content before and after preliminary defluorination and deep defluorination of lithium carbonate in Example 3

[0074] Before fluoride removal (ppm) After fluoride removal (ppm) Lithium bicarbonate solution 16 3.7 Lithium carbonate solid products 500 70

[0075] Example 4

[0076] A method for regenerating waste lithium iron phosphate batteries to prepare battery-grade lithium carbonate, the embodiment comprising the following steps:

[0077] Step S1, pretreatment of raw materials

[0078] The waste lithium iron phosphate battery positive electrode powder and pure water are slurried according to a solid-liquid ratio of 1:25, and then concentrated sulfuric acid and hydrogen peroxide are added for heating and leaching reaction to obtain an oxidative acid leaching slurry, wherein the molar ratio of lithium, sulfuric acid and hydrogen peroxide in the oxidative acid leaching process should satisfy the following: Li:H2SO4:H2O2=1:0.8:0.9; the oxidative acid leaching slurry is then placed in a disc centrifuge, and the temperature is controlled within the range of room temperature to 40°C, and the speed is within the range of 400-600r / min. Under the action of centrifugal force, the solid phase particles are pushed to the drum wall to form sediment, and the liquid phase solution is discharged and collected through a drain pipe, and an acrylic acid-based strong alkaline anion exchange resin is added to the liquid phase solution, and after adsorption saturation, a sodium chloride solution with a concentration of 8-10% is added dropwise, and the solid particles are filtered out after sufficient stirring to obtain a crude lithium carbonate solution;

[0079] Step S2, hydrogenation treatment

[0080] High-purity H2 is introduced into the crude lithium carbonate solution for hydrogenation treatment, and the specific process is: the crude lithium carbonate solution is placed in a reactor and preheated to 40°C, and kept warm for 8 minutes, and H2 is introduced into the reactor and the temperature is gradually increased to 60°C at a rate of 3°C / min and kept warm for 10 minutes, and then the temperature is gradually increased to 100°C at a rate of 5°C / min and kept warm for 10 minutes, and finally the temperature is gradually increased to 160°C at a rate of 5°C / min and kept warm until the solution becomes clear, and the H2 is stopped from being introduced. After the reaction is completed, the reactor is cooled to room temperature to obtain lithium bicarbonate hydrogenated liquid, and the lithium bicarbonate hydrogenated liquid is filtered to obtain a liquid lithium bicarbonate solution;

[0081] Step S3, maintaining the pH of the liquid phase lithium bicarbonate solution at 6-7 and mixing the solution according to n(Al 2+ ):n(F - )=0.5, add aluminum hydroxide, stir and react for 30 minutes, and then filter to obtain a lithium bicarbonate solution with preliminary defluorination;

[0082] Step S4, dissolving 0.2 mol / L ammonium nitrate in 0.2 mol / L nitric acid to obtain liquid A, wherein the amount of ammonium nitrate added accounts for 25% by mass of liquid A, adding 1 mol / L isopropanol to 1 mol / L tetraisopropyl titanate (the volume ratio of isopropanol to tetraisopropyl titanate is 3:5) and stirring at room temperature for 10 min to obtain liquid B, heating liquid A and keeping it warm at 50°C, and then heating liquid B according to n(NH4 + Liquid B was added dropwise in a ratio of 1:1 and the mixture was stirred for 2 h, cooled to room temperature and filtered to dry to obtain modified titanium dioxide particles.

[0083] Step S5, adding 1 kg of modified titanium dioxide particles to the 1 m 3 Stirring in a lithium bicarbonate solution to obtain a lithium bicarbonate solution with deep defluorination;

[0084] Step S6, after solid-liquid separation, the lithium bicarbonate solution with deep defluorination is thermally decomposed at 80° C. and filtered to obtain battery-grade wet lithium carbonate.

[0085] After testing, the fluorine content in the lithium bicarbonate solution after preliminary defluorination and the fluorine content in the lithium bicarbonate solution after deep defluorination (i.e., lithium carbonate solid product) before and after defluorination are compared as shown in Table 4 below.

[0086] Table 4 Comparison of fluorine content before and after preliminary defluorination and deep defluorination of lithium carbonate in Example 4

[0087] Before fluoride removal (ppm) After fluoride removal (ppm) Lithium bicarbonate solution 20 3.8 Lithium carbonate solid products 400 78

[0088] Example 5

[0089] The method for regenerating waste lithium iron phosphate batteries to prepare battery-grade lithium carbonate has the same steps as in Example 1, except that, in step S5, before adding the modified titanium dioxide particles to the lithium bicarbonate solution that has been preliminarily defluorinated, the prepared modified titanium dioxide particles and hydrated titanium dioxide are mixed in a ratio of 10:1 to prepare a mixture, and 1.5 kg of the mixture is added to the 1 m lithium bicarbonate solution that has been preliminarily defluorinated. 3 The solution is stirred in the lithium bicarbonate solution to obtain a lithium bicarbonate solution with deep defluorination.

[0090] After testing, the fluorine content in the lithium bicarbonate solution after preliminary defluorination and the fluorine content in the lithium bicarbonate solution after deep defluorination (i.e., lithium carbonate solid product) before and after defluorination are compared as shown in Table 5 below.

[0091] Table 5 Comparison of fluorine content before and after preliminary defluorination and deep defluorination of lithium carbonate in Example 5

[0092] Before fluoride removal (ppm) After fluoride removal (ppm) Lithium bicarbonate solution 20 2.1 Lithium carbonate solid products 400 52

[0093] It can be seen from the above table that the defluorination effect of the mixture of ammonium-modified titanium dioxide particles and hydrated titanium dioxide is more obvious. This is because the hydrated titanium dioxide further increases the specific surface area for adsorption, making the selective adsorption capacity better, thereby further reducing the fluorine content.

[0094] The above embodiments are only preferred embodiments of the present invention and are not limitations of the technical solutions of the present invention. Any technical solution that can be implemented on the basis of the above embodiments without creative work should be deemed to fall within the scope of protection of the patent of the present invention.

Claims

1. A method for regenerating waste lithium iron phosphate batteries to prepare battery-grade lithium carbonate, characterized in that: The steps include: Step S1, pretreatment of raw materials The waste lithium iron phosphate battery positive electrode powder is subjected to oxidation acid leaching, followed by solid-liquid separation and filtration, and an ion exchange resin is added to the separated liquid phase solution. After adsorption saturation, a sodium chloride solution is added dropwise, and the solution is fully stirred and filtered to remove solid particles to obtain a crude lithium carbonate solution; Step S2, hydrogenation treatment The crude lithium carbonate solution is introduced with H2 for hydrogenation treatment to obtain a lithium bicarbonate hydrogenated liquid, and the lithium bicarbonate hydrogenated liquid is filtered to obtain a liquid lithium bicarbonate solution; Step S3, maintaining the pH of the liquid phase lithium bicarbonate solution in the range of 6 to 7, and adding a certain amount of aluminum hydroxide therein, and after the reaction is completed, filtering to obtain a preliminarily defluorinated lithium bicarbonate solution; Step S4, dissolving ammonium nitrate in nitric acid to obtain liquid A, adding isopropyl alcohol to tetraisopropyl titanate to obtain liquid B, mixing liquid A and liquid B under heating conditions for reaction, and after the reaction is completed, filtering and drying the mixed solution to obtain modified titanium dioxide particles; Step S5, adding the modified carbon dioxide particles of step S4 to the lithium bicarbonate solution preliminarily defluorinated in step S3 to obtain a lithium bicarbonate solution with deep defluorination; Step S6, subjecting the lithium bicarbonate solution from step S5 to deep defluorination to thermal decomposition and solid-liquid separation and filtration to obtain battery-grade lithium carbonate.

2. The method for regenerating waste lithium iron phosphate batteries to prepare battery-grade lithium carbonate according to claim 1, characterized in that: In step S1, the oxidative acid leaching refers to slurrying the waste lithium iron phosphate battery positive electrode powder and pure water according to a solid-liquid ratio of 1:20 to 1:25, and then adding concentrated sulfuric acid and hydrogen peroxide for heating and leaching reaction to obtain an oxidative acid leaching slurry; the solid-liquid separation refers to being carried out in a disc or tubular centrifuge, and controlling the temperature in the range of room temperature to 40°C and the speed in the range of 400 to 600 r / min; the ion exchange resin is a strong alkaline anion exchange resin.

3. The method for regenerating battery-grade lithium carbonate from waste lithium iron phosphate batteries according to claim 2, characterized in that: The waste lithium iron phosphate battery positive electrode powder and the pure water are slurried according to a solid-liquid ratio of 1:20; the molar ratio of lithium, sulfuric acid and hydrogen peroxide in the oxidative acid leaching process should satisfy: Li: H2SO4: H2O2 = 1: (0.5-0.8): (0.6-0.9); the ion exchange resin is an acrylic acid-based strong alkaline anion exchange resin.

4. The method for regenerating battery-grade lithium carbonate from waste lithium iron phosphate batteries according to claim 1, characterized in that: In step S2, the hydrogenation treatment is to preheat the crude lithium carbonate solution in a reactor to 40°C, keep it warm for 5-10 minutes, introduce H2 into the reactor and gradually heat it to 60-70°C at a rate of 1-3°C / min and keep it warm for 5-10 minutes, then gradually heat it to 100-130°C at a rate of 5-10°C / min and keep it warm for 5-10 minutes, and finally gradually heat it to 150-180°C at a rate of 5-10°C / min and keep it warm until the solution becomes clear, stop introducing H2, and cool the reactor to room temperature after the reaction is completed; the filtration method is filter press.

5. The method for regenerating battery-grade lithium carbonate from waste lithium iron phosphate batteries according to claim 1, characterized in that: In step S3, according to n (Al 2+ ):n(F - ) is added with aluminum hydroxide in a ratio of 0.2~0.5, and the reaction time is 20~30min.

6. The method for regenerating battery-grade lithium carbonate from waste lithium iron phosphate batteries according to claim 1, characterized in that: In step S4, the concentration of the nitric acid is 0.2-0.5 mol / L, and the amount of ammonium nitrate added to the liquid A accounts for 20-40% by mass of the liquid A; The volume ratio of isopropyl alcohol to tetraisopropyl titanate in the B solution is 3:5, and the mixture is stirred at room temperature for 10 to 15 minutes; The mixed reaction is specifically as follows: the ammonium nitrate solution is heated and kept at 50°C, then dissolved in nitric acid, and then + The B solution was added dropwise therein at a ratio of ):n(Ti)=1:1, stirred for 2 hours, cooled to room temperature, and filtered to dry.

7. The method for regenerating waste lithium iron phosphate batteries to prepare battery-grade lithium carbonate according to claim 1, characterized in that: In step S4, the prepared modified titanium dioxide is further mixed with hydrated titanium dioxide in a certain ratio to prepare a mixture, and the mixture is added to the lithium bicarbonate solution preliminarily defluorinated in step S3 to obtain a deeply defluorinated lithium bicarbonate solution.

8. The method for regenerating waste lithium iron phosphate batteries to prepare battery-grade lithium carbonate according to claim 7, characterized in that: The certain ratio is (8-10):1, and the amount of the mixture added is 1-1.5 kg / L.

9. The method for regenerating battery-grade lithium carbonate from waste lithium iron phosphate batteries according to claim 1, characterized in that: In step S6, the decomposition temperature of the thermal decomposition is 80-100°C.

10. The method for regenerating battery-grade lithium carbonate from waste lithium iron phosphate batteries according to claim 1, characterized in that: The fluorine content in the lithium bicarbonate solution for preliminary defluorination is 10-20 ppm, and the fluorine content in the lithium bicarbonate solution for deep defluorination is less than 5 ppm.

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