A method for efficiently recycling lithium from waste lithium iron phosphate batteries

Abstract

This invention discloses a method for efficiently recovering lithium from waste lithium iron phosphate batteries, comprising the following steps: 1) lithium extraction with ammonium persulfate; 2) impurity removal from the leachate; 3) preparation of lithium hydroxide using a bipolar membrane; 4) deammoniation reaction; and 5) crystallization and electrochemical reaction. The method for efficiently recovering lithium from waste lithium iron phosphate batteries provided by this invention effectively reduces the use of acid during the leaching process, avoiding a large amount of subsequent neutralization reactions. Simultaneously, by sequentially removing impurities from the leachate, performing bipolar membrane electrolysis, deammoniation reaction, and crystallization, high-purity lithium hydroxide crystals are prepared. Furthermore, the acid or ammonium persulfate obtained from the electrochemical reaction can be recycled within the production system, reducing raw material costs. The experimental steps of this preparation method are simple and controllable, effectively controlling impurities to obtain pure lithium hydroxide products. Additionally, some of the products obtained by this method can be used as raw materials, forming a closed-loop, green, and recyclable process.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of hydrometallurgy, and particularly relates to a method for efficiently recovering lithium in waste lithium iron phosphate batteries. BACKGROUND

[0002] With the popularization of new energy vehicles, lithium ion batteries are widely used. Lithium iron phosphate batteries are widely studied due to their high temperature resistance, high safety, long cycle life and low manufacturing cost. With the increase of the use time of power batteries, the electrolyte and active material are gradually consumed, and lithium dendrites are easily generated, so the capacity gradually decreases. For power lithium battery packs, when the capacity of part of the cells decreases rapidly and the capacity of the part of the cells is too low, the battery capacity cannot be stably output, which easily leads to safety problems. The retired lithium iron phosphate battery contains relatively abundant lithium resources than natural resources. If the lithium resources are recycled, the waste of resources and environmental pollution can be reduced, and the sustainable development of the new energy industry can be ensured. Therefore, it is of great significance to develop an economical and efficient lithium resource recovery method.

[0003] The lithium iron phosphate battery is recycled through a cascade utilization and a recycling utilization approach. When the capacity of the lithium iron phosphate battery is reduced to 20%-80%, the lithium iron phosphate battery is slightly scrapped and can enter the cascade utilization stage and be used for energy storage, communication base stations and user side. When the capacity is reduced to 20% or less, the lithium iron phosphate battery is severely scrapped and will enter the recycling utilization stage. The recycling usually uses a wet recovery method to leach the electrode and selectively extract elements. Generally, an acid such as sulfuric acid, phosphoric acid or oxalic acid is used to dissolve the waste positive electrode material, and the desired product is obtained by adjusting the pH value or adjusting the precipitation / dissolution balance. However, the destruction of the lithium iron phosphate structure in the leaching process requires the addition of an excessive amount of acid, and the adjustment of the pH value also requires the addition of liquid alkali, which leads to a large amount of acid and alkali used in the lithium extraction process and a large amount of wastewater generated. Therefore, it is necessary to develop a more green and environmentally friendly lithium recovery route. SUMMARY

[0004] The present application aims to at least partially solve one of the problems in the related art. To this end, the main purpose of the present application is to provide a method for efficiently recovering lithium in waste lithium iron phosphate batteries, which can effectively extract lithium resources in waste lithium iron phosphate batteries, reduce the use of acid and alkali in the process, and recycle by-products in the process, realize a closed loop, and optimize the product structure.

[0005] The purpose of the present application is achieved by the following technical solutions:

[0006] A method for efficiently recovering lithium in waste lithium iron phosphate batteries, comprising the following steps:

[0007] 1) ammonium persulfate lithium extraction: adding an ammonium persulfate solution to the waste lithium iron phosphate powder for leaching reaction, and then performing solid-liquid separation to obtain a leaching solution;

[0008] 2) Impurity removal of leaching solution: the leaching solution is subjected to adsorption and impurity removal using a resin to obtain a resin-impurity-removed solution, and the resin after impurity removal is regenerated using sulfuric acid;

[0009] 3) Lithium hydroxide preparation by bipolar membrane: bipolar membrane electrodialysis reaction is performed on the resin-impurity-removed solution, and after electrolysis, a sulfuric acid solution is obtained in the acid chamber, and a mixed solution of ammonia and lithium hydroxide is obtained in the base chamber.

[0010] 4) Deamination reaction: the mixed solution of ammonia and lithium hydroxide is subjected to deamination reaction using a deamination membrane to obtain an ammonium sulfate and deamination lithium hydroxide solution;

[0011] 5) Crystallization and electrochemical reaction: the lithium hydroxide solution is subjected to crystallization to obtain lithium hydroxide crystals; and ammonium sulfate is prepared by electrochemical reaction.

[0012] In step 1), the used persulfate has good reducibility, which can oxidize ferrous ions to ferric ions, and iron elements are precipitated in the form of iron phosphate, and the reaction formula is as follows:

[0013] 2LiFePO4 + (NH4)2S2O8 → Li2SO4 + 2FePO4↓ + (NH4)2SO4

[0014] The lithium element in lithium iron phosphate is in the form of ions in the solution, and the iron element is precipitated in the form of iron phosphate, thereby realizing selective separation of iron and lithium elements; persulfate has high selectivity for lithium element, and can leach lithium ions with high leaching rate, while leaching iron with very low leaching rate.

[0015] In step 2), the leaching solution in step 1) is subjected to impurity removal treatment, and hydrogen type resin is used to selectively remove divalent and trivalent cations from the leaching solution, thereby removing calcium, magnesium and iron from lithium sulfate.

[0016] The resin-impurity-removed solution in step 2) is a mixed solution of lithium sulfate and ammonium sulfate;

[0017] In step 4), during the deamination process, the alkaline solution, i.e. the mixed solution of ammonia and lithium hydroxide, in the bipolar membrane base chamber is on the outside of the hollow fiber membrane, the diluted acid produced in the bipolar membrane acid chamber is on the inside of the hollow fiber membrane, ammonium ions are removed from the outside of the hollow fiber membrane to become ammonia gas at high temperature, which is absorbed by sulfuric acid on the inside of the hollow fiber to form ammonium sulfate, and the lithium hydroxide solution after deamination is obtained on the outside of the hollow fiber membrane.

[0018] In some embodiments, the resin in step 2) is a hydrogen type resin, and the column speed of the leaching solution is 5-10 BV / h.

[0019] Further, the hydrogen type resin is a macroporous strong acid cation exchange resin, the functional group is a nuclear grade sulfonic acid group, the main structure is a polystyrene copolymer, and the temperature resistance is 130 DEG C.

[0020] In some embodiments, the sulfuric acid solution prepared in step 3) is further used for regenerating the resin after impurity removal in step 2).

[0021] In some embodiments, in step 4), the pH value of the mixed solution of ammonia and lithium hydroxide is 12-13, and the deamination reaction temperature is 35-40 DEG C.

[0022] In some embodiments, the electrochemical reaction device used in step 5) is: the anode uses a Pt electrode, the cathode uses a graphite electrode or a lead electrode, the anode liquid is an ammonium sulfate solution, and the cathode liquid is a sulfuric acid solution.

[0023] In some embodiments, the ammonium sulfate solution prepared in step 5) is further subjected to an electrochemical reaction to prepare a persulfate solution, and the persulfate solution is recycled as a raw material for the lithium extraction leaching process in step 1).

[0024] Compared with the prior art, the present application has at least the following advantages:

[0025] The method for efficiently recycling lithium in waste lithium iron phosphate batteries provided by the present application effectively reduces the use of acid in the leaching process and avoids a large amount of subsequent neutralization reaction. At the same time, by sequentially removing impurities, bipolar membrane electrolysis, deamination reaction, and crystallization on the leaching solution, high-purity lithium hydroxide crystals are prepared, and the acid (sulfuric acid) or ammonium persulfate prepared by electrochemical reaction can be recycled for the production system, thereby reducing the cost of raw materials. The experimental steps of the preparation method are simple, controllable, and can effectively control impurities to obtain pure lithium hydroxide product. At the same time, part of the product prepared by the method can be used as a raw material to form a closed circulation route, which is green and recyclable. DETAILED DESCRIPTION

[0026] The present application will be further described in detail below in combination with specific examples, which are only descriptive and not limiting, and cannot limit the protection scope of the present application.

[0027] When a range, preferably range, or preferred upper and lower limits of a numerical value are recited, it is to be understood that any and every intervening value, to the lower limit, or to the upper limit, regardless of its proximity to either limit, is encompassed within the scope of the present application. Unless otherwise stated, the numerical ranges listed herein are inclusive of the recited endpoint and all integer and fraction values within that range.

[0028] All percentages, parts, ratios, etc. herein are by weight, unless otherwise indicated.

[0029] The materials, methods, and examples herein are illustrative only and, except as specifically stated, are not intended to be limiting.

[0030] In the following examples, the hydrogen type resin is a macroporous strong acid cation exchange resin, the functional group is a nuclear grade sulfonic acid group, the main structure is a polystyrene copolymer, and the temperature resistance is 130°C.

[0031] In the following examples, during the deamination process, the base produced by the bipolar membrane alkali chamber, i.e., the mixed solution of ammonia and lithium hydroxide, is on the outside of the hollow fiber membrane, the diluted acid produced by the bipolar membrane acid chamber is on the inside of the hollow fiber membrane, the ammonium ions are removed from the outside of the hollow fiber membrane as ammonia gas at high temperature, and the ammonia gas is absorbed by the sulfuric acid on the inside of the hollow fiber to produce ammonium sulfate, and the lithium hydroxide solution after deamination is obtained on the outside of the hollow fiber membrane.

[0032] The electrochemical reaction device used in the electrochemical reaction uses a Pt electrode as the anode and a graphite electrode or a lead electrode as the cathode, the anode liquid is an ammonium sulfate solution, and the cathode liquid is a sulfuric acid solution.

[0033] Example 1

[0034] The method for recycling lithium in waste lithium iron phosphate battery provided by the application comprises the following steps: weighing 100 g of dry waste lithium iron phosphate powder into a beaker (the mass fraction of phosphorus in the waste lithium iron phosphate powder is 18.1%, the mass fraction of iron is 32.2%, and the mass fraction of lithium is 3.9%), adding 110 g of ammonium persulfate, adjusting the solid-liquid ratio to 110 g / L, stirring at a speed of 400 rpm, reacting at 40℃ for 60 minutes, and then performing solid-liquid separation to obtain a leaching solution. The leaching solution is subjected to impurity removal by using a hydrogen resin (the column passing speed of the leaching solution is 6 BV / h), and the solution after the impurity removal by the hydrogen resin (a mixed solution of lithium sulfate and ammonium sulfate) is subjected to bipolar membrane electrodialysis reaction, the voltage is adjusted to 35 V, the current is 2.2 A, pure water is added into an acid-base chamber, the solution after the impurity removal by the hydrogen resin is added into an original solution chamber, a lithium sulfate solution is used as an electrode solution (the electrode solution can be reused), and after electrolysis, a sulfuric acid solution is obtained in the acid chamber, the sulfuric acid solution can be used for regenerating the resin after the impurity removal, so that the resin after the impurity removal can be reused; an ammonia water and lithium hydroxide mixed solution is obtained in the alkali chamber; then the ammonia water and lithium hydroxide mixed solution (the pH value of the ammonia water and lithium hydroxide mixed solution is 12) in the alkali chamber is heated to 35℃ to perform a deamination membrane deamination reaction, the acid inflow is adjusted to 36 L / h, the liquid inflow is adjusted to 18 L / h, dilution of 1% of the bipolar membrane acid chamber product acid is used in the hollow fiber membrane inside of the deamination membrane, the ammonia water and lithium hydroxide mixed solution is subjected to a deamination nitrogen reaction, an ammonium sulfate solution and a lithium hydroxide solution after the deamination nitrogen are obtained; the lithium hydroxide solution after the deamination is subjected to evaporation crystallization to obtain a lithium hydroxide product; and the ammonium sulfate solution is subjected to an electrochemical reaction to prepare ammonium persulfate, the ammonium persulfate can be recycled and used as raw material for the leaching process of the waste lithium iron phosphate powder.

[0035] The sample obtained in the preparation process of the embodiment is analyzed in the application, and the results are shown in Table 1.

[0036] Table 1 Analysis of each sample in the preparation process of Example 1

[0037]

[0038] Example 2

[0039] This invention provides a method for efficiently recovering lithium from waste lithium iron phosphate batteries. 100g of dried lithium iron phosphate powder (containing 18.1% phosphorus, 32.2% iron, and 3.9% lithium by mass) is weighed and added to a beaker. 100g of ammonium persulfate is added, and the solid-liquid ratio is adjusted to 80g / L. The mixture is stirred at 500rpm and reacted at 50°C for 90 minutes. Solid-liquid separation yields a leachate. The leachate is then purified using a hydrogen-form resin (with a column velocity of 5 BV / h). A bipolar membrane electrodialysis reaction was performed on the purified solution (a mixed solution of lithium sulfate and ammonium sulfate) from the hydrogen-form resin. The voltage was adjusted to 35V and the current to 2.2A. Pure water was added to the acid-base chamber, and the purified solution from the hydrogen-form resin was added to the stock solution chamber. Lithium sulfate solution was used as the electrode solution (the electrode solution is reusable). After electrolysis, sulfuric acid solution was obtained in the acid chamber, which can be used to regenerate the purified resin, allowing it to be reused. A mixed solution of ammonia and lithium hydroxide was obtained in the alkali chamber. Then, the mixed solution of ammonia and lithium hydroxide in the alkali chamber was... The pH value is 12) and the temperature is raised to 40℃ to carry out the deammoniation reaction of the deammoniation membrane. The acid feed flow rate is adjusted to 40L / h and the liquid feed flow rate is adjusted to 20L / h. Acid is produced by using a bipolar membrane acid chamber diluted to 1% on the inner side of the hollow fiber membrane of the deammoniation membrane. The ammonia and lithium hydroxide mixed solution is subjected to a deammoniation nitrogen reaction to obtain ammonium sulfate solution and lithium hydroxide solution after ammonia nitrogen removal. The lithium hydroxide solution after ammonia removal is then evaporated and crystallized to obtain lithium hydroxide product. The ammonium sulfate solution is subjected to an electrochemical reaction to prepare ammonium persulfate. The ammonium persulfate can be recycled as a raw material for the leaching process of waste lithium iron phosphate powder.

[0040] This application analyzes the sample obtained during the preparation process of this embodiment, and the results are shown in Table 2:

[0041] Table 2. Analysis of each sample during the preparation process in Example 2.

[0042]

[0043] Example 3

[0044] The present invention provides a method for efficiently recovering lithium from waste lithium iron phosphate batteries. 100g of dry lithium iron phosphate powder is weighed and added to a beaker (the mass fraction of phosphorus in the waste lithium iron phosphate powder is 18.1%, the mass fraction of iron is 32.2%, and the mass fraction of lithium is 3.9%). 100g of ammonium persulfate is added, the solid-liquid ratio is adjusted to 120g / L, the stirring speed is 600rpm, and the reaction is carried out at 30℃ for 150 minutes. The solid and liquid are separated to obtain a leachate. The leachate was purified using hydrogen-form resin (leaching rate 8 BV / h). The purified solution (a mixed solution of lithium sulfate and ammonium sulfate) was then subjected to bipolar membrane electrodialysis. The voltage was adjusted to 35V and the current to 2.2A. Pure water was added to the acid-base chamber, and the purified solution was added to the stock chamber. Lithium sulfate solution was used as the electrode solution, which was reusable. After electrolysis, sulfuric acid solution was obtained in the acid chamber, which could be used to regenerate the purified resin, allowing for its reuse. A mixed solution of ammonia and lithium hydroxide was obtained in the alkali chamber. The mixture of ammonia and lithium hydroxide in the alkali chamber was then... The liquid (a mixed solution of ammonia and lithium hydroxide with a pH of 12) is heated to 50°C to carry out ammonia removal reaction via a deammoniation membrane. The acid feed flow rate is adjusted to 40 L / h and the liquid feed flow rate is adjusted to 20 L / h. Acid is produced in the bipolar membrane acid chamber diluted to 1% on the inner side of the hollow fiber membrane of the deammoniation membrane. The ammonia and lithium hydroxide mixed solution is subjected to a deammoniation reaction to obtain ammonium sulfate solution and lithium hydroxide solution after ammonia removal. The lithium hydroxide solution after ammonia removal is then evaporated and crystallized to obtain lithium hydroxide product. The ammonium sulfate solution is subjected to an electrochemical reaction to prepare ammonium persulfate. This ammonium persulfate can be recycled as a raw material for the leaching process of waste lithium iron phosphate powder.

[0045] This application analyzes the sample obtained during the preparation process of this embodiment, and the results are shown in Table 3:

[0046] Table 3. Analysis of various samples during the preparation process in Example 3.

[0047]

[0048]

[0049] This application also tested the composition of the lithium hydroxide crystals prepared by the methods in Examples 1-3, and the results are shown in Table 4:

[0050] Table 4. Compositional testing of lithium hydroxide crystals in various embodiments.

[0051] LiOH H2O (%) S(％) Fe (%) Mg (%) Al(％) Example 1 99.1 0.001 0.001 0.001 0.001 Example 2 98.5 0.001 0.001 0.001 0.001 Example 3 98.6 0.001 0.001 0.001 0.001

[0052] As can be seen from Tables 1, 2, 3 and 4, the lithium hydroxide product prepared in this application has high purity, reaching the purity of industrial-grade lithium hydroxide, thus realizing the effective recovery of lithium from lithium iron phosphate battery powder.

[0053] Comparative Example 1

[0054] This comparative example provides a method for efficiently recycling waste lithium iron phosphate batteries. This method is basically the same as Example 2, except that it uses a macroporous, strongly acidic cation exchange resin with aminophosphonic acid as the functional group, polystyrene copolymer as the main structure, and a temperature resistance of 60℃. Using this resin for impurity removal, performance tests on the purified solution show that:

[0055] It cannot effectively remove impurities, and the liquid after impurity removal cannot undergo bipolar membrane electrodialysis and other subsequent process steps.

[0056] Table 5. Analysis of each sample during the preparation of Comparative Example 1.

[0057] Li (g / L) S (g / L) NH4 + (g / L) Fe (mg / L) Al (mg / L) Mg (mg / L) Leaching solution 1.49 11.77 6.62 20.4 10.3 2.2 After impurity removal solution 1.47 10.92 6.60 2.8 2.7 1.3

[0058] As shown in Table 5, the resin in this comparative example cannot effectively remove impurities, and the liquid after impurity removal cannot undergo bipolar membrane electrodialysis and other subsequent process steps, thus failing to achieve the goal of recovering lithium from waste lithium iron phosphate batteries.

[0059] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for efficiently recovering lithium from a spent lithium iron phosphate battery, characterized by, It comprises the following steps: 1) lithium extraction with ammonium persulfate: adding ammonium persulfate solution to waste lithium iron phosphate powder for leaching reaction, and then performing solid-liquid separation to obtain a leaching solution; 2) impurity removal of the leaching solution: using a resin to adsorb and remove impurities from the obtained leaching solution, and then obtaining a resin-impurity-removed solution, and using sulfuric acid to regenerate the resin after impurity removal; 3) preparation of lithium hydroxide by bipolar membrane: performing bipolar membrane electrodialysis reaction on the resin-impurity-removed solution, obtaining sulfuric acid solution in the acid chamber and ammonia water and lithium hydroxide mixed solution in the alkali chamber after electrolysis; 4) deamination reaction: using a deamination membrane to perform deamination reaction on the ammonia water and lithium hydroxide mixed solution to obtain ammonium sulfate and deaminated lithium hydroxide solution; 5) crystallization and electrochemical reaction: crystallizing the lithium hydroxide solution to obtain lithium hydroxide crystals; and preparing ammonium persulfate by electrochemical reaction of ammonium sulfate. The resin in step 2) is a hydrogen type resin, which is a macroporous strong acid cation exchange resin, the functional group is a nuclear grade sulfonic acid group, the main structure is polystyrene copolymer, and the temperature resistance is 130℃; The leaching solution has a column speed of 5-10 BV / h; and the sulfuric acid solution prepared in step 3) is used for resin regeneration in step 2).

2. The method for efficiently recovering lithium from spent lithium iron phosphate battery according to claim 1, characterized in that, The leaching temperature of the ammonium persulfate solution used in step 1) is 20-80℃, the mass ratio of the waste lithium iron phosphate powder to ammonium persulfate is (1-2):1, the solid-liquid ratio in the leaching system is 50-500 g / L, and the leaching time is 0.5-5 h.

3. The method for efficiently recovering lithium from spent lithium-iron-phosphate batteries according to claim 2, characterized by, In step 4), the pH value of the ammonia water and lithium hydroxide mixed solution is 12-13, and the deamination reaction temperature is 35-40℃.

4. The method for efficiently recovering lithium from spent lithium-iron-phosphate batteries according to claim 3, characterized by, The electrochemical reaction device used in step 5) is: the anode uses a Pt electrode, the cathode uses a graphite electrode or a lead electrode, the anode liquid is ammonium sulfate solution, and the cathode liquid is sulfuric acid solution.

5. The method for efficiently recovering lithium from spent lithium iron phosphate battery according to claim 4, characterized in that, The ammonium sulfate solution prepared in step 5) is used for electrochemical reaction to prepare ammonium persulfate solution, which can be recycled as raw material for the lithium extraction leaching process in step 1).

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