CN117509581A

CN117509581A - Method for recycling positive electrode material

Info

Publication number: CN117509581A
Application number: CN202311462284.1A
Authority: CN
Inventors: 申屠华剑; 王本平; 胡平平; 谭江豪; 邓龙平
Original assignee: Ningbo Ronbay Lithium Battery Material Co Ltd
Current assignee: Ningbo Ronbay Lithium Battery Material Co Ltd
Priority date: 2023-11-06
Filing date: 2023-11-06
Publication date: 2024-02-06

Abstract

The invention provides a method for recycling a positive electrode material, which comprises the following steps: 1) Mixing lithium iron phosphate powder and deionized water for pulping, and regulating the pH value of a pulping system to 3-5 by phosphoric acid to obtain a mixed solution; 2) Adding Fenton reagent into the mixed solution, and filtering to obtain a first filtrate and a first filter residue; 3) And (3) refining the first filter residue, wherein the refining treatment comprises iron value conversion treatment, so that iron phosphate with purity of more than 99.5% is obtained. According to the positive electrode material recovery method provided by the invention, the addition of the Fenton reagent can oxidize ferrous ions into ferric ions, and the ferric ions are combined with phosphate to generate ferric phosphate precipitates, and the processes of aluminum removal treatment, slag removal, iron valence conversion treatment and sintering treatment are performed, so that the interference of other impurities is avoided, and the purity of the finally obtained ferric phosphate is higher.

Description

Method for recycling positive electrode material

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a method for recycling a positive electrode material.

Background

In recent years, with the continuous development of new energy automobiles, replacement of conventional automobiles has become a necessary trend. The lithium iron phosphate battery is widely applied to the new energy automobile industry because of low preparation cost and high safety performance. In recent years, however, the scrapped amount of lithium iron phosphate batteries tends to increase in multiples, and thus, recovery of waste lithium iron phosphate batteries has been urgent.

In the prior art, the main focus of recovery of waste lithium iron phosphate batteries is on the development of lithium extraction technology, in some methods for recovering ferrophosphorus elements, ferric phosphate is precipitated by adjusting the pH value of a system after ferric phosphate is leached by an acid leaching wet method, and the purity of the recovered ferric phosphate in the method is low. Therefore, developing a method for recovering a positive electrode material with higher purity of the recovered iron phosphate product is a technical problem to be solved in the current stage.

Disclosure of Invention

The invention mainly aims to provide a method for recycling a positive electrode material, which can effectively solve the problem that the purity of recycled ferric phosphate is low and can recycle lithium.

The invention provides a method for recycling a positive electrode material, which comprises the following steps:

1) Mixing lithium iron phosphate powder and deionized water for pulping, and regulating the pH value of a pulping system to 3-5 by phosphoric acid to obtain a mixed solution;

2) Adding Fenton reagent into the mixed solution, and filtering to obtain a first filtrate and a first filter residue;

3) And (3) refining the first filter residue, wherein the refining treatment comprises iron value conversion treatment, so that iron phosphate with purity of more than 99.5% is obtained.

The recovery method as described above, the aluminum removal treatment comprising:

mixing and slurrying the first filter residue and deionized water, adding an aluminum removing agent, and filtering to obtain a second filtrate and a second filter residue;

the molar ratio of the aluminum removing agent to the aluminum is 1-1.2:1.

The recycling method as described above, wherein the slag removal treatment comprises:

and leaching the second filter residue by concentrated sulfuric acid, regulating the pH value of the system to 0-1, and filtering to obtain a third filtrate and a third filter residue.

The recovery method as described above, the iron value conversion process includes: adding iron powder into the third filtrate until no precipitate is generated, adjusting the pH of the system to 5-8, and filtering to obtain a fourth filtrate and a fourth filter residue;

adding hydrogen peroxide and phosphoric acid into the fourth filtrate until no precipitate is generated, controlling the molar ratio of the phosphorus to the iron in the fourth filtrate to be 1-1.2:1, and filtering to obtain the water-containing ferric phosphate.

According to the recovery method, the solid-to-liquid ratio of the first filter residue to the deionized water is 1g:1-50mL.

The concentration of the concentrated sulfuric acid is 6-18mol/L according to the recovery method.

The recovery method as described above, wherein the solid-to-liquid ratio of the lithium iron phosphate powder and deionized water in step 1) is 1g:1-10mL.

According to the recovery method, the Fenton reagent is ferrous phosphate and hydrogen peroxide;

the mol ratio of hydrogen peroxide to ferrous ions in the Fenton reagent is 1-100:1;

the molar ratio of the hydrogen peroxide to the lithium iron phosphate is 1-10:1.

According to the recovery method, the mole ratio of hydrogen peroxide to ferrous ions in the Fenton reagent is 3-5:1.

The recovery method as described above, further comprising: adding saturated sodium carbonate solution into the first filtrate, and filtering to obtain lithium carbonate precipitate;

and washing and drying the lithium carbonate precipitate to obtain lithium carbonate solid.

The invention provides a method for recycling a positive electrode material, which is characterized in that ferrous ions can be oxidized into iron ions by adding Fenton reagent, ferric phosphate precipitates are generated by combining phosphate radicals, and the finally obtained ferric phosphate has higher purity by the processes of aluminum removal treatment, slag removal treatment, iron valence conversion treatment and sintering treatment, so that the interference of other impurities is avoided.

Detailed Description

For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the technical solutions in the embodiments of the present invention will be clearly and completely described in the following in conjunction with the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

3) And (3) carrying out refining treatment comprising aluminum removal treatment, slag removal treatment, iron value transformation treatment and sintering treatment on the first filter residue to obtain the iron phosphate with the purity of more than 99.5%.

It can be appreciated that the retired lithium iron phosphate battery is discharged, disassembled and sorted to obtain lithium iron phosphate powder.

Fenton's reagent refers to a system composed of hydrogen peroxide and ferrous ions and having strong oxidizing property. The principle is that under the acidic condition, hydrogen peroxide generates hydroxyl free radical with strong oxidizing ability in the presence of ferrous ions, and induces reducing ions to be oxidized. For example, in this example, the hydroxyl radical ferrous oxide ion becomes ferric ion.

In one embodiment, the lithium iron phosphate powder and deionized water are mixed to obtain a slurrying system, and the pH of the slurrying system is regulated to 3-5 by phosphoric acid, alternatively, the pH can be any value between 3, 4, 5 or 3-5 to obtain a mixed solution; after Fenton reagent is added into the mixed solution, the system is precipitated and separated out, and the first filtrate and first filter residue are obtained through filtration; and refining the first filter residue, wherein the refining comprises aluminum removal, slag removal, iron value transformation and sintering, so that the purity of the finally obtained ferric phosphate is more than 99.5%.

In the step 1), the pH value of the slurrying system is regulated to 3-5 by phosphoric acid, so that ferric phosphate precipitate generated by subsequent ferric ions can be prevented from being dissolved, and the yield of finally obtained ferric phosphate can be improved. Alternatively, the phosphoric acid concentration is controlled to be 0.1 to 3mol/L, and may be any value between 0.1mol/L,1mol/L,2mol/L,3mol/L, or 0.1 to 3mol/L, and preferably may be 1mol/L. It can be appreciated that if the phosphoric acid concentration is too low, a large amount of phosphoric acid is required to adjust the system pH; if the phosphoric acid concentration is too high, it is not easy to accurately control the pH value and the accuracy is not satisfactory, and therefore, it is necessary to add phosphoric acid of a proper concentration, for example, to control the phosphoric acid concentration to 0.1 to 3mol/L.

In step 2), hydrogen peroxide in the Fenton reagent generates hydroxyl free radical with strong oxidizing capability in the presence of ferrous ions and causes the ferrous ions to be oxidized, for example, the hydroxyl free radical oxidizes the ferrous ions in lithium iron phosphate and the ferrous ions in the Fenton reagent into iron ions, the iron ions are combined with phosphate to generate ferric phosphate precipitate, and the ferric phosphate precipitate can exist stably in an environment with pH value of 3-5. Therefore, the precipitation of the iron element in the lithium iron phosphate is realized in the step 2), the subsequent recovery of the iron element is facilitated, and the interference of the iron element on the recovery of the lithium element can be avoided. And filtering the precipitation system to realize solid-liquid separation of the generated ferric phosphate precipitate and filtrate, wherein the ferric phosphate precipitate is the first filter residue, and the filtrate is the first filtrate. Therefore, the first filtrate contains a large amount of lithium ions and phosphate ions and the content of other metal elements (e.g., iron element) is extremely low. Because the positive current collector of the lithium ion battery is usually aluminum foil, aluminum impurities, such as aluminum oxide or aluminum simple substance, are inevitably carried in when the retired lithium iron phosphate battery is processed to obtain lithium iron phosphate powder, and the aluminum impurities are not dissolved when the pH value of the system is 3-5. And the negative current collector of the lithium ion battery generally adopts copper foil, copper impurities, such as copper oxide or copper simple substance, are inevitably carried in when the retired lithium iron phosphate battery is disassembled to obtain lithium iron phosphate powder, and the copper impurities are insoluble when the pH value of the system is 3-5. In addition, carbon-based compounds, which are negative electrode materials of lithium ion batteries, are inevitably introduced into lithium iron phosphate powder, and thus, the first filter residue contains a large amount of iron phosphate precipitates, a small amount of aluminum impurities, copper impurities and carbon-based compounds, and acid-base insoluble impurities.

Optionally, after Fenton reagent is added into the mixed solution, soaking treatment is performed first, the pH of the system is regulated to 3-5 by using phosphoric acid, and then filtration is performed to obtain a first filtrate and a first filter residue. It can be appreciated that the purpose of the soaking is to fully convert the ferrous ions in the lithium iron phosphate and the ferrous ions in the Fenton reagent to ferric ions, thereby producing a ferric phosphate precipitate. Optionally, the soaking treatment time is less than 8 hours, so that ferrous ions can be completely oxidized into ferric ions to generate ferric phosphate precipitates, time waste is avoided, and the efficiency is low. The soaking treatment temperature can be 25-80 ℃, ferrous ions can be completely oxidized into ferric ions within the temperature range, the reaction condition is mild, the requirement on equipment is low, and the energy consumption is low. It will be appreciated that the pH during the soaking process will rise, probably due to the dissolution of lithium in the lithium iron phosphate in water, resulting in the formation of a strong lithium hydroxide base, so the pH of the system can be maintained at 3-5 by the continuous addition of phosphoric acid during the soaking process, alternatively, the pH can be any value between 3, 4, 5 or 3-5. Optionally, during the soaking process, the system can be stirred, so that the soaking efficiency is improved.

In the step 3), refining the first filter residue, wherein the refining comprises aluminum removal, slag removal, iron value transformation and sintering, specifically, aluminum impurities in the first filter residue are dissolved into a solution to generate soluble aluminum-containing ions, and the soluble aluminum-containing ions are filtered out; dissolving ferric phosphate precipitate and copper impurities in the first filter residue, and filtering to remove non-slag, namely removing carbon-based compounds and acid-base insoluble impurities; then, iron value conversion treatment is carried out, firstly, reducing substances are added into the solution in which ferric phosphate precipitates and copper impurities are dissolved, copper ions are converted into copper ions after the copper impurities are dissolved and are dissolved in the solution, meanwhile, ferric iron in the solution is reduced into ferrous iron, solid-liquid separation is carried out on the solution containing ferrous iron and the copper simple substance through filtration, interference of the copper impurities is avoided, then, oxidizing substances are added to oxidize and convert ferrous iron in the solution into ferric iron, ferric iron and phosphate ions in the solution are combined to generate ferric phosphate precipitates, and in the process, the phosphate ions in the solution are excessive to ensure that the ferric iron is completely converted into ferric phosphate precipitates, and at the moment, the purity of the generated ferric phosphate precipitates is higher and the degree of interference by other impurities is smaller. The generated ferric phosphate precipitate contains crystal water, and then the ferric phosphate containing the crystal water is sintered, for example, the ferric phosphate containing the crystal water is placed in a muffle furnace, the sintering temperature is controlled to be 180-200 ℃, the sintering time is controlled to be 2-4 hours, and the purity of the ferric phosphate is more than 99.5% after the crystal water is removed.

In the embodiment, the addition of Fenton reagent can oxidize ferrous ions into ferric ions, and the ferric ions are combined with phosphate to generate ferric phosphate precipitates, and then the processes of aluminum removal, slag removal, iron valence conversion and sintering are performed, so that the interference of other impurities is avoided, and the purity of the finally obtained ferric phosphate is higher.

In some embodiments of the invention, the dealumination treatment comprises:

the molar ratio of the aluminum removing agent to the aluminum is 1-1.2:1.

It can be appreciated that the first filter residue contains aluminum impurities, so that the purity of the finally obtained iron phosphate is high, and the aluminum impurities need to be removed in order to avoid interference of the aluminum impurities. In the embodiment, the first filter residue and deionized water are mixed to obtain a slurrying system, and then an aluminum removing agent is added into the slurrying system, wherein the molar ratio of the aluminum removing agent to aluminum is 1-1.2:1, and the second filter residue are obtained through filtration.

Specifically, the first filter residue and deionized water are mixed to obtain a slurrying system, and then an aluminum removing agent is added into the slurrying system, wherein the aluminum removing agent is an alkaline solution, such as ammonia water, caustic soda or sodium carbonate, preferably, the aluminum removing agent is caustic soda, namely, a strong sodium oxide solution, and the molar ratio of the aluminum removing agent to the aluminum in the first filter residue is controlled to be 1-1.2:1, so that aluminum impurities contained in the first filter residue are completely removed. Adding an alkaline aluminum removing agent to enable aluminum impurities in the first filter residue to generate metaaluminate radicals, dissolving the metaaluminate radicals in the solution, filtering to obtain second filtrate containing the metaaluminate radicals, and discarding the second filtrate according to different types of the added alkaline solution to realize the purpose of removing aluminum; the second filter residue contains ferric phosphate, copper impurities, carbon-based compounds and acid-base insoluble impurities.

In the embodiment, aluminum impurities are removed by adding an aluminum removing agent, so that when iron phosphate precipitates, the aluminum impurities are prevented from accompanying the precipitation, and the purity of the iron phosphate product is improved.

In some embodiments of the invention, the slag removal treatment comprises:

It can be appreciated that the second filter residue contains slag-free, i.e. carbon-based compounds and acid-base-insoluble impurities, and that the slag-free impurities need to be removed in order to avoid interference of the slag-free impurities and to make the purity of the finally obtained iron phosphate higher. In the embodiment, concentrated sulfuric acid is added into the second filter residue, the second filter residue is leached, the pH value of the system is regulated to be 0-1, and the third filter residue are obtained through filtration.

Specifically, adding concentrated sulfuric acid into the second filter residue, dissolving ferric phosphate and copper impurities in the second filter residue, regulating the pH value of the system to 0-1, preventing ferric phosphate dissolved in the concentrated sulfuric acid from generating precipitation, reacting the copper impurities with the concentrated sulfuric acid to generate copper ions after the concentrated sulfuric acid is added, and filtering to obtain a third filtrate containing phosphate ions, sulfate ions, iron ions and copper ions; the third filter residue contains carbon-based compounds and acid-base-insoluble impurities, and the third filter residue is discarded, so that the purpose of slag removal is realized.

In the embodiment, the second filter residue is leached by adding concentrated sulfuric acid, the pH value of the system is regulated, the non-slag is removed by filtering, the interference of the non-slag on the purity of the ferric phosphate product is avoided, and the purity of the ferric phosphate product is improved.

In some embodiments of the invention, the iron value conversion process comprises: adding iron powder into the third filtrate until no precipitate is generated, adjusting the pH of the system to 5-8, and filtering to obtain a fourth filtrate and a fourth filter residue;

adding hydrogen peroxide and phosphoric acid into the fourth filtrate until no precipitate is generated, controlling the molar ratio of phosphorus to iron in the fourth filtrate to be 1-1.2:1, and filtering to obtain the water-containing ferric phosphate.

It can be understood that the third filtrate contains phosphate ions, sulfate ions, iron ions and copper ions, in order to make the purity of the finally obtained ferric phosphate higher, the copper ions in the third filtrate need to be removed, and meanwhile, the valence state of the iron ions needs to be kept unchanged, and in the embodiment, the reducing iron powder is selected to reduce the copper ions into copper simple substance so as to remove the copper ions. Therefore, the iron value conversion process in this embodiment includes: adding iron powder into the third filtrate until no precipitate is generated, adjusting the pH of the system to 5-8, optionally, the pH can be any value between 5, 6, 7, 8 or 5-8, and filtering to obtain fourth filtrate and fourth filter residue; adding hydrogen peroxide and phosphoric acid into the fourth filtrate until no precipitate is generated, wherein the molar ratio of phosphorus element to iron element in the fourth filtrate is 1-1.2:1, optionally, the molar ratio of phosphorus element to iron element in the fourth filtrate can be any value between 1:1,1.1:1,1.2:1 or 1-1.2:1, and filtering to obtain the ferric phosphate containing water.

Specifically, reducing iron powder is added into the third filtrate, copper ions in the third filtrate are reduced into copper simple substance and separated out in a precipitation form, meanwhile, iron ions in the third filtrate are reduced into ferrous ions by the reducing iron powder, and the addition of the iron powder is stopped when the copper simple substance precipitation is not generated any more. The pH value of the system is adjusted to 5-8, so that ferrous ions do not generate precipitate, only copper simple substance exists in a precipitate form, sulfate ions, phosphate ions and ferrous ions are contained in the obtained fourth filter residue, the copper simple substance is contained in the fourth filter residue, the fourth filter residue is abandoned, the purpose of copper removal is achieved, the content of iron element and phosphorus element in the fourth filter residue is detected, and the subsequent control of the content ratio of the iron element to the phosphorus element is facilitated. Adding hydrogen peroxide and phosphoric acid into the fourth filtrate, oxidizing ferrous ions in the fourth filtrate into ferric ions by the oxidation of the hydrogen peroxide, combining the ferric ions with phosphate to generate ferric phosphate precipitates, and stopping adding the hydrogen peroxide when the ferric phosphate precipitates are not generated any more. According to the detected contents of the iron element and the phosphorus element in the fourth filtrate, the added phosphoric acid is controlled to enable the mole ratio of the phosphorus element to the iron element in the fourth filtrate to be 1-1.2:1, and preferably, the mole ratio of the phosphorus element to the iron element in the fourth filtrate to be 1.05:1, so that ferric ions and phosphate radicals can be combined to completely generate ferric phosphate precipitation, and excessive phosphorus element waste can be avoided. Meanwhile, oxygen can be continuously introduced into the system, for example, the introduction amount of the oxygen is controlled to be 3L/min, so that the oxygen content in the fourth filtrate is increased, the efficiency of converting ferrous ions into ferric ions is improved, and the efficiency of generating ferric phosphate precipitates can also be improved. The iron phosphate obtained by filtration is iron phosphate containing crystal water.

In the embodiment, iron powder is added to convert copper ions into copper simple substance, the copper simple substance is removed through filtration, the influence of copper impurities on the purity of ferric phosphate is avoided, iron powder reduces the iron ions into ferrous ions, hydrogen peroxide is added to oxidize the ferrous ions into ferric ions, the ferric ions are combined with phosphate to generate ferric phosphate, the phosphate is excessive, and the iron element in the fourth filtrate can be completely converted into ferric phosphate, so that the purity of the finally obtained ferric phosphate is higher, and the yield is also higher.

In some embodiments of the invention, the solids to liquid ratio of the first filter residue to deionized water is 1g:1-50mL.

In one embodiment, the solids to liquid ratio of the first filter residue to deionized water may be controlled to be 1g:1-50mL to better slurry the first filter residue.

Alternatively, the solids to liquid ratio of the first filter residue to deionized water may be any value between 1g:10mL, 1g:20mL, 1g:30mL, 1g:40mL, 1g:50mL, or 1g:1-50mL.

In the embodiment, the solid-to-liquid ratio of the first filter residue to the deionized water is controlled to be 1g:1-50mL, so that the first filter residue can be slurried better, and the subsequent recycling of ferric phosphate in the first filter residue is facilitated.

In some embodiments of the invention, the concentration of concentrated sulfuric acid is from 6 to 18mol/L.

It will be appreciated that the second filter residue contains iron phosphate, copper impurities, carbon-based compounds and acid-base-insoluble impurities, and that in order to remove the carbon-based compounds and acid-base-insoluble impurities in the second filter residue, the iron phosphate and copper impurities in the second filter residue may be dissolved and filtered to remove the carbon-based compounds and acid-base-insoluble impurities in the second filter residue. In the embodiment, the iron phosphate and copper impurities in the second filter residue are leached out by adopting the concentrated sulfuric acid with the concentration of 6-18mol/L, namely, the iron phosphate and copper impurities are dissolved in the concentrated sulfuric acid. Alternatively, the concentration of the concentrated sulfuric acid may be any value of 6mol/L, 7mol/L, 8mol/L, 9mol/L, 10mol/L, 11mol/L, 12mol/L, 13mol/L, 14mol/L, 15mol/L, 16mol/L, 17mol/L, 18mol/L, or 6 to 18mol/L, and preferably the concentration of the concentrated sulfuric acid is 18mol/L. If the concentration of the concentrated sulfuric acid is too low and the oxidizing property is weak, the iron phosphate and copper impurities cannot be fully dissolved; if the concentration of the concentrated sulfuric acid is too high, the requirements on equipment and the like are high, so that the concentration of the concentrated sulfuric acid is controlled to be 6-18mol/L in the embodiment, and the concentration is a proper concentration.

In the embodiment, the concentrated sulfuric acid with the concentration of 6-18mol/L is adopted to fully leach out the ferric phosphate and copper impurities in the second filter residue so as to remove carbon-based compounds and acid-alkali insoluble impurities, so that the interference of the carbon-based compounds and the acid-alkali insoluble impurities on the purity of the ferric phosphate can be reduced, and the purity of the finally prepared ferric phosphate can be improved.

In some embodiments of the invention, the solid to liquid ratio of lithium iron phosphate powder to deionized water in step 1) is 1g:1-10mL.

In one embodiment, the solid to liquid ratio of lithium iron phosphate powder to deionized water may be controlled to be 1g:1-10mL to better slurry the lithium iron phosphate.

Alternatively, the solid to liquid ratio of lithium iron phosphate powder to deionized water may be any value between 1g:1mL, 1g:2mL, 1g:3mL, 1g:4mL, 1g:5mL, 1g:6mL, 1g:7mL, 1g:8mL, 1g:9mL, 1g:10mL, or 1g:1-10mL.

In the embodiment, the solid-to-liquid ratio of the lithium iron phosphate powder to the deionized water is controlled to be 1g:1-10mL, so that the lithium iron phosphate powder can be slurried better, and the full-component recycling of the lithium iron phosphate element in the lithium iron phosphate can be facilitated.

In some embodiments of the invention, the Fenton reagent is ferrous phosphate and hydrogen peroxide;

Fenton's reagent refers to a system composed of hydrogen peroxide and ferrous ions and having strong oxidizing property. Alternatively, the compound providing ferrous ions in the Fenton reagent may be ferrous sulfate, ferrous phosphate, preferably the compound providing ferrous ions is ferrous phosphate. Namely, the Fenton reagent in the embodiment consists of ferrous phosphate and hydrogen peroxide, wherein the molar ratio of the hydrogen peroxide to ferrous ions in the Fenton reagent is controlled to be 1-100:1, and the molar ratio of the hydrogen peroxide to lithium iron phosphate is controlled to be 1-10:1. Optionally, the concentration of hydrogen peroxide in the Fenton reagent is not higher than 30%, preferably, the concentration of hydrogen peroxide is 10%. It can be appreciated that when the concentration of hydrogen peroxide is too low, the generated hydroxyl radicals are too few to fully oxidize all ferrous ions into ferric ions; when the concentration of the hydrogen peroxide is too high, the hydrogen peroxide is decomposed, and hydroxyl free radicals with strong oxidizing ability are not generated, so that the concentration of the hydrogen peroxide in the Fenton reagent is proper, for example, the concentration of the hydrogen peroxide is controlled to be not higher than 30%.

In one embodiment, adding ferrous phosphate powder into a slurrying system of lithium iron phosphate powder with pH of 3-5 and deionized water, after uniformly mixing, gradually dropwise adding hydrogen peroxide with concentration of 10%, controlling the molar ratio of hydrogen peroxide to ferrous ions in Fenton reagent to be 1-100:1, and controlling the molar ratio of hydrogen peroxide to lithium iron phosphate to be 1-10:1. Under an acidic condition, hydrogen peroxide in the Fenton reagent generates hydroxyl free radicals with strong oxidizing capability in the presence of ferrous ions, the ferrous ions are triggered to be oxidized into iron ions, the iron ions are combined with phosphate ions to generate ferric phosphate precipitates, and the generated ferric phosphate precipitates and filtrate are subjected to solid-liquid separation by filtering a precipitation system. It can be understood that the hydrogen peroxide in the Fenton reagent should be added excessively, and because the hydrogen peroxide is excessive, ferrous ions can be completely converted into ferric ions, and ferric phosphate precipitates are generated, so that the yield of the finally obtained ferric phosphate is higher. Optionally, the molar ratio of hydrogen peroxide to ferrous ions in the Fenton reagent may be any value between 1:1, 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1, or 1-100:1; the molar ratio of hydrogen peroxide to lithium iron phosphate may be any value between 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, or 1-10:1. Preferably, the molar ratio of the hydrogen peroxide to the lithium iron phosphate is controlled to be 2-3:1.

In the embodiment, the Fenton reagent is composed of ferrous phosphate and hydrogen peroxide, the molar ratio of the hydrogen peroxide to ferrous ions in the Fenton reagent is controlled to be 1-100:1, and the molar ratio of the hydrogen peroxide to the lithium iron phosphate is controlled to be 1-10:1, so that the ferrous ions in the system can be completely converted into ferric phosphate precipitates, the finally obtained ferric phosphate yield is higher, the hydrogen peroxide in the Fenton reagent is decomposed into hydroxyl free radicals at a high speed, and the oxidation rate is also higher, so that the reaction speed of the reaction is also higher.

In some embodiments of the invention, the molar ratio of hydrogen peroxide to ferrous ions in the Fenton reagent is 3-5:1.

Alternatively, the molar ratio of hydrogen peroxide to ferrous ions in the Fenton reagent may be any value between 3:1, 4:1, 5:1, or 3-5:1.

In the embodiment, the molar ratio of the hydrogen peroxide to the ferrous ions in the Fenton reagent is controlled to be 3-5:1, so that the hydrogen peroxide is not wasted, the ferrous ions in the system can be completely oxidized into the ferric ions and finally converted into ferric phosphate precipitates, and the finally obtained ferric phosphate has higher yield.

In some embodiments of the invention, further comprising: adding saturated sodium carbonate solution into the first filtrate, and filtering to obtain lithium carbonate precipitate;

washing and drying the lithium carbonate precipitate to obtain lithium carbonate solid.

It can be understood that the first filtrate contains a large amount of lithium ions and phosphate ions, and other metal elements (e.g., iron elements) are extremely low in content, so that the value utilization rate of the resources is greatly improved, and the lithium ions in the first filtrate need to be recycled. According to the embodiment, the saturated sodium carbonate solution is added into the first filtrate, the solution is filtered to obtain the lithium carbonate precipitate, the lithium carbonate precipitate is washed and dried to obtain the lithium carbonate solid, and the recycling of lithium elements in the lithium iron phosphate powder is realized.

In one embodiment, an excess saturated sodium carbonate solution is added to the first filtrate to completely convert lithium ions in the first filtrate into lithium carbonate precipitate for precipitation, and in order to accelerate the reaction speed and make the reaction more complete, the first filtrate can be heated, and the excess saturated sodium carbonate solution is added under the condition of stirring to fully react to generate lithium carbonate precipitate. Filtering the solution containing the lithium carbonate precipitate to realize solid-liquid separation, obtaining the lithium carbonate precipitate, washing the obtained lithium carbonate precipitate for a plurality of times by using deionized water, for example, washing for 3-5 times, removing impurities, putting the solution into a vacuum drying oven for drying, for example, controlling the temperature of the vacuum drying oven to be 105 ℃, drying for 2-4 hours, removing excessive water, and finally obtaining the dried lithium carbonate solid.

According to the embodiment, the saturated sodium carbonate solution is added into the first filtrate, the solution is filtered, the lithium carbonate precipitate is obtained, and the lithium carbonate solid obtained through washing and drying is high in purity, so that the recycling of lithium elements is realized, and the value utilization rate of resources is greatly improved.

The technical scheme of the invention is further described below by combining specific embodiments.

Example 1

The method for recycling the positive electrode material of the embodiment comprises the following steps:

1) Mixing 50g of lithium iron phosphate powder with 50mL of deionized water for pulping, and regulating the pH of a pulping system to 3.5 by using phosphoric acid with the concentration of 1mol/L to obtain a mixed solution;

2) Adding Fenton reagent into the mixed solution, namely adding 75g of ferrous phosphate powder, uniformly mixing, gradually dropwise adding 220g of 10% hydrogen peroxide to ensure that the molar ratio of the hydrogen peroxide to ferrous ions is 3:1 and the molar ratio of the hydrogen peroxide to the lithium iron phosphate is 2:1, stirring and soaking for 4 hours at 25 ℃, stabilizing the pH value of a phosphoric acid regulating system with the concentration of 1mol/L at 3.5 in the soaking process, filtering after the soaking is finished, obtaining a first filtrate and a first filter residue, and testing the content of impurity aluminum in the first filter residue;

3) Taking 50g of first filter residue, adding 50mL of deionized water into the first filter residue, mixing and slurrying, adding aluminum removing agent sodium hydroxide to enable the molar ratio of the aluminum removing agent to the aluminum in the first filter residue to be 1.2:1, and filtering to obtain second filtrate and second filter residue;

4) Adding 18mol/L concentrated sulfuric acid into the second filter residue to enable the molar ratio of the concentrated sulfuric acid to the lithium iron phosphate to be 1.2:1, adjusting the pH value of the system to be 1, and filtering to obtain a third filtrate and a third filter residue;

5) Adding reduced iron powder into the third filtrate until no precipitate is generated, adjusting the pH of the system to 7, and filtering to obtain a fourth filtrate and a fourth filter residue;

6) Adding phosphoric acid into the fourth filtrate to enable the molar ratio of the phosphorus to the iron in the fourth filtrate to be 1.02:1, adding hydrogen peroxide until no precipitate is generated, and filtering to obtain water-containing ferric phosphate;

7) Placing the water-containing ferric phosphate in a muffle furnace at 200 ℃ for sintering for 4 hours to obtain the ferric phosphate with higher purity;

8) And adding an excessive saturated sodium carbonate solution into the first filtrate to obtain lithium carbonate precipitate, filtering, adding deionized water with the volume of 6 times to wash for 3 times, and putting into a 105 ℃ vacuum drying oven to dry for 2 hours to obtain lithium carbonate solid.

The yield of lithium refers to the ratio of the content of lithium in the lithium carbonate solid to the content of lithium in the lithium iron phosphate powder;

the yield of iron refers to the ratio of the content of iron in iron phosphate to the content of iron in lithium iron phosphate powder, the content of iron in ferrous phosphate, and the amount of iron powder added.

Examples 2 to 24

Examples 2-24 were identical to example 1, except that the individual parameters were different and the specific parameters are shown in Table 1.

Comparative example 1

The comparative example was substantially the same as the method of example 1, except that hydrogen peroxide was not added in step 2), and specific parameters are shown in Table 1.

Comparative example 2

This comparative example is essentially the same as example 1 except that no ferrous phosphate powder was added in step 2), and the specific parameters are shown in Table 1.

Comparative example 3

This comparative example was essentially identical to the process of example 1, except that the pH of the system was controlled to 1 in step 1), and the specific parameters are shown in Table 1.

Comparative example 4

The method for recovering the positive electrode material of the comparative example comprises the following steps:

2) Adding Fenton reagent into the mixed solution, namely adding 75g of ferrous phosphate powder, uniformly mixing, gradually dropwise adding 220g of 10% hydrogen peroxide to ensure that the molar ratio of the hydrogen peroxide to ferrous ions is 3:1 and the molar ratio of the hydrogen peroxide to lithium iron phosphate is 2:1, stirring and soaking for 4 hours at 25 ℃ after the addition is finished, stabilizing the pH value of a phosphoric acid regulating system with the concentration of 1mol/L at 3.5 in the soaking process, and filtering after the soaking is finished to obtain a first filtrate and a first filter residue;

3) Adding deionized water with the volume of 6 times into the first filter residue, washing for 5 times, and putting into a 105 ℃ vacuum drying oven for drying for 4 hours to obtain ferric phosphate solid. And adding an excessive saturated sodium carbonate solution into the first filtrate to obtain lithium carbonate precipitate, filtering, adding deionized water with the volume of 6 times to wash for 3 times, and putting into a 105 ℃ vacuum drying oven to dry for 2 hours to obtain lithium carbonate solid. The specific parameters are shown in Table 1.

TABLE 1

From the above examples and comparative examples, it is apparent from Table 1 that the recovery method of the positive electrode material according to the present invention provides a higher purity of the finally obtained iron phosphate.

As can be seen from the comparison between the example 1 and the comparative examples 1-2, the addition of Fenton reagent in the method for recovering the positive electrode material provided by the invention can completely convert ferrous ions in the system into ferric phosphate precipitates, so that the yield of finally obtained ferric phosphate is higher.

As can be seen from the comparison between the example 1 and the comparative example 3, the method for recovering the positive electrode material provided by the invention can avoid the dissolution of ferric phosphate precipitate by adjusting the pH of the system to 3-5, so that the yield of the finally obtained ferric phosphate is higher.

As is clear from the comparison between the example 1 and the comparative example 4, the method for recycling the positive electrode material provided by the invention has the advantages that the aluminum removal treatment, slag removal treatment, iron value transformation treatment and sintering treatment can avoid the interference of other impurity ions, so that the purity of the finally obtained ferric phosphate is higher.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.

Claims

1. The method for recycling the positive electrode material is characterized by comprising the following steps of:

2. The recycling method according to claim 1, wherein the aluminum removal treatment includes:

the molar ratio of the aluminum removing agent to the aluminum is 1-1.2:1.

3. The recycling method according to claim 2, wherein the slag removal treatment includes:

4. The recovery method according to claim 3, wherein the iron value conversion process includes: adding iron powder into the third filtrate until no precipitate is generated, adjusting the pH of the system to 5-8, and filtering to obtain a fourth filtrate and a fourth filter residue;

5. The recovery method of claim 2, wherein the solids to liquid ratio of the first filter residue to deionized water is 1g:1-50mL.

6. The recovery method according to claim 3, wherein the concentration of the concentrated sulfuric acid is 6 to 18mol/L.

7. The recovery method according to claim 1, wherein the solid-to-liquid ratio of the lithium iron phosphate powder and deionized water in step 1) is 1g:1-10mL.

8. The recovery method according to any one of claims 1 to 7, wherein the Fenton reagent is ferrous phosphate and hydrogen peroxide;

9. The recovery method according to claim 8, wherein the molar ratio of hydrogen peroxide to ferrous ions in the Fenton reagent is 3-5:1.

10. The recycling method according to any one of claims 1 to 9, further comprising: adding saturated sodium carbonate solution into the first filtrate, and filtering to obtain lithium carbonate precipitate;