阅读说明：本技术 一种废旧磷酸铁锂电池资源化的处理方法 (Resource treatment method for waste lithium iron phosphate batteries ) 是由 欧阳红勇 祝宏帅 张欢 程友星 吕正中 曾文强 李亚德 骆锦红 于 2021-10-26 设计创作，主要内容包括：本发明公开了一种废旧磷酸铁锂电池资源化的处理方法,采用优先提锂工艺耦合无水磷酸铁合成技术,提高锂回收率的同时直接获得电池级碳酸锂产品,且提锂后的第一浸出渣可直接酸浸获得磷铁溶液用于制备无水磷酸铁产品,可综合回收废旧磷酸铁锂电池中锂、铁、磷、铜、铝、氟、石墨粉等多组分,有利于简化废旧电池活性材料的回收工艺,有用元素回收率高,制备的无水磷酸铁和碳酸锂均为电池级,回收的石墨碳产品纯度高。通过简单,环保的过程实现了废旧磷酸铁锂电池各种资源的综合回收利用,且该方法成本较低,适用于工业应用。(The invention discloses a resource treatment method of waste lithium iron phosphate batteries, which adopts a technology of preferentially extracting lithium coupled with an anhydrous iron phosphate synthesis technology, directly obtains a battery-grade lithium carbonate product while improving the recovery rate of lithium, and directly performs acid leaching on first leaching residues after lithium extraction to obtain a ferro-phosphorus solution for preparing the anhydrous iron phosphate product, so that multiple components of lithium, iron, phosphorus, copper, aluminum, fluorine, graphite powder and the like in the waste lithium iron phosphate batteries can be comprehensively recovered, the recovery process of active materials of the waste batteries can be simplified, the recovery rate of useful elements is high, the prepared anhydrous iron phosphate and lithium carbonate are both battery-grade, and the purity of the recovered graphite carbon product is high. The comprehensive recycling of various resources of the waste lithium iron phosphate battery is realized through a simple and environment-friendly process, and the method is low in cost and suitable for industrial application.)

1. A resource treatment method for waste lithium iron phosphate batteries is characterized by comprising the following steps:

s1: discharging, disassembling and sorting the waste lithium iron phosphate battery to obtain a shell, a diaphragm, copper, aluminum and anode and cathode mixed powder;

s2: roasting the anode and cathode mixed powder to obtain a roasted product;

s3: carrying out oxidation leaching operation on the roasting product, and separating to obtain a first leaching solution and first leaching slag;

s4: carrying out impurity removal and refining operation on the first leaching solution to obtain a lithium sulfate solution, carrying out lithium precipitation operation on the lithium sulfate solution, and separating to obtain a lithium carbonate product;

s5: performing acid leaching operation on the first leaching residue, and separating to obtain a second leaching solution and a second leaching residue;

s6: washing and removing impurities from the second leaching residue to obtain a graphite carbon product;

s7: adjusting the proportion of fluorine, sodium and aluminum in the second leaching solution, then adding a first alkali reagent to carry out a first reaction, and separating to obtain a refined ferro-phosphorus solution and a sodium fluoroaluminate solid;

s8: and adjusting the iron-phosphorus ratio in the refined ferrophosphorus solution, adding a first oxidant, adding a second alkali reagent, performing a second reaction to generate hydrated ferric phosphate, and performing aging crystallization, washing, calcining and dehydration on the hydrated ferric phosphate to obtain an anhydrous ferric phosphate product.

2. The method for recycling the waste lithium iron phosphate batteries according to claim 1, wherein the electrolyte is volatilized in the disassembling and sorting process in the step S1 and the fluorine-containing tail gas generated in the roasting operation process in the step S2 is absorbed by alkali to obtain sodium fluoride, and the sodium fluoride is used in the first reaction, or the fluorine-containing tail gas is directly introduced into the second leachate to be used in the first reaction.

3. The method for recycling the waste lithium iron phosphate batteries according to claim 1, wherein the oxidative leaching operation in the step S3 comprises the following steps: and immersing the roasted product into a sulfuric acid solution, and adding a second oxidant, wherein the pH value is 1-2, and the leaching temperature is 10-90 ℃ for leaching for 0.1-5 h.

4. The resource treatment method of the waste lithium iron phosphate batteries according to claim 1, characterized in that the impurity removal and refining operation in the step S4 comprises the following steps: and adding iron powder into the first leaching solution to carry out primary impurity removal, filtering, adding a third alkali reagent to carry out secondary impurity removal, filtering, and then carrying out tertiary impurity removal by adopting resin to finally obtain the refined lithium sulfate solution.

5. The resource processing method of the waste lithium iron phosphate batteries according to claim 4, wherein the lithium deposition operation in the step S4 comprises the following steps: and adding a sodium carbonate solution into the refined lithium sulfate solution, precipitating to generate lithium carbonate, and washing and drying to obtain a lithium carbonate product.

6. The method for recycling the waste lithium iron phosphate batteries according to claim 1, wherein the acid leaching operation in the step S5 comprises the following steps: and immersing the first leaching residue into a certain amount of sulfuric acid for leaching reaction, controlling the concentration of the sulfuric acid in a reaction end point system of the leaching reaction to be 0.05-1mol/L, and filtering and separating to obtain the second leaching solution and the second leaching residue.

7. The resource treatment method of the waste lithium iron phosphate batteries according to claim 1, characterized in that: and in the step S7, adding a fluorine source and a sodium source into the second leaching solution to adjust the molar ratio of fluorine to aluminum in the second leaching solution to be 3-8: 1, and the molar ratio of sodium to aluminum to be 3-10: 1.

8. The resource treatment method of the waste lithium iron phosphate batteries according to claim 1, characterized in that: the first reaction condition in the step S7 is that the pH value of the second leaching solution is controlled to be 1-3, the reaction temperature is 10-90 ℃, and the reaction time is 0.1-5 h.

9. The resource treatment method of the waste lithium iron phosphate batteries according to claim 1, characterized in that: and in the step S8, adding a phosphorus source into the refined ferrophosphorus solution to adjust the molar ratio of iron to phosphorus to be 0.8-1.2: 1.

10. The resource treatment method of the waste lithium iron phosphate batteries according to claim 9, characterized in that: the second reaction condition in the step S8 is that the pH value of the refined ferrophosphorus solution is controlled to be 1.5-2.5, the reaction temperature is 60-90 ℃, and the reaction time is 1-5 h.

Technical Field

The invention relates to the technical field of lithium battery recovery, in particular to a resource treatment method of waste lithium iron phosphate batteries.

Background

The technical key of the recovery treatment of the waste lithium iron phosphate batteries is the recovery and utilization of the waste lithium iron phosphate positive electrode materials, and the currently reported methods mainly comprise two types: a method for repairing waste lithium iron phosphate anode material and a method for recycling lithium iron phosphorus of the waste lithium iron phosphate anode material.

Chinese patent CN110277602B discloses a method for repairing and regenerating lithium iron phosphate positive electrode materials in waste batteries, which comprises the steps of calcining a lithium iron phosphate positive electrode piece obtained by disassembly to obtain waste lithium iron phosphate; dispersing waste lithium iron phosphate into deionized water, adding a surfactant, a soluble ferric salt and hydrogen peroxide, and stirring to obtain a solution containing the lithium iron phosphate; adding an ammonium dihydrogen phosphate solution into the solution containing the lithium iron phosphate, stirring, and drying to obtain iron phosphate-coated lithium iron phosphate powder; and mixing the lithium iron phosphate powder coated by the iron phosphate with lithium salt, and calcining to obtain the repaired and regenerated lithium iron phosphate cathode material. However, the waste lithium iron phosphate anode material has great charge-discharge state and structure difference, metal impurities such as copper, aluminum and the like cannot be avoided being mixed in the disassembly process, and the introduced impurities are difficult to remove in the material repair process, so that the waste lithium iron phosphate anode material repair method is difficult to realize industrialization.

Chinese patent CN113285135A discloses a method for recycling multiple components of waste lithium iron phosphate batteries, which comprises the following steps: breaking, disassembling and separating the shells of the discharged waste lithium iron phosphate batteries; treating the battery cell to obtain a solvent recovery solution; crushing and sorting the battery core to obtain lithium iron phosphate coarse powder, copper powder and aluminum powder; adding the lithium iron phosphate coarse powder into acid liquor for reaction, filtering to obtain acid leaching solution and carbon slag, washing the carbon slag with water, and drying to obtain high-carbon graphite; adjusting the pH value of the pickle liquor, adding a reducing agent for copper removal, and filtering to obtain a copper removal liquor and copper slag; adding an oxidant and a proper amount of phosphorus source into the decoppered liquid to obtain ferric orthophosphate; adding the iron precipitation liquid into alkali liquor to obtain molten aluminum and aluminum slag; adding the precipitated aluminum liquid into alkali liquor to obtain alkaline liquid and alkaline slag; and (4) evaporating and concentrating the alkalized solution to obtain a lithium-rich solution, and adding the lithium-rich solution into a sodium carbonate solution to obtain lithium carbonate. The method realizes the resource utilization of the lithium iron phosphorus of the waste lithium iron phosphate cathode material, but the method does not remove aluminum before the procedure of synthesizing the ferric phosphate, which causes the standard exceeding of aluminum impurities in the ferric phosphate product, and after the ferric phosphate is deposited, the alkaline solution is evaporated and concentrated to obtain a lithium-rich solution which is added into the sodium carbonate solution to obtain the lithium carbonate, so that the recovery rate of lithium is not high, and the direct synthesis of the battery-grade lithium carbonate product is difficult to realize.

Therefore, the existing process for recycling waste lithium iron phosphate batteries, in particular the process for recycling the waste lithium iron phosphate positive electrode materials, has the defects that the industrialization is difficult to realize by a repair method, the flow of the wet treatment process for recycling the lithium iron phosphate resources is long and complicated, the iron phosphate products do not meet the requirement of battery grade indexes, the recovery rate of lithium is not high, the direct synthesis of the battery grade lithium carbonate product is difficult to realize, a large amount of waste water and waste residues are generated, and the industrial application and popularization of the recycling of the waste lithium iron phosphate batteries are influenced due to poor technical economy and environmental protection.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide a recycling treatment method of waste lithium iron phosphate batteries, which is simple, environment-friendly and low in cost, can realize comprehensive recycling of various resources of the waste lithium iron phosphate batteries, can especially synthesize battery-grade anhydrous iron phosphate and battery-grade lithium carbonate products, and is suitable for industrial application.

In order to achieve the purpose, the invention adopts the following technical scheme:

a resource treatment method for waste lithium iron phosphate batteries is characterized by comprising the following steps:

s1: discharging, disassembling and sorting the waste lithium iron phosphate battery to obtain a shell, a diaphragm, copper, aluminum and anode and cathode mixed powder;

s2: roasting the anode and cathode mixed powder to obtain a roasted product;

s3: carrying out oxidation leaching operation on the roasting product, and separating to obtain a first leaching solution and first leaching slag;

s4: carrying out impurity removal and refining operation on the first leaching solution to obtain a lithium sulfate solution, carrying out lithium precipitation operation on the lithium sulfate solution, and separating to obtain a lithium carbonate product;

s5: performing acid leaching operation on the first leaching residue, and separating to obtain a second leaching solution and a second leaching residue;

s6: washing and removing impurities from the second leaching residue to obtain a graphite carbon product;

s7: adjusting the proportion of fluorine, sodium and aluminum in the second leaching solution, then adding a first alkali reagent to carry out a first reaction, and separating to obtain a refined ferro-phosphorus solution and a sodium fluoroaluminate solid;

s8: and adjusting the iron-phosphorus ratio in the refined ferrophosphorus solution, adding a first oxidant, adding a second alkali reagent, performing a second reaction to generate hydrated ferric phosphate, and performing aging crystallization, washing, calcining and dehydration on the hydrated ferric phosphate to obtain an anhydrous ferric phosphate product.

Further, in the step S1, the electrolyte is volatilized in the disassembling and sorting process, and the fluorine-containing tail gas generated in the roasting operation process in the step S2 is absorbed by alkali to obtain sodium fluoride, and the sodium fluoride is used for the first reaction, or the fluorine-containing tail gas is directly introduced into the second leachate to be used for the first reaction.

Further, the oxidation leaching operation in the step S3 includes the following steps: and immersing the roasted product into a sulfuric acid solution, adding a second oxidant, and leaching for 0.1-5 h under the conditions that the pH is 1-2 and the leaching temperature is 10-90 ℃.

Further, the impurity removal and purification operation in the step S4 includes the following steps: and adding iron powder into the first leaching solution to carry out primary impurity removal, filtering, adding a third alkali reagent to carry out secondary impurity removal, filtering, and then carrying out tertiary impurity removal by adopting resin to finally obtain the refined lithium sulfate solution.

Further, the lithium deposition operation in the step S4 includes the following steps: and adding a sodium carbonate solution into the lithium sulfate solution, precipitating to generate lithium carbonate, and washing and drying to obtain a lithium carbonate product.

Further, the acid leaching operation in the step of S5 comprises the following steps: and immersing the first leaching residue into a certain amount of sulfuric acid for leaching reaction, controlling the concentration of the sulfuric acid in a reaction end point system of the leaching reaction to be 0.05-1mol/L, and filtering and separating to obtain the second leaching solution and the second leaching residue.

Further, in the step S7, the fluorine source and the sodium source are added into the second leaching solution to adjust the molar ratio of fluorine to aluminum in the second leaching solution to be (3-8) to 1, and the molar ratio of sodium to aluminum is (3-10) to 1.

Further, the conditions of the first reaction in the step S7 are that the pH of the second leaching solution is controlled to be 1-3, the reaction temperature is 10-90 ℃, and the reaction time is 0.1-5 h.

Further, in the step S8, the phosphorus source is added into the refined ferrophosphorus solution to adjust the molar ratio of iron to phosphorus to be 0.8-1.2: 1.

Further, the second reaction in the step S8 is performed under the conditions that the pH of the refined ferrophosphorus solution is controlled to be 1.5 to 2.5, the reaction temperature is 60 to 90 ℃, and the reaction time is 1 to 5 hours.

Compared with the prior art, the invention has the following advantages:

(1) according to the technical scheme, a lithium extraction process is preferentially coupled with an anhydrous iron phosphate synthesis technology, a battery-grade lithium carbonate product is directly obtained while the lithium recovery rate is improved, and the first leaching residue after lithium extraction can be directly subjected to acid leaching to obtain a ferrophosphorus solution for preparing the anhydrous iron phosphate product.

(2) The method adopts aluminum fluoride coprecipitation to synthesize the sodium fluoroaluminate, can simultaneously realize the treatment of fluorine-containing tail gas in the recovery process of the waste lithium iron phosphate battery and the removal of aluminum impurities in the second leaching solution, and the obtained sodium fluoroaluminate can also be used as a raw material in the electrolytic aluminum industry.

(3) According to the technical scheme, multiple components such as lithium, iron, phosphorus, copper, aluminum, fluorine and graphite powder in the waste lithium iron phosphate battery can be comprehensively recovered, the recovery process of the active materials of the waste battery is facilitated to be simplified, the recovery rate of useful elements is high, the prepared anhydrous iron phosphate and lithium carbonate are both battery grade, and the purity of the recovered graphite carbon product is high. The comprehensive recycling of various resources of the waste lithium iron phosphate battery is realized through a simple and environment-friendly process, and the method is low in cost and suitable for industrial application.

Drawings

Fig. 1 is a process flow chart of resource treatment of waste lithium iron phosphate batteries in embodiment 1 of the invention.

Detailed Description

The present invention will be described in further detail below with reference to specific embodiments and examples in conjunction with the accompanying drawings, but the embodiments of the present invention are not limited thereto. All the raw materials and reagents used in the present invention are commercially available raw materials and reagents, unless otherwise specified. In the examples, the components are used in g and mL in parts by mass.

S1: discharging, disassembling and sorting the waste lithium iron phosphate battery to obtain a shell, a diaphragm, copper, aluminum and anode and cathode mixed powder.

In one embodiment, the discharge in step S1 is non-saline discharge, preferably resistance discharge or carbon powder conductor physical discharge. It should be noted that, during the discharge of brine, there is a possibility that the electrolyte leaks and flows into brine to pollute the environment, and the brine may flow into the inside of the battery to pollute the recovered product, so resistance discharge or physical discharge of a carbon powder conductor is preferable.

In one embodiment, the fluorine-containing tail gas volatilized from the electrolyte during the disassembling and sorting in the step S1 may be absorbed by alkali to obtain sodium fluoride, and the sodium fluoride is used in the first reaction, or the fluorine-containing tail gas is directly introduced into the second leachate to be used in the first reaction.

The invention has the advantages that the alkali can be sodium hydroxide, the main component of the electrolyte contains lithium hexafluorophosphate, the lithium hexafluorophosphate is easily decomposed into phosphorus pentafluoride gas when exposed to air or heated, and the phosphorus pentafluoride gas can generate toxic and strong corrosive hydrogen fluoride in humid air, so that the fluorine-containing tail gas generated in the decomposition and disassembly process due to the exposure of the electrolyte to the air is recycled in the technical scheme of the invention, and firstly, the electrolyte can be more environment-friendly and safer, and secondly, the fluorine element in the electrolyte can be fully utilized to recycle the fluorine element.

S2: and roasting the anode and cathode mixed powder to obtain a roasted product.

In one embodiment, the calcination in step S2 is performed at 400-800 ℃ for 0.1-5 h, preferably 0.5-3 h, in a nitrogen atmosphere.

It should be noted that the calcination operation is mainly used for removing organic matters, such as residual electrolyte, binder PVDF, and the like, and can reduce impurities in the positive and negative electrode mixed powder, and the removal of the binder is beneficial to the subsequent recovery operation of the positive and negative electrode mixed powder, and improves the leaching efficiency.

In one embodiment, the fluorine-containing tail gas generated during the roasting operation may be absorbed by alkali to obtain sodium fluoride, and the sodium fluoride is used in the first reaction, or the fluorine-containing tail gas is directly introduced into the second leaching solution for the first reaction. Wherein the base is sodium hydroxide.

S3: and carrying out oxidation leaching operation on the roasted product, and separating to obtain a first leaching solution and first leaching slag.

In one embodiment, the oxidative leaching operation in the step S3 includes the steps of: immersing the roasted product into a sulfuric acid solution, adding a second oxidant, and leaching for 0.1-5 h under the conditions that the pH is 1-2 and the leaching temperature is 10-90 ℃; preferably, leaching is carried out for 0.5-3 h at the leaching temperature of 20-60 ℃.

It should be noted that the baked product is mainly LiFePO, which is an active material of the positive electrode₄And graphitic carbon, LiFePO of the negative electrode₄Leaching of Li in sulphuric acid⁺、Fe²⁺、PO₄ ^3-Second oxidizing agentMixing Fe²⁺Is oxidized into Fe³⁺At this time, Fe³⁺And PO₄ ^3-Formation of weak acid insoluble FePO₄〃2H₂And O, completing the lithium extraction operation, and finally separating to obtain a first leaching solution containing lithium and a first leaching residue containing hydrated iron phosphate and graphite.

In one embodiment, the solid-to-liquid ratio of the roasted product to the sulfuric acid solution is 1: 2-10; preferably 1 to (3-6).

In one embodiment, the second oxidant is at least one of hydrogen peroxide, oxygen and air; the second oxidant is added in an amount of Fe in the reaction system²⁺Total oxidation to Fe³⁺1 to 2 times of the theoretical amount, preferably 1.1 to 1.3 times.

It should be noted that the use of oxidants such as hydrogen peroxide, oxygen and air does not introduce new impurity ions into the system.

S4: and (3) carrying out impurity removal and refining operation on the first leaching solution to obtain a lithium sulfate solution, carrying out lithium precipitation operation on the lithium sulfate solution, and separating to obtain a lithium carbonate product.

It should be noted that, through the operations of impurity removal and refining of the first leaching solution and lithium precipitation, high-value recovery of lithium in the waste lithium iron phosphate batteries is achieved.

In one embodiment, the impurity removal and purification operation in the step S4 includes the following steps: adding iron powder into the first leaching solution to remove impurities for the first time, filtering, adding a third alkali reagent to remove impurities for the second time, filtering, and then removing impurities for the third time by adopting resin to finally obtain a refined lithium sulfate solution.

The first leaching solution contains various metal ion impurities, and the main purpose of adding iron powder in the primary impurity removal process is two, namely, the copper ions contained in the first leaching solution are reduced to copper simple substance precipitate to be removed, and acid in the first leaching solution can be neutralized, and the iron powder and a sulfuric acid solution can react to generate ferrous sulfate and hydrogen; a third alkali reagent is added during secondary impurity removal, and is mainly used for removing impurities such as iron, aluminum, calcium, magnesium and the like in the first leaching solution in a precipitation generation mode; and the third impurity removal adopts resin impurity removal, so that the first leaching solution can be subjected to deep impurity removal, and residual metal impurity ions which are not removed by precipitation are removed to obtain a refined lithium sulfate solution.

In one embodiment, the iron powder is added in such an amount that no bubbles are formed in the first leach solution after the addition. It should be noted that when the bubbles are no longer generated, it is indicated that most of the sulfuric acid in the first inlet/outlet solution is neutralized.

In one embodiment, the third base reagent is at least one of ammonia, lithium hydroxide, and the like; the third alkali reagent is added in an amount of adjusting the pH value of the first leaching solution to 10-11. It should be noted that the third alkali reagent, such as ammonia water, lithium hydroxide, etc., can react with iron, aluminum, calcium, magnesium in the first leaching solution to form iron hydroxide, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, etc., and the pH is adjusted to 10 to 11, which is beneficial to the faster and more complete formation of impurity precipitates under strong alkali conditions.

In one embodiment, the resin is a cation exchange resin or a metal chelating resin. The resin selectively adsorbs metal impurities in the solution, and thereby metal ions (Fe) having a high valence are generated³⁺、Fe²⁺、Cu²⁺、Ca²⁺、Mg²⁺) Generally, the lithium sulfate is preferentially adsorbed and has weak adsorption capacity to low-price metal, so that the refined lithium sulfate solution is obtained after the first leaching solution is deeply subjected to impurity removal by resin.

In one embodiment, the lithium deposition operation in the step S4 includes the following steps: and adding a sodium carbonate solution into the refined lithium sulfate solution, precipitating to generate lithium carbonate, and washing and drying to obtain a lithium carbonate product.

In one embodiment, the sodium carbonate solution is a saturated sodium carbonate solution, and the amount of the sodium carbonate solution added is 1.0 to 1.2 times, preferably 1.1 times, the reaction equivalent.

In one embodiment, the lithium deposition operation is preferably performed at 70-90 ℃, the solubility of sodium carbonate, lithium sulfate and lithium carbonate is reduced along with the temperature increase, but at the same temperature, the solubility of lithium carbonate is far less than that of sodium carbonate and lithium sulfate, and the content of impurities in the lithium carbonate deposition can be reduced, so that the lithium deposition efficiency and the lithium carbonate purity can be improved at higher temperature.

In one embodiment, the washing may be performed several times using hot pure water. The lithium carbonate has a low solubility in hot water, and sodium ions and ammonium ions adhering to the surface of the lithium carbonate can be removed as much as possible by washing the lithium carbonate with the hot pure water.

S5: and performing acid leaching operation on the first leaching residue, and separating to obtain a second leaching solution and a second leaching residue.

In one embodiment, the acid leaching operation in the step of S5 comprises the following steps: and (3) immersing the first leaching residue into a certain amount of sulfuric acid for leaching reaction, controlling the concentration of the sulfuric acid in a reaction end point system of the leaching reaction to be 0.05-1mol/L, and filtering and separating to obtain a second leaching solution and second leaching residue.

In one embodiment, the leaching reaction is carried out at a leaching temperature of 20-60 ℃ for 0.5-3 h.

In one embodiment, the concentration of sulfuric acid in the reaction end system of the leaching reaction is preferably 0.05-0.25 mol/L.

In one embodiment, the solid-to-liquid ratio of the first leaching residue to the sulfuric acid solution is 1: 2-10; preferably 1 to (3-6).

It should be noted that the first leaching residue is mainly a mixed solid of hydrated iron phosphate and graphite, and the acid leaching operation on the first leaching residue is mainly to separate the hydrated iron phosphate from the graphite.

S6: and washing and removing impurities from the second leaching residue to obtain a graphite carbon product.

In one embodiment, the washing and impurity removal in the step S6 is to wash the second leaching residue with acid and then with water, so that the metal ions and anions in the second leaching residue can be removed.

In one embodiment, the acid washing may be performed using at least one of nitric acid, hydrochloric acid, and the like, and preferably, the acid washing is performed using hydrochloric acid.

In one embodiment, the washing and impurity removal can adopt multi-stage countercurrent washing, so that the impurity removal effect of the second leaching residue can be improved, and reagents used for washing can be saved.

In one embodiment, the graphite carbon product can be shaped by roasting in a protective atmosphere to obtain a high-quality graphite product.

S7: and adjusting the proportion of fluorine, sodium and aluminum in the second leaching solution, then adding a first alkali reagent to carry out a first reaction, and separating to obtain a refined ferro-phosphorus solution and sodium fluoroaluminate solids.

It should be noted that, aluminum foil is used as a main component of the positive electrode of the lithium battery, aluminum impurities are inevitably introduced into the positive electrode active material, and special impurity removal is absolutely necessary during the recovery process, and particularly in the technical scheme of the present invention, a sulfuric acid solution is used for leaching a roasted product in the step S3, then hydrated iron phosphate is precipitated, and aluminum phosphate is likely to be precipitated simultaneously during the precipitation of the hydrated iron phosphate, so that a second leaching solution obtained by leaching a first leaching residue in the step S5 actually contains aluminum impurities, and therefore, in the step S7, by adjusting the ratio of fluorine, sodium and aluminum in the second leaching solution and controlling reaction conditions, the aluminum impurities are precipitated and separated in the form of sodium fluoroaluminate, on one hand, the sodium fluoroaluminate can be further used for aluminum industry recovery, and on the other hand, a fluorine-containing tail gas generated in the technical scheme of the present application can also form closed-loop digestion, so that fluorine elements, fluorine-containing tail gas, and fluorine-containing impurities in the lithium iron phosphate battery can be simultaneously dissolved in the lithium battery, Aluminum element and sodium element in the alkali reagent are recovered.

In one embodiment, the adjustment in the step S7 is to add a fluorine source and a sodium source to the second leaching solution to adjust the molar ratio of fluorine to aluminum in the second leaching solution to be 3-8: 1, preferably 5.5-6.5: 1; the molar ratio of sodium to aluminum is (3-10) to 1, preferably (3-6) to 1.

In one embodiment, the fluorine source may be at least one of sodium fluoride, ammonium fluoride, hydrogen fluoride, ferric fluoride, and the like; the sodium source may be at least one of sodium fluoride, sodium carbonate, sodium hydroxide, sodium sulfate, and the like.

In one embodiment, the alkaline reagent is at least one of sodium hydroxide, ammonia, and the like.

In one embodiment, the first reaction in the step S7 is performed under the conditions that the pH of the second leaching solution is controlled to be 1-3, the reaction temperature is 10-90 ℃, and the reaction time is 0.1-5 hours; preferably, the reaction is carried out for 0.5 to 2 hours at the temperature of 20 to 60 ℃.

In one embodiment, the separation may be by membrane filtration.

S8: and adjusting the iron-phosphorus ratio in the refined ferrophosphorus solution, adding a first oxidant, adding an alkali reagent to perform a second reaction to generate hydrated ferric phosphate, and aging, crystallizing, washing, calcining and dehydrating the hydrated ferric phosphate to obtain an anhydrous ferric phosphate product.

In one embodiment, the step of S8 is performed by adding a phosphorus source into the refined ferrophosphorus solution to adjust the molar ratio of iron to phosphorus to be 0.8-1.2: 1.

In one embodiment, the phosphorus source can be a chemical such as phosphoric acid that provides phosphate ions.

In one embodiment, the first oxidant in step S8 is preferably hydrogen peroxide; the second alkaline agent may be at least one of sodium hydroxide, ammonia, and the like.

In one embodiment, the first oxidizing agent is added in an amount that will cause Fe to be present in the reaction system²⁺Total oxidation to Fe³⁺1 to 2 times of the theoretical amount, preferably 1.1 to 1.3 times.

In one embodiment, the second reaction in the step S8 is performed under the conditions that the pH of the refined ferrophosphorus solution is controlled to be 1.5 to 2.5, the reaction temperature is 60 to 90 ℃, and the reaction time is 1 to 5 hours. In this way, water and iron phosphate are produced by controlling the conditions of the second reaction.

In one embodiment, the aging crystallization in the step S8 is performed by aging crystallization of water and iron phosphate with a phosphoric acid solution, wherein the concentration of the phosphoric acid solution is 2% to 10%, preferably 5%.

In one embodiment, the aged crystallized phosphoric acid solution may be used as a phosphorus source to adjust the iron-phosphorus ratio of the ferrophosphorus solution. Therefore, the phosphoric acid solution can be fully utilized, the generation of waste liquid is reduced, and the recovery process is more environment-friendly.

In one embodiment, the calcination dehydration is performed at 500-750 ℃ for 0.5-3 h, preferably 550-650 ℃ for 1.5-2.5 h.

Example 1

S1: discharging, disassembling and sorting the waste lithium iron phosphate battery to obtain a shell, a diaphragm, copper, aluminum and anode and cathode mixed powder, wherein fluorine-containing tail gas volatilized by electrolyte in disassembling and sorting can be absorbed by sodium hydroxide to obtain sodium fluoride, and the obtained sodium chloride is used in the step S7;

s2: roasting the anode and cathode mixed powder for 3h at 600 ℃ under the nitrogen atmosphere condition to obtain a roasted product, wherein fluorine-containing tail gas generated in the roasting operation process can be absorbed by sodium hydroxide to obtain sodium fluoride, and the obtained sodium chloride is used in the step S7;

s3: immersing 1 part by mass of the roasted product into 3 parts by volume of sulfuric acid solution, adding hydrogen peroxide, leaching for 2 hours at the pH value of 1 and the leaching temperature of 60 ℃, and separating to obtain a first leaching solution and first leaching residues;

s4: adding iron powder into the first leaching solution for primary impurity removal until the addition of the iron powder is such that bubbles are not generated in the first leaching solution any longer, precipitating and filtering, adding lithium hydroxide to adjust the pH value to 11 for secondary impurity removal, precipitating and filtering, then removing impurities for three times by using chelate resin, finally obtaining a refined lithium sulfate solution, adding a saturated sodium carbonate solution into the refined lithium sulfate solution for lithium precipitation to generate lithium carbonate precipitate, and washing and drying to obtain a lithium carbonate product;

s5: immersing 1 part by mass of first leaching residue into 6 parts by volume of sulfuric acid, leaching for 1h at the leaching temperature of 60 ℃, controlling the concentration of the sulfuric acid in a reaction end point system to be 0.25mol/L, and filtering and separating to obtain a second leaching solution and second leaching residue;

s6: washing the second leaching residue with hydrochloric acid, washing with pure water for multiple times to obtain graphite carbon, and roasting and shaping the graphite carbon in a protective atmosphere to obtain a high-quality graphite product;

s7: adding sodium fluoride and sodium carbonate into the second leaching solution to adjust the molar ratio of fluorine to aluminum in the second leaching solution to be 6.5: 1 and the molar ratio of sodium to aluminum to be 3: 1, then adding sodium hydroxide to adjust the pH value to be 2, reacting for 1h at the temperature of 50 ℃, and separating to obtain refined ferro-phosphorus solution and sodium fluoroaluminate solid;

s8: adding phosphoric acid into the refined ferrophosphorus solution to adjust the molar ratio of iron to phosphorus to be 1.2: 1, adding hydrogen peroxide, adding sodium hydroxide to adjust the pH value to be 1.5, reacting for 1h at 90 ℃ to obtain hydrated ferric phosphate precipitate, then placing the hydrated ferric phosphate precipitate into 5% phosphoric acid solution for aging and crystallization for 2h, washing for multiple times, and calcining for 2h at 550 ℃ to obtain an anhydrous ferric phosphate product.

Example 2

S1: discharging, disassembling and sorting the waste lithium iron phosphate battery to obtain a shell, a diaphragm, copper, aluminum and anode and cathode mixed powder, wherein fluorine-containing tail gas volatilized by the electrolyte in the disassembling and sorting is directly introduced into the second leaching solution in the step S7;

s2: roasting the anode and cathode mixed powder for 0.5h at 800 ℃ under the nitrogen atmosphere condition to obtain a roasted product, and directly introducing fluorine-containing tail gas generated in the roasting operation process into the second leaching solution in the step S7;

s3: immersing 1 part by mass of the roasted product into 6 parts by volume of sulfuric acid solution, adding hydrogen peroxide, leaching for 3 hours at the pH value of 2 and the leaching temperature of 20 ℃, and separating to obtain a first leaching solution and first leaching residues;

s4: adding iron powder into the first leaching solution for primary impurity removal until the addition of the iron powder is such that bubbles are not generated in the first leaching solution, precipitating and filtering, adding lithium hydroxide to adjust the pH value to 10 for secondary impurity removal, precipitating and filtering, then adopting cation exchange resin for tertiary impurity removal to finally obtain a refined lithium sulfate solution, adding a saturated sodium carbonate solution into the refined lithium sulfate solution for lithium precipitation to generate lithium carbonate precipitate, generating lithium carbonate precipitate, and washing and drying to obtain a lithium carbonate product;

s5: immersing 1 part by mass of first leaching residue into 3 parts by volume of sulfuric acid, leaching for 2 hours at the leaching temperature of 40 ℃, controlling the concentration of the sulfuric acid in a reaction end-point system to be 0.05mol/L, and filtering and separating to obtain a second leaching solution and second leaching residue;

s6: washing the second leaching residue with nitric acid, washing with pure water for multiple times to obtain graphite carbon, and roasting and shaping the graphite carbon in a protective atmosphere to obtain a high-quality graphite product;

s7: adding ammonium fluoride and sodium fluoride into the second leaching solution to adjust the molar ratio of fluorine to aluminum in the second leaching solution to be 5.5: 1 and the molar ratio of sodium to aluminum to be 6: 1, then adding sodium hydroxide to adjust the pH value to 1, reacting for 0.5h at the temperature of 60 ℃, and separating to obtain refined ferro-phosphorus solution and sodium fluoroaluminate solid;

s8: adding phosphoric acid into the refined ferrophosphorus solution to adjust the molar ratio of iron to phosphorus to be 0.8: 1, adding hydrogen peroxide, adding sodium hydroxide to adjust the pH value to be 2.5, reacting for 5 hours at the temperature of 60 ℃ to obtain hydrated ferric phosphate precipitate, then putting the hydrated ferric phosphate precipitate into 2% phosphoric acid solution for aging and crystallization for 3 hours, washing for multiple times, and calcining for 1.5 hours at the temperature of 550 ℃ to obtain an anhydrous ferric phosphate product.

Example 3

S1: discharging, disassembling and sorting the waste lithium iron phosphate battery to obtain a shell, a diaphragm, copper, aluminum and anode and cathode mixed powder, wherein fluorine-containing tail gas volatilized by electrolyte in disassembling and sorting can be absorbed by sodium hydroxide to obtain sodium fluoride, and the obtained sodium chloride is used in the step S7;

s2: roasting the anode and cathode mixed powder for 1h at 500 ℃ under the nitrogen atmosphere condition to obtain a roasted product, wherein fluorine-containing tail gas generated in the roasting operation process can be absorbed by sodium hydroxide to obtain sodium fluoride, and the obtained sodium chloride is used in the step S7;

s3: immersing 1 part by mass of the roasted product into 3 parts by volume of sulfuric acid solution, adding hydrogen peroxide, leaching for 3 hours at the pH value of 1.5 and the leaching temperature of 90 ℃, and separating to obtain a first leaching solution and first leaching residues;

s4: adding iron powder into the first leaching solution for primary impurity removal until the addition amount of the iron powder is such that bubbles are not generated in the first leaching solution any longer, precipitating and filtering, adding lithium hydroxide to adjust the pH value to 11 for secondary impurity removal, precipitating and filtering, then removing impurities for three times by using chelate resin to finally obtain a refined lithium sulfate solution, adding a saturated sodium carbonate solution into the refined lithium sulfate solution for lithium precipitation to generate lithium carbonate precipitate, generating lithium carbonate precipitate, and washing and drying to obtain a lithium carbonate product;

s5: immersing 1 part by mass of first leaching residue into 10 parts by volume of sulfuric acid, leaching for 3 hours at the leaching temperature of 20 ℃, controlling the concentration of the sulfuric acid in a reaction end point system to be 0.2mol/L, and filtering and separating to obtain a second leaching solution and second leaching residue;

s6: washing the second leaching residue with hydrochloric acid, washing with pure water for multiple times to obtain graphite carbon, and roasting and shaping the graphite carbon in a protective atmosphere to obtain a high-quality graphite product;

s7: adding sodium fluoride and sodium hydroxide into the second leaching solution to adjust the molar ratio of fluorine to aluminum in the second leaching solution to be 8: 1 and the molar ratio of sodium to aluminum to be 10: 1, then adding sodium hydroxide to adjust the pH value to 3, reacting for 2h at the temperature of 20 ℃, and separating to obtain refined ferro-phosphorus solution and sodium fluoroaluminate solid;

s8: adding phosphoric acid into the refined ferrophosphorus solution to adjust the molar ratio of iron to phosphorus to be 1: 1, adding hydrogen peroxide, adding sodium hydroxide to adjust the pH value to be 2, reacting for 3 hours at the temperature of 80 ℃ to obtain hydrated ferric phosphate precipitate, then putting the hydrated ferric phosphate precipitate into 10% phosphoric acid solution for aging and crystallization for 1 hour, washing for multiple times, and calcining for 1.5 hours at the temperature of 650 ℃ to obtain an anhydrous ferric phosphate product.

The content of lithium carbonate and anhydrous iron phosphate prepared in this example is measured, and the specific results are shown in table 1, and it can be seen from table 1 that the finally prepared lithium carbonate and anhydrous iron phosphate can reach the battery grade.

The above embodiments are the best mode for carrying out the present invention, but the embodiments of the present invention are not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be regarded as equivalent substitutions and are included in the scope of the present invention.