阅读说明：本技术 一种废旧磷酸铁锂电池正极物料回收的方法 (Method for recycling anode materials of waste lithium iron phosphate batteries ) 是由 柴艮风 曹笃盟 汤波 张明兰 王甲琴 吴晖君 王悦 陈天翼 李兰兰 吴芳 何艳 于 2021-08-25 设计创作，主要内容包括：本发明涉及一种废旧磷酸铁锂电池正极物料回收的方法,该方法包括以下步骤：⑴将废旧磷酸铁锂电池正极粉料加水,制成浆料,该浆料预热后添加98%的硫酸进行浸出,浸出完成后经固液分离,分别得到浸出液和浸出渣；⑵浸出液调节pH值后,加入铁粉置换除铜,继续调节pH值,经沉淀除铝、固液分离,即得除杂后溶液；⑶补加磷酸钠调节铁磷的质量比；⑷将双氧水通入底液的液面以下,同时用喷洒设备喷洒加入碱液和除杂后溶液,并调节pH,待溶液中的铁完全氧化且沉淀后陈化5～7h,经固液分离分别得到磷酸铁沉淀和含锂溶液；⑸含锂溶液调pH值,经蒸发浓缩、固液分离,得到滤液；该滤液通入二氧化碳,即得沉淀锂。本发明简单高效,易于批量工业化生产。(The invention relates to a method for recovering a positive material of a waste lithium iron phosphate battery, which comprises the following steps: the method comprises the steps of adding water into waste lithium iron phosphate battery positive electrode powder to prepare slurry, preheating the slurry, adding 98% sulfuric acid to leach, and performing solid-liquid separation after leaching to obtain leachate and leaching residues respectively; after the pH value of the leachate is adjusted, adding iron powder for replacement copper removal, continuously adjusting the pH value, and obtaining a solution after impurity removal through precipitation aluminum removal and solid-liquid separation; thirdly, supplementing sodium phosphate to adjust the mass ratio of iron to phosphorus; introducing hydrogen peroxide below the liquid level of the base liquid, spraying the solution with alkali liquor and the solution after impurity removal by using spraying equipment, adjusting the pH, aging for 5-7 hours after iron in the solution is completely oxidized and precipitated, and performing solid-liquid separation to obtain iron phosphate precipitate and lithium-containing solution respectively; regulating the pH value of the lithium-containing solution, and carrying out evaporation concentration and solid-liquid separation to obtain a filtrate; introducing carbon dioxide into the filtrate to obtain the lithium precipitate. The method is simple and efficient, and is easy for batch industrial production.)

1. A method for recycling a positive material of a waste lithium iron phosphate battery comprises the following steps:

adding water into waste lithium iron phosphate battery positive electrode powder to prepare 0.1-0.3 kg/L of slurry, adding 0.28-0.32L of sulfuric acid with the volume concentration of 98% into 1kg of waste lithium iron phosphate battery positive electrode powder after the slurry is preheated for leaching, and performing solid-liquid separation after the leaching is finished to respectively obtain leachate and leaching residues;

adding alkali liquor into the leachate to adjust the pH value to 1.5-2.5, adding iron powder to replace and remove copper, continuously adding alkali liquor to adjust the pH value to 3.3-3.5, and performing precipitation, aluminum removal and solid-liquid separation to obtain a solution after impurity removal; the mass of the iron powder is 1.1-1.2 times of that of the leaching solution;

thirdly, supplementing sodium phosphate according to the contents of iron and phosphorus in the solution after impurity removal to adjust the mass ratio of iron to phosphorus to be 0.97-1.02: 1;

a double-layer stirring paddle is arranged in the reaction container, pure water or the solution after iron deposition is added to serve as a base solution, the base solution is enabled to submerge into the first stirring paddle, stirring and heating are carried out at the linear speed of more than or equal to 4m/s until the temperature is 50-70 ℃, and a sulfuric acid solution with the volume concentration of 10-50% is added to adjust the pH value to 3.3-4.0; then introducing hydrogen peroxide below the liquid level of the base solution through a pipeline, simultaneously spraying and adding alkali liquor and the solution obtained in the step III after impurity removal through spraying equipment, adjusting the pH value of the solution to 3.3-4.0, aging for 5-7 hours after iron in the solution is completely oxidized and precipitated, and respectively obtaining iron phosphate precipitate and lithium-containing solution through solid-liquid separation;

fifthly, adjusting the pH value of the lithium-containing solution to 10.0-11.5, evaporating and concentrating the solution until the lithium concentration in the solution is 12-15 g/L, and carrying out solid-liquid separation to obtain a filtrate; introducing carbon dioxide with the flow rate of 20-40L/h into the filtrate at the temperature of 90-100 ℃, and obtaining the precipitated lithium.

2. The method for recycling the positive electrode material of the waste lithium iron phosphate battery as claimed in claim 1, wherein the method comprises the following steps: the method comprises the steps of discharging, disassembling, peeling, crushing and separating the waste lithium iron phosphate battery positive electrode powder.

3. The method for recycling the positive electrode material of the waste lithium iron phosphate battery as claimed in claim 2, wherein the method comprises the following steps: the waste lithium iron phosphate battery refers to a waste battery pack or a waste single battery.

4. The method for recycling the positive electrode material of the waste lithium iron phosphate battery as claimed in claim 2, wherein the method comprises the following steps: the stripping and breaking means is manual or mechanical.

5. The method for recycling the positive electrode material of the waste lithium iron phosphate battery as claimed in claim 1, wherein the method comprises the following steps: the waste lithium iron phosphate battery positive electrode powder is produced in the synthesis process and the battery production process of the positive electrode material.

6. The method for recycling the positive electrode material of the waste lithium iron phosphate battery as claimed in claim 1, wherein the method comprises the following steps: the leaching condition in the step refers to that the temperature is 50-80 ℃ and the time is 3-4 h.

7. The method for recycling the positive electrode material of the waste lithium iron phosphate battery as claimed in claim 1, wherein the method comprises the following steps: the second step and the alkali liquor in the fourth step are sodium hydroxide solutions with the concentration of 100-200 g/L.

8. The method for recycling the positive electrode material of the waste lithium iron phosphate battery as claimed in claim 1, wherein the method comprises the following steps: the condition for replacing the copper in the step II is that the temperature is 60-70 ℃ and the time is 15-30 min.

9. The method for recycling the positive electrode material of the waste lithium iron phosphate battery as claimed in claim 1, wherein the method comprises the following steps: the method comprises the step of precipitating and removing aluminum in the step II, wherein the temperature is 60-70 ℃, and the time is 2-8 hours.

10. The method for recycling the positive electrode material of the waste lithium iron phosphate battery as claimed in claim 1, wherein the method comprises the following steps: and step four, the mass of hydrogen peroxide is 0.55-0.6 times of the iron content in the solution after impurity removal.

Technical Field

The invention relates to the technical field of waste battery recovery, in particular to a method for recovering a positive material of a waste lithium iron phosphate battery.

Background

The lithium iron phosphate has good cycle performance, low price, good safety and quick charging potential, so the demand of the lithium iron phosphate battery is rapidly increased along with the rapid development of the domestic electric automobile industry, and the lithium iron phosphate battery is basically used for automobiles with higher safety requirements such as the electric bus at present. As these lithium iron phosphate batteries go to the end of life, we have to face a troublesome problem, the recycling of the spent batteries.

At present, the recovery of waste lithium iron phosphate power batteries is mainly based on a wet process, and the pretreated waste lithium iron phosphate active material is dissolved by an acid leaching method, then impurity elements such as aluminum and copper are removed by purification, and finally metal elements in a leaching solution are recovered. Aluminum ions are used as impurity elements in sulfuric acid leaching solution, and when metal elements are subsequently recovered in the form of iron phosphate and lithium carbonate precursors, the electrochemical performance of the sulfuric acid leaching solution is affected due to the introduction of the impurity elements.

Aiming at the characteristic of large market share of lithium iron phosphate batteries in China, environmental functional material research groups of the institute of urban environmental research of the Chinese academy of sciences develop a method for preparing hydroxyl iron phosphate by hydrothermally treating a positive plate of the lithium iron phosphate battery to recycle the waste lithium iron phosphate battery. After the lithium iron phosphate battery is fully discharged, a positive plate containing the lithium iron phosphate material can be obtained by disassembling, and the positive plate and the aluminum foil can be effectively peeled and separated after hydrothermal treatment at 180 ℃ for 5 hours. Main low-value components of the hydrothermal product are converted into hydroxyl Ferric Phosphate (FPOH), and the material can be used for adsorbing lead heavy metal ions and efficiently catalyzing hydrogen peroxide to degrade organic pollutants such as dye methylene blue. The research provides a method for treating wastes with processes of wastes against one another for recycling the wastes of the lithium iron phosphate batteries with high lithium ion battery occupation ratio in China.

The waste lithium iron phosphate battery is discharged and disassembled at first by Tianjin university of technology, the residual electrolyte is treated by using low-concentration NaOH, the DMC, DEC, EC and the like are separated according to the physical characteristics of different solvents in the electrolyte, such as density, solubility, boiling point and the like, and the solvent salt LiPF₆Decomposition occurs in the aqueous solution as shown in the following formula. It can then be recovered by filtration. In the process, the separated positive electrode LFP material is mixed with certain Li₂CO₃After that, in Ar/H₂The regenerated LFP material can be obtained by heat treatment at different temperatures under the atmosphere.

LiPF₆+H₂O→POF₃↑+HF+LiF↓

Most of the recovery processing methods of the waste lithium iron phosphate batteries are in the laboratory research stage, and some methods are difficult to realize, high in cost and complex in process during real industrialization; and the pyrogenic process has large energy consumption, large equipment investment and low recycling economy. Therefore, under the condition that the lithium iron phosphate battery is used for the mature electric vehicle, effective recovery of the waste lithium iron phosphate battery by using a method which is low in cost, easy to realize industrialization, simple in operation and feasible in process is urgently needed to be found.

Disclosure of Invention

The invention aims to solve the technical problem of providing a method for recovering the anode material of the waste lithium iron phosphate battery, which is simple, efficient and easy for industrial production.

In order to solve the problems, the method for recycling the anode material of the waste lithium iron phosphate battery comprises the following steps:

adding water into waste lithium iron phosphate battery positive electrode powder to prepare 0.1-0.3 kg/L of slurry, adding 0.28-0.32L of sulfuric acid with the volume concentration of 98% into 1kg of waste lithium iron phosphate battery positive electrode powder after the slurry is preheated for leaching, and performing solid-liquid separation after the leaching is finished to respectively obtain leachate and leaching residues;

adding alkali liquor into the leachate to adjust the pH value to 1.5-2.5, adding iron powder to replace and remove copper, continuously adding alkali liquor to adjust the pH value to 3.3-3.5, and performing precipitation, aluminum removal and solid-liquid separation to obtain a solution after impurity removal; the mass of the iron powder is 1.1-1.2 times of that of the leaching solution;

thirdly, supplementing sodium phosphate according to the contents of iron and phosphorus in the solution after impurity removal to adjust the mass ratio of iron to phosphorus to be 0.97-1.02: 1;

a double-layer stirring paddle is arranged in the reaction container, pure water or the solution after iron deposition is added to serve as a base solution, the base solution is enabled to submerge into the first stirring paddle, stirring and heating are carried out at the linear speed of more than or equal to 4m/s until the temperature is 50-70 ℃, and acid liquor is added to adjust the pH value to 3.3-4.0; then introducing hydrogen peroxide below the liquid level of the base solution through a pipeline, simultaneously spraying and adding alkali liquor and the solution obtained in the step III after impurity removal through spraying equipment, adjusting the pH value of the solution to 3.3-4.0, aging for 5-7 hours after iron in the solution is completely oxidized and precipitated, and respectively obtaining iron phosphate precipitate and lithium-containing solution through solid-liquid separation;

fifthly, adjusting the pH value of the lithium-containing solution to 10.0-11.5, evaporating and concentrating the solution until the lithium concentration in the solution is 12-15 g/L, and carrying out solid-liquid separation to obtain a filtrate; introducing carbon dioxide with the flow rate of 20-40L/h into the filtrate at the temperature of 90-100 ℃, and obtaining the precipitated lithium.

The method comprises the steps of discharging, disassembling, peeling, crushing and separating the waste lithium iron phosphate battery positive electrode powder.

The waste lithium iron phosphate battery refers to a waste battery pack or a waste single battery.

The stripping and breaking means is manual or mechanical.

The waste lithium iron phosphate battery positive electrode powder is produced in the synthesis process and the battery production process of the positive electrode material.

The leaching condition in the step refers to that the temperature is 50-80 ℃ and the time is 3-4 h.

The second step and the alkali liquor in the fourth step are sodium hydroxide solutions with the concentration of 100-200 g/L.

The condition for replacing the copper in the step II is that the temperature is 60-70 ℃ and the time is 15-30 min.

The method comprises the step of precipitating and removing aluminum in the step II, wherein the temperature is 60-70 ℃, and the time is 2-8 hours.

And step four, the mass of hydrogen peroxide is 0.55-0.6 times of the iron content in the solution after impurity removal.

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

1. according to the invention, the waste lithium iron phosphate battery is disassembled, crushed and separated to obtain the anode powder which is high in purity and contains a small amount of copper and aluminum, the anode powder is leached only by using sulfuric acid in the leaching process, and hydrogen peroxide is not added in the leaching process for oxidation. The purpose is to avoid that a large amount of bubbles are generated by adding hydrogen peroxide in the leaching process, so that powder floats and overflows to influence the leaching effect; secondly, the iron concentration of the leachate is high, if iron is oxidized into ferric iron, iron phosphate precipitation can be generated by adjusting the pH value to be more than 1.5 during impurity removal, and even ferric hydroxide precipitation can be generated possibly, so that impurity removal cannot be realized; and the PH value of the ferrous phosphate and hydroxide precipitate is higher, so that the impurity removal of the leachate can be simply realized, and the ferric phosphate is oxidized and precipitated after the impurity removal.

2. According to the invention, iron powder is added into the acid-leached lithium iron phosphate anode powder solution to replace and remove copper, and excessive iron powder is added, so that the copper removal depth in the solution is improved, and high-concentration ferrous iron in the solution is not oxidized. Meanwhile, the pH value of the aluminum removal is not too high so as to avoid the generation of ferrous phosphate or aluminum phosphate.

3. In the invention, because the iron powder added in the copper removing process is slightly excessive, a proper amount of sodium phosphate is added into the solution after impurity removal according to the content ratio of iron to phosphorus in the solution, so that the proportion of iron to phosphorus is in a required range.

4. The method comprises the steps of adding a base solution into a reactor in the iron phosphate synthesis process, adding the solution, oxidant hydrogen peroxide and alkali liquor into the base solution in a concurrent flow manner after impurity removal, and strictly controlling the liquid adding speed of the solution in the synthesis process, namely controlling the concentration of iron and phosphate radical in the solution and controlling the acidity in the synthesis process, thereby synthesizing the high-quality iron phosphate.

5. The solution after ferric phosphate precipitation mainly contains sodium and lithium, but possibly other impurities, the pH value of the solution is adjusted, impurity precipitation is generated through filtration, the sodium sulfate is evaporated and concentrated to crystallize, the lithium ion concentration is improved, the impurity concentration is concentrated, lithium precipitation is performed after filtration, and the impurity content of the obtained lithium carbonate is greatly reduced.

6. The method is simple and efficient, and is easy for batch industrial production. By adopting the method, the recovery rate of the iron phosphate is more than 98.5%, the recovery rate of the lithium is more than 90%, and the aim of effectively recovering the waste lithium iron phosphate battery at low cost is fulfilled.

Detailed Description

A method for recycling a positive material of a waste lithium iron phosphate battery comprises the following steps:

the method comprises the steps of adding water into the positive electrode powder of the waste lithium iron phosphate batteries to prepare 0.1-0.3 kg/L of slurry, adding 0.28-0.32L of sulfuric acid with the volume concentration of 98% into the positive electrode powder of the waste lithium iron phosphate batteries after the slurry is preheated, leaching at the temperature of 50-80 ℃ for 3-4 hours. And after leaching, carrying out solid-liquid separation to respectively obtain a leaching solution and leaching residues. The iron in the leaching solution is ferrous iron; the main component of the leaching residue is carbon negative electrode powder (graphite) which is a negative electrode material of the battery.

The waste lithium iron phosphate anode powder is leached only by adding acid, no oxidant is added, a large amount of bubbles are generated when hydrogen peroxide is added in the leaching section, and leached ferrous iron is oxidized into ferric iron in the leaching process, so that subsequent impurity removal is difficult. Only acid is added during leaching, the leaching of lithium, iron and phosphorus in the lithium iron phosphate can be ensured, and the impurity removal effect can be ensured because the PH value of phosphate and hydroxide precipitation of ferrous iron is higher.

Wherein: the anode powder of the waste lithium iron phosphate battery is obtained by discharging, disassembling, stripping, crushing and separating the waste lithium iron phosphate battery. The battery anode powder material also contains a certain amount of aluminum powder and copper powder after being crushed.

The waste lithium iron phosphate battery refers to a waste battery pack or a waste single battery. The manner of peeling and crushing refers to a manual method or a mechanical method.

The waste lithium iron phosphate battery anode powder can also be waste lithium iron phosphate battery anode powder produced in the synthesis process of an anode material and the production process of batteries.

And adding alkali liquor into the leachate to adjust the pH value to 1.5-2.5, and then adding iron powder to remove copper by replacement, wherein the conditions for removing copper by replacement are that the temperature is 60-70 ℃, and the time is 15-30 min, so that iron in the solution is prevented from being oxidized. Continuously adding a sodium hydroxide solution with the concentration of 100-200 g/L to adjust the pH value to 3.3-3.5, precipitating at the temperature of 60-70 ℃ to remove aluminum, and carrying out solid-liquid separation after 2-8 h to obtain a solution after impurity removal; the mass of the iron powder is 1.1-1.2 times of the mass of the leaching solution.

Iron powder is added to the solution of ferrous iron to displace copper and a slight excess of iron powder inhibits the oxidation of ferrous iron to ferric iron precipitation in the solution. Adjusting the pH value of the solution to 3.3-3.5, and aging for a sufficient time to remove the aluminum content below the required amount. The liquid-solid ratio is improved as much as possible in the leaching process, and copper and aluminum in the solution after impurity removal can be reduced to below 0.005 g/L.

According to the content of iron and phosphorus in the solution after impurity removal, supplementing sodium phosphate to adjust the mass ratio of iron to phosphorus to be 0.97-1.02: 1.

and a double-layer stirring paddle is arranged in the reaction container, pure water or the solution after iron deposition is added to serve as a base liquid, and the base liquid is made to submerge in the first stirring paddle. Because the stirring strength is high in the iron phosphate precipitation process, the base solution and the added iron solution are required to be quickly mixed in a short time, and therefore stirring and heating are carried out at a linear speed of more than or equal to 4m/s until the temperature is 50-70 ℃, and acid liquor is added to adjust the pH value to 3.3-4.0; and then introducing hydrogen peroxide below the liquid level of the base solution through a pipeline, simultaneously spraying and adding alkali liquor and the solution obtained in the step III after impurity removal by using spraying equipment, adjusting the pH value of the solution to 3.3-4.0, aging for 5-7 hours after iron in the solution is completely oxidized and precipitated, and respectively obtaining iron phosphate precipitate and lithium-containing solution through solid-liquid separation.

The ferric phosphate is synthesized by adding the solution after leaching and impurity removal of the lithium iron phosphate, alkali liquor and oxidant hydrogen peroxide into the base solution in parallel flow, so that the generated ferric phosphate has uniform granularity and high product quality.

Wherein: the acid solution is a sulfuric acid solution with the volume concentration of 10-50%. The mass of the hydrogen peroxide is 0.55-0.6 times of the iron content in the solution after impurity removal.

Regulating the pH value of the lithium-containing solution to 10.0-11.5, evaporating and concentrating until the lithium concentration in the solution is 12-15 g/L, and carrying out solid-liquid separation to obtain a filtrate; introducing carbon dioxide with the flow rate of 20-40L/h into the filtrate at the temperature of 90-100 ℃, and obtaining the precipitated lithium.

Lithium is recovered by a traditional precipitation method, the pH value of the solution after iron precipitation is adjusted to 10.0-11.5 for impurity removal, evaporation and concentration are carried out until the concentration of lithium in the solution is 12-15 g/L, and impurity ions in the solution can also be precipitated. Because the sodium content in the lithium solution is high, carbon dioxide is introduced to precipitate lithium after the solution is concentrated, and sodium carbonate is not used to precipitate lithium, so that sodium sulfate crystallization caused by too high sodium concentration in the solution is avoided.

Collecting a certain amount of waste lithium iron phosphate batteries, discharging, disassembling, and mechanically crushing and separating to obtain the positive powder of the waste lithium iron phosphate batteries, wherein the material contains a small amount of copper and aluminum. This material was used as the starting material in the following examples. Preparing 200g/L of alkali liquor for later use.

Embodiment 1 is a method for recycling a positive electrode material of a waste lithium iron phosphate battery, comprising the following steps:

the method comprises the steps of adding 500mL of water into 100g of lithium iron phosphate anode powder, pulping, preheating, adding sulfuric acid for leaching, performing solid-liquid separation after leaching is completed at the leaching temperature of 70 ℃ for 4h to obtain leachate and leaching residues, wherein the leachate mainly contains phosphorus, iron and lithium, and also contains trace copper and aluminum.

And secondly, adding alkali liquor into the leachate to adjust the pH value to 2.0, adding 0.5g of iron powder to replace and remove copper, wherein the copper removal time is 0.5h, continuously adding alkali liquor to adjust the pH value to 3.3, removing aluminum, and removing aluminum for 6h, and carrying out solid-liquid separation to obtain a solution after impurity removal.

And 3g of sodium phosphate is added into the leaching solution after impurity removal.

150mL of pure water is added into a beaker, the beaker is placed in a water bath for preheating, the synthesis temperature is 55 ℃, acid is added to adjust the pH value of the base solution to 3.5, alkali liquor, hydrogen peroxide and lithium iron phosphate are added in a parallel flow manner to leach the solution after impurity removal, the pH value of the base solution is controlled to be 3.3-4.0, and the liquid adding time is 1 h. The aging time is 6 h. And (4) carrying out solid-liquid separation to obtain iron phosphate precipitate, wherein the filtrate is a lithium solution.

And fifthly, introducing carbon dioxide to precipitate lithium when the lithium solution is evaporated and concentrated until the lithium content in the solution is 13g/L, carrying out solid-liquid separation at the lithium precipitation temperature of 95 ℃ for 1h, wherein the filtrate contains 2-3 g/L, and the solution can be used for circularly extracting lithium or leaching.

Embodiment 2 is a method for recycling a positive electrode material of a waste lithium iron phosphate battery, including the steps of:

the method comprises the steps of adding 5L of water into 1kg of lithium iron phosphate positive electrode powder, pulping, preheating, adding sulfuric acid for leaching, performing solid-liquid separation after leaching is completed at the leaching temperature of 80 ℃ for 3h to obtain leachate and leaching residues, wherein the leachate mainly contains phosphorus, iron and lithium, and also contains trace copper and aluminum.

And secondly, adding alkali liquor into the leachate to adjust the pH value to 1.5, adding 4.5g of iron powder to replace and remove copper, wherein the copper removal time is 0.5h, continuously adding alkali liquor to adjust the pH value to 3.5, removing aluminum, and removing aluminum for 7h, and carrying out solid-liquid separation to obtain a solution after impurity removal.

And adding 27g of sodium phosphate into the leaching solution after removing impurities.

Adding 1.5L of pure water into a reactor, placing the reactor in a water bath for preheating, adjusting the pH value of a base solution to 3.5 by adding acid at the synthesis temperature of 60 ℃, adding alkali liquor, hydrogen peroxide and lithium iron phosphate in parallel to leach the impurity-removed solution, controlling the pH value of the base solution to be 3.3-4.0, and adding liquid for 2 hours. The aging time is 7 h. And (4) carrying out solid-liquid separation to obtain iron phosphate precipitate, wherein the filtrate is a lithium solution.

And fifthly, introducing carbon dioxide to precipitate lithium when the lithium solution is evaporated and concentrated until the lithium content in the solution is 15g/L, carrying out solid-liquid separation at the lithium precipitation temperature of 94 ℃ for 1h, wherein the filtrate contains 2-3 g/L, and the solution can be used for circularly extracting lithium or leaching.

Embodiment 3 is a method for recycling a positive electrode material of a waste lithium iron phosphate battery, comprising the following steps:

the method comprises the steps of adding 50L of water into 10kg of lithium iron phosphate positive electrode powder, pulping, preheating, adding sulfuric acid for leaching, wherein the leaching temperature is 75 ℃, the leaching time is 4 hours, and after leaching, carrying out solid-liquid separation to obtain leachate and leaching residues, wherein the leachate mainly contains phosphorus, iron and lithium, and also contains trace copper and aluminum.

And adding alkali liquor into the leachate to adjust the pH value to 1.5, adding 405g of iron powder to replace and remove copper, wherein the copper removal time is 1h, continuously adding alkali liquor to adjust the pH value to 3.5, removing aluminum, and performing solid-liquid separation to obtain a solution after impurity removal, wherein the aluminum removal time is 7 h.

And 226g of sodium phosphate is added into the leaching solution after the impurities are removed.

And adding 15L of pure water into the reaction kettle, placing the reaction kettle in a water bath for preheating, adjusting the pH value of the base solution to 3.5 by adding acid at the synthesis temperature of 65 ℃, adding alkali liquor, hydrogen peroxide and lithium iron phosphate in a parallel flow manner to leach the impurity-removed solution, controlling the pH value of the base solution to be 3.3-4.0, and adding liquid for 1 h. The aging time is 8 h. And (4) carrying out solid-liquid separation to obtain iron phosphate precipitate, wherein the filtrate is a lithium solution.

And fifthly, introducing carbon dioxide to precipitate lithium when the lithium solution is evaporated and concentrated until the lithium content in the solution is 15g/L, carrying out solid-liquid separation at the lithium precipitation temperature of 95 ℃ for 1h, wherein the filtrate contains 2-3 g/L, and the solution can be used for circularly extracting lithium or leaching.