Method for recovering lithium and iron phosphate from waste lithium iron phosphate

Abstract

The application provides a method for recovering lithium and iron phosphate from waste lithium iron phosphate. The method comprises the following steps: providing crude lithium iron phosphate slag; preparing a slurry from the crude lithium iron phosphate slag, introducing a gas Cl2 into the slurry, adding a catalyst FeCl3, and performing a catalytic oxidation lithium extraction reaction; filtering the reacted slurry to obtain a lithium-containing filtrate and a crude iron phosphate filter residue; crystallizing lithium chloride in the lithium-containing filtrate to obtain purified lithium chloride; and performing acid leaching and washing on the crude iron phosphate filter residue, and filtering the acid leaching and washing residue to obtain an iron phosphate precursor. The method can realize full-element recovery of lithium iron phosphate from waste lithium iron phosphate, and can improve energy utilization.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material technology, specifically, it relates to a method for the complete recovery of lithium and iron phosphate from waste lithium iron phosphate. Background Technology

[0002] Lithium iron phosphate batteries have become one of the most widely used lithium-ion batteries due to their advantages such as high specific energy, good thermal stability, high cycle life, low cost, and low pollution.

[0003] Currently, lithium iron phosphate (LFP) recycling processes include pyrometallurgical and hydrometallurgical methods. Pyrometallurgical processes cannot directly recycle LFP and are often used as an auxiliary method for repairing LFP materials. However, the electrochemical performance of LFP materials repaired through pyrometallurgical processes is poor and does not meet the standards for power batteries.

[0004] Hydrometallurgical processes are the primary industrial method for recovering lithium iron phosphate. Typically, a hydrometallurgical process includes the following steps: completely leaching the waste lithium iron phosphate with acid solutions such as HCl and H₂SO₄ to obtain lithium containing Li₂. + Fe 2+ and PO4 3- The process involves using an acidic solution; precipitating iron as FePO4 by adding alkali and an oxidizing agent; and then recovering lithium as lithium carbonate by adding sodium carbonate. Hydrometallurgical processes mostly involve lengthy leaching and precipitation processes, resulting in long process cycles and the consumption of large amounts of organic solvents, acids, and alkalis. Therefore, hydrometallurgical recovery processes are environmentally unfriendly and costly, hindering their commercial development.

[0005] Existing technology discloses a method for recovering lithium iron phosphate using ferric salts. The recovered waste lithium iron phosphate is added to a ferric salt solution and reacted to obtain ferric hydroxide, ferric phosphate slag, and a leached lithium-ion solution. This method can leach out some lithium and has simple process steps, showing improvement over hydrometallurgical processes. However, this method requires a large amount of ferric salt, has a low leaching rate, an excessively long overall reaction time, and results in significant waste of ferric salt, making complete recycling impossible.

[0006] Existing technology also discloses a method for the comprehensive utilization of waste lithium iron phosphate materials. This method includes the following steps: uniformly mixing waste lithium iron phosphate materials with chloride and then calcining; introducing chlorine gas into the cooled calcined mixture and then carrying out a high-temperature reaction; condensing the reaction exhaust gas to obtain sublimated anhydrous ferric chloride product; leaching the mixture after reacting with chlorine gas with water and filtering to obtain an aqueous solution containing lithium chloride; and evaporating and crystallizing the obtained aqueous solution containing lithium chloride. This method requires one high-temperature calcination and one high-temperature reaction, resulting in extremely high energy consumption, and chlorine gas poses a danger during the high-temperature calcination reaction. Furthermore, this method does not recover the iron phosphate product, therefore it cannot achieve complete recovery of lithium iron phosphate.

[0007] Therefore, in the recycling technology of waste lithium iron phosphate, there is an urgent need for a high-efficiency recycling method that can improve energy utilization and achieve full element recovery of lithium iron phosphate from waste lithium iron phosphate. Summary of the Invention

[0008] The purpose of this invention is to provide a highly efficient recovery method for recovering all elements of lithium iron phosphate from waste lithium iron phosphate.

[0009] A further objective of this invention is to provide a method for recovering lithium and iron phosphate from waste lithium iron phosphate that can significantly improve energy efficiency.

[0010] The specific technical solution of the present invention is as follows.

[0011] On one hand, the present invention provides a method for recovering lithium and iron phosphate from waste lithium iron phosphate, comprising:

[0012] Provide crude lithium iron phosphate slag;

[0013] The crude lithium iron phosphate residue is made into a slurry, and gas Cl2 is introduced into the slurry while the catalyst FeCl3 is added to carry out a catalytic oxidation lithium extraction reaction.

[0014] The reacted slurry was filtered to obtain lithium-containing filtrate and coarse iron phosphate filter residue;

[0015] The lithium chloride in the lithium-containing filtrate is crystallized to obtain purified lithium chloride;

[0016] The crude ferric phosphate filter residue was subjected to acid leaching, and the resulting ferric phosphate precursor was obtained by filtration after acid leaching.

[0017] The ferric phosphate precursor was calcined to obtain ferric phosphate.

[0018] Optionally, the crude lithium iron phosphate residue is obtained by removing impurities from waste lithium iron phosphate.

[0019] Preferably, the waste lithium iron phosphate includes the positive electrode material of waste lithium batteries;

[0020] Preferably, the impurities include at least one of metallic materials, organic matter, and carbon materials;

[0021] Preferably, the metallic material includes at least one of copper and aluminum;

[0022] Preferably, the organic material includes at least one of an organic electrolyte and an organic binder.

[0023] Optionally, the removal of impurities from waste lithium iron phosphate includes: screening out metallic materials such as copper foil using a vibrating screen; calcining away organic materials such as organic electrolytes and / or organic binders under an inert atmosphere; removing carbon by flotation; and washing with dilute acid to remove metallic materials such as aluminum, thereby obtaining aluminum-containing waste acid and crude lithium iron phosphate precursor filter residue.

[0024] Preferably, lithium iron phosphate, after the organic matter has been calcined off, is added to water and stirred to separate the carbon floating on the surface of the liquid.

[0025] Optionally, the organic binder and organic electrolyte are removed by calcination in an inert atmosphere such as nitrogen or argon at a calcination temperature of 300–800°C; preferably, the calcination temperature is 450°C, 500°C or 600°C; preferably, the calcination time is 0.5–4 hours, more preferably 1.0 hour, 1.5 hours, 2.0 hours, 2.5 hours or 3.0 hours.

[0026] Optionally, one or more dilute acids selected from hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid are used to wash the waste lithium iron phosphate after flotation carbon removal to remove metal materials; preferably, the pH of the dilute acid is 1.0 to 4.0, more preferably 2.0, 2.5, or 3.0; preferably, the acid washing time is 0.5 to 2 hours, more preferably 0.5 hours, 1.0 hour, or 1.5 hours; preferably, the aluminum-containing waste liquid is recycled to the dilute acid washing aluminum removal process for reuse.

[0027] Optionally, the step of preparing the crude lithium iron phosphate slag into a slurry includes mixing the crude lithium iron phosphate slag with water to prepare the slurry, wherein the solid-liquid ratio in the slurry is 80 g / L to 220 g / L.

[0028] Optionally, for every 100g of crude lithium iron phosphate slag processed, the flow rate V of gas Cl2 introduced into the slurry is... Cl2 The flow rate is 0.5–5 L / min, preferably 0.7–1.3 L / min.

[0029] Optionally, the molar ratio m of the catalyst FeCl3 to the lithium iron phosphate in the crude lithium iron phosphate residue is 0.05 to 1; preferably, the molar ratio m is 0.2 to 0.5.

[0030] Optionally, the molar ratio m of catalyst FeCl3 to lithium iron phosphate in crude lithium iron phosphate slag, and the flow rate V of gas Cl2 introduced into the slurry per 100g of crude lithium iron phosphate slag treated are specified. Cl2 It satisfies the following equation (1):

[0031] 0.25≤ m×V Cl2 ≤0.35 (1).

[0032] Optionally, in the catalytic oxidation lithium extraction reaction, the reaction temperature is 40–80°C and the reaction time is 10–60 minutes;

[0033] Preferably, the reaction temperature is 50–70°C; preferably, the reaction time is 11–35 minutes.

[0034] Optionally, the acid leaching includes: leaching the crude ferric phosphate filter residue with a mixed acid at a temperature of 70–95°C for 2–5 hours; filtering after acid leaching to obtain ferric phosphate precursor and mixed acid waste liquid; and recycling the mixed acid waste liquid back to the acid leaching process for reuse.

[0035] Preferably, the mixed acid comprises phosphoric acid and hydrochloric acid;

[0036] Preferably, the concentration of H3PO4 in the mixed acid is 0.1–5.0 mol / L, and the molar ratio of H3PO4 to HCl is 1–10;

[0037] Preferably, the concentration of H3PO4 in the mixed acid is 0.5–3 mol / L, and the molar ratio of H3PO4 to HCl is 3–6;

[0038] Preferably, the acid immersion process is carried out at a temperature of 80–90°C for 3–4 hours.

[0039] Optionally, calcining the iron phosphate precursor to obtain iron phosphate includes: calcining the iron phosphate precursor at a temperature of 500 to 1000°C, so that the lithium ion vacancies in the iron phosphate precursor are burned off to achieve the transformation of the spatial structure, thereby obtaining iron phosphate.

[0040] Preferably, the roasting temperature is 700–800℃;

[0041] Preferably, the roasting time is 1 to 6 hours, more preferably, the roasting time is 2 to 4 hours.

[0042] The method for recovering lithium and iron phosphate from waste lithium iron phosphate according to the present invention can produce the following beneficial technical effects: The method of the present invention uses a dual synergistic catalytic-lithium extraction system of catalyst FeCl3 and strong oxidant Cl2, that is, it utilizes the strong oxidizing property of chlorine gas Cl2 to leach lithium from crude lithium iron phosphate slag, while the catalyst FeCl3 passes through Fe... 2+ with Fe 3+ The method of interconversion accelerates lithium leaching, thereby achieving a highly efficient recovery of all elements of lithium iron phosphate from waste lithium iron phosphate; furthermore, the method of the present invention can significantly improve energy utilization by recycling various chemical reagents. Attached Figure Description

[0043] Figure 1 This is a process flow diagram for recycling lithium from waste lithium iron phosphate and battery-grade lithium iron phosphate.

[0044] Figure 2 This is the XRD pattern of iron phosphate obtained in Example 3.

[0045] Figure 3 This is the XRD pattern of the iron phosphate precursor obtained in Comparative Example 4.

[0046] Figure 4 These are photographs of the ferric phosphate obtained in Example 3 and the ferric phosphate precursor obtained in Comparative Example 4. Detailed Implementation

[0047] The following describes specific embodiments of the present invention in detail. These specific embodiments and the following examples are exemplary and intended to further illustrate the technical solutions of the present invention. The terminology used is only for describing specific implementations and is not intended to limit certain features of the technical solutions of the present invention.

[0048] According to one embodiment of the present invention, a method for recovering lithium and iron phosphate from waste lithium iron phosphate is provided, comprising: providing crude lithium iron phosphate residue; preparing the crude lithium iron phosphate residue into a slurry, introducing Cl2 gas into the slurry while adding FeCl3 catalyst to carry out a catalytic oxidation lithium extraction reaction; filtering the slurry after the reaction to obtain a lithium-containing filtrate and crude iron phosphate filter residue; crystallizing lithium chloride from the lithium-containing filtrate to obtain purified lithium chloride; acid leaching the crude iron phosphate filter residue, filtering after acid leaching to obtain an iron phosphate precursor; and calcining the iron phosphate precursor to obtain iron phosphate.

[0049] The method according to the above embodiments of the present invention uses a dual synergistic catalytic lithium extraction system of catalyst FeCl3 and strong oxidant Cl2, that is, the strong oxidizing property of Cl2 is used to leach Li ions from LiFePO4, while the catalyst FeCl3 passes through Fe... 2+ with Fe 3+Interconversion is used to accelerate Li ion leaching, enabling cyclic leaching of Li ions and increasing the reaction rate. The method of this invention utilizes a selective and efficient lithium extraction technology via catalytic oxidation to recover lithium and iron phosphate in high yields, achieving efficient recovery of all elements (lithium, iron, and phosphorus) from waste lithium iron phosphate.

[0050] To better understand the recycling method of the present invention and its beneficial technical effects, the technical solution of the present invention and the beneficial technical effects produced by each step are described in detail below.

[0051] The method for recovering lithium and iron phosphate from waste lithium iron phosphate according to embodiments of the present invention mainly includes the following four steps: Step 1, providing crude lithium iron phosphate slag; Step 2, catalytic oxidation to extract lithium; Step 3, acid leaching and purification of crude iron phosphate; Step 4, calcining the iron phosphate precursor.

[0052] Step 1: Provide crude lithium iron phosphate slag

[0053] The crude lithium iron phosphate slag is obtained from recycled waste lithium iron phosphate cathode material. Preferably, the waste lithium iron phosphate is the cathode material of a spent lithium battery. If the recycled waste lithium iron phosphate cathode material contains a significant amount of impurities such as at least one of metallic materials, organic matter, and carbon materials, then this step includes a step of removing the impurities, or the method described above by the present invention includes a step of removing impurities before providing the crude lithium iron phosphate slag step.

[0054] If the recycled waste lithium iron phosphate cathode material contains a significant amount of metallic materials such as copper foil and / or aluminum, the impurity removal step includes screening out the metallic copper foil, preferably by a vibrating screen; and / or washing with dilute acid to remove the metallic aluminum, thereby obtaining aluminum-containing waste acid and crude lithium iron phosphate filter residue.

[0055] If the recycled waste lithium iron phosphate cathode material contains a significant amount of organic materials such as organic binders and / or organic electrolytes, the impurity removal step includes calcining off the organic electrolytes and / or organic binders under an inert atmosphere.

[0056] If the recycled waste lithium iron phosphate cathode material contains a significant amount of carbon material, the impurity removal step further includes flotation to remove carbon. Preferably, the lithium iron phosphate, after the organic matter has been calcined off, is added to water and stirred to separate the carbon floating on the liquid surface.

[0057] If the recycled waste lithium iron phosphate cathode material contains significant amounts of metallic materials such as copper foil and aluminum, organic materials such as organic binders and organic electrolytes, and carbon materials, the impurity removal steps may sequentially include: screening out the metallic copper foil; calcining the organic electrolyte and organic binder under an inert atmosphere; flotation to remove carbon; and washing with dilute acid to remove metallic aluminum materials.

[0058] Preferably, the organic binder and organic electrolyte are removed by calcination in an inert atmosphere such as nitrogen or argon at a calcination temperature of 300–800°C. Preferably, the inert gas flow rate is 0.1–2 L / min relative to 100 g of crude lithium iron phosphate slag processed, and is preferably 0.5 L / min, 1.0 L / min, 1.5 L / min, or 1.8 L / min. Preferably, the calcination temperature is 450°C, 500°C, or 600°C; preferably, the calcination time is 0.5–4 hours, more preferably 1.0 hour, 1.5 hours, 2.0 hours, 2.5 hours, or 3.0 hours.

[0059] Preferably, one or more dilute acids selected from hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid are used to wash the waste lithium iron phosphate after flotation carbon removal to remove metallic materials such as aluminum. Preferably, the pH of the dilute acid is 1.0 to 4.0, and more preferably, the pH is 2.0, 2.5, or 3.0. Preferably, the acid washing time is 0.5 to 2 hours, more preferably 0.5 hours, 1.0 hour, or 1.5 hours.

[0060] Preferably, the waste lithium iron phosphate after carbon removal by flotation is added to a dilute acid solution to wash away metallic materials such as aluminum, and the washing is carried out under stirring at a stirring speed of 100-700 r / min; more preferably, the washing is carried out at stirring speeds of 200 r / min, 300 r / min, 400 r / min, 500 r / min or 600 r / min.

[0061] Preferably, the aluminum-containing waste liquid is recycled to a dilute acid washing process to remove metal materials (such as aluminum) for reuse, thereby improving energy efficiency and saving chemical raw materials.

[0062] Step 2: Catalytic oxidation leaching for lithium extraction

[0063] Crude lithium iron phosphate residue is prepared into a slurry. Cl2 gas is introduced into the slurry, and FeCl3 catalyst is added simultaneously to initiate a catalytic oxidation reaction for lithium extraction. The resulting slurry is filtered to obtain a lithium-containing filtrate and crude lithium iron phosphate residue. Purified lithium chloride is obtained by crystallizing the lithium chloride from the lithium-containing filtrate.

[0064] Preferably, the step of preparing the crude lithium iron phosphate slag into a slurry includes mixing the crude lithium iron phosphate slag with water to prepare the slurry, wherein the solid-liquid ratio in the slurry is 80 g / L to 220 g / L. Preferably, the solid-liquid ratio is 100 g / L to 200 g / L.

[0065] Preferably, for every 100g of crude lithium iron phosphate slag processed, the flow rate V of gas Cl2 introduced into the slurry is... Cl2The flow rate is 0.5 to 5 L / min, preferably 0.55 to 4.0 L / min, even more preferably 0.6 to 3.0 L / min, more preferably 0.65 to 2.0 L / min, and even more preferably 0.7 to 1.3 L / min.

[0066] Preferably, the molar ratio m of the catalyst FeCl3 to the lithium iron phosphate in the crude lithium iron phosphate residue is 0.05 to 2. The molar ratio m is preferably 0.05 to 1.5, more preferably 0.05 to 1.0, even more preferably 0.1 to 0.8, and even more preferably 0.2 to 0.5.

[0067] Preferably, the molar ratio m of catalyst FeCl3 to lithium iron phosphate in crude lithium iron phosphate slag, and the flow rate V of gas Cl2 introduced into the slurry per 100g of crude lithium iron phosphate slag treated are specified. Cl2 It satisfies the following equation (1):

[0068] 0.25≤ m×V Cl2 ≤0.35 (1).

[0069] Preferably, in the catalytic oxidation lithium extraction reaction, the reaction temperature is 40–80°C, and the reaction time is 10–60 minutes. Preferably, the reaction temperature is 50–70°C, more preferably 55°C, 60°C, or 65°C. Preferably, the reaction time is 11–35 minutes, more preferably 15 minutes, 20 minutes, 25 minutes, or 30 minutes.

[0070] The inventors believe that the above-mentioned method of the present invention achieves efficient recovery of lithium, iron, and phosphorus from waste lithium iron phosphate by using a dual synergistic catalytic extraction system of catalyst FeCl3 and strong oxidant Cl2. Not limited to theory, the inventors believe that the method of the present invention mainly achieves the inventive objective based on the following mechanism:

[0071] (1) Cl2 gas has strong oxidizing properties. When introduced into an aqueous solution, it provides an acidic environment for the reaction, forming a gas-liquid-solid three-phase reaction with lithium iron phosphate. This increases the contact area between the reactants, thereby accelerating the reaction rate. The specific reaction equation is as follows:

[0072] 2LiFePO4 + Cl2 → 2FePO4 + 2LiCl

[0073] Cl₂ + H₂O → HCl + HClO

[0074] 2LiFePO4+HCl+HClO→2FePO4+2LiCl+H2O

[0075] (2) The catalyst FeCl3 salt also has strong oxidizing properties. Using FeCl3 as a catalyst, it provides Fe to initiate the reaction in the early stage. 3+ Fe3+ With PO4 in LiFePO4 3- Combined to form FePO4, releasing Fe 2+ Fe 2+ Then oxidized by chlorine gas to Fe 3+ This repeated cycle achieves the continuous recovery of lithium iron phosphate. The specific reaction equation is as follows:

[0076] LiFePO4+FeCl3→FePO4+FeCl2+LiCl

[0077] 2FeCl2 + Cl2 → 2FeCl3

[0078] Therefore, in the method of this invention, the gaseous Cl2 and the catalyst FeCl3 have a synergistic effect: chlorine acts as a strong oxidant to react with lithium iron phosphate to leach lithium; simultaneously, chlorine oxidizes the FeCl3-catalyzed Fe... 2+ This enables the cyclic catalytic oxidation and leaching of lithium using FeCl3; the FeCl3 catalyst provides the Fe required to initiate the reaction in the early stages. 3+ Fe 3+ With PO4 in LiFePO4 3- Combined to form FePO4, releasing Fe 2+ The catalysis promotes the entire reaction process, thereby facilitating and accelerating the rapid leaching of Li ions.

[0079] Filtering the reacted slurry yields a lithium-containing filtrate and coarse iron phosphate filter residue. The filtrate is then recycled back into the lithium leaching process. After multiple cycles of lithium leaching, the Li ion concentration in the filtrate can be enriched to a certain level. The maximum enrichment concentration of lithium chloride can reach 95 g / L. By recycling the filtrate back into the lithium leaching process multiple times, energy utilization efficiency can be improved and chemical raw materials can be saved.

[0080] Lithium chloride is crystallized from the lithium-containing filtrate by utilizing the difference in saturation concentration between lithium chloride and ferric chloride. Evaporation and crystallization concentration are performed, and when the lithium chloride concentration reaches saturation solubility, the lithium chloride will crystallize out due to the difference in solubility between lithium chloride and ferric chloride. For example, when the solution temperature is 50°C, the saturation of lithium chloride is approximately 85 g / L.

[0081] Step 3: Purification by leaching crude ferric phosphate

[0082] The crude ferric phosphate filter residue obtained in step two above is subjected to acid leaching, and then filtered to obtain the ferric phosphate precursor.

[0083] Preferably, the acid leaching step includes: leaching the crude ferric phosphate filter residue with a mixed acid at a temperature of 70–95°C for 2–5 hours; filtering after acid leaching to obtain ferric phosphate precursor and mixed acid waste liquid; and recycling the mixed acid waste liquid back to the acid leaching process for reuse.

[0084] Preferably, the mixed acid comprises phosphoric acid and hydrochloric acid.

[0085] Preferably, the concentration of H3PO4 in the mixed acid is 0.1–5.0 mol / L, and the molar ratio of H3PO4 to HCl is 1–10, more preferably 2–8. Preferably, the concentration of H3PO4 in the mixed acid is 0.5–3 mol / L, and the molar ratio of H3PO4 to HCl is 3–6, more preferably 3.2–5.

[0086] Preferably, the acid immersion process is carried out at a temperature of 80–90°C for 3–4 hours.

[0087] Step 4: Calcining the ferric phosphate precursor

[0088] The method of the present invention further includes the step of calcining the iron phosphate precursor to obtain iron phosphate. Preferably, the method includes calcining the iron phosphate precursor at a temperature of 500-1000°C, so that the lithium ion vacancies in the iron phosphate precursor are burned off to achieve a transformation of the spatial structure, thereby obtaining iron phosphate.

[0089] Preferably, the roasting temperature is 700–800°C. Preferably, the roasting time is 1–6 hours.

[0090] By calcining the iron phosphate precursor as described above, a battery-grade iron phosphate material with superior electrical performance can be obtained, namely, an iron phosphate material without vacancy defects and with a more complete crystal structure. Preferably, the calcination temperature is 700–800°C, and the calcination time is 2–4 hours.

[0091] The method according to the present invention is applicable not only to the recycling of waste lithium iron phosphate materials, but also to the recycling of modified lithium iron phosphate materials including modified lithium manganese iron phosphate.

[0092] The method of the present invention greatly improves the lithium extraction rate by using a dual synergistic catalytic leaching system of catalyst FeCl3 and strong oxidant Cl2. Compared with the traditional acid leaching and alkali precipitation process, the method of the present invention has fewer process steps, faster reaction rate, and less chemical reagents such as acids and alkalis. Furthermore, the chemical reagents in the method of the present invention can be recycled, are environmentally friendly, and have high economic value.

[0093] Example

[0094] The technical solution and beneficial effects of the present invention will be further illustrated below through specific embodiments.

[0095] Example 1

[0096] Recover lithium and iron phosphate from spent lithium iron phosphate using the following steps.

[0097] Step 1: Remove impurities from waste lithium iron phosphate.

[0098] 100g of waste lithium iron phosphate was separated from impurities and metallic copper foil using a vibrating screen. After separation, the lithium iron phosphate waste (Li content 3.99% by mass) was placed in a rotary tube furnace and calcined at 450℃ for 2 hours under a nitrogen atmosphere to remove organic binders and organic electrolytes. Then, carbon removal was performed by flotation; the calcined lithium iron phosphate was added to water and stirred to separate the carbon floating on the surface. The carbon-removed lithium iron phosphate waste was placed in a dilute hydrochloric acid solution with pH 3.0 and stirred for 30 minutes to remove metallic aluminum impurities. Filtering yielded 97g of crude lithium iron phosphate slag and aluminum-containing waste acid. The aluminum-containing waste acid was then recycled to the dilute hydrochloric acid solution for aluminum removal.

[0099] Step 2: Catalytic oxidation leaching for lithium extraction

[0100] Water was added to 97g of crude lithium iron phosphate residue obtained in the above steps to prepare a slurry with a solid-liquid ratio of 200g / L. This slurry was placed in a reactor, and 9.89g of anhydrous ferric chloride was added (the molar ratio of FeCl3 to LFP in the crude lithium iron phosphate residue was 0.1). The stirring speed in the reactor was 400r / min, the reaction temperature was 50℃, and chlorine gas was introduced at a flow rate V per 100g of crude lithium iron phosphate residue processed. Cl2 Chlorine gas was introduced at a rate of 5.0 L / min, and the reaction time was 35 minutes. The slurry after the reaction was filtered to obtain a filtrate containing FeCl3 and LiCl and a crude ferric phosphate filter residue.

[0101] After one reaction, the Li content in the filtrate was 7.74 g / L, and the mass of the crude ferric phosphate filter residue was 91.73 g. The filtrate was circulated three times, concentrating the Li concentration to 23.20 g / L. Taking advantage of the different crystallinities of lithium chloride and ferric chloride, the filtrate was evaporated and concentrated at 100°C, reaching a lithium chloride concentration of 128 g / L. Lithium chloride then crystallized and precipitated, and filtration separated the lithium chloride (the saturated solubility of lithium chloride at 100°C is 128 g / L, and that of ferric chloride is 536 g / L). Drying yielded lithium chloride with a purity of 99.1%.

[0102] Step 3: Acid leaching and purification of crude ferric phosphate filter residue

[0103] The crude ferric phosphate filter residue was purified by acid leaching with a mixed acid at a solid-liquid ratio of 200 g / L. The mixed acid consisted of 2.0 mol / L H3PO4 and 0.5 mol / L HCl, i.e., a molar ratio of H3PO4:HCl of 4:1. The leaching time was 4 hours, the leaching temperature was 80℃, and the stirring rate was 500 r / min. After acid leaching and purification, the ferric phosphate precursor and the mixed acid filtrate were obtained by filtration. The mixed acid filtrate was recycled to the acid leaching purification process. The ferric phosphate precursor was calcined at 800℃ for 2 hours to obtain structurally stable battery-grade ferric phosphate. The purity of the ferric phosphate was 99.5%, and the recovery rate of ferric phosphate reached 98.5%.

[0104] Example 2

[0105] Recover lithium and iron phosphate from spent lithium iron phosphate using the following steps.

[0106] Step 1: Remove impurities from waste lithium iron phosphate.

[0107] 100g of waste lithium iron phosphate was separated from impurities, including metallic copper foil, using a vibrating screen. After separation, the waste lithium iron phosphate (Li content 3.99% by mass) was placed in a rotary tube furnace and roasted at 500℃ for 2 hours under a nitrogen atmosphere to remove organic binders and organic electrolytes. Then, carbon removal was performed by flotation; the roasted lithium iron phosphate was added to water and stirred to separate the carbon floating on the surface. The decarbonized lithium iron phosphate waste was placed in a dilute hydrochloric acid solution with pH 2.5 and stirred for 60 minutes to remove metallic aluminum impurities. Filtering yielded 96.8g of crude lithium iron phosphate slag and aluminum-containing waste acid. The aluminum-containing waste acid was recycled to the dilute hydrochloric acid solution for aluminum removal.

[0108] Step 2: Catalytic oxidation leaching for lithium extraction

[0109] Water was added to the 96.8g of crude lithium iron phosphate residue obtained in the above steps to prepare a slurry with a solid-liquid ratio of 100g / L. This slurry was placed in a reactor, and 19.78g of anhydrous ferric chloride was added (the molar ratio of FeCl3 to LFP in the crude lithium iron phosphate residue was 0.2). The stirring speed in the reactor was 500r / min, the reaction temperature was 60℃, and chlorine gas was introduced at a flow rate V per 100g of crude lithium iron phosphate residue processed. Cl2 Chlorine gas was introduced at a rate of 1.9 L / min, and the reaction time was 23 minutes. The slurry after the reaction was filtered to obtain a filtrate containing FeCl3 and LiCl and a crude ferric phosphate residue.

[0110] After one reaction, the Li content in the filtrate was 3.89 g / L, and the mass of the crude ferric phosphate filter residue was 92.27 g. After six cycles of circulation, the Li concentration was concentrated to 23.34 g / L. Taking advantage of the different crystallinities of lithium chloride and ferric chloride, the filtrate was evaporated and concentrated at 100°C, reaching a lithium chloride concentration of 128 g / L. Lithium chloride then crystallized out, and filtration separated it. Drying yielded lithium chloride with a purity of 99.0%.

[0111] Step 3: Acid leaching and purification of crude ferric phosphate filter residue

[0112] The crude ferric phosphate filter residue was purified by acid leaching with a mixed acid at a solid-liquid ratio of 100 g / L. The mixed acid consisted of 1.5 mol / L H3PO4 and 0.5 mol / L HCl, i.e., an H3PO4:HCl molar ratio of 3:1. The leaching time was 4 hours, the leaching temperature was 90℃, and the stirring rate was 500 r / min. After acid leaching and purification, the ferric phosphate precursor and the mixed acid filtrate were obtained by filtration. The mixed acid filtrate was recycled to the acid leaching purification process. The ferric phosphate precursor was calcined at 700℃ for 2 hours to obtain structurally stable battery-grade ferric phosphate. The purity of the ferric phosphate reached 99.5%, and the recovery rate was 99.32%.

[0113] Example 3

[0114] Recover lithium and iron phosphate from spent lithium iron phosphate using the following steps.

[0115] Step 1: Remove impurities from waste lithium iron phosphate.

[0116] 100g of waste lithium iron phosphate was separated from impurities and metallic copper foil using a vibrating screen. After separation, the lithium iron phosphate waste (Li content 3.99% by mass) was placed in a rotary tube furnace and roasted at 600℃ for 2 hours under an argon atmosphere to remove organic binders and organic electrolytes. Then, carbon removal was performed by flotation; the roasted lithium iron phosphate was added to water and stirred to separate the carbon floating on the surface. The decarbonized lithium iron phosphate waste was placed in a dilute hydrochloric acid solution with pH 2.0 and stirred for 60 minutes to remove metallic aluminum impurities. Filtering yielded 97g of crude lithium iron phosphate slag and aluminum-containing waste acid. The aluminum-containing waste acid was recycled to the dilute hydrochloric acid solution for aluminum removal.

[0117] Step 2: Catalytic oxidation leaching for lithium extraction

[0118] Water was added to 97g of crude lithium iron phosphate residue obtained in the above steps to prepare a slurry with a solid-liquid ratio of 100g / L. This slurry was placed in a reactor, and 50.0g of anhydrous ferric chloride was added (the molar ratio of FeCl3 to LFP in the crude lithium iron phosphate residue was 0.5). The stirring speed in the reactor was 500r / min, the reaction temperature was 70℃, and chlorine gas was introduced at a flow rate V per 100g of crude lithium iron phosphate residue processed. Cl2 Chlorine gas was introduced at a rate of 0.7 L / min, and the reaction time was 11 minutes. The slurry after the reaction was filtered to obtain a filtrate containing FeCl3 and LiCl and a crude ferric phosphate residue.

[0119] After one reaction, the Li content in the filtrate was 3.98 g / L, and the mass of the crude ferric phosphate filter residue was 92 g. After six cycles of circulation, the Li concentration was concentrated to 23.88 g / L. Taking advantage of the different crystallinities of lithium chloride and ferric chloride, the filtrate was evaporated and concentrated at 100°C, reaching a lithium chloride concentration of 128 g / L. Lithium chloride then crystallized out, and filtration separated it. Drying yielded lithium chloride with a purity of 99.4%.

[0120] Step 3: Acid leaching and purification of crude ferric phosphate filter residue

[0121] The crude ferric phosphate filter residue was purified by acid leaching with a mixed acid at a solid-liquid ratio of 100 g / L. The mixed acid consisted of 3.0 mol / L H3PO4 and 0.5 mol / L HCl, i.e., an H3PO4:HCl molar ratio of 6:1. The leaching time was 4 hours, the leaching temperature was 80℃, and the stirring rate was 400 r / min. After acid leaching and purification, the ferric phosphate precursor and the mixed acid filtrate were obtained by filtration. The mixed acid filtrate was recycled to the acid leaching and purification process. The ferric phosphate precursor was calcined at 700℃ for 2 hours to obtain structurally stable battery-grade ferric phosphate. The purity of the ferric phosphate reached 99.6%, and the recovery rate was 99.51%. The XRD pattern of the recovered ferric phosphate is shown in [reference needed]. Figure 2 .

[0122] Example 4

[0123] Recover lithium and iron phosphate from spent lithium iron phosphate using the following steps.

[0124] Step 1: Remove impurities from waste lithium iron phosphate.

[0125] 10 kg of waste lithium iron phosphate was separated from impurities, including metallic copper foil, using a vibrating screen. After separation, the waste lithium iron phosphate (Li content 3.99% by mass) was placed in a rotary tube furnace and roasted at 600°C for 2 hours under a nitrogen atmosphere to remove organic binders and organic electrolytes. Then, carbon removal was performed by flotation; the roasted lithium iron phosphate was added to water and stirred to separate the carbon floating on the surface. The decarbonized lithium iron phosphate waste was placed in a dilute hydrochloric acid solution with pH 2.0 and stirred for 60 minutes to remove metallic aluminum impurities. Filtering yielded 9.70 kg of crude lithium iron phosphate slag and aluminum-containing waste acid. The aluminum-containing waste acid was recycled to the dilute hydrochloric acid solution for aluminum removal.

[0126] Step 2: Catalytic oxidation leaching for lithium extraction

[0127] Water was added to 9.70 kg of crude lithium iron phosphate residue obtained in the above steps to prepare a slurry with a solid-liquid ratio of 100 g / L. This slurry was placed in a reactor, and 2.0 kg of anhydrous ferric chloride was added (the molar ratio of FeCl3 to LFP in the crude lithium iron phosphate residue was 0.2). The stirring speed in the reactor was 500 r / min, the reaction temperature was 60℃, and chlorine gas was introduced at a flow rate V per 100 g of crude lithium iron phosphate residue processed. Cl2 Chlorine gas was introduced at a rate of 1.9 L / min, and the reaction time was 23 minutes. The slurry after the reaction was filtered to obtain a filtrate containing FeCl3 and LiCl and a crude ferric phosphate residue.

[0128] After one reaction, the Li content in the filtrate was 3.89 g / L, and the mass of the crude ferric phosphate filter residue was 9.30 kg. After ten cycles of circulation, the Li concentration was concentrated to 39.4 g / L. Taking advantage of the different crystallinities of lithium chloride and ferric chloride, the filtrate was evaporated and concentrated at 100°C until the lithium chloride concentration reached 128 g / L. Lithium chloride then crystallized out, and filtration separated it. Drying yielded lithium chloride with a purity of 99.3%.

[0129] Step 3: Acid leaching and purification of crude ferric phosphate filter residue

[0130] The crude ferric phosphate filter residue was purified by acid leaching with a mixed acid at a solid-liquid ratio of 100 g / L. The mixed acid consisted of 0.5 mol / L H3PO4 and 0.1 mol / L HCl, i.e., an H3PO4:HCl molar ratio of 5:1. The leaching time was 4 hours, the leaching temperature was 80℃, and the stirring rate was 500 r / min. After acid leaching and purification, the ferric phosphate precursor and the mixed acid filtrate were obtained by filtration. The mixed acid filtrate was recycled to the acid leaching purification process. The ferric phosphate precursor was calcined at 700℃ for 2 hours to obtain structurally stable battery-grade ferric phosphate. The purity of the ferric phosphate reached 99.5%, and the recovery rate was 99.21%.

[0131] Example 5

[0132] Recover lithium and iron phosphate from spent lithium iron phosphate using the following steps.

[0133] Step 1: Remove impurities from waste lithium iron phosphate.

[0134] 10 kg of waste lithium iron phosphate was separated from impurities, including metallic copper foil, using a vibrating screen. After separation, the waste lithium iron phosphate (Li content 3.99% by mass) was placed in a rotary tube furnace and roasted at 500°C for 2 hours under a nitrogen atmosphere to remove organic binders and organic electrolytes. Then, carbon removal was performed by flotation; the roasted lithium iron phosphate was added to water and stirred to separate the carbon floating on the surface. The decarbonized lithium iron phosphate waste was placed in an acidic solution (pH 2.0) prepared with dilute hydrochloric acid and sulfuric acid, stirred for 60 minutes to remove metallic aluminum impurities, and filtered to obtain 9.65 kg of crude lithium iron phosphate slag and aluminum-containing waste acid. The aluminum-containing waste acid was recycled to the dilute hydrochloric acid solution for aluminum removal.

[0135] Step 2: Catalytic oxidation leaching for lithium extraction

[0136] Water was added to the 9.65 kg of crude lithium iron phosphate residue obtained in the above steps to prepare a slurry with a solid-liquid ratio of 200 g / L. This slurry was placed in a reactor, and 50.0 kg of anhydrous ferric chloride was added (the molar ratio of FeCl3 to LFP in the crude lithium iron phosphate residue was 0.5). The stirring speed in the reactor was 400 r / min, the reaction temperature was 70℃, and chlorine gas was introduced at a flow rate V per 100 g of crude lithium iron phosphate residue processed. Cl2 The flow rate was 0.7 L / min, the reaction time was 11 minutes, and the solution containing FeCl3 and LiCl and the crude ferric phosphate residue were obtained by filtration.

[0137] After one reaction, the Li content in the filtrate was 7.88 g / L, and the mass of the crude ferric phosphate filter residue was 9.37 kg. After ten cycles of circulation, the Li concentration was concentrated to 79.0 g / L. Taking advantage of the different crystallinity of lithium chloride and ferric chloride, the filtrate was evaporated and concentrated at 100°C until the lithium chloride concentration reached 128 g / L, at which point lithium chloride crystallized out. Filtration separated the lithium chloride, and drying yielded lithium chloride with a purity of 99.0%.

[0138] Step 3: Acid leaching and purification of crude ferric phosphate filter residue

[0139] The crude ferric phosphate filter residue was purified by acid leaching with a mixed acid at a solid-liquid ratio of 100 g / L. The mixed acid consisted of 1 mol / L H3PO4 and 0.2 mol / L HCl, i.e., an H3PO4:HCl molar ratio of 5:1. The leaching time was 3 hours, the leaching temperature was 90℃, and the stirring rate was 500 r / min. After acid leaching and purification, the ferric phosphate precursor and the mixed acid filtrate were obtained by filtration. The mixed acid filtrate was recycled to the acid leaching purification process. The ferric phosphate precursor was calcined at 700℃ for 4 hours to obtain structurally stable battery-grade ferric phosphate. The purity of the ferric phosphate reached 99.3%, and the recovery rate was 99.19%.

[0140] Example 6

[0141] Example 6 follows the same process steps and conditions as Example 3, except that the molar ratio of FeCl3 to LFP in the crude lithium iron phosphate slag is 0.2, and the flow rate of chlorine gas is V. Cl2 The flow rate was 1.3 L / min, and the reaction time was 15 minutes. The ferric phosphate obtained in Example 6 had a purity of 99.3% and a recovery rate of 99.5%.

[0142] Comparative Example 1

[0143] Comparison with Example 3

[0144] 100g of waste lithium iron phosphate was separated from impurities, including copper foil, using a vibrating screen. After separation, the waste lithium iron phosphate (Li content 3.99% by mass) was placed in a muffle furnace and roasted at 600℃ for 2 hours in air to remove organic binders, organic electrolytes, and carbon. After roasting, the color of the lithium iron phosphate waste changed from blackish-gray to reddish-brown, likely due to the partial decomposition of lithium iron phosphate into Li3Fe2(PO4)3 and Fe2O3 caused by high-temperature roasting in air.

[0145] The lithium iron phosphate waste was then placed in a dilute hydrochloric acid solution with pH=2.0 and stirred for 60 minutes to remove metallic aluminum impurities. After filtration, 90.2g of crude lithium iron phosphate slag was obtained.

[0146] Water was added to 90.2 g of the crude lithium iron phosphate residue obtained in the above steps to prepare a slurry with a solid-liquid ratio of 100 g / L. This slurry was placed in a reactor, and 50 g of anhydrous ferric chloride was added (the molar ratio of FeCl3 to LFP in the crude lithium iron phosphate residue was 0.5). The stirring speed in the reactor was 500 r / min, the reaction temperature was 70℃, and chlorine gas was introduced at a flow rate V per 100 g of crude lithium iron phosphate residue processed. Cl2 Chlorine gas was introduced at a rate of 1.5 L / min, and the reaction time was 60 minutes.

[0147] After one reaction, the Li content in the filtrate was only 1.02 g / L, the lithium recovery rate was 26.36%, and the filter residue was a mixture of lithium iron phosphate, iron oxide, and iron phosphate. Subsequent purification and other treatments could not yield iron phosphate.

[0148] The only difference between Comparative Example 1 and Example 3 is that air was used for roasting in the step of removing impurities from the waste lithium iron phosphate. The lithium recovery rate of Comparative Example 1 from the waste lithium iron phosphate was much lower than that of Example 3. This indicates that an inert gas atmosphere is required in the impurity removal step; otherwise, high-temperature roasting in air or an oxidizing atmosphere will cause the lithium iron phosphate to decompose, which is detrimental to the subsequent lithium leaching reaction.

[0149] Comparative Example 2

[0150] Comparison with Example 2

[0151] 100g of waste lithium iron phosphate was separated from impurities and metallic copper foil using a vibrating screen. After separation, the lithium iron phosphate waste (Li content 3.99% by mass) was placed in a rotary tube furnace and calcined at 500℃ for 2 hours under a nitrogen atmosphere to remove organic binders and organic electrolytes. Then, carbon removal was performed by flotation; the calcined lithium iron phosphate was added to water and stirred to separate the carbon floating on the surface. The decarbonized lithium iron phosphate waste was placed in a dilute hydrochloric acid solution with pH 2.5 and stirred for 60 minutes to remove metallic aluminum impurities. Filtering yielded 96.8g of crude lithium iron phosphate slag and aluminum-containing waste acid. The aluminum-containing waste acid was recycled to the dilute hydrochloric acid solution for aluminum removal.

[0152] Water was added to 96.8 g of crude lithium iron phosphate residue obtained in the above steps to prepare a slurry with a solid-liquid ratio of 100 g / L. This slurry was placed in a reactor, with a stirring rate of 500 r / min and a reaction temperature of 60℃. Chlorine gas was introduced at a flow rate V per 100 g of crude lithium iron phosphate residue processed. Cl2 Chlorine gas was introduced at a rate of 1.9 L / min, and the reaction time was 65 minutes. The slurry after the reaction was filtered to obtain a filtrate containing FeCl3 and LiCl and a crude ferric phosphate filter residue.

[0153] After one reaction, the Li content in the filtrate was 3.02 g / L, and the mass of the crude ferric phosphate filter residue was 93.5 g. After five cycles of circulation, the Li concentration was concentrated to 18.15 g / L. Taking advantage of the different crystallinities of lithium chloride and ferric chloride, the filtrate was evaporated and concentrated at 100°C, causing lithium chloride to crystallize and precipitate. Filtration separated the lithium chloride, and after filtration and drying, lithium chloride with a purity of 99.0% was obtained.

[0154] The coarse ferric phosphate filter residue was purified by acid leaching with a mixed acid, with a solid-liquid ratio of 100 g / L. The mixed acid consisted of 1.5 mol / L H3PO4 and 0.5 mol / L HCl, i.e., an H3PO4:HCl molar ratio of 3:1. The acid leaching time was 4 hours, the leaching temperature was 90℃, and the stirring rate was 500 r / min. After acid leaching purification, the ferric phosphate precursor and the mixed acid filtrate were obtained by filtration. The ferric phosphate precursor was calcined at 700℃ for 2 hours to obtain ferric phosphate with a purity of 95.8% and a ferric phosphate recovery rate of 73.45%.

[0155] Table 1 Comparison of leaching time and recovery rate between Examples 1-5 and Comparative Example 2

[0156] name Catalytic oxidation leaching lithium extraction reaction time (minutes) Ferric phosphate recovery rate Example 1 35 98.50％ Example 2 23 99.32％ Example 3 11 99.51％ Example 4 23 99.21％ Example 5 11 99.5％ Comparative Example 2 65 73.45％

[0157] As shown in Table 1 above, the difference between Comparative Example 2 and Examples 1-5 is that FeCl3 catalyst was not added; especially compared with Example 2, the only difference is the absence of FeCl3 catalyst. The recovery rate of iron phosphate from waste lithium iron phosphate in Comparative Example 2 is lower than that in Examples 1-5, particularly in Example 2, and the reaction time is significantly longer. This indicates that adding FeCl3 catalyst to the method of the present invention significantly accelerates the reaction rate, shortens the leaching time, improves the recovery rate of iron phosphate, and increases the purity of the recovered iron phosphate.

[0158] Comparative Example 3

[0159] Comparison with Example 2

[0160] The only difference between Comparative Example 3 and Example 2 is that in step 3, the crude ferric phosphate is purified by acid leaching with a single acid.

[0161] Specifically, the crude ferric phosphate filter residue obtained in step two was purified by acid leaching. The acid added during acid leaching was 0.5 mol / L HCl, and the solid-liquid ratio in the slurry was 100 g / L. The leaching time was 4 hours, the leaching temperature was 90℃, and the stirring rate was 500 r / min. After acid leaching and purification, the ferric phosphate precursor and hydrochloric acid filtrate were obtained by filtration. The ferric phosphate precursor was then calcined at 700℃ for 2 hours. Because ferric phosphate is unstable in HCl alone, it was corroded. The final ferric phosphate obtained had a purity of 99.3%, with a recovery rate of only 60.3%.

[0162] Comparing Comparative Example 3 with Example 2, it can be seen that using mixed acids for acid leaching purification can maintain the stability of ferric phosphate and improve the recovery rate of ferric phosphate.

[0163] Comparative Example 4

[0164] The difference between Comparative Example 4 and Example 3 is that the obtained ferric phosphate precursor was not subjected to calcination treatment. The XRD pattern of the uncalcined ferric phosphate precursor in Comparative Example 4 is shown below. Figure 3 As shown.

[0165] Figure 2 This is the XRD pattern of the calcined FePO4 precursor from Example 3. (From...) Figure 3 and Figure 2 The results show that the iron phosphate precursor obtained in Comparative Example 4 is not a FePO4 product with a complete crystal structure. After high-temperature calcination, the crystal form of the iron phosphate precursor changes, and a pure FePO4 product with a complete crystal structure can be obtained.

[0166] Figure 4 These are photographs of the calcined FePO4 product in Example 3 and the uncalcined FePO4 precursor in Comparative Example 4. The color changes before and after calcination also show that after the leaching reaction, lithium is immersed in the solution to obtain the iron phosphate precursor. At this point, due to the presence of vacancies caused by the lack of lithium, the iron phosphate is not fully formed, and the color remains unchanged, still showing the blackish-gray color of lithium iron phosphate. However, after calcination, the crystal structure changes, the lithium vacancies collapse, and the iron phosphate is formed, changing its color from the previous blackish-gray of lithium iron phosphate to the white of iron phosphate.

[0167] This invention uses FeCl 3- The Cl2 dual-synergistic catalytic leaching system can achieve a recovery rate of over 98.5% and a purity of over 99.3% for recovering iron phosphate from waste lithium iron phosphate. Furthermore, the leaching reaction time for processing 100g of lithium iron phosphate waste can be as low as 11-15 minutes, which greatly shortens the leaching time and enables efficient and rapid continuous recycling of lithium iron phosphate.

[0168] All equivalent structural changes made by those skilled in the art based on the present invention specification and claims should also be included within the scope of patent protection of this invention.

Claims

1. A method for recovering lithium and iron phosphate from spent lithium iron phosphate, comprising: Provide crude lithium iron phosphate slag; The crude lithium iron phosphate residue is made into a slurry, and gas Cl2 is introduced into the slurry while the catalyst FeCl3 is added to carry out a catalytic oxidation lithium extraction reaction. The reacted slurry was filtered to obtain lithium-containing filtrate and coarse iron phosphate filter residue; The lithium chloride in the lithium-containing filtrate is crystallized to obtain purified lithium chloride; The crude ferric phosphate filter residue was acid-leached and then filtered to obtain the ferric phosphate precursor. as well as The ferric phosphate precursor was calcined to obtain ferric phosphate.

2. The method according to claim 1, wherein, The crude lithium iron phosphate slag is obtained by removing impurities from waste lithium iron phosphate, wherein the impurities include at least one of metallic materials, organic matter, and carbon materials; the metallic materials include at least one of metallic copper and metallic aluminum; and the organic matter includes at least one of organic electrolytes and organic binders.

3. The method according to claim 2, wherein, The process of removing impurities from waste lithium iron phosphate includes: screening out copper foil through a vibrating screen; roasting the organic matter under an inert atmosphere; removing carbon by flotation; and washing with dilute acid to remove aluminum, thereby obtaining aluminum-containing waste acid and the crude lithium iron phosphate slag.

4. The method according to claim 3, wherein, The carbon removal by flotation includes adding lithium iron phosphate (after calcining off organic matter) to water and stirring to separate the carbon floating on the liquid surface.

5. The method according to claim 3 or 4, wherein, Organic binders and organic electrolytes are removed by calcination at a temperature of 300~800℃ under an inert atmosphere of nitrogen or argon.

6. The method according to claim 5, wherein, The roasting temperature is 450℃, 500℃ or 600℃.

7. The method according to claim 5, wherein, The roasting time is 0.5 to 4 hours.

8. The method according to claim 7, wherein, The roasting time is 1.0 hour, 1.5 hours, 2.0 hours, 2.5 hours or 3.0 hours.

9. The method according to claim 3, wherein, Waste lithium iron phosphate after flotation carbon removal is washed with one or more dilute acids selected from hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid to remove the metallic aluminum material.

10. The method according to claim 9, wherein, The pH of the dilute acid is 1.0 to 4.

0.

11. The method according to claim 10, wherein, The pH of the dilute acid is 2.0, 2.5, or 3.

0.

12. The method according to claim 9, wherein, The acid washing time is 0.5 to 2 hours.

13. The method according to claim 12, wherein, The pickling time is 0.5 hours, 1.0 hour, or 1.5 hours.

14. The method according to claim 9, wherein, The aluminum-containing waste acid is recycled to a dilute acid washing process for aluminum removal so that it can be reused.

15. The method according to claim 1, wherein, The process of preparing crude lithium iron phosphate slag into a slurry includes: mixing crude lithium iron phosphate slag with water to prepare a slurry, wherein the solid-liquid ratio in the slurry is 80 g / L to 220 g / L.

16. The method according to claim 1, wherein, For every 100g of crude lithium iron phosphate slag processed, the flow rate V of gas Cl2 introduced into the slurry is... Cl2 The flow rate is 0.5~5 L / min.

17. The method of claim 16, wherein, Flow rate V of the introduced gas Cl2 Cl2 The flow rate is 0.7~1.3 L / min.

18. The method according to claim 1, wherein, The molar ratio m of catalyst FeCl3 to lithium iron phosphate in crude lithium iron phosphate slag is 0.05~1.

19. The method according to claim 18, wherein, The molar ratio m is 0.2~0.

5.

20. The method according to claim 16 or 17, wherein, The molar ratio m of catalyst FeCl3 to lithium iron phosphate in crude lithium iron phosphate residue, and the flow rate V of Cl2 gas introduced into the slurry per 100g of crude lithium iron phosphate residue treated. Cl2 Satisfy the following equation (1): 0.25≤ m×V Cl2 ≤0.35 (1)。 21. The method according to claim 1, wherein, In the catalytic oxidation lithium extraction reaction, the reaction temperature is 40~80℃ and the reaction time is 10~60 minutes.

22. The method according to claim 21, wherein, The reaction temperature is 50~70℃, and the reaction time is 11~35 minutes.

23. The method according to claim 1, wherein, The acid leaching process includes: leaching the crude ferric phosphate filter residue with a mixed acid at a temperature of 70-95°C for 2-5 hours; filtering the residue after acid leaching to obtain ferric phosphate precursor and mixed acid waste liquid; and recycling the mixed acid waste liquid back into the acid leaching process for reuse.

24. The method according to claim 23, wherein, The mixed acid includes phosphoric acid and hydrochloric acid.

25. The method of claim 24, wherein, The concentration of H3PO4 in the mixed acid is 0.1~5.0 mol / L, and the molar ratio of H3PO4 to HCl is 1~10.

26. The method of claim 24, wherein, The concentration of H3PO4 in the mixed acid is 0.5~3 mol / L, and the molar ratio of H3PO4 to HCl is 3~6.

27. The method according to claim 23, wherein, The acid immersion process is carried out at a temperature of 80~90℃ for 3~4 hours.

28. The method according to claim 1, wherein, The process of obtaining iron phosphate by calcining the iron phosphate precursor includes calcining the iron phosphate precursor at a temperature of 500~1000°C, thereby burning off the lithium ion vacancies in the iron phosphate precursor to achieve a transformation of the spatial structure, thereby obtaining iron phosphate.

29. The method according to claim 28, wherein, The roasting temperature is 700~800℃.

30. The method according to claim 28, wherein, The roasting time is 1 to 6 hours.

31. The method according to claim 28, wherein, The roasting time is 2 to 4 hours.

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