Method for recovering iron and lithium in black powder pickle liquor of retired lithium iron phosphate battery

Abstract

The invention relates to a method for recovering iron and lithium in black powder pickle liquor of a retired lithium iron phosphate battery, and belongs to the technical field of lithium ion batteries and solid waste resource utilization. The method mainly comprises the following steps: carrying out oxidation treatment on lithium-rich pickle liquor to obtain lithium-rich oxidized acid liquor, and carrying out lithium-rich system-phosphorus iron hot crystallization treatment on the lithium-rich oxidized acid liquor to obtain lithium-rich liquor and a lithium-phosphorus iron compound; washing the lithium-phosphorus-iron compound with water to obtain washing liquid and microspheric hydrated iron phosphate; the lithium-rich liquid is used for preparing lithium phosphate or lithium carbonate according to target demand guidance; according to the method, 100% recovery of the lithium element in the black powder pickle liquor of the retired lithium ion battery can be effectively achieved, and meanwhile high-added-value recovery of iron is achieved.

Description

TECHNICAL FIELD

[0001] The application relates to a method for recovering iron and lithium from black powder acid leaching solution of retired lithium iron phosphate batteries, and belongs to the technical field of lithium ion batteries and solid waste resource utilization. BACKGROUND

[0002] With the rapid development of the new energy automobile industry, lithium iron phosphate batteries have become one of the mainstream technical routes in the field of power batteries due to their high safety, long cycle life and low cost. However, the recycling problem of a large number of retired lithium iron phosphate batteries has become increasingly prominent, and the efficient recovery of valuable metals in the retired lithium iron phosphate black powder has become a technical difficulty in the industry. The retired lithium iron phosphate black powder commonly contains lithium iron phosphate, copper foil, aluminum foil, acetylene black, graphite and other materials. In the wet recovery process, the process route of 'acid leaching-impurity removal-lithium extraction' is usually adopted. In the acid leaching stage, inorganic acids such as sulfuric acid and hydrochloric acid are used to transfer the valuable metals in the black powder into the solution, and hydrogen peroxide is used as an oxidizing agent to realize the selective leaching of iron and phosphorus elements.

[0003] The lithium-rich acid leaching solution obtained after selective leaching usually contains lithium, phosphorus, iron, copper, aluminum and other elements. At present, a step-by-step impurity removal method is usually adopted to separate copper and aluminum elements first to obtain a lithium-rich acid leaching solution containing iron and phosphorus. Among them, the iron powder replacement method and the sulfidation copper removal method are usually used to separate copper. Although the iron powder replacement method can effectively remove copper elements, it will cause the concentration of iron ions in the solution to be too high, increase the difficulty of subsequent iron-lithium separation and cause waste of iron resources; the well-designed sulfidation copper removal method has low cost, reasonable resource utilization, simple process and broader industrial production prospects.

[0004] How to selectively recover lithium, phosphorus and iron from the lithium-rich acid leaching solution containing iron and phosphorus is the core of the process, which is directly related to the value of the final product and the environmental, economic and social benefits of the overall process. The current methods mainly include oxidation precipitation method, solvent extraction method and direct regeneration of lithium iron phosphate. However, most of these methods are aimed at high-concentration iron-containing solutions (without lithium), and for low-concentration iron-containing solutions obtained after selective leaching (i.e. lithium-rich acid leaching solution), the iron recovery rate is usually less than 85%, and the lithium recovery rate is generally less than 90%. Patent CN106684485A and patent CN116002646A both adjust the pH under normal pressure conditions, add an oxidizing agent, and heat to generate iron phosphate precipitate. This process is prone to side reactions, the conditions are harsh, the separation of iron elements is not complete, and the effect on lithium elements is not considered. Patent CN115124012A adjusts the pH by adding ammonia water and heats to generate an iron phosphate precursor. This method consumes a large amount of ammonia water, which is a serious resource consumption, and the purity of the iron phosphate is low, resulting in poor economic benefits. Patent CN109207730A uses ultrafiltration-nanofiltration-reverse osmosis combined technology to separate iron elements and obtain concentrated lithium, but this method has high operating cost, causes waste of iron elements and affects the lithium recovery rate.

[0005] In summary, for the resource utilization of lithium-rich acid leaching solution containing iron and phosphorus, the current technology has the problems of low lithium recovery rate, high iron and phosphorus loss rate, and incomplete element separation. Therefore, developing a new technology that can simultaneously realize efficient recovery of iron, phosphorus and lithium, deep removal of impurities, simplification of process flow and environmental friendliness is of great significance to promote the resource utilization of retired lithium iron phosphate batteries. In particular, for the characteristics of the acid leaching solution after copper removal, researching innovative methods for selective separation and high-value recovery of iron, phosphorus and lithium will be the key direction to break through the current industry bottleneck. SUMMARY

[0006] Therefore, the present application aims to provide a method for recovering iron and lithium from black powder acid leaching solution of retired lithium iron phosphate batteries. This method innovatively facilitates the complete separation of iron elements from the acid leaching solution, obtaining high-value microspherical hydrated iron phosphate, and selecting the type of lithium product according to the target demand. This method has high purity of lithium carbonate and lithium phosphate, high lithium recovery rate, and realizes iron element regeneration, with simple operation, low cost, environmental friendliness, good environmental, economic and social benefits, and broad industrialization prospects. To achieve the above purpose, the technical solution of the present application is as follows.

[0007] A method for recovering iron and lithium from black powder acid leaching solution of retired lithium iron phosphate batteries, the method steps comprising:

[0008] (1) Targeted sulfidation: below 80℃, drop sulfurized salt solution into the black powder acid leaching solution and stir for targeted sulfidation reaction for more than 10min, after the reaction, solid-liquid separation is performed to obtain acid sulfurized slag and lithium-rich acid leaching solution; the lithium-rich acid leaching solution contains Fe 2+ ;

[0009] (2) Oxidation: pass oxidizing gas into the lithium-rich acid leaching solution for oxidation treatment, so that Fe 2+ in the lithium-rich acid leaching solution is completely oxidized to Fe 3+ , after the treatment, lithium-rich oxidized acid solution is obtained; the flow rate of the oxidizing gas is 50-200mL / min;

[0010] (3) Lithium-rich system-phosphorus iron hydrothermal crystallization: add phosphoric acid and phosphate to the lithium-rich oxidized acid solution, mix thoroughly to obtain a reaction solution, and place the reaction solution in a hydrothermal reaction kettle for hydrothermal crystallization treatment, after the treatment, solid-liquid separation is performed to obtain a lithium-rich liquid and a lithium-phosphorus-iron composite; the hydrothermal crystallization temperature is 80-240℃, the reaction time is 2-72h, the stirring speed is 100-800rpm, the pH of the reaction solution is 1-3, and the molar ratio of phosphorus elements to iron elements in the reaction solution is 2-10:1, and the volume ratio of the reaction solution to the inner container volume of the reaction kettle is 0.2-0.8:1;

[0011] (4) water washing: the lithium-phosphorus-iron complex is subjected to water washing treatment, and after the treatment, solid-liquid separation is performed to obtain a washing solution and microspherical hydrated iron phosphate.

[0012] Preferably, in step (1), the ratio of the amount of substance of sulfur element in the sulfide salt solution to the sum of the amounts of substance of copper and iron elements in the acid leaching solution is 2-10:1, the concentration of the sulfide salt solution is less than or equal to 5 mol / L, the dropping speed of the sulfide salt solution is less than or equal to 50 mL / min, and the stirring speed is greater than or equal to 300 rpm; more preferably, in step (1), the lithium-rich copper-containing acid leaching solution contains Li + , Cu 2+ , Al 3+ , Fe 3+ , and PO4 3- ; the sulfide salt is one or more of sodium sulfide, potassium sulfide, and ammonium sulfide; the concentration of the sulfide salt solution is 0.001-5 mol / L, and the dropping speed is 0.1-50 mL / min; the targeted sulfidation reaction temperature is 0-80℃, the reaction time is 10-720 min, and the stirring speed is 300-1200 rpm.

[0013] Preferably, in step (2), the lithium-rich acid leaching solution further contains Li + , Fe 2+ , PO4 3- , SO4 2- ions.

[0014] Preferably, in step (2), the oxidizing gas is air, oxygen, or ozone.

[0015] Preferably, in step (3), the phosphate salt is one or more of NaH2PO4, KH2PO4, and NH4H2PO4.

[0016] Preferably, in step (3), the components of the lithium-phosphorus-iron complex are dihydrate iron phosphate and lithium-phosphorus adsorbate.

[0017] Preferably, in step (4), the water washing is performed until the pH of the washing solution is greater than or equal to 6.

[0018] Preferably, according to the target requirement orientation, to obtain a lithium phosphate product, the method further comprises the following steps: adding an alkali and a phosphate salt into the lithium-rich solution in step (3) to perform phosphatization treatment, and after the treatment, solid-liquid separation is performed to obtain a waste alkali solution and lithium phosphate. More preferably, the alkali is one or more of NaOH, KOH, and NH3·H2O; the phosphate salt is one or more of NaH2PO4, KH2PO4, and NH4H2PO4; during the phosphatization treatment, the pH is controlled to be 8-12, the reaction temperature is 60-95℃, and the reaction time is 30-180 min.

[0019] Preferably, according to the target demand orientation, for obtaining the lithium carbonate product, the method further comprises the following steps: adding an alkali into the lithium-rich liquid in step (3) to perform a dephosphorization treatment, after the treatment, performing a solid-liquid separation to obtain an alkali lithium liquid and a lithium phosphate; performing a concentration treatment on the alkali lithium liquid, after the treatment, obtaining a high-concentration alkali lithium liquid; adding a carbonate into the high-concentration alkali lithium liquid to perform a carbonation treatment, after the treatment, performing a solid-liquid separation to obtain a waste alkali liquid and lithium carbonate. More preferably, the alkali is one or more of NaOH, KOH and NH3·H2O; during the dephosphorization treatment, the pH is controlled to be 11-12, the reaction temperature is 60-70 DEG C, and the reaction time is 30-180 min; the lithium ion concentration in the high-concentration alkali lithium liquid is 20-60 g / L -1 ; the carbonate is one or more of Na2CO3, K2CO3 and (NH4)2CO3, the molar ratio of carbonate to lithium element in the high-concentration alkali lithium liquid is greater than or equal to 0.55:1; during the carbonation treatment, the pH is controlled to be 10-13, the reaction temperature is 0-90 DEG C, and the reaction time is 30-300 min.

[0020] Preferably, sulfuric acid is added into the waste alkali liquid to perform a neutralization treatment, after the treatment, obtaining a neutral wastewater.

[0021] Beneficial effects

[0022] The application provides a method for recovering iron and lithium from retired lithium iron phosphate battery black powder acid leaching liquid, and the main process is as follows: after the lithium-rich acid leaching liquid is subjected to oxidation treatment, a lithium-rich oxidized acid solution is obtained, the solution is subjected to lithium-rich system-phosphorus iron hydrothermal crystallization treatment, and a lithium-rich liquid and a lithium-phosphorus iron compound are obtained; the lithium-phosphorus iron compound is subjected to water washing treatment to obtain a washing liquid and microspherical hydrated iron phosphate, and the washing liquid can be reused in the lithium-rich system-phosphorus iron hydrothermal crystallization step; according to the target demand orientation, the lithium-rich liquid can be subjected to phosphatization treatment to obtain a waste alkali liquid and lithium phosphate; or the lithium-rich liquid can be subjected to dephosphorization treatment to obtain an alkali lithium liquid and lithium phosphate; after the alkali lithium liquid is subjected to concentration and carbonation treatment, a waste alkali liquid and lithium carbonate are obtained; after the waste alkali liquid is subjected to neutralization treatment, a neutral wastewater that can be discharged is obtained.

[0023] The method provided by the application can effectively realize 100% recovery of lithium elements in retired lithium ion battery black powder acid leaching liquid, and simultaneously realize high-value recovery of iron, the purity of microspherical hydrated iron phosphate is greater than 99.9%, the solution used in the process can be recycled, is friendly to the environment, has good economic benefits, and realizes resource utilization of retired lithium ion battery black powder acid leaching liquid.

[0024] The application provides a method for recovering iron and lithium from retired lithium iron phosphate battery black powder acid leaching liquid, and the main reaction equation of the lithium-rich system-phosphorus iron hydrothermal crystallization process is as follows: Fe 3+ + 2H2O = Fe (OH) 2 + + 2H+ Fe + H3PO4 = Fe(H2PO4) 3+ + H3PO4 = Fe(H2PO4) 2+ + H + Fe(OH)2 + Fe(H2PO4) + + H3PO4 = 2FePO4·2H2O + 3H 2+ Fe(OH)2 + 4FeHPO4 + + 3H2O = Fe5(PO4)4(OH)3·2H2O + 5H 3+ Fe + H3PO4 = FeHPO4 + + 2H + Fe(OH)2 + FeHPO4 + + 3H2O = Fe(OH)3 + 3H + Fe + H3PO4 = FePO4·2H2O + Fe + H3PO4 = FePO4·2H2O 3+ Fe + H3PO4 = FePO4·2H2O + Fe + H3PO4 = FePO4·2H2O

[0025] In the lithium-rich system-phosphorus iron hydrothermal crystallization process, the reaction system temperature, time, pH, stirring speed, the ratio of solution volume to reaction kettle inner container volume, the molar ratio of phosphorus element to iron element in the solution and other conditions need to be strictly controlled. Among them, the reaction temperature, the molar ratio of phosphorus element to iron element in the solution, pH and other conditions directly affect the reaction and change the reaction process; the stirring speed, the ratio of solution volume to reaction kettle inner container volume and other conditions have a great influence on the product morphology and reaction speed. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a process flow diagram of the method for recovering iron and lithium from black powder acid leaching solution of retired lithium iron phosphate battery.

[0027] Figure 2 It is the XRD test result of the microspherical hydrated iron phosphate.

[0028] Figure 3 It is the SEM test result of the microspherical hydrated iron phosphate.

[0029] DETAILED DESCRIPTION

[0030] The application will be further described in detail below in combination with specific embodiments.

[0031] Retired lithium iron phosphate batteries mainly consist of a battery casing, positive electrode material (lithium iron phosphate), negative electrode material (graphite), current collector (copper foil, aluminum foil), separator, lithium salt electrolyte, binder, and conductive agent. Industrially, through pretreatment steps such as discharge, mechanical crushing, sieving, and calcination, most of the aluminum foil can be separated, and the separator, lithium salt electrolyte, binder, and conductive agent can be decomposed to obtain a black powder material containing lithium iron phosphate, graphite, copper foil, and aluminum foil.

[0032] In the following examples, the lithium-rich acid leaching solution of retired lithium iron phosphate battery black powder was prepared by the following method: Leaching agents with sulfuric acid and hydrogen peroxide concentrations of 0.30 mol / L and 2.18 mol / L, respectively, were prepared. The solid-liquid ratio of black powder material to leaching agent was 10 g: 115 mL. After the leaching agent was heated to 60°C, the black powder material was added, and the reaction was carried out at 60°C and 400 rpm for 3 h to obtain a lithium-rich copper-containing acid leaching solution and acid leaching residue. The lithium-rich copper-containing acid leaching solution (containing Li...) was then... + Cu 2+ Al 3+ Fe 3+ PO4 3- A sodium sulfide solution with a concentration of 0.001 mol / L was prepared, with the ratio of sulfur content in the solution to the sum of copper and iron content in the lithium-rich copper-containing acid leaching solution being 4:1. The reaction temperature was set at 20℃ and the stirring speed at 1200 rpm. The prepared sodium sulfide solution was added dropwise to the lithium-rich copper-containing acid leaching solution at a rate of 0.1 mL / min, and the reaction was allowed to proceed for 180 min. After solid-liquid separation, acidic sulfide slag and lithium-rich acid leaching solution were obtained.

[0033] like Figure 1 As shown, a method for recovering iron and lithium from the acid leaching solution of retired lithium iron phosphate battery black powder includes the following steps:

[0034] (1) Oxidation: Oxidizing gas is passed into the lithium-rich acid leaching solution for oxidation treatment. After treatment, a small amount of solution is taken, and the Fe content in the solution is detected by colorimetric reagent method. 2+ Completely oxidized to Fe 3+ Then, a lithium-rich oxidizing acid solution is obtained.

[0035] (2) Lithium-rich system - phosphorus iron hydrothermal crystallization: Phosphoric acid and phosphate (system) salt mixed reagents are added to lithium-rich oxidizing acid solution. After thorough mixing, the liquid is placed in a hydrothermal reactor for hydrothermal crystallization treatment. After the treatment, solid and liquid are separated to obtain lithium-rich solution and lithium phosphorus iron complex.

[0036] (3) Water washing: The lithium-phosphorus iron complex is washed with water. After the treatment, the solid and liquid are separated to obtain the washing solution and microspheres of hydrated iron phosphate. The washing solution can be reused in step (2).

[0037] (4) According to the target demand orientation, in order to obtain lithium phosphate product, the following treatment can be carried out: alkali and phosphate salt are added to the lithium-rich liquid in step (2) to carry out phosphating treatment, after the treatment is completed, solid-liquid separation is carried out to obtain waste alkali liquid and lithium phosphate. In some examples, in the phosphating, the alkali is one of NaOH, KOH, NH3H2O; the phosphate salt is one or more of NaH2PO4, KH2PO4 and NH4H2PO4. In some examples, in the phosphating, the pH is controlled to be 8-12, for example, it can be 8, 9, 10, 11, 12. In some examples, in the phosphating, the reaction temperature is 60-95°C, for example, it can be 60°C, 70°C, 80°C, 90°C, 95°C. In some examples, in the phosphating, the reaction time is 30-180 min, for example, it can be 30 min, 60 min, 90 min, 120 min, 150 min, 180 min.

[0038] or according to the target demand orientation, in order to obtain lithium carbonate product, the following treatment can be carried out: alkali is added to the lithium-rich liquid in step (2) to carry out dephosphorization treatment, after the treatment is completed, solid-liquid separation is carried out to obtain alkali lithium liquid and lithium phosphate. Concentration: the alkali lithium liquid is subjected to concentration treatment, after the treatment is completed, high-concentration alkali lithium liquid is obtained. Carbonation: carbonate is added to the high-concentration alkali lithium liquid to carry out carbonation treatment, after the treatment is completed, solid-liquid separation is carried out to obtain waste alkali liquid and lithium carbonate. In some examples, in the dephosphorization, the alkali is one or more of NaOH, KOH and NH3H2O. In some examples, in the dephosphorization, the pH is controlled to be 12, the reaction temperature is 60°C, the reaction time is 180 min, and the stirring speed is 400 rpm. In some examples, in the concentration, the lithium ion concentration in the high-concentration alkali lithium liquid is 20-60 g / L, for example, it can be 20 g / L, 30 g / L, 40 g / L, 50 g / L, 60 g / L. -1 -1 -1 -1 -1 -1 In some examples, in the carbonation, the carbonate is one of Na2CO3, K2CO3 and (NH4)2CO3, and the molar ratio of carbonate to lithium element should be greater than or equal to 0.55:1. In some examples, in the carbonation, the pH is controlled to be 10-13, for example, it can be 10, 11, 12, 13. In some examples, in the carbonation, the reaction temperature is 0-90°C, for example, it can be 0°C, 5°C, 10°C, 20°C, 30°C, 40°C, 50°C, 70°C, 90°C. In some examples, in the carbonation, the reaction time is 30-300 min, for example, it can be 30 min, 60 min, 90 min, 120 min, 180 min, 240 min, 300 min.

[0039] ​​​​​(5) Neutralization: adding sulfuric acid to the waste lye for neutralization treatment, and obtaining neutralized waste water after the treatment, which meets the discharge standard.

[0040] In some examples, in step (1), oxidation, Li + , Fe 2+ , PO4 3- , SO4 2- , and the like ions exist in the lithium-rich acid leaching solution. + , K + , NH4 + , and the like ions may exist.

[0041] In some examples, in step (1), oxidation, the oxidizing gas is one of air, oxygen, and ozone.

[0042] In some examples, in step (1), oxidation, the flow rate of the oxidizing gas is 50-200 mL / min, for example, it can be 50 mL / min, 100 mL / min, 150 mL / min, or 200 mL / min.

[0043] In some examples, in step (1), oxidation, the colorimetric reagent method detection method is as follows: potassium thiocyanate solution is added to the taken lithium-rich oxidizing acid solution, which presents a blood red color; then o-phenanthroline solution is added, which does not present an orange red color, indicating that Fe 2+ has been completely oxidized to Fe 3+ .

[0044] In some examples, in step (2), lithium-rich system-phosphorus iron hydrothermal crystallization, the phosphoric acid (salt) can be one of NaH2PO4, KH2PO4, and NH4H2PO4.

[0045] In some examples, in step (2), lithium-rich system-phosphorus iron hydrothermal crystallization, the hydrothermal crystallization temperature is 80-240°C, for example, it can be 80°C, 100°C, 120°C, 140°C, 160°C, 180°C, 200°C, 220°C, or 240°C.

[0046] In some examples, in step (2), lithium-rich system-phosphorus iron hydrothermal crystallization, the reaction time is 2-72 h, for example, it can be 2 h, 6 h, 12 h, 18 h, 24 h, 36 h, 48 h, 60 h, or 72 h.

[0047] In some examples, in step (2), lithium-rich system-phosphorus iron hydrothermal crystallization, the stirring speed is 100-800 rpm, for example, it can be 100 rpm, 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, or 800 rpm.

[0048] In some examples, in step (2), in the lithium-rich system-phosphorus iron hydrothermal crystallization, the pH of the lithium-rich oxidized acid solution is 1-3, for example, it can be 1, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0.

[0049] In some examples, in step (2), in the lithium-rich system-phosphorus iron hydrothermal crystallization, the molar ratio of phosphorus to iron in the solution is 2-10:1, for example, it can be 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1.

[0050] In some examples, in step (2), in the lithium-rich system-phosphorus iron hydrothermal crystallization, the volume ratio of the solution to the volume of the reactor inner container is 0.2-0.8:1, for example, it can be 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1.

[0051] In some examples, in step (2), in the lithium-rich system-phosphorus iron hydrothermal crystallization, the main components of the lithium-phosphorus-iron complex are iron phosphate dihydrate and lithium-phosphorus adsorbate.

[0052] In some examples, in step (3), in the water washing, the water washing effect is that the pH of the last washing solution is ≥6.

[0053] In some examples, in step (3), in the water washing, the ion species in the washing solution are the same as those in the lithium-rich oxidized acid solution.

[0054] Preferably, in step (5), the neutralization effect is that the pH of the neutralized wastewater is 6-7.

[0055] Example 1

[0056] The present embodiment provides a method for recovering iron and lithium from retired lithium iron phosphate battery black powder acid leaching solution, which comprises the following steps:

[0057] (1) Oxidation: air is introduced into the lithium-rich acid leaching solution at a flow rate of 100 mL / min for oxidation treatment. After the treatment is completed, a small amount of solution is taken, potassium thiocyanate solution is added to the taken solution, which is blood red, and then o-phenanthroline solution is added, which is orange red, indicating that Fe 2+ has been completely oxidized to Fe 3+ After that, a lithium-rich oxidized acid solution is obtained.

[0058] (2) Lithium-rich system-phosphorus iron hydrothermal crystallization: prepare a certain concentration of H3PO4 and NaH2PO4 acid solution, add lithium-rich oxidizing acid solution to mix, until the molar ratio of phosphorus element to iron element in the solution is 2:1 and pH = 1; place the mixed solution in a hydrothermal reactor (the volume ratio of the mixed solution to the inner container of the reactor is 0.5:1), and hydrothermal reaction is carried out at a reaction temperature of 80°C and a stirring speed of 400 rpm for 24 hours; after the reaction is completed, the temperature is lowered to room temperature, and solid-liquid separation is performed, to obtain a lithium-rich solution and a lithium-phosphorus-iron compound.

[0059] (3) Water washing: the lithium-phosphorus-iron compound is subjected to 3 times of water washing treatment, and the pH of the last washing solution is ≥6; after the treatment is completed, solid-liquid separation is performed, to obtain a washing solution and microspherical hydrated iron phosphate. The washing solution can be used as a raw material for step (2). The XRD and SEM test results of the microspherical hydrated iron phosphate are shown in Figs. 2 and 3. Figures 2-3

[0060] (4) De-phosphorization: prepare a certain concentration of NaOH solution, add it to the lithium-rich solution until pH = 12, and place the mixed solution in a 60°C, 400 rpm environment for reaction for 180 minutes; after the reaction is completed, solid-liquid separation is performed, to obtain an alkaline lithium solution and lithium phosphate.

[0061] (5) Concentration: the alkaline lithium solution in step (4) is subjected to concentration treatment, and after the treatment is completed, a high-concentration alkaline lithium solution with a lithium concentration of 60 g / L is obtained. -1

[0062] (6) Carbonation: prepare a certain concentration of NaOH and Na2CO3 alkali solution (the amount of Na2CO3 is 1.1 times the theoretical amount), add it to the high-concentration alkaline lithium solution until pH = 12, and place the mixed solution in a 70°C, 400 rpm environment for reaction for 120 minutes; after the reaction is completed, solid-liquid separation is performed, to obtain a waste alkali solution and lithium carbonate.

[0063] (7) Neutralization: add sulfuric acid to the waste alkali solution for neutralization treatment, and after the treatment is completed, a neutral waste water is obtained, which meets the discharge standard.

[0064] In this embodiment, after the lithium-rich system-phosphorus iron hydrothermal crystallization, the iron element separation rate is 100%, and the lithium element retention rate is 99.9%; after the water washing, the purity of the obtained hydrated iron phosphate is 99.9%, which is a micron-sized spherical particle with uniform particle size; the purity of the obtained lithium phosphate by phosphatization is 99.9%; and the purity of the obtained lithium carbonate by carbonation is 99.9%. The products obtained by the process can be used in the field of lithium ion battery material production, and have extremely high economic value. This example realizes efficient recovery of lithium elements from the retired lithium iron phosphate battery black powder acid leaching solution, freely selects a lithium extraction scheme according to the target demand, obtains high-purity lithium products and high-value-added hydrated iron phosphate products, and realizes high-value-added recovery of lithium and iron elements from the retired lithium iron phosphate battery black powder acid leaching solution.​​

[0065] Example 2

[0066] The present embodiment provides a method for recovering iron and lithium from a retired lithium iron phosphate battery black powder acid leaching solution, comprising the following steps:

[0067] (1) Oxidation: ozone is passed into the lithium-rich acid leaching solution at a flow rate of 50 mL / min for oxidation treatment. After the treatment is completed, a small amount of solution is taken, potassium thiocyanate solution is added to the taken solution, which turns blood red, then o-phenanthroline solution is added, which shows no orange red, indicating that Fe 2+ has been completely oxidized to Fe 3+ After that, a lithium-rich oxidized acid solution is obtained.

[0068] (2) Lithium-rich system-phosphorus iron hydrothermal crystallization: prepare a certain concentration of H3PO4 and KH2PO4 acid solution, add the lithium-rich oxidized acid solution to mix, until the molar ratio of phosphorus element to iron element in the solution is 5:1 and the pH is 3; place the mixed solution in a hydrothermal reaction kettle (the volume ratio of the mixed solution to the inner volume of the reaction kettle is 0.8:1), and hydrothermal reaction is carried out at a reaction temperature of 160°C and a stirring speed of 800 rpm for 60h, after the reaction is completed, the temperature is lowered to room temperature by standing, and solid-liquid separation is performed, to obtain a lithium-rich solution and a lithium-phosphorus-iron compound.

[0069] (3) Water washing: the lithium-phosphorus-iron compound is subjected to 3 times of water washing treatment, and the pH of the last washing solution is ≥6, after the treatment is completed, solid-liquid separation is performed, to obtain a washing solution and a microspherical hydrated iron phosphate. The washing solution can be used as a raw material for step (2).

[0070] (4) De-phosphorization: prepare a certain concentration of KOH solution, add it to the lithium-rich solution until the pH is 12, and place the mixed solution in a 60°C, 400 rpm environment for reaction for 180 min, after the reaction is completed, solid-liquid separation is performed, to obtain an alkaline lithium solution and lithium phosphate.

[0071] (5) Concentration: the alkaline lithium solution in step (4) is subjected to concentration treatment, after the treatment is completed, a high-concentration alkaline lithium solution with a lithium concentration of 40 g / L -1 is obtained.

[0072] (6) Carbonation: prepare a certain concentration of KOH and K2CO3 alkali solution (the amount of K2CO3 is 1.1 times the theoretical amount), add it to the high-concentration alkaline lithium solution until the pH is 10, and place the mixed solution in a 90°C, 400 rpm environment for reaction for 60 min, after the reaction is completed, solid-liquid separation is performed, to obtain a waste alkali solution and lithium carbonate.

[0073] (7) Neutralization: sulfuric acid is added to the waste alkali solution for neutralization treatment, after the treatment is completed, a neutral wastewater is obtained, which meets the discharge standard.

[0074] In this embodiment, after the lithium-rich system-phosphorus iron hydrothermal crystallization, the iron element separation rate is 100%, and the lithium element retention rate is 99.8%; after washing, the purity of the obtained hydrated ferric phosphate is 99.8%, which is a micron-sized spherical particle with uniform particle size; the purity of the obtained lithium phosphate obtained by phosphorylation is 99.9%; the purity of the lithium carbonate obtained by carbonation is 99.9%. The products obtained by the process can be used for lithium ion battery material production, and have very high economic value. This example realizes efficient recovery of lithium elements in the spent lithium iron phosphate battery black powder acid leaching solution, freely selects the lithium extraction scheme according to the target demand, obtains high-purity lithium products and high-value hydrated ferric phosphate products, and realizes high-value recovery of lithium and iron elements in the spent lithium iron phosphate battery black powder acid leaching solution.

[0075] Example 3

[0076] The present embodiment provides a method for recovering iron and lithium from a spent lithium iron phosphate battery black powder acid leaching solution, comprising the following steps:

[0077] (1) Oxidation: air is introduced into the lithium-rich acid leaching solution at a flow rate of 200 mL / min for oxidation treatment. After the treatment is completed, a small amount of solution is taken, potassium thiocyanate solution is added to the taken solution, which turns blood red, and then o-phenanthroline solution is added, which does not turn orange red, indicating that Fe 2+ has been completely oxidized to Fe 3+ , and a lithium-rich oxidized acid solution is obtained.

[0078] (2) Lithium-rich system-phosphorus iron hydrothermal crystallization: prepare a certain concentration of H3PO4 and NH4H2PO4 acid solution, mix with the lithium-rich oxidized acid solution, and adjust the solution to a molar ratio of phosphorus element to iron element of 10:1 and a pH of 2; place the mixed solution in a hydrothermal reaction kettle (the volume ratio of the mixed solution to the inner container volume of the reaction kettle is 0.2:1), and hydrothermal reaction is carried out at a reaction temperature of 240°C and a stirring speed of 100 rpm for 8h. After the reaction is completed, the temperature is lowered to room temperature, solid-liquid separation is performed, and a lithium-rich solution and a lithium-phosphorus-iron compound are obtained.

[0079] (3) Washing: the lithium-phosphorus-iron compound is washed with water for 3 times, and the pH of the last washing solution is ≥6. After the treatment is completed, solid-liquid separation is performed, and a washing solution and a microspherical hydrated ferric phosphate are obtained. The washing solution can be used as a raw material for step (2).

[0080] (4) De-phosphorization: prepare a certain concentration of NH4OH solution, add it to the lithium-rich solution to a pH of 12, and place the mixed solution in a 60°C, 400 rpm environment for 180 min. After the reaction is completed, solid-liquid separation is performed, and an alkaline lithium solution and lithium phosphate are obtained.

[0081] (5) Concentration: the alkaline lithium solution in step (4) is concentrated. After the treatment is completed, a high-concentration alkaline lithium solution with a lithium concentration of 20 g / L is obtained. -1 .

[0082] (6) Carbonation: Prepare a certain concentration of NH-H2O and (NH4)2CO3 lye ((NH4)2CO3 is 1.1 times the theoretical amount), add it to the high-concentration alkali lithium liquid to pH = 13, and place the mixed solution in 10°C, 400 rpm conditions for 300 min. After the reaction is completed, solid-liquid separation is performed to obtain waste lye and lithium carbonate.

[0083] (7) Neutralization: Add sulfuric acid to the waste lye for neutralization treatment. After the treatment is completed, neutral waste water is obtained, which meets the discharge standard.

[0084] In this embodiment, after the lithium-rich system-phosphorus iron hydrothermal crystallization, the iron element separation rate is 100%, and the lithium element retention rate is 99.9%. After washing, the purity of the obtained hydrated iron phosphate is 99.9%, which is micron-sized spherical particles with uniform particle size. The purity of the lithium phosphate obtained by phosphating is 99.9%, and the purity of the lithium carbonate obtained by carbonation is 99.9%. The products obtained by the process can be used for lithium ion battery material production, and have very high economic value. This example realizes efficient recovery of lithium elements in the retired lithium iron phosphate battery black powder acid leaching liquid, freely selects the lithium extraction scheme according to the target demand, obtains high-purity lithium products and high-value-added hydrated iron phosphate products, and realizes high-value-added recovery of lithium and iron elements in the retired lithium iron phosphate battery black powder acid leaching liquid.

[0085] Example 4

[0086] The embodiment provides a method for recovering iron and lithium from a retired lithium iron phosphate battery black powder acid leaching liquid, which comprises the following steps:

[0087] (1) Oxidation: ozone is passed into the lithium-rich acid leaching liquid at a flow rate of 150 mL / min for oxidation treatment. After the treatment is completed, a small amount of solution is taken, potassium thiocyanate solution is added to the taken solution, which turns blood red, and then o-phenanthroline solution is added, which does not turn orange red, indicating that Fe 2+ has been completely oxidized to Fe 3+ After that, a lithium-rich oxidized acid solution is obtained.

[0088] (2) Lithium-rich system-phosphorus iron hydrothermal crystallization: prepare a certain concentration of H3PO4 and NaH2PO4 acid solution, add it to the lithium-rich oxidized acid solution, mix until the molar ratio of phosphorus element to iron element in the solution is 3:1 and the pH is 1.2; place the mixed solution in a hydrothermal reaction kettle (the volume ratio of the mixed solution to the inner container volume of the reaction kettle is 0.5:1), and hydrothermal reaction is carried out at a reaction temperature of 100°C and a stirring speed of 400 rpm for 36h. After the reaction is completed, it is placed to room temperature, solid-liquid separation is performed, and a lithium-rich liquid and a lithium-phosphorus-iron compound are obtained.

[0089] (3) Water washing: the lithium-phosphorus-iron complex is subjected to 3 times of water washing treatment, and the pH of the last washing solution is greater than or equal to 6. After the treatment is completed, solid-liquid separation is performed to obtain a washing solution and microspherical hydrated iron phosphate.

[0090] (4) Phosphating: a certain concentration of NaOH and NaH2PO4alkali solution is prepared, and is added into the lithium-rich solution until the pH is 10. The mixed solution is placed in a 60°C, 400 rpm condition for 120 min. After the reaction is completed, solid-liquid separation is performed to obtain waste alkali solution and lithium phosphate.

[0091] (5) Neutralization: sulfuric acid is added to the waste alkali solution for neutralization treatment. After the treatment is completed, neutral waste water is obtained, which meets the discharge standard.

[0092] In this embodiment, after the lithium-rich system-phosphorus-iron hydrothermal crystallization, the separation rate of iron element is 100%, and the retention rate of lithium element is 100%. After water washing, the purity of the obtained hydrated iron phosphate is 99.9%, which is micron-sized spherical particles with uniform particle size. The purity of the lithium phosphate obtained by phosphating is 99.9%. The products obtained by the process can be used for lithium ion battery material production, and have extremely high economic value. This example realizes efficient recovery of lithium element from the spent lithium iron phosphate battery black powder acid leaching solution. According to the target demand, the lithium extraction scheme is freely selected to obtain high-purity lithium products and high-value-added hydrated iron phosphate products, and realizes high-value-added recovery of lithium and iron elements from the spent lithium iron phosphate battery black powder acid leaching solution.

[0093] Example 5

[0094] This embodiment provides a method for recovering iron and lithium from a spent lithium iron phosphate battery black powder acid leaching solution, which comprises the following steps:

[0095] (1) Oxidation: oxygen is introduced into the lithium-rich acid leaching solution at a flow rate of 100 mL / min for oxidation treatment. After the treatment is completed, a small amount of solution is taken, potassium thiocyanate solution is added to the taken solution, which turns blood red, and then o-phenanthroline solution is added, which does not turn orange red, indicating that Fe 2+ has been completely oxidized to Fe 3+ After that, a lithium-rich oxidized acid solution is obtained.

[0096] (2) Lithium-rich system-phosphorus-iron hydrothermal crystallization: a certain concentration of H3PO4and KH2PO4acid solution is prepared, and is added into the lithium-rich oxidized acid solution for mixing until the molar ratio of phosphorus element to iron element in the solution is 5:1 and the pH is 2.6. The mixed solution is placed in a hydrothermal reaction kettle (the volume ratio of the mixed solution to the inner container volume of the reaction kettle is 0.7:1), and is subjected to hydrothermal reaction at a reaction temperature of 180°C and a stirring speed of 800 rpm for 72 h. After the reaction is completed, the temperature is lowered to room temperature by standing, and then solid-liquid separation is performed to obtain a lithium-rich solution and a lithium-phosphorus-iron complex.

[0097] (3) Water washing: the lithium-phosphorus-iron complex is subjected to 3 times of water washing treatment, and the pH of the last washing solution is greater than or equal to 6. After the treatment is completed, solid-liquid separation is performed to obtain a washing solution and microspherical hydrated iron phosphate.

[0098] (4) Phosphating: a KOH and KH2PO4 alkali solution of a certain concentration is prepared, and is added into the lithium-rich solution until the pH is 8. The mixed solution is placed in a condition of 80°C and 400 rpm for reaction for 180 min. After the reaction is completed, solid-liquid separation is performed to obtain waste alkali solution and lithium phosphate.

[0099] (5) Neutralization: sulfuric acid is added into the waste alkali solution for neutralization treatment. After the treatment is completed, neutralized waste water is obtained, which meets the discharge standard.

[0100] In this embodiment, after the lithium-rich system-phosphorus-iron hydrothermal crystallization, the separation rate of iron element is 100%, and the retention rate of lithium element is 99.9%. After water washing, the purity of the obtained hydrated iron phosphate is 99.8%, which is micron-sized spherical particles with uniform particle size. The purity of the lithium phosphate obtained by phosphating is 99.9%. The products obtained by the process can be used for lithium ion battery material production, and have extremely high economic value. This example realizes efficient recovery of lithium element from the black powder acid leaching solution of the retired lithium iron phosphate battery, freely selects the lithium extraction scheme according to the target demand, obtains high-purity lithium product and high-value-added hydrated iron phosphate product, and realizes high-value-added recovery of lithium and iron elements from the black powder acid leaching solution of the retired lithium iron phosphate battery.

[0101] Example 6

[0102] This embodiment provides a method for recovering iron and lithium from a black powder acid leaching solution of a retired lithium iron phosphate battery, which comprises the following steps:

[0103] (1) Oxidation: oxygen is introduced into the lithium-rich acid leaching solution at a flow rate of 50 mL / min for oxidation treatment. After the treatment is completed, a small amount of solution is taken, potassium thiocyanate solution is added to the taken solution, which turns blood red, and then o-phenanthroline solution is added, which does not turn orange red, indicating that Fe 2+ has been completely oxidized to Fe 3+ After that, a lithium-rich oxidized acid solution is obtained.

[0104] (2) Lithium-rich system-phosphorus-iron hydrothermal crystallization: an H3PO4 and NH4H2PO4 acid solution of a certain concentration is prepared, and is added into the lithium-rich oxidized acid solution for mixing until the molar ratio of phosphorus element to iron element in the solution is 8:1 and the pH is 2. The mixed solution is placed in a hydrothermal reaction kettle (the volume ratio of the mixed solution to the inner container volume of the reaction kettle is 0.3:1), and is subjected to hydrothermal reaction under the condition of a reaction temperature of 240°C and a stirring speed of 200 rpm for 2 h. After the reaction is completed, the temperature is lowered to room temperature by standing, and then solid-liquid separation is performed to obtain a lithium-rich solution and a lithium-phosphorus-iron complex.

[0105] (3) Water washing: the lithium-phosphorus-iron complex is subjected to 3 times of water washing treatment, and the pH of the last washing liquid is greater than or equal to 6. After the treatment is completed, solid-liquid separation is performed to obtain washing liquid and microspherical hydrated iron phosphate.

[0106] (4) Phosphating: an alkali solution of NH4H2O and NH4H2PO4 of a certain concentration is prepared, and is added into the lithium-rich liquid until the pH is 11. The mixed solution is placed under the condition of 95°C and 400 rpm for 30 min. After the reaction is completed, solid-liquid separation is performed to obtain waste alkali solution and lithium phosphate.

[0107] (5) Neutralization: sulfuric acid is added into the waste alkali solution for neutralization treatment. After the treatment is completed, neutral waste water is obtained, which meets the discharge standard.

[0108] In this embodiment, after the lithium-rich system-phosphorus-iron hydrothermal crystallization, the separation rate of iron element is 100%, and the retention rate of lithium element is 99.9%. After water washing, the purity of the obtained hydrated iron phosphate is 99.9%, which is micron-sized spherical particles with uniform particle size. The purity of the lithium phosphate obtained by phosphating is 99.9%. The products obtained by the process can be used for the production of lithium ion battery materials, and have extremely high economic value. This example realizes the efficient recovery of lithium element from the spent lithium iron phosphate battery black powder acid leaching liquid. According to the target demand, the lithium extraction scheme is freely selected to obtain high-purity lithium products and high-value-added hydrated iron phosphate products, and realizes the high-value-added recovery of lithium and iron elements from the spent lithium iron phosphate battery black powder acid leaching liquid.

[0109] Comparative Example 1

[0110] In this comparative example, except that the reaction temperature in the lithium-rich system-phosphorus-iron hydrothermal crystallization in step (1) is set to 60°C, the other steps and conditions are the same as those in Example 1.

[0111] In this comparative example, after the lithium-rich system-phosphorus-iron hydrothermal crystallization, the separation rate of iron element is 87.2%, and the retention rate of lithium element is 85.6%. After water washing, the purity of the obtained hydrated iron phosphate is 80.0%, which is micron-sized amorphous particles. The purity of the lithium phosphate obtained by dephosphorization is 73.9%. The purity of the lithium carbonate obtained by carbonation is 96.2%.

[0112] Comparative Example 2

[0113] In this comparative example, except that the pH in the lithium-rich system-phosphorus-iron hydrothermal crystallization in step (1) is set to 4, the other steps and conditions are the same as those in Example 1.

[0114] In this comparative example, after the lithium-rich system-phosphorus-iron hydrothermal crystallization, the separation rate of iron element is 100%, and the retention rate of lithium element is 80.2%. After water washing, the purity of the obtained hydrated iron phosphate is 91.6%, which is micron-sized spherical particles with uniform particle size. The purity of the lithium phosphate obtained by dephosphorization is 99.9%. The purity of the lithium carbonate obtained by carbonation is 99.8%.

[0115] Comparative Example 3

[0116] In this comparative example, the stirring rate in the lithium-rich system-phosphorus iron hydrothermal crystallization in step (1) was set to 0, i.e., static hydrothermal reaction, and the other steps and conditions were the same as in Example 1.

[0117] In this comparative example, after the lithium-rich system-phosphorus iron hydrothermal crystallization, the iron element separation rate was 98.6%, and the lithium element retention rate was 97.9%; after washing, the purity of the hydrated iron phosphate obtained was 99.8%, and the micron-sized spherical particles were uneven in size; the purity of the lithium phosphate obtained by removing phosphorus was 97.3%; and the purity of the lithium carbonate obtained by carbonation was 99.9%.

[0118] Comparative Example 4

[0119] In this comparative example, the molar ratio of phosphorus element to iron element in the solution in the lithium-rich system-phosphorus iron hydrothermal crystallization in step (1) was set to 1:1, and the other steps and conditions were the same as in Example 1.

[0120] In this comparative example, after the lithium-rich system-phosphorus iron hydrothermal crystallization, the iron element separation rate was 80.3%, and the lithium element retention rate was 89.7%; after washing, the purity of the hydrated iron phosphate obtained was 72.5%, and the micron-sized spherical particles were uneven in size; the purity of the lithium phosphate obtained by removing phosphorus was 70.4%; and the purity of the lithium carbonate obtained by carbonation was 91.4%.

[0121] Comparative Example 5

[0122] In this comparative example, the reaction time in the lithium-rich system-phosphorus iron hydrothermal crystallization in step (1) was set to 1 h, and the other steps and conditions were the same as in Example 1.

[0123] In this comparative example, after the lithium-rich system-phosphorus iron hydrothermal crystallization, the iron element separation rate was 81.1%, and the lithium element retention rate was 91.9%; after washing, the purity of the hydrated iron phosphate obtained was 95.0%, and the micron-sized particles were uniform in size, which was smaller than in Example 1; the purity of the lithium phosphate obtained by removing phosphorus was 90.2%; and the purity of the lithium carbonate obtained by carbonation was 99.7%.

[0124] Comparative Example 6

[0125] In this comparative example, the ratio of the solution volume to the inner container volume in the lithium-rich system-phosphorus iron hydrothermal crystallization in step (1) was set to 0.1:1, and the other steps and conditions were the same as in Example 1.

[0126] In the present comparative example, after hydrothermal crystallization of the lithium-rich system-phosphorus iron, the iron element separation rate is 86.2%, and the lithium element retention rate is 90.4%; after washing, the purity of the hydrated ferric phosphate obtained is 95.9%, and the micron-sized spherical particles present uneven particle size; the purity of the lithium phosphate obtained by removing phosphorus is 86.7%; and the purity of the lithium carbonate obtained by carbonation is 95.6%.

[0127] The key indicators of the above examples and comparative examples are summarized, and the results are shown in Table 1.

[0128] Table 1

[0129]

[0130]

[0131] It can be known from the comparison of Examples 1-6 that when the reaction parameters are set within the reaction condition range of the present application, the hydrothermal crystallization of the lithium-rich system-phosphorus iron can be fully carried out, the iron element separation rate is 100%, the lithium element retention rate is greater than 99.9%, the purity of the hydrated ferric phosphate obtained after washing is greater than 99.8%, and the micron-sized spherical particles present uniform particle size; the purity of the lithium phosphate obtained by removing phosphorus and phosphating is greater than 99.9%; and the purity of the lithium carbonate obtained by carbonation is greater than 99.9%. Finally, high-efficiency lithium retention of black powder leaching solution is realized, and high-value hydrated ferric phosphate material is synergistically recovered.

[0132] It can be known from the comparison of Example 1 and Comparative Example 1 that when the lithium-rich system-phosphorus iron is hydrothermally crystallized, when the reaction temperature is less than 80℃, the temperature reduction is not conducive to the reaction, and a large amount of hydroxy ferric phosphate is generated by the side reaction; the hydrated ferric phosphate generated by the main reaction presents an amorphous shape, has a strong entrainment and adsorption effect on lithium, and further affects the subsequent phosphorus removal and carbonation steps. In this comparative example, the iron separation rate is only 87.2%, the lithium retention rate is 85.6%, and the purity of the hydrated ferric phosphate, lithium phosphate and lithium carbonate is 80.0%, 73.9% and 96.2%, respectively.

[0133] It can be known from the comparison of Example 1 and Comparative Example 2 that when the lithium-rich system-phosphorus iron is hydrothermally crystallized, when the pH is greater than 3, the increase of the pH leads to a change in the reaction system, and Fe(OH)3colloid is generated by the reaction. The double electric layer structure formed by the colloid has a strong adsorption effect on lithium. In this comparative example, the iron separation rate is 100%, the lithium retention rate is 80.2%, and the purity of the hydrated ferric phosphate, lithium phosphate and lithium carbonate is 91.6%, 99.9% and 99.8%, respectively.

[0134] As can be seen from the comparison between Example 1 and Comparative Example 3, when the lithium-rich system-phosphorus-iron is hydrothermally crystallized, the stirring rate is less than 100 rpm, i.e. the solution system in the reactor is close to static, the solution system uniformity is poor, the nucleation efficiency is low, crystallization is dominant, the iron element is not completely reacted, and the obtained hydrated ferric phosphate presents spherical particles with uneven particle size. In this comparative example, the iron separation rate is 98.6%, the lithium retention rate is 97.9%, and the purity of hydrated ferric phosphate, lithium phosphate and lithium carbonate is 99.8%, 97.3% and 99.9%, respectively.

[0135] As can be seen from the comparison between Example 1 and Comparative Example 4, when the lithium-rich system-phosphorus-iron is hydrothermally crystallized, the molar ratio of phosphorus element to iron element in the solution is less than 2:1, the iron element is not completely reacted, the reaction tends to generate amorphous ferric hydroxyphosphate, and the adsorption on lithium is strong, which is difficult to separate from hydrated ferric phosphate. In this comparative example, the iron separation rate is 80.3%, the lithium retention rate is 89.7%, and the purity of hydrated ferric phosphate, lithium phosphate and lithium carbonate is 72.5%, 70.4% and 91.4%, respectively.

[0136] As can be seen from the comparison between Example 1 and Comparative Example 5, when the lithium-rich system-phosphorus-iron is hydrothermally crystallized, the reaction time is less than 2 h, the reaction is not completely finished, the nucleation-crystallization process is stopped, the "precipitation-dissolution" balance is destroyed, the iron element is not completely involved in the reaction, and part of the lithium is entrained by the product. In this comparative example, the iron separation rate is 81.1%, the lithium retention rate is 91.9%, and the purity of hydrated ferric phosphate, lithium phosphate and lithium carbonate is 95.0%, 90.2% and 99.7%, respectively.

[0137] As can be seen from the comparison between Example 1 and Comparative Example 6, when the lithium-rich system-phosphorus-iron is hydrothermally crystallized, the ratio of solution volume to reactor inner container volume is less than 0.2:1, a large amount of solvent is evaporated, the reaction system pressure is too small, the concentration of each element in the solution is too high, a side reaction occurs, the iron element is not completely reacted, and lithium is entrained. In this comparative example, the iron separation rate is 86.2%, the lithium retention rate is 90.4%, and the purity of hydrated ferric phosphate, lithium phosphate and lithium carbonate is 95.9%, 86.7% and 95.6%, respectively.

[0138] In summary, the application includes but is not limited to the above examples, any equivalent replacement or partial improvement made within the spirit and principles of the application shall be considered within the protection scope of the application.

Claims

1. A method for recovering iron and lithium from a black powder acid leaching solution of a retired lithium iron phosphate battery, characterized in that: The method steps include: (1) Targeted sulfidation: under 80°C, a sulfidation salt solution is added dropwise into the black powder acid leaching solution and stirred to carry out the targeted sulfidation reaction for more than 10 min, after the reaction is completed, solid-liquid separation is carried out, and an acid sulfidation residue and a lithium-rich acid leaching solution are obtained; the lithium-rich acid leaching solution contains Fe 2+ ; (2) Oxidation: an oxidizing gas is introduced into the lithium-rich acid leaching solution for oxidation treatment, so that Fe 2+ is completely oxidized to Fe 3+ , and after the treatment, a lithium-rich oxidized acid solution is obtained; the flow rate of the oxidizing gas is 50-200 mL / min; (3) Lithium-rich system-phosphorus iron hydrothermal crystallization: phosphoric acid and phosphate are added into the lithium-rich oxidizing acid solution, mixed to obtain a reaction solution, and the reaction solution is placed in a hydrothermal reactor for hydrothermal crystallization treatment. After the treatment, solid-liquid separation is performed to obtain a lithium-rich solution and a lithium-phosphorus-iron compound; the hydrothermal crystallization temperature is 80-240℃, the reaction time is 2-72h, the stirring speed is 100-800rpm, the pH of the reaction solution is 1-3, the molar ratio of phosphorus element to iron element in the reaction solution is 2-10:1, and the volume ratio of the reaction solution to the volume of the reactor inner container is 0.2-0.8:1; (4) Water washing: the lithium-phosphorus-iron compound is subjected to water washing treatment, and after the treatment, solid-liquid separation is performed to obtain a washing solution and a microspherical hydrated iron phosphate.

2. The method for recovering iron and lithium from the acid leaching solution of retired lithium iron phosphate battery black powder as described in claim 1, characterized in that: In step (1), the molar ratio of sulfur element in the sulfide salt solution to the sum of copper and iron elements in the acid leaching solution is 2-10:1, the concentration of the sulfide salt solution is less than or equal to 5mol / L, the dropping speed of the sulfide salt solution is less than or equal to 50mL / min, and the stirring speed is greater than or equal to 300rpm.

3. The method for recovering iron and lithium from the acid leaching solution of retired lithium iron phosphate battery black powder as described in claim 2, characterized in that: The lithium-rich copper-containing acid leaching solution contains Li + , Cu 2+ , Al 3+ , Fe 3+ and PO4 3- ; the sulfidation salt is one or more of sodium sulfide, potassium sulfide and ammonium sulfide; the sulfidation salt solution concentration is 0.001-5 mol / L, the dropping speed is 0.1-50 mL / min; the target sulfidation reaction temperature is 0-80℃, the reaction time is 10-720 min; and the stirring speed is 300-1200 rpm.

4. The method for recovering iron and lithium from the acid leaching solution of retired lithium iron phosphate battery black powder as described in claim 1, characterized in that: In step (2), the lithium-rich acid leaching solution also contains Li + , Fe 2+ , PO4 3- , SO4 2- ions; And / or, the oxidizing gas is air, oxygen or ozone.

5. The method for recovering iron and lithium from the acid leaching solution of retired lithium iron phosphate battery black powder as described in claim 1, characterized in that: In step (3), the phosphate is one or more of NaH2PO4, KH2PO4 and NH4H2PO4.

6. The method for recovering iron and lithium from the acid leaching solution of retired lithium iron phosphate battery black powder as described in claim 1, characterized in that: In step (3), the composition of the lithium-phosphorus-iron compound is dihydrate iron phosphate and lithium-phosphorus adsorbate.

7. The method for recovering iron and lithium from the acid leaching solution of retired lithium iron phosphate battery black powder as described in claim 1, characterized in that: In step (4), the water washing is performed until the pH of the washing solution is greater than or equal to 6.

8. The method according to any one of claims 1 to 7, characterized in that: The method further includes the following steps: an alkali and a phosphate are added to the lithium-rich solution in step (3) for phosphatization treatment, and after the treatment, solid-liquid separation is performed to obtain a waste alkali solution and lithium phosphate; preferably, the alkali is one or more of NaOH, KOH and NH3·H2O; the phosphate is one or more of NaH2PO4, KH2PO4 and NH4H2PO4; during the phosphatization treatment, the pH is controlled at 8-12, the reaction temperature is 60-95℃, and the reaction time is 30-180min.

9. The method according to any one of claims 1 to 7, characterized in that: The method further comprises the following steps: adding an alkali into the lithium-rich solution in step (3) to perform a dephosphorization treatment, after the treatment, performing a solid-liquid separation to obtain an alkali lithium solution and a lithium phosphate; performing a concentration treatment on the alkali lithium solution, after the treatment, obtaining a high-concentration alkali lithium solution; adding a carbonate into the high-concentration alkali lithium solution to perform a carbonation treatment, after the treatment, performing a solid-liquid separation to obtain a waste alkali solution and a lithium carbonate; preferably, the alkali is one or more of NaOH, KOH and NH3·H2O; during the dephosphorization treatment, the pH is controlled to be 11-12, the reaction temperature is 60-70℃, and the reaction time is 30-180 min; the lithium ion concentration in the high-concentration alkali lithium solution is 20-60 g / L -1 ; the carbonate is one or more of Na2CO3, K2CO3 and (NH4)2CO3, the molar ratio of carbonate to lithium element in the high-concentration alkali lithium solution is greater than or equal to 0.55:1; during the carbonation treatment, the pH is controlled to be 10-13, the reaction temperature is 0-90℃, and the reaction time is 30-300 min.

10. A method for recovering iron and lithium from the acid leaching solution of retired lithium iron phosphate battery black powder as described in claim 8 or 9, characterized in that: Sulfuric acid is added to the waste alkali solution for neutralization treatment, and after the treatment, a neutral waste water is obtained.

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