Method for removing aluminum and copper from a ferric phosphate residue and use thereof

Abstract

A method for removing aluminum and copper from a ferric phosphate residue and the use thereof, the method comprising: subjecting a ferric phosphate residue to acid leaching to obtain an acid leaching solution; then mixing iron simple substance with the acid leaching solution to perform a first copper removal reaction, then mixing same with a soluble sulfide, such as sodium sulfide, and performing a second copper removal reaction, so as to obtain a copper-removed acid leaching solution; mixing an extractant with the copper-removed acid leaching solution, and performing extraction to obtain a ferrous phosphate solution and an aluminum-rich organic phase, thereby completing the removal of aluminum and copper. The present invention uses iron powder and a soluble sulfide for deep removal of copper and then extracts aluminum by using an extractant having high selectivity on aluminum, thus achieving the separation and removal of aluminum and copper. Using the iron powder and soluble sulfide can convert ferric iron in the system into ferrous iron, thereby preventing the loss of iron element during aluminum extraction processes, ensuring the recovery ratio of ferric phosphate to be greater than 99%, and effectively improving the purity of the obtained ferrous phosphate solution.

Description

A method for removing aluminum and copper from ferrophosphorus slag and its use Technical Field

[0001] Embodiments of the present application relate to the field of battery material recycling, such as a method for removing aluminum and copper from ferrophosphorus slag and its use. Background Art

[0002] In recent years, lithium-ion batteries, with their significant advantages such as high specific capacity, stable performance, and long service life, have greatly promoted the application and development of power batteries for new energy vehicles. Among the various cathode materials, lithium iron phosphate is the mainstream lithium battery product on the market, holding a large market share due to its low production cost and high safety performance.

[0003] With the increase in the use of lithium iron phosphate, the number of waste lithium iron phosphate batteries has also increased rapidly. Their high-value processing and recycling has gradually become an urgent problem to be solved in the industry.

[0004] Generally, in waste lithium iron phosphate batteries, lithium iron phosphate accounts for about 30-35% of the mass, copper foil and aluminum foil account for about 10%, and the content of valuable metal elements Li, Fe, Cu and Al far exceeds the content of corresponding elements in natural minerals. Therefore, waste lithium iron phosphate batteries are also raw materials with great recycling value.

[0005] Considering that Al, Cu and Fe have similar properties and are difficult to separate from each other, the presence of these impurities will affect the recovery of ferrophosphorus slag to prepare battery-grade iron phosphate, affect the purity and yield of iron phosphate, and further affect the electrochemical properties of lithium iron phosphate battery positive electrode materials prepared using iron phosphate.

[0006] Currently, for removing aluminum and copper impurities from ferrophosphorus slag after lithium extraction, there are related technologies that use alkali to leaching impurities, or use adsorbents to absorb aluminum, and there are also related technologies that use acidic solutions for impurity removal and purification. For example, CN114852983A discloses a method for extracting battery-grade iron phosphate from ferrophosphorus waste slag, a byproduct of recycled waste lithium batteries. The method comprises immersing the ferrophosphorus waste slag powder in a sodium hydroxide solution for reaction to remove aluminum; placing the ferrophosphorus waste slag after aluminum removal in a muffle furnace and calcining it at high temperature in an air atmosphere to remove carbon; adding a low-concentration acid solution to the ferrophosphorus waste slag powder after aluminum and carbon removal and heating it to react to remove copper impurities; adding acid solution to the ferrophosphorus waste slag powder after copper removal, heating it for leaching reaction, and filtering to obtain an acid leaching solution; adjusting the pH value of the acid leaching solution, and filtering, washing, and drying it in sequence to obtain hydrated iron phosphate. However, the impurity content in the iron phosphate recovered and prepared by these methods still does not meet the application standards of battery-grade iron phosphate. In addition, the process flow is complicated, the efficiency is low, the impurity removal effect is poor, and the purity and yield of the obtained iron phosphate product are low.

[0007] CN114920226A discloses a method for removing aluminum and copper impurities from ferrophosphorus slag after lithium extraction from lithium iron phosphate batteries. The method involves mixing the ferrophosphorus slag with a fluoride salt and calcining it to produce a calcined slag containing aluminum and copper fluorides. The calcined slag is then mixed with water and subjected to a leaching reaction under a specific pH value. Solid-liquid separation is then performed to produce a leachate containing aluminum and copper complexes and the impurity-removed ferrophosphorus slag. This method does not require acid or base leaching and can achieve deep removal of Al and Cu impurities, but it does require the use of fluoride salts, which are relatively expensive and contain fluorine.

[0008] Therefore, a new solution needs to be developed to effectively remove and separate the aluminum and copper elements in ferrophosphorus slag, so that the ferrophosphorus can be enriched with high purity, so as to facilitate the subsequent preparation of high-purity ferrophosphate products and realize the high-value recycling of ferrophosphorus slag.

[0009] Summary of the Invention

[0010] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0011] The present application provides a method for removing aluminum and copper from ferrophosphorus slag and its use. The method comprises acid leaching the ferrophosphorus slag to obtain an acid leaching solution; then mixing elemental iron with the acid leaching solution to perform a first copper removal reaction; then mixing with a soluble sulfide, such as sodium sulfide, to perform a second copper removal reaction to obtain a copper-removing acid leaching solution; then mixing an extractant with the copper-removing acid leaching solution to perform extraction to obtain a ferrophosphorus solution and an organic phase containing aluminum, thereby completing the removal of aluminum and copper. The present application utilizes iron powder and soluble sulfides for deep copper removal, and then uses an extractant with high selectivity for aluminum to extract aluminum, thereby completing the separation and removal of aluminum and copper. The use of iron powder and soluble sulfides can convert trivalent iron in the system into divalent iron, thereby avoiding the loss of iron during the aluminum extraction process, ensuring a ferrophosphorus recovery rate greater than 99%, and effectively improving the purity of the resulting ferrophosphorus solution.

[0012] In a first aspect, embodiments of the present application provide a method for removing aluminum and copper from ferrophosphorus slag, the method comprising:

[0013] acid leaching the ferrophosphorus slag to obtain an acid leaching solution;

[0014] The iron element is mixed with the acid leaching solution to perform a first copper removal reaction, and then the soluble sulfide is mixed to perform a second copper removal reaction to obtain a copper removal acid leaching solution;

[0015] The extractant is mixed with the copper removal acid leaching solution to perform extraction to obtain a ferrophosphorus solution and an aluminum-containing organic phase, thereby completing the removal of aluminum and copper.

[0016] The present application subjects ferrophosphorus slag to acid leaching to fully dissolve the valuable metal elements phosphorus, iron, copper, and aluminum in the slag. The resulting leachate is first subjected to iron powder for copper removal, and then subjected to deep copper removal using a soluble sulfide, such as sodium sulfide. At the same time, the iron powder can reduce trivalent iron to divalent iron. At this time, sodium sulfide does not affect the iron and causes it to precipitate. The divalent iron converted in the system can avoid the loss of iron elements by extracting trivalent iron simultaneously during the subsequent aluminum extraction process. Subsequently, the present application uses an extraction system with high selectivity for aluminum to extract aluminum, which can deeply remove aluminum impurities in the leachate. The entire process of the method has a high utilization rate of ferrophosphorus in the ferrophosphorus slag, and the ferrophosphorus recovery rate can be greater than 99%. At the same time, the problem of poor separation effect of metallic aluminum impurities in the ferrophosphorus slag recovery process is solved, thereby facilitating the subsequent acquisition of battery-grade ferric phosphate with higher purity.

[0017] The following are preferred technical solutions of this application, but are not intended to limit the technical solutions provided in this application. Through the following technical solutions, the technical objectives and beneficial effects of this application can be better achieved and realized.

[0018] As a preferred technical solution of the present application, the ferrophosphorus slag includes the ferrophosphorus slag obtained after lithium extraction from waste lithium iron phosphate battery materials.

[0019] Preferably, the iron content in the ferrophosphorus slag is ≥24% by mass, such as 24%, 27%, 30%, 35% or 40%, the phosphorus content is ≥15%, such as 15%, 18%, 20%, 23% or 25%, the aluminum content is ≥1.5% by mass, such as 1.5%, 1.8%, 2.1%, 2.4% or 2.5%, and the copper content is ≥0.01%, such as 0.01%, 0.05%, 0.08%, 0.11%, 0.13%, 0.15% or 0.2%, but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0020] Preferably, the ferrophosphorus slag is first slurried by adding water, and then concentrated acid is added for acid leaching.

[0021] Preferably, the solid-liquid mass ratio of the water-added slurry is 1:(2-5), for example, 1:2, 1:2.3, 1:2.6, 1:2.9, 1:3.2, 1:3.5, 1:3.8, 1:4.1, 1:4.4, 1:4.7 or 1:5, etc., but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0022] Preferably, the amount of the concentrated acid is 0.5 to 2 times the molar amount of iron in the ferrophosphorus slag, for example, 0.5 times, 0.7 times, 1 times, 1.2 times, 1.4 times, 1.6 times, 1.8 times or 2 times, but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0023] Preferably, the acid leaching temperature is 50-80°C, for example, 50°C, 53°C, 56°C, 59°C, 62°C, 65°C, 68°C, 71°C, 74°C, 77°C or 80°C, and the time is 1-3h, for example, 1h, 1.2h, 1.4h, 1.6h, 1.8h, 2h, 2.2h, 2.4h, 2.6h, 2.8h or 3h, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0024] As a preferred technical solution of the present application, the iron element includes iron powder.

[0025] Preferably, the amount of the iron element is 1 to 2 times the molar amount of the iron element in the acid leaching solution, for example, 1 time, 1.2 times, 1.4 times, 1.6 times, 1.8 times or 2 times, but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0026] The present application preferably uses an amount of elemental iron that exceeds the molar amount of iron in the acid leaching solution. On the one hand, the trivalent iron element can be reduced to the divalent iron element. On the other hand, the excess elemental iron can reduce the copper element. Since the content of copper in the ferrophosphorus slag is relatively small, the excess elemental iron is sufficient to reduce the copper. Of course, those skilled in the art can adaptively adjust the amount of elemental iron according to the actual total molar amount of iron and copper elements in the acid leaching solution.

[0027] Preferably, the first copper removal reaction is followed by filtration, and a soluble sulfide is added to the filtrate to perform a second copper removal reaction to obtain a copper removal acid leaching solution.

[0028] Preferably, the amount of the soluble sulfide is 1.5 to 2 times the molar amount of the residual copper element in the filtrate, for example, 1.5 times, 1.6 times, 1.7 times, 1.8 times, 1.9 times or 2 times, but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0029] Preferably, the soluble sulfide comprises alkali metal sulfide and / or ammonium sulfide, and the alkali metal sulfide comprises sodium sulfide and / or potassium sulfide.

[0030] The present application prefers that the amount of soluble sulfide such as sodium sulfide is in excess relative to the residual copper element. On the one hand, it can ensure the deep removal of the copper element. On the other hand, the excess sodium sulfide can further reduce the trace trivalent iron ions in the solution, further reducing the loss of iron in the subsequent extraction process.

[0031] As a preferred technical solution of the present application, the extractant includes an ionic liquid, and the ionic liquid contains an anionic and cationic structure.

[0032] Preferably, the substance providing a cationic structure includes a quaternary ammonium salt and / or a quaternary phosphonium salt.

[0033] Preferably, the substance providing a cationic structure includes any one of methyltrioctylammonium chloride, tetrabutylammonium chloride, tetraoctylammonium chloride or tetraheptylammonium chloride, or a combination of at least two thereof. Typical but non-limiting examples of the combination include a combination of methyltrioctylammonium chloride and tetrabutylammonium chloride, a combination of methyltrioctylammonium chloride and tetraoctylammonium chloride, a combination of methyltrioctylammonium chloride and tetraheptylammonium chloride, a combination of tetrabutylammonium chloride and tetraoctylammonium chloride, a combination of methyltrioctylammonium chloride and tetraheptylammonium chloride, or a combination of tetraoctylammonium chloride and tetraheptylammonium chloride.

[0034] Preferably, the substance providing an anionic structure includes any one of di(2-ethylhexyl)phosphate, bis(2,4,4-trimethylpentyl)phosphonic acid, 2-ethyl-2,5-dimethylhexanoic acid or sec-octylphenoxyacetic acid, or a combination of at least two thereof. Typical but non-limiting examples of the combination include a combination of di(2-ethylhexyl)phosphate and bis(2,4,4-trimethylpentyl)phosphonic acid, a combination of di(2-ethylhexyl)phosphate and 2-ethyl-2,5-dimethylhexanoic acid, or a combination of bis(2,4,4-trimethylpentyl)phosphonic acid and sec-octylphenoxyacetic acid.

[0035] Preferably, the extraction further uses a diluent, and the diluent and the extractant constitute the extraction organic phase.

[0036] Preferably, the volume ratio of the extractant to the diluent is 1:(0.3-3), for example, 1:0.3, 1:0.6, 1:0.9, 1:1.2, 1:1.5, 1:1.8, 1:2.1, 1:2.4, 1:2.7 or 1:3, etc., but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0037] Preferably, the diluent includes any one or a combination of at least two of methyl isobutyl ketone, methyl tert-butyl ether, ethyl acetate, cyclohexane or dichloromethane. Typical but non-limiting examples of the combination include a combination of methyl isobutyl ketone and methyl tert-butyl ether, a combination of methyl isobutyl ketone and ethyl acetate, a combination of methyl isobutyl ketone and cyclohexane, a combination of methyl isobutyl ketone and dichloromethane, a combination of methyl tert-butyl ether and ethyl acetate, a combination of methyl tert-butyl ether and cyclohexane, a combination of methyl tert-butyl ether and dichloromethane, a combination of ethyl acetate and cyclohexane or a combination of cyclohexane and dichloromethane.

[0038] Preferably, the volume ratio of the extracted organic phase to the copper removal acid leaching solution is (1-3):1, for example, 1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1, 2:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1 or 3:1, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0039] As a preferred technical solution of the present application, the method further includes removing water from the aluminum-rich organic phase and then performing electrodeposition to obtain metallic aluminum and an aluminum-depleted organic phase, and the aluminum-depleted organic phase is reused as an extractant.

[0040] The present application uses an extraction system with high electrical conductivity and high selectivity for aluminum to extract aluminum; in the process of extraction using a specific extractant, a functionalized ionic liquid composed of quaternary ammonium salts, quaternary phosphonium salt cations and phosphate and carboxylic acid anions combines with Al(III), and through the synergistic effect between the functionalized anions and cations, it has a stronger extraction ability and selectivity for Al(III) than traditional extractants. By directly electroplating in the aluminum-rich organic phase after aluminum extraction to obtain metallic aluminum, effective separation of iron and aluminum in the acid leaching solution and high-value utilization of aluminum can be achieved. Since the organic phase after electroplating is reused, the effective connection between the ferrophosphorus slag removal of aluminum impurities and the electroplating of metallic aluminum can be achieved, which can effectively reduce production costs. At the same time, high-value-added metallic aluminum can be generated, further improving the resource recycling rate of the ferrophosphorus slag recovery process.

[0041] In a second aspect, an embodiment of the present application provides a preparation method for recovering ferric phosphate from ferrophosphorus slag, the preparation method comprising:

[0042] Using the method described in the first aspect, removing aluminum and copper from ferrophosphorus slag to obtain a ferrophosphorus solution;

[0043] The ferrophosphorus solution, an alkali source, an iron source and / or a phosphorus source are mixed and subjected to precipitation reaction to obtain ferric phosphate dihydrate, which is then roasted to obtain ferric phosphate.

[0044] As a preferred technical solution of the present application, the iron source and / or phosphorus source makes the phosphorus-iron molar ratio in the system reach (1-1.1):1, for example, 1:1, 1:1.01, 1:1.02, 1:1.03, 1:1.04, 1:1.05, 1:1.06, 1:1.07, 1:1.08, 1:1.09 or 1:1.1, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0045] Preferably, the alkaline source comprises aqueous ammonia.

[0046] Preferably, the alkaline source is used to adjust the pH to control the endpoint pH of the precipitation reaction to be 1.8 to 2.2, such as 1.8, 1.85, 1.9, 1.95, 2, 2.05, 2.1, 2.15 or 2.2, etc., but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0047] Preferably, the iron source includes any one or a combination of at least two of ferric sulfate, ferric chloride or ferric nitrate. Typical but non-limiting examples of the combination include a combination of ferric sulfate and ferric chloride, a combination of ferric sulfate and ferric nitrate, or a combination of ferric chloride and ferric nitrate.

[0048] Preferably, the phosphorus source includes any one of diammonium phosphate, sodium phosphate, ammonium phosphate or monoammonium hydrogen phosphate, or a combination of at least two thereof. Typical but non-limiting examples of the combination include a combination of diammonium phosphate and sodium phosphate, a combination of diammonium phosphate and ammonium phosphate, a combination of diammonium phosphate and monoammonium hydrogen phosphate, a combination of sodium phosphate and ammonium phosphate, a combination of ammonium phosphate and monoammonium hydrogen phosphate, or a combination of ammonium phosphate and monoammonium hydrogen phosphate.

[0049] As a preferred technical solution of the present application, the preparation method further uses hydrogen peroxide for the mixing.

[0050] Preferably, the amount of hydrogen peroxide is 1 to 1.5 times the molar amount of iron element in the system, for example, 1 time, 1.1 times, 1.2 times, 1.3 times, 1.4 times or 1.5 times, etc., but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0051] Preferably, the precipitation reaction temperature is 60-90°C, for example, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C or 90°C, and the time is 1-2h, for example, 1h, 1.2h, 1.4h, 1.6h, 1.8h or 2h, but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0052] Preferably, the calcination temperature is 450-650°C, for example, 450°C, 470°C, 490°C, 510°C, 530°C, 550°C, 570°C, 590°C, 610°C, 630°C or 650°C, and the calcination time is 3-6h, for example, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h or 6h, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0053] In a third aspect, an embodiment of the present application provides an iron phosphate obtained according to the preparation method described in the second aspect.

[0054] In a fourth aspect, an embodiment of the present application provides a lithium iron phosphate positive electrode material, which is prepared using the iron phosphate described in the third aspect.

[0055] Compared with the related technical solutions, the embodiments of the present application have at least the following beneficial effects:

[0056] In the embodiment of the present application, ferrophosphorus slag is subjected to acid leaching to fully dissolve the valuable metal elements phosphorus, iron, copper, and aluminum in the slag. The resulting leachate is first subjected to copper removal using iron powder, and then deeply copper removal using soluble sulfides. At the same time, the iron powder can reduce trivalent iron to divalent iron. At this time, the soluble sulfides do not affect the iron and cause it to precipitate. The divalent iron converted in the system can avoid the loss of iron elements by extracting trivalent iron during the subsequent aluminum extraction process. Subsequently, the present application uses an extraction system with high selectivity for aluminum to extract aluminum, which can deeply remove aluminum impurities in the leachate. The entire process of the method has a high utilization rate of ferrophosphorus in the ferrophosphorus slag, and the ferrophosphorus recovery rate can be greater than 99%. At the same time, the problem of poor separation effect of metallic aluminum impurities in the ferrophosphorus slag recovery process is solved, thereby facilitating the subsequent acquisition of battery-grade iron phosphate with higher purity.

[0057] The embodiments of the present application utilize an extraction system with high electrical conductivity and high selectivity for aluminum to extract aluminum. This allows for the direct electrodeposition of metallic aluminum in the aluminum-rich organic phase after aluminum extraction, thereby achieving effective separation of iron and aluminum in the acid leaching solution and high-value utilization of aluminum. Because the organic phase after electrodeposition is reused, the effective connection between the ferrophosphorus slag removal of aluminum impurities and the electrodeposition of metallic aluminum can be achieved, effectively reducing production costs. At the same time, high-value-added metallic aluminum can be generated, further improving the resource recycling rate of the ferrophosphorus slag recovery process.

[0058] Still other aspects will become apparent upon reading and understanding the detailed description. DETAILED DESCRIPTION

[0059] The technical solution of this application is further explained below through specific implementation methods.

[0060] Those skilled in the art should understand that the embodiments are only intended to help understand the present application and should not be regarded as specific limitations of the present application.

[0061] Example 1

[0062] This embodiment provides a method for removing aluminum and copper from ferrophosphorus slag and preparing ferric phosphate, the method comprising the following steps:

[0063] (1) taking waste lithium iron phosphate ferrophosphorus slag after lithium extraction, wherein the mass content of phosphorus is 21.05%, iron is 36.97%, aluminum is 1.8%, and copper is 0.01%, adding water to prepare slurry according to a solid-liquid mass ratio of 1:3, and then adding concentrated sulfuric acid with a molar amount that is 1 times the molar amount of iron in the ferrophosphorus slag, leaching at a temperature of 70°C for 2h, and then filtering to obtain an acid leaching solution;

[0064] (2) adding iron powder in an amount 1.5 times the molar amount of iron in the solution to the acid leaching solution obtained in step (1) to remove copper, reacting for 1.5 hours and filtering, adding sodium sulfide in an amount 1.8 times the theoretical amount of residual copper ions in the solution to the filtrate and reacting for 0.5 hours to perform deep copper removal, thereby obtaining a copper-removed acid leaching solution;

[0065] (3) using an ionic liquid formed by methyl trioctyl ammonium chloride and di(2-ethylhexyl) phosphate as an extractant and methyl isobutyl ketone as a diluent, the two are mixed at a volume ratio of 1:1 to obtain an extracted organic phase, the extracted organic phase and the acid leaching solution obtained in step (2) are fully mixed, and aluminum is extracted at a phase ratio of R(O / A)=2:1 to obtain a ferrophosphorus solution and an aluminum-containing organic phase, thereby completing the removal of aluminum and copper;

[0066] (4) adding a molecular desiccant to the extracted aluminum-rich organic phase to remove water and obtain an anhydrous aluminum-rich organic phase, using a silver sheet as a working electrode and a carbon electrode as a reference electrode and a counter electrode, and performing electrodeposition at an electrode potential of -3 V to obtain metallic aluminum and an aluminum-poor organic phase, and the aluminum-poor organic phase is returned to step (3) as an extracted organic phase and continued to be used for aluminum extraction, thereby realizing the recycling of the organic phase;

[0067] (5) Adding ferric sulfate and ammonium dihydrogen phosphate to the ferrophosphorus solution obtained in step (3) to adjust the molar ratio of phosphorus to iron in the system to 1.05:1, and adding hydrogen peroxide in an amount 1.3 times the molar amount of iron, and then adding ammonia water to adjust the pH to 2, and reacting for 1.5 hours. After the reaction is completed, solid-liquid separation is performed to obtain a dihydrate ferric phosphate precipitate, which is placed in a muffle furnace and calcined at 500° C. for 4 hours to obtain high-purity ferric phosphate.

[0068] Example 2

[0069] This embodiment provides a method for removing aluminum and copper from ferrophosphorus slag and preparing ferric phosphate, the method comprising the following steps:

[0070] (1) taking waste lithium iron phosphate ferrophosphorus slag after lithium extraction, wherein the mass content of phosphorus is 21.15%, iron is 37.21%, aluminum is 1.8%, and copper is 0.01%, adding water to prepare slurry according to a solid-liquid mass ratio of 1:5, and then adding concentrated sulfuric acid with a molar amount twice that of the molar amount of iron in the ferrophosphorus slag, leaching at a temperature of 80°C for 1 hour, and then filtering to obtain an acid leaching solution;

[0071] (2) adding iron powder twice the molar amount of iron in the solution to the acid leaching solution obtained in step (1) to remove copper, reacting for 1.5 hours and then filtering, adding sodium sulfide twice the theoretical amount of residual copper ions in the solution to the filtrate and reacting for 0.5 hours to perform deep copper removal, thereby obtaining a copper-removed acid leaching solution;

[0072] (3) using an ionic liquid formed by tetrabutylammonium chloride and 2-ethyl-2,5-dimethylhexanoic acid as an extractant and ethyl acetate as a diluent, the two are mixed at a volume ratio of 2:3 to obtain an extracted organic phase, the extracted organic phase and the acid leaching solution obtained in step (2) are fully mixed, and aluminum is extracted at a phase ratio of R(O / A)=2:1 to obtain a ferrophosphorus solution and an aluminum-containing organic phase, thereby completing the removal of aluminum and copper;

[0073] (4) adding a molecular desiccant to the extracted aluminum-rich organic phase to remove water and obtain an anhydrous aluminum-rich organic phase, using a silver sheet as a working electrode and a carbon electrode as a reference electrode and a counter electrode, and performing electrodeposition at an electrode potential of -4 V to obtain metallic aluminum and an aluminum-poor organic phase, and the aluminum-poor organic phase is returned to step (3) as an extracted organic phase and continued to be used for aluminum extraction, thereby realizing the recycling of the organic phase;

[0074] (5) Adding ferric sulfate and ammonium dihydrogen phosphate to the ferrophosphorus solution obtained in step (3) to adjust the molar ratio of phosphorus to iron in the system to 1.1:1, and adding hydrogen peroxide in an amount 1.5 times the molar amount of iron, and then adding ammonia water to adjust the pH to 2.2, and reacting for 2 hours. After the reaction is completed, solid-liquid separation is performed to obtain dihydrated ferric phosphate precipitate, which is placed in a muffle furnace and calcined at 650° C. for 3 hours to obtain high-purity ferric phosphate.

[0075] Example 3

[0076] This embodiment provides a method for removing aluminum and copper from ferrophosphorus slag and preparing ferric phosphate, the method comprising the following steps:

[0077] (1) taking waste lithium iron phosphate ferrophosphorus slag after lithium extraction, wherein the mass content of phosphorus is 21.15%, iron is 37.21%, aluminum is 1.8%, and copper is 0.01%, adding water to prepare slurry according to a solid-liquid mass ratio of 1:2, and then adding concentrated sulfuric acid with a molar amount of 0.5 times the molar amount of iron in the ferrophosphorus slag, leaching at a temperature of 50°C for 3h, and then filtering to obtain an acid leaching solution;

[0078] (2) adding iron powder in an amount of 1 times the molar amount of iron in the solution to the acid leaching solution obtained in step (1) to remove copper, reacting for 1.5 hours and then filtering, adding sodium sulfide in an amount of 1.5 times the theoretical amount of residual copper ions in the solution to the filtrate and reacting for 0.5 hours to perform deep copper removal, thereby obtaining a copper-removed acid leaching solution;

[0079] (3) using an ionic liquid formed by tetraoctyl ammonium chloride and secondary octylphenoxyacetic acid as an extractant and ethyl acetate as a diluent, the two are mixed at a volume ratio of 3:2 to obtain an extracted organic phase, the extracted organic phase and the acid leaching solution obtained in step (2) are fully mixed, and aluminum is extracted at a phase ratio of R(O / A)=3:1 to obtain a ferrophosphorus solution and an aluminum-containing organic phase, thereby completing the removal of aluminum and copper;

[0080] (4) adding a molecular desiccant to the extracted aluminum-rich organic phase to remove water and obtain an anhydrous aluminum-rich organic phase, using a silver sheet as a working electrode and a carbon electrode as a reference electrode and a counter electrode, and performing electrodeposition at an electrode potential of -2 V to obtain metallic aluminum and an aluminum-poor organic phase, and returning the aluminum-poor organic phase to step (3) as an extracted organic phase and continuing to be used for aluminum extraction, thereby realizing the recycling of the organic phase;

[0081] (5) Adding ferric sulfate and ammonium dihydrogen phosphate to the ferrophosphorus solution obtained in step (3) to adjust the molar ratio of phosphorus to iron in the system to 1:1, and adding hydrogen peroxide in an amount that is 1 times the molar amount of iron, and then adding ammonia water to adjust the pH to 1.8, and reacting for 2 hours. After the reaction is completed, solid-liquid separation is performed to obtain a dihydrate ferric phosphate precipitate, which is placed in a muffle furnace and calcined at 450° C. for 6 hours to obtain high-purity ferric phosphate.

[0082] Example 4

[0083] This embodiment provides a method for removing aluminum and copper from ferrophosphorus slag and preparing ferric phosphate. In the method, in step (2), the amount of sodium sulfide is adjusted from 1.8 times the theoretical amount of residual copper ions in the solution to 1.2 times. Apart from this, the other conditions are exactly the same as those in Example 1.

[0084] Example 5

[0085] This embodiment provides a method for removing aluminum and copper from ferrophosphorus slag and preparing ferric phosphate. In the method, in step (2), the amount of sodium sulfide is adjusted from 1.8 times the theoretical amount of residual copper ions in the solution to 1.5 times. Apart from this, other conditions are exactly the same as those in Example 1.

[0086] Example 6

[0087] This embodiment provides a method for removing aluminum and copper from ferrophosphorus slag and preparing ferric phosphate. In the method, in step (2), the amount of sodium sulfide is adjusted from 1.8 times the theoretical amount of residual copper ions in the solution to 2 times. Apart from this, other conditions are exactly the same as those in Example 1.

[0088] Example 7

[0089] This embodiment provides a method for removing aluminum and copper from ferrophosphorus slag and preparing ferric phosphate. In the method, in step (2), the amount of sodium sulfide is adjusted from 1.8 times the theoretical amount of residual copper ions in the solution to 2.3 times. Apart from this, the other conditions are exactly the same as those in Example 1.

[0090] Example 8

[0091] This embodiment provides a method for removing aluminum and copper from ferrophosphorus slag and preparing ferric phosphate. The method uses only di(2-ethylhexyl) phosphate as an extractant and does not use methyltrioctylammonium chloride. Except for the above, other conditions are exactly the same as those in Example 1.

[0092] Example 9

[0093] This embodiment provides a method for removing aluminum and copper from ferrophosphorus slag and preparing ferric phosphate. In the method, in step (3), the volume ratio of the extractant to the diluent is adjusted from 1:1 to 1:0.1. Except for the above, other conditions are exactly the same as those in Example 1.

[0094] Example 10

[0095] This embodiment provides a method for removing aluminum and copper from ferrophosphorus slag and preparing ferric phosphate. In the method, in step (3), the volume ratio of the extractant to the diluent is adjusted from 1:1 to 1:0.3. Except for the above, other conditions are exactly the same as those in Example 1.

[0096] Example 11

[0097] This embodiment provides a method for removing aluminum and copper from ferrophosphorus slag and preparing ferric phosphate. In the method, in step (3), the volume ratio of the extractant to the diluent is adjusted from 1:1 to 1:3. Except for the above, other conditions are exactly the same as those in Example 1.

[0098] Example 12

[0099] This embodiment provides a method for removing aluminum and copper from ferrophosphorus slag and preparing ferric phosphate. In the method, in step (3), the volume ratio of the extractant to the diluent is adjusted from 1:1 to 1:3.3. Except for the above, other conditions are exactly the same as those in Example 1.

[0100] Comparative Example 1

[0101] This comparative example provides a method for removing aluminum and copper from ferrophosphorus slag and preparing ferric phosphate. The method does not use an organic phase extraction step to extract aluminum, that is, steps (3) and (4) are not performed. The copper-removing acid leaching solution obtained in step (2) is directly used as a ferrophosphorus solution in step (5). Except for the above, the other conditions are exactly the same as those in Example 1.

[0102] Comparative Example 2

[0103] This comparative example provides a method for removing aluminum and copper from ferrophosphorus slag and preparing ferric phosphate. The method does not use sodium sulfide, that is, step (2) comprises: adding iron powder in an amount 1.5 times the molar amount of iron in the solution to the acid leaching solution obtained in step (1) to remove copper, reacting for 1.5 hours, and then filtering to obtain a copper-removed acid leaching solution. Except for the above, the other conditions are exactly the same as those in Example 1.

[0104] The ferric phosphate obtained in Examples 1-12 and Comparative Examples 1-2 was tested, and the composition index (mass content), purity and aluminum recovery rate of the ferric phosphate were obtained as shown in Table 1.

[0105] Table 1 Note: “ / ” in Table 1 indicates that the Al recovery rate cannot be calculated or does not need to be calculated.

[0106] As can be seen from Table 1:

[0107] When the aluminum extraction step is not performed during the impurity removal process, the aluminum impurities in the iron phosphate formed will be high, which will greatly reduce the purity of the iron phosphate and affect the electrochemical performance of the subsequently prepared lithium iron phosphate positive electrode material. Since the aluminum extraction step is not performed, the aluminum in the leachate cannot be recovered.

[0108] When sodium sulfide is not added or its content is too low, the copper impurity content in the leachate is high, and the existing trivalent iron is extracted at the same time during the subsequent aluminum extraction process, thereby affecting the purity of the iron phosphate and the aluminum recovery rate is not high; excessive sodium sulfide content can easily lead to the precipitation of ferrous sulfide in the solution, resulting in the introduction of impurities and reducing the purity of the iron phosphate;

[0109] The difference between Example 12 and Example 1 is that the extractant is changed to di(2-ethylhexyl) phosphate, which does not have ionic liquid properties. Since this organic system is not conductive, aluminum electrodeposition cannot be performed, and aluminum recovery cannot be performed.

[0110] It can be seen from Examples 13-16 that selecting a suitable ratio of extractant to diluent is beneficial to improving the extraction rate of aluminum, thereby reducing the content of impurity aluminum in ferric phosphate and improving the purity of ferric phosphate.

[0111] The present application uses the above-mentioned embodiments to illustrate the detailed structural features of the present application. However, the present application is not limited to the above-mentioned detailed structural features, that is, it does not mean that the present application must rely on the above-mentioned detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present application, equivalent replacements of selected components of the present application, addition of auxiliary components, selection of specific methods, etc., all fall within the scope of protection and disclosure of the present application.

[0112] The preferred embodiments of the present application are described in detail above. However, the present application is not limited to the specific details of the above embodiments. Within the technical concept of the present application, various simple modifications can be made to the technical solution of the present application, and these simple modifications all fall within the scope of protection of the present application.

[0113] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner unless there is any contradiction. In order to avoid unnecessary repetition, this application will not further describe various possible combinations.

[0114] In addition, the various implementation methods of the present application may be arbitrarily combined, and as long as they do not violate the concept of the present application, they should also be regarded as the contents disclosed in the present application.

Claims

1. A method for removing aluminum and copper from ferrophosphorus slag, comprising: acid leaching the ferrophosphorus slag to obtain an acid leaching solution; The iron element is mixed with the acid leaching solution to perform a first copper removal reaction, and then the soluble sulfide is mixed to perform a second copper removal reaction to obtain a copper removal acid leaching solution; The extractant is mixed with the copper removal acid leaching solution to extract and obtain a ferrophosphorus solution and an alumina organic phase, thereby completing the removal of aluminum and copper.

2. The method according to claim 1, wherein: The ferrophosphorus slag includes the ferrophosphorus slag obtained after lithium is extracted from waste lithium iron phosphate battery materials.

3. The method according to claim 2, wherein: The ferrophosphorus slag has an iron content of ≥24% by mass, a phosphorus content of ≥15% by mass, an aluminum content of ≥1.5% by mass, and a copper content of ≥0.01% by mass.

4. The method according to claim 2 or 3, wherein: The ferrophosphorus slag is firstly slurried by adding water, and then concentrated acid is added for acid leaching.

5. The method according to claim 4, wherein: The solid-liquid mass ratio of the water-adding slurry is 1:(2-5); Preferably, the amount of the concentrated acid is 0.5 to 2 times the molar amount of iron in the ferrophosphorus slag; Preferably, the acid leaching temperature is 50-80° C. and the time is 1-3 hours.

6. The method according to any one of claims 1 to 5, wherein: The iron element includes iron powder; Preferably, the amount of the iron element is 1 to 2 times the molar amount of the iron element in the acid leaching solution; Preferably, the first copper removal reaction is followed by filtration, and a soluble sulfide is added to the filtrate to perform a second copper removal reaction to obtain a copper removal acid leaching solution; Preferably, the amount of the soluble sulfide is 1.5 to 2 times the molar amount of the copper element remaining in the filtrate; Preferably, the soluble sulfide comprises alkali metal sulfide and / or ammonium sulfide.

7. The method according to any one of claims 1 to 6, wherein: The extractant includes an ionic liquid, and the ionic liquid contains an anion and a cation structure; Preferably, the substance providing the cationic structure comprises a quaternary ammonium salt and / or a quaternary phosphonium salt; Preferably, the substance providing the cationic structure includes any one of methyltrioctyl ammonium chloride, tetrabutyl ammonium chloride, tetraoctyl ammonium chloride or tetraheptyl ammonium chloride, or a combination of at least two thereof; Preferably, the substance providing the anionic structure includes any one of di(2-ethylhexyl)phosphate, bis(2,4,4-trimethylpentyl)phosphonic acid, 2-ethyl-2,5-dimethylhexanoic acid or sec-octylphenoxyacetic acid or a combination of at least two thereof; Preferably, the extraction further uses a diluent, and the diluent and the extractant constitute an extraction organic phase; Preferably, the volume ratio of the extractant to the diluent is 1:(0.3-3); Preferably, the diluent comprises any one or a combination of at least two of methyl isobutyl ketone, methyl tert-butyl ether, ethyl acetate, cyclohexane or dichloromethane; Preferably, the volume ratio of the extracted organic phase to the copper removal acid leaching solution is (1-3):

1.

8. The method according to any one of claims 1 to 7, wherein: The method further comprises removing water from the aluminum-rich organic phase and then subjecting it to electrodeposition to obtain metallic aluminum and an aluminum-poor organic phase, wherein the aluminum-poor organic phase is reused as an extractant.

9. A method for recovering ferric phosphate from ferrophosphorus slag, comprising: Using the method described in any one of claims 1 to 8, removing aluminum and copper from ferrophosphorus slag to obtain a ferrophosphorus solution; The ferrophosphorus solution, the alkali source and the iron source and / or the phosphorus source are mixed, and a precipitation reaction is carried out to obtain ferric phosphate dihydrate, and then the mixture is calcined to obtain ferric phosphate.

10. The preparation method according to claim 9, wherein: The iron source and / or phosphorus source makes the phosphorus-iron molar ratio in the system reach (1-1.1):

1.

11. The preparation method according to claim 9 or 10, wherein: The alkaline source includes aqueous ammonia; Preferably, the alkaline source is used to adjust the pH to control the endpoint pH of the precipitation reaction to be 1.8 to 2.

2.

12. The preparation method according to any one of claims 9 to 11, wherein: The iron source includes any one of ferric sulfate, ferric chloride or ferric nitrate, or a combination of at least two thereof; Preferably, the phosphorus source includes any one of diammonium phosphate, sodium phosphate, ammonium phosphate or monoammonium hydrogen phosphate, or a combination of at least two thereof.

13. The preparation method according to any one of claims 9 to 12, wherein: The preparation method also uses hydrogen peroxide to carry out the mixing; Preferably, the amount of hydrogen peroxide used is 1 to 1.5 times the molar amount of iron in the system; Preferably, the precipitation reaction temperature is 60-90°C and the time is 1-2h; Preferably, the calcination temperature is 450-650° C. and the calcination time is 3-6 hours.

14. An iron phosphate, wherein: Obtained according to the preparation method according to any one of claims 9 to 13.

15. A lithium iron phosphate positive electrode material, wherein: It is prepared using the iron phosphate described in claim 14.

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