Method for removing aluminum and copper from phosphorous iron slag and use thereof
By combining acid leaching and extraction with electrodeposition technology, the problem of poor separation of aluminum and copper impurities in iron phosphate slag was solved, achieving the preparation of high-purity iron phosphate and improving the electrochemical performance of lithium iron phosphate battery cathode materials.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- GUANGDONG BRUNP RECYCLING TECH CO LTD
- Filing Date
- 2023-09-20
- Publication Date
- 2026-08-04
AI Technical Summary
Existing technologies are unable to effectively remove and separate aluminum and copper impurities from iron phosphate slag, which affects the purity and yield of iron phosphate and leads to a decline in the electrochemical performance of lithium iron phosphate battery cathode materials. Furthermore, existing methods are complex and inefficient.
Valuable metal elements in phosphate slag are dissolved by acid leaching, copper is deeply removed by iron powder and soluble sulfides, aluminum is then extracted by a highly selective extractant, and the separation and removal of aluminum and copper are achieved by electrodeposition technology.
It achieves efficient separation of aluminum and copper in phosphate slag, with a phosphate recovery rate of over 99%, improved purity, reduced production costs, increased resource recycling rate, and the generation of high-value-added metallic aluminum.
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Abstract
Description
Technical Field
[0001] This application relates to the field of battery material recycling, such as a method for removing aluminum and copper from phosphorus-iron slag and its uses. Background Technology
[0002] In recent years, lithium-ion batteries have demonstrated significant advantages such as high specific capacity, stable performance, and long service life, greatly promoting the application and development of power batteries for new energy vehicles. Among numerous cathode materials, lithium iron phosphate is currently the mainstream lithium battery product on the market, holding a large market share due to its lower manufacturing cost and higher safety performance.
[0003] With the increasing use of lithium iron phosphate batteries, the number of used lithium iron phosphate batteries has also increased rapidly. High-value processing and recycling of these batteries has gradually become an urgent problem to be solved in the industry.
[0004] Typically, in waste lithium iron phosphate batteries, lithium iron phosphate accounts for about 30-35% of the mass, while copper and aluminum foil account for about 10%. The content of valuable metal elements such as Li, Fe, Cu, and Al far exceeds the content of the 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 recycling of iron phosphate slag to prepare battery-grade iron phosphate, affecting the purity and yield of iron phosphate, and thus affecting the electrochemical performance of lithium iron phosphate battery cathode materials prepared using iron phosphate.
[0006] Currently, for the removal of aluminum and copper impurities from lithium-ion ferrophosphate slag, there are technologies that utilize alkali leaching to remove impurities, or adsorbents to adsorb aluminum, as well as technologies that utilize acidic solutions for purification. For example, CN114852983A discloses a method for extracting battery-grade iron phosphate from iron phosphate slag, a byproduct of recycling waste lithium batteries. The method involves leaching iron phosphate slag powder into a sodium hydroxide solution to remove aluminum; placing the aluminum-removed iron phosphate slag in a muffle furnace and calcining it at high temperature in air to remove carbon; adding the aluminum- and carbon-removed iron phosphate slag powder to a low-concentration acid solution and heating it to remove copper impurities; adding acid to the copper-removed iron phosphate slag powder and heating it to carry out a leaching reaction, filtering to obtain an acid leaching solution; adjusting the pH value of the acid leaching solution, and then filtering, washing, and drying it sequentially to obtain hydrated iron phosphate. However, the impurity content in the iron phosphate recovered by these methods still does not meet the application standards for battery-grade iron phosphate. Moreover, the process is complex, inefficient, and has poor impurity removal effect, resulting in low purity and yield of the iron phosphate product.
[0007] CN114920226A discloses a method for removing aluminum and copper impurities from lithium iron phosphate (LFP) battery slag after lithium extraction. This method involves mixing the LFP slag with fluoride salts and calcining it to obtain calcined slag containing aluminum and copper fluorides. The calcined slag is then mixed with water and leached under specific pH conditions, followed by solid-liquid separation to obtain a leachate containing aluminum and copper complexes and the purified LFP slag. This method eliminates the need for acid-base leaching and achieves deep removal of Al and Cu impurities, but it requires the use of expensive fluoride salts containing fluorine.
[0008] Therefore, a new solution needs to be developed to effectively remove and separate aluminum and copper elements from ferrophosphate slag, so as to enrich ferrophosphate with high purity, so as to facilitate the subsequent preparation of high-purity ferrophosphate products and realize the high-value recycling of ferrophosphate slag. Summary of the Invention
[0009] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.
[0010] This application provides a method for removing aluminum and copper from ferrophosphate slag and its application. The method involves acid leaching the ferrophosphate slag to obtain an acid leaching solution; then mixing elemental iron with the acid leaching solution for a first copper removal reaction; followed by mixing with a soluble sulfide, such as sodium sulfide, for a second copper removal reaction to obtain a copper-removed acid leaching solution; finally, mixing an extractant with the copper-removed acid leaching solution for extraction to obtain a ferrophosphate solution and an aluminum-rich organic phase, thus completing the removal of aluminum and copper. This application utilizes iron powder and soluble sulfides for deep copper removal, followed by extraction of aluminum using an extractant with high selectivity for aluminum, thereby achieving the separation and removal of aluminum and copper. The use of iron powder and soluble sulfides converts ferric iron to ferrous iron in the system, thus avoiding the loss of iron during aluminum extraction, ensuring a ferrophosphate recovery rate greater than 99%, and effectively improving the purity of the obtained ferrophosphate solution.
[0011] In a first aspect, embodiments of this application provide a method for removing aluminum and copper from ferrophosphate slag, the method comprising:
[0012] The phosphorus-iron slag is acid-leached to obtain an acid leaching solution;
[0013] Iron is mixed with acid leaching solution to carry out the first copper removal reaction, and then soluble sulfides are mixed in to carry out the second copper removal reaction to obtain copper removal acid leaching solution.
[0014] The extractant is mixed with the copper-removing acid leaching solution and extracted to obtain a phosphorus-iron solution and an aluminum-rich organic phase, thus completing the removal of aluminum and copper.
[0015] This application involves acid leaching of ferrophosphate slag to fully dissolve the valuable metal elements phosphorus, iron, copper, and aluminum in the slag. The resulting leachate is first treated with iron powder to remove copper, followed by deep copper removal with soluble sulfides, such as sodium sulfide. Simultaneously, the iron powder can reduce ferric iron to ferrous iron. At this point, sodium sulfide does not affect the iron and prevent it from precipitating. The ferrous iron converted in the system can avoid the simultaneous extraction of ferric iron during the subsequent aluminum extraction process, thus preventing the loss of iron. Subsequently, this application employs an extraction system with high selectivity for aluminum to extract aluminum, which can deeply remove aluminum impurities from the leachate. The entire process of this method has a high utilization rate of ferrophosphate in the ferrophosphate slag, with a ferrophosphate recovery rate greater than 99%. It also solves the problem of poor separation of metallic aluminum impurities during the recovery of ferrophosphate slag, thereby facilitating the subsequent acquisition of high-purity battery-grade iron phosphate.
[0016] The following are preferred technical solutions of this application, but are not intended to limit the technical solutions provided in this application. The technical objectives and beneficial effects of this application can be better achieved through the following technical solutions.
[0017] As a preferred technical solution of this application, the phosphorus iron slag includes phosphorus iron slag after lithium extraction from waste lithium iron phosphate battery materials.
[0018] Preferably, the iron content in the phosphorus-iron slag is ≥24%, such as 24%, 27%, 30%, 35% or 40%, etc.; the phosphorus content is ≥15%, such as 15%, 18%, 20%, 23% or 25%, etc.; the aluminum content is ≥1.5%, such as 1.5%, 1.8%, 2.1%, 2.4% or 2.5%, etc.; and the copper content is ≥0.01%, such as 0.01%, 0.05%, 0.08%, 0.11%, 0.13%, 0.15% or 0.2%, etc., but it is not limited to the listed values. Other unlisted values within the above range are also applicable.
[0019] Preferably, the phosphorus-iron slag is first slurried with water, and then concentrated acid is added for acid leaching.
[0020] Preferably, the solid-liquid mass ratio of the water-added slurry is 1:(2~5), such as 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, but it is not limited to the listed values. Other unlisted values within the above range are also applicable.
[0021] Preferably, the amount of concentrated acid used is 0.5 to 2 times the molar amount of iron in the ferrophosphate slag, such as 0.5 times, 0.7 times, 1 time, 1.2 times, 1.4 times, 1.6 times, 1.8 times or 2 times, but it is not limited to the listed values. Other unlisted values within the above range are also applicable.
[0022] Preferably, the acid leaching temperature is 50~80℃, such as 50℃, 53℃, 56℃, 59℃, 62℃, 65℃, 68℃, 71℃, 74℃, 77℃ or 80℃, and the time is 1~3h, such as 1h, 1.2h, 1.4h, 1.6h, 1.8h, 2h, 2.2h, 2.4h, 2.6h, 2.8h or 3h, but it is not limited to the listed values. Other unlisted values within the above range are also applicable.
[0023] As a preferred technical solution of this application, the elemental iron includes iron powder.
[0024] Preferably, the amount of elemental iron used is 1 to 2 times the molar amount of iron in the acid leaching solution, such as 1, 1.2, 1.4, 1.6, 1.8 or 2 times, but it is not limited to the listed values. Other unlisted values within the above range are also applicable.
[0025] In this application, the amount of elemental iron used exceeds the molar amount of iron in the acid leaching solution. On the one hand, this can reduce ferric iron to ferrous iron. On the other hand, the excess elemental iron can reduce copper. Since the copper content in the phosphate slag is relatively low, the excess elemental iron is sufficient to reduce copper. Of course, those skilled in the art can adjust the amount of elemental iron according to the actual total molar amount of iron and copper in the acid leaching solution.
[0026] Preferably, after the first copper removal reaction, the solution is filtered, and a soluble sulfide is added to the filtrate to carry out a second copper removal reaction, thereby obtaining a copper-removed acid leaching solution.
[0027] Preferably, the amount of the soluble sulfide is 1.5 to 2 times the molar amount of copper remaining in the filtrate, such as 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 unlisted values within the above range are also applicable.
[0028] Preferably, the soluble sulfide includes alkali metal sulfides and / or ammonium sulfide, wherein the alkali metal sulfide includes sodium sulfide and / or potassium sulfide.
[0029] This application preferably uses an excess of soluble sulfides, such as sodium sulfide, relative to the residual copper. On the one hand, this ensures the deep removal of copper; on the other hand, the excess sodium sulfide can further reduce trace amounts of ferric ions in the solution, further reducing the loss of iron during subsequent extraction.
[0030] As a preferred technical solution of this application, the extractant includes an ionic liquid, which contains anionic and cationic structures.
[0031] Preferably, the substances providing the cationic structure include quaternary ammonium salts and / or quaternary phosphine salts.
[0032] Preferably, the substance providing the cationic structure includes any one or a combination of at least two of methyltrioctylammonium chloride, tetrabutylammonium chloride, tetraoctylammonium chloride, or tetraheptylammonium chloride, wherein typical but non-limiting examples of the combination include the combination of methyltrioctylammonium chloride and tetrabutylammonium chloride, the combination of methyltrioctylammonium chloride and tetraoctylammonium chloride, the combination of tetrabutylammonium chloride and tetraoctylammonium chloride, the combination of methyltrioctylammonium chloride and tetraheptylammonium chloride, or the combination of tetraoctylammonium chloride and tetraheptylammonium chloride.
[0033] Preferably, the substance providing the anionic structure includes any one or a combination of at least two of di(2-ethylhexyl) phosphate, bis(2,4,4-trimethylpentyl)phosphonic acid, 2-ethyl-2,5-dimethylhexanoic acid, or sec-octylphenoxyacetic acid. Typical but non-limiting examples of such combinations include combinations of di(2-ethylhexyl) phosphate and bis(2,4,4-trimethylpentyl)phosphonic acid, combinations of di(2-ethylhexyl) phosphate and 2-ethyl-2,5-dimethylhexanoic acid, or combinations of bis(2,4,4-trimethylpentyl)phosphonic acid and sec-octylphenoxyacetic acid.
[0034] Preferably, the extraction further uses a diluent, which, together with the extractant, forms an extraction organic phase.
[0035] Preferably, the volume ratio of the extractant to the diluent is 1:(0.3~3), such as 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. Other unlisted values within the above range are also applicable.
[0036] 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. Typical but non-limiting examples of such combinations include combinations of methyl isobutyl ketone and methyl tert-butyl ether, combinations of methyl isobutyl ketone and ethyl acetate, combinations of methyl isobutyl ketone and cyclohexane, combinations of methyl isobutyl ketone and dichloromethane, combinations of methyl tert-butyl ether and ethyl acetate, combinations of methyl tert-butyl ether and cyclohexane, combinations of methyl tert-butyl ether and dichloromethane, combinations of ethyl acetate and cyclohexane, or combinations of cyclohexane and dichloromethane.
[0037] Preferably, the volume ratio of the extracting 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, but it is not limited to the listed values. Other unlisted values within the above range are also applicable.
[0038] As a preferred technical solution of this application, the method further includes dehydrating the aluminum-rich organic phase and then performing electrodeposition to obtain metallic aluminum and an aluminum-poor organic phase, wherein the aluminum-poor organic phase is reused as an extractant.
[0039] This application employs an extraction system with high electrical conductivity and high selectivity for aluminum. During the extraction process using a specific extractant, a functionalized ionic liquid composed of quaternary ammonium salts, quaternary phosphine salts, and phosphate esters and carboxylic acid anions combines with Al(III). Through the synergistic effect between the functionalized cations and anions, it exhibits stronger extraction capacity and selectivity for Al(III) than traditional extractants. Metallic aluminum is obtained by direct electrodeposition in the aluminum-rich organic phase after aluminum extraction, achieving effective separation of iron and aluminum in the acid leaching solution and high-value utilization of aluminum. Since the organic phase after electrodeposition is reused, the process of removing aluminum impurities from iron phosphate slag and electrodepositing metallic aluminum is effectively integrated, significantly reducing production costs. Simultaneously, high-value-added metallic aluminum is generated, further improving the resource recycling rate of the iron phosphate slag recovery process.
[0040] Secondly, embodiments of this application provide a method for recovering ferric phosphate from ferric phosphate slag, the method comprising:
[0041] Using the method described in the first aspect, aluminum and copper are removed from the ferrophosphorus slag to obtain a ferrophosphorus solution;
[0042] A phosphorus iron solution, an alkaline source, and an iron source and / or a phosphorus source are mixed and subjected to a precipitation reaction to obtain ferric phosphate dihydrate, which is then calcined to obtain ferric phosphate.
[0043] As a preferred technical solution of this application, the iron source and / or phosphorus source make the phosphorus-iron molar ratio in the system reach (1~1.1):1, such as 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 not limited to the listed values. Other unlisted values within the above range are also applicable.
[0044] Preferably, the alkali source includes ammonia.
[0045] Preferably, the alkali source is used to adjust the pH and 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, but it is not limited to the listed values. Other unlisted values within the above range are also applicable.
[0046] Preferably, the iron source includes any one or a combination of at least two of ferric sulfate, ferric chloride, or ferric nitrate, and typical but non-limiting examples of such combinations include combinations of ferric sulfate and ferric chloride, ferric sulfate and ferric nitrate, or ferric chloride and ferric nitrate.
[0047] Preferably, the phosphorus source includes any one or a combination of at least two of ammonium dihydrogen phosphate, sodium phosphate, ammonium phosphate, or monohydrogen phosphate. Typical but non-limiting examples of such combinations include combinations of ammonium dihydrogen phosphate and sodium phosphate, combinations of ammonium dihydrogen phosphate and ammonium phosphate, combinations of ammonium dihydrogen phosphate and monohydrogen phosphate, combinations of sodium phosphate and ammonium phosphate, combinations of ammonium phosphate and monohydrogen phosphate, or combinations of ammonium phosphate and monohydrogen phosphate.
[0048] As a preferred technical solution of this application, the preparation method further uses hydrogen peroxide for the mixing.
[0049] Preferably, the amount of hydrogen peroxide used is 1 to 1.5 times the molar amount of iron in the system, such as 1, 1.1, 1.2, 1.3, 1.4 or 1.5 times, but it is not limited to the listed values. Other unlisted values within the above range are also applicable.
[0050] Preferably, the temperature of the precipitation reaction is 60~90℃, such as 60℃, 65℃, 70℃, 75℃, 80℃, 85℃ or 90℃, and the time is 1~2h, such as 1h, 1.2h, 1.4h, 1.6h, 1.8h or 2h, but it is not limited to the listed values. Other unlisted values within the above range are also applicable.
[0051] Preferably, the roasting temperature is 450~650℃, such as 450℃, 470℃, 490℃, 510℃, 530℃, 550℃, 570℃, 590℃, 610℃, 630℃ or 650℃, and the time is 3~6h, such as 3h, 3.5h, 4h, 4.5h, 5h, 5.5h or 6h, but it is not limited to the listed values. Other unlisted values within the above range are also applicable.
[0052] Thirdly, embodiments of this application provide an iron phosphate, obtained according to the preparation method described in the second aspect.
[0053] Fourthly, embodiments of this application provide a lithium iron phosphate cathode material, prepared using the iron phosphate described in the third aspect.
[0054] Compared with related technical solutions, the embodiments of this application have at least the following beneficial effects:
[0055] In this embodiment, the phosphorus-iron slag is acid-leached to fully dissolve the valuable metal elements phosphorus, iron, copper, and aluminum in the slag. The resulting leachate is first treated with iron powder to remove copper, and then with soluble sulfides for further copper removal. Simultaneously, the iron powder can reduce ferric iron to ferrous iron. At this time, the soluble sulfides do not affect the iron and prevent it from precipitating. The ferrous iron converted in the system can avoid the simultaneous extraction of ferric iron during the subsequent aluminum extraction process, thus avoiding the loss of iron elements. Subsequently, this application uses an extraction system with high selectivity for aluminum to extract aluminum, which can deeply remove aluminum impurities from the leachate. The entire process of the method has a high utilization rate of phosphorus and iron in the phosphorus-iron slag, and the phosphorus and iron recovery rate can be greater than 99%. At the same time, it solves the problem of poor separation effect of metallic aluminum impurities in the phosphorus-iron slag recovery process, thereby facilitating the subsequent obtaining of high-purity battery-grade iron phosphate.
[0056] This application employs an extraction system with high electrical conductivity and high selectivity for aluminum for aluminum extraction. Metallic aluminum can then be obtained directly by electrodeposition in the aluminum-rich organic phase following aluminum extraction, thereby achieving effective separation of iron and aluminum in the acid leaching solution and high-value utilization of aluminum. Since the organic phase after electrodeposition is reused, the process of removing aluminum impurities from the phosphate slag and electrodepositing metallic aluminum is effectively integrated, significantly reducing production costs. Simultaneously, it generates high-value-added metallic aluminum, further improving the resource recycling rate of the phosphate slag recovery process.
[0057] After reading and understanding the detailed description, other aspects can be understood. Detailed Implementation
[0058] The technical solution of this application will be further described below through specific implementation methods.
[0059] Those skilled in the art should understand that the embodiments described are merely illustrative of this application and should not be construed as specific limitations on this application.
[0060] Example 1
[0061] This embodiment provides a method for removing aluminum and copper from ferrophosphate slag and preparing ferrophosphate, the method comprising the following steps:
[0062] (1) Take the phosphorus iron slag after lithium extraction from waste lithium iron phosphate, in which the mass content of phosphorus is 21.05%, iron is 36.97%, aluminum is 1.8% and copper is 0.01%. Add water to make a slurry according to the solid-liquid mass ratio of 1:3. Then add concentrated sulfuric acid with a molar amount equal to 1 molar amount of iron in the phosphorus iron slag. After leaching at 70℃ for 2 hours, filter to obtain acid leaching solution.
[0063] (2) Add iron powder with a molar amount of iron in the solution to the acid leaching solution obtained in step (1) to remove copper. After reacting for 1.5 hours, filter the solution. Add sodium sulfide with a theoretical amount of residual copper ions in the solution with a molar amount of iron in the solution to the filtrate and react for 0.5 hours to remove copper deeply, and obtain copper-removed acid leaching solution.
[0064] (3) Using the ionic liquid formed by methyltrioctylammonium chloride and di(2-ethylhexyl) phosphate as the extractant and methyl isobutyl ketone as the diluent, the two are mixed at a volume ratio of 1:1 to obtain the extractable organic phase. The extractable organic phase and the acid leaching solution obtained in step (2) are thoroughly mixed and aluminum is extracted under the condition of R(O / A) = 2:1 to obtain the phosphorus iron solution and the aluminum-rich organic phase, thus completing the removal of aluminum and copper.
[0065] (4) After adding a molecular desiccant to the aluminum-rich organic phase after extraction to remove water, an anhydrous aluminum-rich organic phase is obtained. Using a silver sheet as the working electrode and a carbon electrode as the reference electrode and counter electrode, electrodeposition is performed at an electrode potential of -3V to obtain metallic aluminum and aluminum-poor organic phase. The aluminum-poor organic phase is returned to step (3) as the extraction organic phase and is used for aluminum extraction to achieve the recycling of organic phase.
[0066] (5) Add ferric sulfate and ammonium dihydrogen phosphate to the ferric phosphorus solution obtained in step (3) to adjust the molar ratio of ferric phosphorus to 1.05:1, add hydrogen peroxide with a molar amount of 1.3 times that of iron, and then add ammonia to adjust the pH to 2. After the reaction is completed, the solid and liquid are separated to obtain ferric phosphorus dihydrate precipitate, which is placed in a muffle furnace and calcined at 500°C for 4 hours to obtain high-purity ferric phosphorus.
[0067] Example 2
[0068] This embodiment provides a method for removing aluminum and copper from ferrophosphate slag and preparing ferrophosphate, the method comprising the following steps:
[0069] (1) Take the phosphorus iron slag after lithium extraction from waste lithium iron phosphate, in which the mass content of phosphorus is 21.15%, iron is 37.21%, aluminum is 1.8% and copper is 0.01%. Add water to make a slurry according to the solid-liquid mass ratio of 1:5. Then add concentrated sulfuric acid with a molar amount twice that of iron in the phosphorus iron slag. After leaching at 80℃ for 1 hour, filter to obtain acid leaching solution.
[0070] (2) Add iron powder twice the molar amount of iron in the solution to the acid leaching solution obtained in step (1) to remove copper. After reacting for 1.5 hours, filter the solution. Add sodium sulfide twice the theoretical amount of residual copper ions in the solution to the filtrate and react for 0.5 hours to remove copper deeply, and obtain copper-removed acid leaching solution.
[0071] (3) Using the ionic liquid formed by tetrabutylammonium chloride and 2-ethyl-2,5-dimethylhexanoic acid as the extractant and ethyl acetate as the diluent, the two are mixed at a volume ratio of 2:3 to obtain the extractable organic phase. The extractable organic phase and the acid leaching solution obtained in step (2) are thoroughly mixed and aluminum is extracted at a ratio of R(O / A) = 2:1 to obtain the phosphorus iron solution and the aluminum-rich organic phase, thus completing the removal of aluminum and copper.
[0072] (4) After adding a molecular desiccant to the aluminum-rich organic phase after extraction to remove water, an anhydrous aluminum-rich organic phase is obtained. Using a silver sheet as the working electrode and a carbon electrode as the reference and counter electrode, electrodeposition is performed at an electrode potential of -4V to obtain metallic aluminum and aluminum-poor organic phase. The aluminum-poor organic phase is returned to step (3) as the extraction organic phase and is used for aluminum extraction to achieve the recycling of organic phase.
[0073] (5) Add ferric sulfate and ammonium dihydrogen phosphate to the ferric phosphorus solution obtained in step (3) to adjust the molar ratio of ferric phosphorus to 1.1:1, add hydrogen peroxide with a molar amount of 1.5 times that of iron, and then add ammonia to adjust the pH to 2.2. After the reaction is completed, the solid and liquid are separated to obtain ferric phosphorus dihydrate precipitate, which is placed in a muffle furnace and calcined at 650°C for 3 hours to obtain high-purity ferric phosphorus.
[0074] Example 3
[0075] This embodiment provides a method for removing aluminum and copper from ferrophosphate slag and preparing ferrophosphate, the method comprising the following steps:
[0076] (1) Take the phosphorus iron slag after lithium extraction from waste lithium iron phosphate, in which the mass content of phosphorus is 21.15%, iron is 37.21%, aluminum is 1.8% and copper is 0.01%. Add water to make a slurry according to the solid-liquid mass ratio of 1:2, and then add concentrated sulfuric acid with a molar amount of 0.5 times that of iron in the phosphorus iron slag. After leaching at 50℃ for 3 hours, filter to obtain acid leaching solution.
[0077] (2) Add iron powder equal to 1 molar amount of iron in the solution to the acid leaching solution obtained in step (1) to remove copper. After reacting for 1.5 hours, filter the solution. Add sodium sulfide equal to 1.5 times the theoretical amount of residual copper ions in the solution to the filtrate and react for 0.5 hours to remove copper deeply, and obtain copper-removed acid leaching solution.
[0078] (3) Using the ionic liquid formed by tetraoctylammonium chloride and sec-octylphenoxyacetic acid as the extractant and ethyl acetate as the diluent, the two are mixed at a volume ratio of 3:2 to obtain the extractable organic phase. The extractable organic phase and the acid leaching solution obtained in step (2) are thoroughly mixed and aluminum is extracted at a ratio of R(O / A) = 3:1 to obtain a phosphorus iron solution and an aluminum-rich organic phase, thus completing the removal of aluminum and copper.
[0079] (4) After adding a molecular desiccant to the aluminum-rich organic phase after extraction to remove water, an anhydrous aluminum-rich organic phase is obtained. Using a silver sheet as the working electrode and a carbon electrode as the reference electrode and counter electrode, electrodeposition is performed at an electrode potential of -2V to obtain metallic aluminum and aluminum-poor organic phase. The aluminum-poor organic phase is returned to step (3) as the extraction organic phase and is used for aluminum extraction to achieve the recycling of organic phase.
[0080] (5) Add ferric sulfate and ammonium dihydrogen phosphate to the ferric phosphorus solution obtained in step (3) to adjust the molar ratio of ferric phosphorus to 1:1, add hydrogen peroxide with a molar amount equal to the molar amount of iron, and then add ammonia to adjust the pH to 1.8. After the reaction is completed, the solid and liquid are separated to obtain ferric phosphorus dihydrate precipitate, which is placed in a muffle furnace and calcined at 450°C for 6 hours to obtain high-purity ferric phosphorus.
[0081] Example 4
[0082] This embodiment provides a method for removing aluminum and copper from ferrophosphate slag and preparing ferric phosphate. In step (2), the amount of sodium sulfide is adjusted from 1.8 times to 1.2 times the theoretical amount of residual copper ions in the solution. Otherwise, the other conditions are exactly the same as in Example 1.
[0083] Example 5
[0084] This embodiment provides a method for removing aluminum and copper from ferrophosphate slag and preparing ferric phosphate. In step (2), the amount of sodium sulfide is adjusted from 1.8 times to 1.5 times the theoretical amount of residual copper ions in the solution. Otherwise, the other conditions are exactly the same as in Example 1.
[0085] Example 6
[0086] This embodiment provides a method for removing aluminum and copper from ferrophosphate slag and preparing ferric phosphate. In step (2), the amount of sodium sulfide is adjusted from 1.8 times to 2 times the theoretical amount of residual copper ions in the solution. Apart from this, the other conditions are exactly the same as in Example 1.
[0087] Example 7
[0088] This embodiment provides a method for removing aluminum and copper from ferrophosphate slag and preparing ferric phosphate. In step (2), the amount of sodium sulfide is adjusted from 1.8 times to 2.3 times the theoretical amount of residual copper ions in the solution. Otherwise, the other conditions are exactly the same as in Example 1.
[0089] Example 8
[0090] This embodiment provides a method for removing aluminum and copper from ferrophosphate slag and preparing ferric phosphate. The method uses only di(2-ethylhexyl) phosphate as the extractant and does not use methyltrioctylammonium chloride. Except for the above, the other conditions are exactly the same as in Example 1.
[0091] Example 9
[0092] This embodiment provides a method for removing aluminum and copper from ferrophosphate slag and preparing ferrophosphate. In step (3), the volume ratio of extractant to diluent is adjusted from 1:1 to 1:0.1. Except for the above, the other conditions are exactly the same as in Example 1.
[0093] Example 10
[0094] This embodiment provides a method for removing aluminum and copper from ferrophosphate slag and preparing ferrophosphate. In step (3), the volume ratio of extractant to diluent is adjusted from 1:1 to 1:0.3. Except for the above, the other conditions are exactly the same as in Example 1.
[0095] Example 11
[0096] This embodiment provides a method for removing aluminum and copper from ferrophosphate slag and preparing ferrophosphate. In step (3), the volume ratio of extractant to diluent is adjusted from 1:1 to 1:3. Except for the above, the other conditions are exactly the same as in Example 1.
[0097] Example 12
[0098] This embodiment provides a method for removing aluminum and copper from ferrophosphate slag and preparing ferrophosphate. In step (3), the volume ratio of extractant to diluent is adjusted from 1:1 to 1:3.3. Except for the above, the other conditions are exactly the same as in Example 1.
[0099] Comparative Example 1
[0100] This comparative example provides a method for removing aluminum and copper from ferrophosphate slag and preparing ferrophosphate. The method does not use an extractive organic phase to extract aluminum, that is, it does not perform steps (3) and (4). Instead, the copper-free acid leaching solution obtained in step (2) is directly used as the ferrophosphate solution in step (5). Except for the above, the other conditions are exactly the same as in Example 1.
[0101] Comparative Example 2
[0102] This comparative example provides a method for removing aluminum and copper from iron phosphate slag and preparing iron phosphate. The method does not use sodium sulfide. That is, step (2) is: adding iron powder with a molar amount of iron 1.5 times that in the solution to remove copper into the acid leaching solution obtained in step (1), reacting for 1.5 hours and then filtering to obtain copper-removed acid leaching solution. Except for the above, the other conditions are exactly the same as in Example 1.
[0103] The iron phosphate obtained in Examples 1-12 and Comparative Examples 1-2 were tested, and the composition index (mass content), purity, and aluminum recovery rate of iron phosphate were obtained as shown in Table 1.
[0104] Table 1
[0105]
[0106] Note: In Table 1, " / " indicates that Al recovery rate cannot be calculated or is not necessary.
[0107] As can be seen from Table 1:
[0108] If the aluminum extraction step is not performed during the impurity removal process, the resulting iron phosphate will have a high aluminum content, which will greatly reduce the purity of the iron phosphate and affect the electrochemical performance of the subsequently prepared lithium iron phosphate cathode material. Since the aluminum extraction step is not performed, the aluminum in the leachate cannot be recovered.
[0109] When sodium sulfide is not added or its content is too low, the copper impurity content in the leachate is high, and the trivalent iron present is also extracted during the subsequent aluminum extraction process, thus affecting the purity of ferric phosphate and the aluminum recovery rate is not high. Excessive sodium sulfide content can easily lead to the formation of ferrous sulfide precipitate in the solution, resulting in the introduction of impurities and reducing the purity of ferric phosphate.
[0110] The difference between Example 8 and Example 1 is that the extractant was changed. The extractant was di(2-ethylhexyl) phosphate, which does not have ionic liquid properties. Since the organic system is not conductive, aluminum electrodeposition cannot be performed and aluminum cannot be recovered.
[0111] Examples 9-12 show that selecting a suitable ratio of extractant and diluent is beneficial to improving the aluminum extraction rate, thereby reducing the aluminum content in ferric phosphate and improving the purity of ferric phosphate.
[0112] This application illustrates its detailed structural features through the above embodiments, but it is not limited to these detailed structural features, meaning that this application does not necessarily rely on them for implementation. Those skilled in the art should understand that any improvements to this application, equivalent substitutions of selected components, additions of auxiliary components, and selection of specific methods all fall within the protection and disclosure scope of this application.
[0113] The preferred embodiments of this application have been described in detail above. However, this application is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this application, various simple modifications can be made to the technical solution of this application, and these simple modifications all fall within the protection scope of this application.
[0114] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this application will not describe the various possible combinations separately.
[0115] Furthermore, various different implementations of this application can be combined in any way, as long as they do not violate the spirit of this application, they should also be regarded as the content disclosed in this application.
Claims
1. A method for removing aluminum and copper from phosphorus-iron slag, comprising the following steps: The phosphorus-iron slag is acid-leached to obtain an acid leaching solution; Iron is mixed with acid leaching solution to carry out the first copper removal reaction, and then soluble sulfides are mixed in to carry out the second copper removal reaction to obtain copper removal acid leaching solution. The extractant is mixed with a copper-removing acid leaching solution. The extractant comprises an ionic liquid containing anionic and cationic structures. Substances providing cationic structures include quaternary ammonium salts and / or quaternary phosphine salts, and substances providing anionic structures include any one or a combination of at least two of di(2-ethylhexyl) phosphate, bis(2,4,4-trimethylpentyl)phosphonic acid, 2-ethyl-2,5-dimethylhexanoic acid, or sec-octylphenoxyacetic acid; the extraction also uses a diluent, wherein the extractant and the diluent constitute the extracting organic phase at a volume ratio of 1:(0.3~1.2); 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; extraction is performed to obtain a phosphorus-iron solution and an aluminum-rich organic phase, thus completing the removal of aluminum and copper; After removing water from the aluminum-rich organic phase, electrodeposition is performed to obtain metallic aluminum and an aluminum-poor organic phase. The aluminum-poor organic phase is then reused as an extractant.
2. The method according to claim 1, wherein, The phosphorus iron slag includes phosphorus iron slag obtained after lithium extraction from waste lithium iron phosphate battery materials.
3. The method according to claim 2, wherein, The iron phosphate slag contains ≥24% iron, ≥15% phosphorus, ≥1.5% aluminum, and ≥0.01% copper by mass.
4. The method according to claim 2 or 3, wherein, The phosphorus-iron slag is first slurried with 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-added pulp is 1:(2~5).
6. The method according to claim 4, wherein, The amount of concentrated acid used is 0.5 to 2 times the molar amount of iron in the ferrophosphate slag.
7. The method according to claim 4, wherein, The acid leaching temperature is 50~80℃, and the time is 1~3h.
8. The method according to claim 1, wherein, The elemental iron includes iron powder.
9. The method according to claim 1, wherein, The amount of elemental iron used is 1 to 2 times the molar amount of iron in the acid leaching solution.
10. The method according to claim 1, wherein, After the first copper removal reaction, the solution is filtered, and a soluble sulfide is added to the filtrate to carry out a second copper removal reaction, resulting in a copper-removed acid leaching solution.
11. The method according to claim 10, wherein, The amount of the soluble sulfide used is 1.5 to 2 times the molar amount of copper element remaining in the filtrate.
12. The method according to claim 1, wherein, The soluble sulfides include alkali metal sulfides and / or ammonium sulfide.
13. The method according to claim 1, wherein, Substances providing a cationic structure include any one or a combination of at least two of methyltrioctylammonium chloride, tetrabutylammonium chloride, tetraoctylammonium chloride, or tetraheptylammonium chloride.
14. The method according to claim 1, wherein, The volume ratio of the extracted organic phase to the copper-removing acid leaching solution is (1~3):
1.
15. A method for recovering ferric phosphate from ferrophosphate slag, comprising: Using the method described in any one of claims 1-14, aluminum and copper are removed from the ferrophosphorus slag to obtain a ferrophosphorus solution; A phosphorus iron solution, an alkaline source, and an iron source and / or a phosphorus source are mixed and subjected to a precipitation reaction to obtain ferric phosphate dihydrate, which is then calcined to obtain ferric phosphate.
16. The preparation method according to claim 15, wherein, The iron source and / or phosphorus source make the phosphorus-iron molar ratio in the system reach (1~1.1):
1.
17. The preparation method according to claim 15, wherein, The alkaline source includes ammonia.
18. The preparation method according to claim 15, wherein, The alkali source is used to adjust the pH, controlling the final pH of the precipitation reaction to be 1.8~2.
2.
19. The preparation method according to claim 15, wherein, The iron source includes any one or a combination of at least two of ferric sulfate, ferric chloride, or ferric nitrate.
20. The preparation method according to claim 15, wherein, The phosphorus source includes any one or a combination of at least two of the following: ammonium dihydrogen phosphate, sodium phosphate, ammonium phosphate, or monohydrogen phosphate.
21. The preparation method according to claim 15, wherein, The preparation method also uses hydrogen peroxide for the mixing.
22. The preparation method according to claim 21, wherein, The amount of hydrogen peroxide used is 1 to 1.5 times the molar amount of iron in the system.
23. The preparation method according to claim 15, wherein, The precipitation reaction is carried out at a temperature of 60-90℃ for 1-2 hours.
24. The preparation method according to claim 15, wherein, The roasting temperature is 450~650℃ and the time is 3~6h.