Methods for decarbonizing lithium-extracted ferrophosphate slag and methods for preparing ferrophosphate from lithium-extracted ferrophosphate slag

Abstract

This disclosure relates to a method for decarbonizing lithium-extracted ferrophosphate slag and a method for preparing ferrophosphate from lithium-extracted ferrophosphate slag. The method for decarbonizing lithium-extracted ferrophosphate slag includes the following steps: dispersing lithium-extracted ferrophosphate slag in water to obtain a ferrophosphate slag dispersion; applying a magnetic field below the ferrophosphate slag dispersion; adding a strong oxidizing agent to the ferrophosphate slag dispersion to carry out an oxidative activation reaction; after the reaction is complete, adding an aromatic ether, a foaming agent, and an inhibitor and stirring evenly to obtain an activated dispersion; introducing a collector and air together into the activated dispersion for flotation; and separating the solid and liquid phases to obtain decarbonized ferrophosphate slag.

Description

Technical Field

[0001] This disclosure relates to the field of lithium-ion battery recycling, and in particular to a method for decarbonizing lithium-extracted ferrophosphate slag and a method for preparing ferrophosphate from lithium-extracted ferrophosphate slag. Background Technology

[0002] In recent years, the new energy vehicle industry has developed rapidly. Lithium-ion batteries, with their significant advantages such as high specific capacity, stable performance, and long service life, have become the power batteries for new energy vehicles. In particular, lithium iron phosphate batteries, due to their lower manufacturing cost and higher safety performance, are one of the mainstream lithium battery products on the market. With the increasing use of lithium iron phosphate batteries, the number of waste lithium iron phosphate batteries has also increased rapidly. If not processed and recycled in a timely manner, they will cause serious environmental pollution. Therefore, the recycling and disposal of waste lithium iron phosphate batteries is extremely important.

[0003] Currently, the recycling of spent lithium iron phosphate (LFP) batteries mainly utilizes wet processing. Lithium in the spent LFP is primarily recovered by leaching and then adding carbonates to form high-value lithium carbonate. The lithium-extraction phosphate slag, a byproduct of lithium recovery from spent LFP, is primarily treated in several ways: forming phosphate fertilizer, producing iron oxide, direct disposal, or regenerating it into iron phosphate. However, the current process of regenerating iron phosphate from the lithium-extraction phosphate slag suffers from low purity and poor applicability. Specifically, during the process of crushing and pyrolyzing spent LFP batteries to obtain the cathode mixture, a large amount of carbon remains in the roasted cathode mixture. Direct acid leaching of the lithium-extraction phosphate slag with this carbon residue results in the carbon being discharged as insoluble slag. However, the carbon not only carries away valuable elements and leaching acid from the cathode, reducing the recovery rate of valuable components Fe and P, but also consumes additional leaching materials, increasing recycling costs. Furthermore, the carbon-insoluble slag, due to the presence of metals and acid, risks being classified as hazardous waste.

[0004] The related technology CN115893355A discloses a method of preparing ferrophosphate slag into a slurry and then adding inhibitors, collectors and frothers to the flotation cell to obtain carbon in the foam layer and ferrophosphate slag at the bottom of the cell. However, the carbon content in the ferrophosphate slag obtained by the above flotation method is still relatively high, and the carbon after flotation has a high iron phosphate content. Summary of the Invention

[0005] Based on this, the purpose of this disclosure is to provide a method for decarbonizing lithium-extracted ferrophosphate slag and a method for preparing ferric phosphate from lithium-extracted ferrophosphate slag. The method for decarbonizing lithium-extracted ferrophosphate slag involves setting a magnetic field below the ferrophosphate slag dispersion, causing ferric phosphate in the ferrophosphate slag to be adsorbed below the dispersion under the influence of the magnetic field. This increases the difference in floatability between ferric phosphate and carbon particles in the ferrophosphate slag, ensuring that most of the carbon particles are dispersed above the ferric phosphate, achieving initial separation of carbon particles from ferric phosphate. Next, a strong oxidizing agent is introduced to oxidize and activate the carbon particles in the ferric phosphate, forming carbon-oxygen functional groups on the surface of the carbon particles adsorbed with ferric phosphate at the bottom of the tank. These carbon-oxygen functional groups can interact with the strongly polar oxygen atoms of aromatic ethers, promoting the separation of carbon particles from the ferrophosphate slag. Then, the aromatic ether... Aromatic groups bond with the hydrophobic regions on the surface of carbon particles via π bonds, significantly improving the hydrophobicity of the carbon particles. Inhibitors adsorb onto the surface of iron phosphate, enhancing the hydrophilicity of the iron phosphate slag and further promoting the separation of carbon particles from the slag. Finally, a collector is introduced, which works synergistically with aromatic ethers, allowing it to spread efficiently on the surface of the carbon particles, further promoting the separation of carbon particles from the iron phosphate slag. Under the synergistic effect of the aforementioned magnetic field, strong oxidizing activator, aromatic ether, inhibitor, and collector, the separation rate of carbon particles in the iron phosphate slag is significantly improved, achieving deep removal of carbon impurities from the iron phosphate slag. This improves the purity of the prepared iron phosphate and solves the problem of high impurity content and poor product performance when iron phosphate slag generated during the recycling of waste lithium iron phosphate batteries is used to prepare battery-grade iron phosphate.

[0006] A method for removing carbon from phosphorus-iron slag after lithium extraction includes the following steps:

[0007] The lithium-extracted iron phosphate slag is dispersed in water to obtain an iron phosphate slag dispersion, and a magnetic field is applied below the iron phosphate slag dispersion.

[0008] A strong oxidizing agent was added to the phosphorus iron slag dispersion to carry out an oxidative activation reaction. After the reaction was complete, aromatic ether, foaming agent and inhibitor were added and stirred evenly to obtain an activated dispersion.

[0009] The collector and air are introduced into the activated dispersion for flotation, and solid-liquid separation is performed to obtain carbon-removed, phosphorus- and iron-removed slag.

[0010] The method for removing carbon from lithium-extraction iron phosphate slag disclosed herein involves setting a magnetic field below the iron phosphate slag dispersion. This magnetic field causes the iron phosphate in the iron phosphate slag to be adsorbed below the dispersion, increasing the difference in floatability between iron phosphate and carbon particles in the iron phosphate slag. This ensures that most of the carbon particles are dispersed above the iron phosphate, achieving initial separation of carbon particles from iron phosphate. Next, a strong oxidizing agent is introduced to oxidize and activate the carbon particles in the iron phosphate, forming carbon-oxygen functional groups on the surface of the carbon particles adsorbed with iron phosphate at the bottom of the tank. These carbon-oxygen functional groups can interact with the strongly polar oxygen atoms of aromatic ethers, promoting the separation of carbon particles from the iron phosphate slag. Finally, the aromatic groups in the aromatic ethers bond with the hydrophobic regions on the surface of the carbon particles via π-bonds. The process significantly improves the hydrophobicity of carbon particles. Inhibitors adsorb onto the surface of iron phosphate, enhancing the hydrophilicity of the iron phosphate slag and further promoting the separation of carbon particles from the slag. Finally, a collector is introduced, which works synergistically with aromatic ethers to efficiently spread on the surface of the carbon particles, further promoting separation. Under the synergistic effect of the aforementioned magnetic field, strong oxidizing activator, aromatic ether, inhibitor, and collector, the separation rate of carbon particles in the iron phosphate slag is significantly improved, achieving deep removal of carbon impurities from the slag. This improves the purity of the prepared iron phosphate and solves the problem of high impurity content and poor product performance when iron phosphate slag generated during the recycling of waste lithium iron phosphate batteries is reprocessed into battery-grade iron phosphate.

[0011] In one embodiment, the particle size of the lithium-extracted ferrophosphorus slag is <20mm, and the solid content of the ferrophosphorus slag dispersion is 20%–40%. If the particle size of the ferrophosphorus slag is greater than 20mm, some carbon particles will be trapped inside the ferrophosphorus slag, affecting the carbon particle separation rate; if the solid content of the ferrophosphorus slag dispersion is less than 20%, the flotation efficiency is low; if the solid content of the ferrophosphorus slag dispersion is greater than 40%, the flotation separation effect is poor.

[0012] In one embodiment, the strength of the magnetic field is 10. 4 T~10 6 T. Magnetic field strength less than 10 4 T, the difference in floatability between ferrophosphate slag and carbon is small, resulting in insufficient separation of ferrophosphate slag and carbon particles during flotation, thus reducing carbon particle recovery rate; magnetic field strength greater than 10 6 T, phosphorus iron slag is prone to accumulation, which causes some carbon particles to be coated inside the accumulated phosphorus iron slag, affecting the carbon particle separation rate.

[0013] In one embodiment, the mass ratio of the strong oxidizing agent to the lithium-extracted phosphate slag is (1:0.6) to (1:0.8). The strong oxidizing agent comprises a mixed solution of dichromate and perchlorate in a mass ratio of 1:1, and the mass fraction of the mixed solution is 85%. When the mass ratio of the strong oxidizing agent to the lithium-extracted phosphate slag is less than 1:0.6, the oxidation and activation of the carbon particles are incomplete, affecting the subsequent carbon particle separation rate. When the mass ratio is greater than 1:0.8, excessive amounts of the strong oxidizing agent are used, increasing costs, with little impact on the carbon particle separation rate, resulting in low cost-effectiveness.

[0014] In one embodiment, the oxidation activation reaction is carried out by stirring at 50°C to 70°C for 0.5 h to 2.5 h.

[0015] In one embodiment, the aromatic ether is 0.01% to 0.05% of the mass of the lithium-extracted ferrophosphate slag, and the aromatic ether includes one of anisole, phenethyl ether, and phenylpropyl ether. If the mass of the aromatic ether is less than 0.01% of the mass of the lithium-extracted ferrophosphate slag, the interaction and bonding between the aromatic ether and the carbon particle surface is insufficient, affecting the separation rate of the carbon particles. If the mass of the aromatic ether is greater than 0.05% of the mass of the lithium-extracted ferrophosphate slag, excessive use of aromatic ether does not significantly improve the separation rate of carbon particles and increases costs.

[0016] In one embodiment, the mass of the foaming agent is 0.01% to 0.05% of the mass of the lithium-extracted ferrophosphate slag, and the foaming agent includes one of N-methylpyrrolidone and N,N-dimethylformamide. If the mass of the foaming agent is less than 0.01% of the mass of the lithium-extracted ferrophosphate slag, insufficient foaming results in poor carbon particle separation; if the mass of the foaming agent is greater than 0.05% of the mass of the lithium-extracted ferrophosphate slag, excessive foaming results in an overly thick foam layer, affecting the carbon particle separation rate.

[0017] In one embodiment, the mass of the inhibitor is 0.05% to 0.2% of the mass of the lithium-extracted ferrophosphate slag. The inhibitor includes one of sodium carbonate, fluorosilicic acid, sodium tripolyphosphate, sodium hexametaphosphate, and sodium tartrate. If the mass of the inhibitor is less than 0.05% of the mass of the lithium-extracted ferrophosphate slag, the inhibitor's coverage on the slag surface is insufficient, affecting the separation effect of carbon particles from the slag. If the mass of the inhibitor is greater than 0.2% of the mass of the lithium-extracted ferrophosphate slag, excessive inhibitor usage does not significantly improve the separation rate of carbon particles and increases costs.

[0018] In one embodiment, the collector comprises a first collector and a second collector. The first collector is prepared by mixing citrate ester, surfactant, and sodium hydroxide in water and reacting at 40°C to 80°C for 30 to 60 minutes. The second collector is kerosene. By mixing the water-soluble first collector and the oil-based second collector, and by adding a surfactant to the water-soluble first collector, the dispersibility and adsorption performance of the collector at room temperature are improved, thereby increasing the collector's ability to collect carbon particles.

[0019] In one embodiment, the mass of the first collector is 0.03% to 0.2% of the mass of the phosphorus iron slag in the activated dispersion, and the mass ratio of the first collector to the second collector is (1:1.7) to (1:1.5).

[0020] In one embodiment, the mass ratio of the citrate ester, the sodium hydroxide, the surfactant, and the water is (3-4):(1.1-1.3):1:(1.5-2.5).

[0021] In one embodiment, the surfactant includes one of sodium oleate, sodium stearate, sodium dodecyl sulfate, dodecylamine, and sodium dodecylbenzene sulfonate.

[0022] This disclosure also provides a method for preparing iron phosphate from lithium-extraction iron phosphate slag, comprising the following steps:

[0023] The lithium-extracted phosphorus-iron slag is decarbonized according to any of the above-described methods to obtain decarbonized phosphorus-iron slag.

[0024] The decarbonized iron slag is acid-leached, and after solid-liquid separation, an acid leaching solution is obtained. Iron powder is added to the acid leaching solution, and after solid-liquid separation, a separation solution is obtained. A cation exchange resin is added to the separation solution to obtain an iron phosphate solution.

[0025] The method for preparing ferric phosphate from lithium-extracted ferric phosphate slag involves adding iron powder to an acid leaching solution, removing copper from the solution through a displacement reaction, and then removing aluminum from the separation solution using a cation exchange resin to obtain a pure ferric phosphate solution.

[0026] In one embodiment, the acid used in the acid leaching includes one of sulfuric acid, hydrochloric acid, and phosphoric acid.

[0027] In one embodiment, the acid contains H + Fe in the decarbonized phosphorus iron slag 3+ The molar ratio is (3:1) to (4:1). H + Fe in the decarbonized phosphorus iron slag 3+The molar ratio is controlled at (3:1) to (4:1) to ensure that the ferric phosphate exists in a free form after acid leaching, which facilitates the subsequent copper removal and aluminum removal steps.

[0028] In one embodiment, the molar amount of Fe in the iron powder is equal to the molar amount of Cu in the separation solution. 2+ One to two times the molar amount of Fe in the iron powder. The molar amount of Fe in the iron powder is equal to the molar amount of Cu in the separation solution. 2+ If the molar amount is less than 1, copper removal is incomplete; the molar amount of Fe in the iron powder is equal to the molar amount of Cu in the separation solution. 2+ Adding more than twice the molar amount of iron powder has no significant effect on removing copper, increases costs, and results in low cost-effectiveness.

[0029] In one embodiment, the method further includes the following steps: adjusting the pH of the ferric phosphate solution to 1-2.5 to generate ferric phosphate precipitate, separating the solid and liquid, and then washing, drying and dehydrating to obtain anhydrous ferric phosphate product.

[0030] The beneficial effects of this disclosure are as follows:

[0031] 1. Deep removal of carbon impurities from ferrophosphate slag after lithium extraction was achieved. Specifically, a magnetic field was set below the ferrophosphate slag dispersion, causing ferric phosphate in the slag to be adsorbed below the dispersion under the influence of the magnetic field. This increased the difference in floatability between ferric phosphate and carbon particles in the ferrophosphate slag, ensuring that most of the carbon particles were dispersed above the ferric phosphate, achieving initial separation of carbon particles from ferric phosphate. Then, a strong oxidizing agent was introduced to oxidize and activate the carbon particles in the ferric phosphate, forming carbon-oxygen functional groups on the surface of the carbon particles adsorbed with ferric phosphate at the bottom of the tank. These carbon-oxygen functional groups can interact with the strongly polar oxygen atoms of the aromatic ether, promoting the separation of carbon particles from the ferrophosphate slag. Finally, the aromatic groups in the aromatic ether interact with the carbon particles... The π-bonded hydrophobic regions on the surface significantly enhance the hydrophobicity of the carbon particles. Inhibitors adsorb onto the surface of iron phosphate, increasing the hydrophilicity of the iron phosphate slag and further promoting the separation of carbon particles from the slag. Finally, a collector is introduced, which works synergistically with aromatic ethers, allowing it to spread efficiently on the surface of the carbon particles, further promoting separation. Under the synergistic effect of the aforementioned magnetic field, strong oxidizing agent, aromatic ether, inhibitor, and collector, the separation rate of carbon particles in the iron phosphate slag is significantly improved, thereby increasing the purity of the prepared iron phosphate. This solves the problem of high impurity content and poor product performance in the reprocessing of battery-grade iron phosphate from iron phosphate slag generated during the recycling of waste lithium iron phosphate batteries.

[0032] 2. The resource utilization of decarbonized phosphorus iron slag has been realized, and Cu, Al and anhydrous ferric phosphate products have been obtained from the decarbonized phosphorus iron slag. Specifically, the decarbonized phosphorus iron slag is acid-leached, and iron powder is added to the acid leaching solution. Copper in the acid leaching solution is removed by displacement reaction, and aluminum in the separation solution is removed by cation exchange resin to obtain a pure ferric phosphate solution.

[0033] 3. By limiting the particle size of the phosphate slag to greater than 20mm, some carbon particles are prevented from being encased inside the phosphate slag, thus ensuring the separation rate of carbon particles.

[0034] 4. By limiting the solid content of the phosphorus iron slag dispersion to 20% to 40%, the flotation effect of the phosphorus iron slag is guaranteed, avoiding low flotation efficiency due to a solid content of less than 20% and poor separation effect due to a solid content of more than 40%.

[0035] 5. By limiting the magnetic field strength to 10 4 T~10 6 T ensures that the magnetic field can increase the difference in floatability between the phosphorus-iron slag and carbon after lithium extraction, thus avoiding the problem of magnetic field strength being less than 10. 4 T results in a small increase in the difference in floatability between ferrophosphate slag and carbon, leading to insufficient separation of ferrophosphate slag and carbon particles during flotation and reducing carbon particle recovery rate; on the other hand, it avoids magnetic field strength greater than 10 6 T, the accumulation of phosphorus-iron slag causes some carbon particles to be encapsulated within the accumulated phosphorus-iron slag, affecting the separation rate of carbon particles.

[0036] 6. By limiting the mass ratio of strong oxidizing activator to lithium-extracted phosphorus iron slag to (1:0.6) to (1:0.8), the carbon particles are ensured to be properly oxidized and activated. If the mass ratio of strong oxidizing activator to lithium-extracted phosphorus iron slag is less than 1:0.6, the oxidation and activation of carbon particles will be incomplete, affecting the subsequent carbon particle separation rate. If the mass ratio of strong oxidizing activator to lithium-extracted phosphorus iron slag is greater than 1:0.8, the amount of strong oxidizing activator used will be excessive, increasing costs, and the effect on carbon particle separation rate will be insignificant, resulting in low cost-effectiveness.

[0037] 7. By limiting the mass of aromatic ether to 0.01% to 0.05% of the mass of the lithium-extracted ferrophosphate slag, it is ensured that the aromatic ether can fully interact and bond with the carbon particle surface, thus guaranteeing the carbon particle separation rate. If the mass of aromatic ether accounts for less than 0.01% of the mass of the lithium-extracted ferrophosphate slag, the interaction and bonding between the aromatic ether and the carbon particle surface is insufficient, affecting the carbon particle separation rate. If the mass of aromatic ether accounts for more than 0.05% of the mass of the lithium-extracted ferrophosphate slag, the amount of aromatic ether used is excessive, which does not significantly improve the carbon particle separation rate and increases costs.

[0038] 8. By limiting the mass of the frother to 0.01% to 0.05% of the mass of the lithium-extracted phosphate slag, the amount of foam during flotation is ensured to be appropriate. If the mass of the frother accounts for less than 0.01% of the mass of the lithium-extracted phosphate slag, there will be too little foam and the separation effect of carbon particles will be poor. If the mass of the frother accounts for more than 0.05% of the mass of the lithium-extracted phosphate slag, there will be too much foam and the foam layer will be too thick, which will affect the separation rate of carbon particles.

[0039] 9. By limiting the mass of the inhibitor to 0.05% to 0.2% of the mass of the lithium-extracted ferrophosphate slag, sufficient coverage of the ferrophosphate slag surface by the inhibitor is ensured. If the mass of the inhibitor accounts for less than 0.05% of the mass of the lithium-extracted ferrophosphate slag, the coverage of the ferrophosphate slag surface by the inhibitor is insufficient, affecting the separation effect of carbon particles and ferrophosphate slag. If the mass of the inhibitor accounts for more than 0.2% of the mass of the lithium-extracted ferrophosphate slag, the amount of inhibitor used is too large, and the improvement of the separation rate of carbon particles is not significant, increasing costs.

[0040] 10. By mixing a water-soluble first collector and an oil-based second collector, and adding a surfactant to the water-soluble first collector, the dispersibility and adsorption performance of the collector at room temperature are improved, thereby increasing the collector's ability to collect carbon particles.

[0041] 11. By limiting the H+ in the acid during acid leaching + Fe in decarbonized phosphorus iron slag 3+ The molar ratio is (3:1) to (4:1) to ensure that the ferric phosphate exists in a free form after acid leaching, which facilitates the subsequent copper removal and aluminum removal steps.

[0042] To better understand and implement this disclosure, it is described in detail below. Detailed Implementation

[0043] Example 1

[0044] This embodiment provides a method for decarbonizing lithium-extracted ferrophosphate slag and a method for preparing ferrophosphate from the lithium-extracted ferrophosphate slag. The carbon content of the lithium-extracted ferrophosphate slag in this embodiment is 4.55 wt%. The method for decarbonizing the lithium-extracted ferrophosphate slag in this embodiment includes the following steps:

[0045] The lithium-extracted ferrophosphate slag is crushed into granular materials with a particle size of 5 mm. These granular materials are placed in a flotation cell, and water with a solid content of 30% is added to disperse the granular materials, resulting in a ferrophosphate slag dispersion. A magnetic field with a strength of 10 is applied to the bottom of the flotation cell (i.e., below the ferrophosphate slag dispersion). 5 The magnetic field of T;

[0046] A strong oxidizing agent was added to the bottom of the flotation cell containing the aforementioned phosphorus-iron slag dispersion to carry out an oxidative activation reaction. After the reaction was complete, an aromatic ether, a frother, and an inhibitor were added and stirred evenly to obtain an activated dispersion. The mass ratio of the strong oxidizing agent to the lithium-extracted phosphorus-iron slag was 1:0.7. The strong oxidizing agent was a mixed solution of dichromate and perchlorate in a 1:1 mass ratio, with a mass fraction of 85%. The oxidative activation reaction was carried out by stirring at 60°C for 1.5 hours. The aromatic ether was 0.03% of the mass of the lithium-extracted phosphorus-iron slag, and anisole was used. The frother was 0.03% of the mass of the lithium-extracted phosphorus-iron slag, and N-methylpyrrolidone was used. The inhibitor was 0.1% of the mass of the lithium-extracted phosphorus-iron slag, and sodium carbonate was used.

[0047] The collector and air were introduced together into the activated dispersion for flotation, resulting in solid-liquid separation to obtain a floating solid carbon layer and a settling decarbonized phosphorus-iron slag. The collector included a first collector and a second collector. The mass of the first collector was 0.1% of the mass of the phosphorus-iron slag in the activated dispersion, and the mass ratio of the first collector to the second collector was 1:1.6. The first collector was prepared by mixing citrate, surfactant, and sodium hydroxide in water and reacting at 60°C for 40 minutes. The mass ratio of citrate, sodium hydroxide, surfactant, and water was 3.5:1.2:1:2, and sodium stearate was used as the surfactant. The second collector was kerosene. Testing showed that the carbon content of the decarbonized phosphorus-iron slag in this embodiment was 0.11 wt%, and the carbon separation rate was 97.6%.

[0048] The method for preparing iron phosphate from lithium-extraction iron phosphate slag described in this embodiment includes the following steps:

[0049] The lithium-extracting phosphorus-iron slag was decarbonized according to the aforementioned method to obtain decarbonized phosphorus-iron slag.

[0050] Carbon-removed iron slag with 85% phosphoric acid was acid-leached. After solid-liquid separation, an acid leaching solution was obtained. Iron powder was added to the acid leaching solution, and the mixture was stirred for 2 hours. Solid-liquid separation was then performed to obtain a separated solution, which was passed through a macroporous strongly acidic cation exchange resin at a flow rate of 1 BV / h to obtain a pure iron phosphate solution. During acid leaching, H... + Fe in decarbonized phosphorus iron slag 3+ The molar ratio is 3.5:1; when iron powder is added, the molar amount of Fe in the iron powder is equal to the molar amount of Cu in the separation solution. 2+ 1.5 times the molar amount.

[0051] The pH of the ferric phosphate solution was adjusted to 2 by adding ammonia dropwise, resulting in ferric phosphate precipitate. After solid-liquid separation, the precipitate was washed, dried, and dehydrated to obtain anhydrous ferric sulfate. Testing showed that the purity of the anhydrous ferric sulfate product in this embodiment was 99.8%, and the recovery rate of the ferric phosphate slag was 99.5%.

[0052] Example 2

[0053] This embodiment provides a method for decarbonizing lithium-extracted ferrophosphate slag and a method for preparing ferrophosphate from the lithium-extracted ferrophosphate slag. The carbon content of the lithium-extracted ferrophosphate slag in this embodiment is 4.55 wt%. The method for decarbonizing the lithium-extracted ferrophosphate slag in this embodiment includes the following steps:

[0054] The lithium-extracting ferrophosphate slag is crushed into granular materials with a particle size of 10 mm. These granular materials are placed in a flotation cell, and water with a solid content of 20% is added to disperse the granular materials, resulting in a ferrophosphate slag dispersion. A magnetic field with a strength of 10 is applied to the bottom of the flotation cell (i.e., below the ferrophosphate slag dispersion). 4 The magnetic field of T;

[0055] A strong oxidizing agent is added to the bottom of a flotation cell containing the aforementioned phosphorus-iron slag dispersion to initiate an oxidation activation reaction. After the reaction is complete, an aromatic ether, a frother, and an inhibitor are added and stirred until homogeneous to obtain an activated dispersion. The mass ratio of the strong oxidizing agent to the lithium-extracted phosphorus-iron slag is 1:0.6. The strong oxidizing agent is a mixed solution of dichromate and perchlorate in a 1:1 mass ratio, with a mass fraction of 85%. The oxidation activation reaction is carried out by stirring at 70°C for 0.5 hours. The aromatic ether is 0.01% of the mass of the lithium-extracted phosphorus-iron slag, and anisole is used. The frother is 0.01% of the mass of the lithium-extracted phosphorus-iron slag, and N-methylpyrrolidone is used. The inhibitor is 0.05% of the mass of the lithium-extracted phosphorus-iron slag, and sodium carbonate is used.

[0056] The collector and air were introduced together into the activated dispersion for flotation, resulting in solid-liquid separation to obtain a floating solid carbon layer and a settling decarbonized phosphorus-iron slag. The collector included a first collector and a second collector. The mass of the first collector was 0.03% of the mass of the phosphorus-iron slag in the activated dispersion, and the mass ratio of the first collector to the second collector was 1:1.5. The first collector was prepared by mixing citrate, surfactant, and sodium hydroxide in water and reacting at 40°C for 60 minutes. The mass ratio of citrate, sodium hydroxide, surfactant, and water was 3:1.1:1:1.5, and sodium stearate was used as the surfactant. The second collector was kerosene. Testing showed that the carbon content of the decarbonized phosphorus-iron slag in this embodiment was 0.15 wt%, and the carbon separation rate was 96.7%.

[0057] The method for preparing iron phosphate from lithium-extraction iron phosphate slag described in this embodiment includes the following steps:

[0058] The lithium-extracting phosphorus-iron slag was decarbonized according to the aforementioned method to obtain decarbonized phosphorus-iron slag.

[0059] Carbon-removed iron slag with 85% phosphoric acid was acid-leached. After solid-liquid separation, an acid leaching solution was obtained. Iron powder was added to the acid leaching solution, and the mixture was stirred for 3 hours. Solid-liquid separation was then performed to obtain a separated solution, which was passed through a macroporous strongly acidic cation exchange resin at a flow rate of 1 BV / h to obtain a pure iron phosphate solution. During acid leaching, H... + Fe in decarbonized phosphorus iron slag 3+ The molar ratio is 3:1; when iron powder is added, the molar amount of Fe in the iron powder is equal to the molar amount of Cu in the separation solution. 2+ One molar amount.

[0060] The pH of the ferric phosphate solution was adjusted to 1 by adding ammonia dropwise, resulting in ferric phosphate precipitate. After solid-liquid separation, the precipitate was washed, dried, and dehydrated to obtain anhydrous ferric sulfate. Testing showed that the purity of the anhydrous ferric sulfate product in this embodiment was 99.7%, and the recovery rate of the ferric phosphate slag was 99.5%.

[0061] Example 3

[0062] This embodiment provides a method for decarbonizing lithium-extracted ferrophosphate slag and a method for preparing ferrophosphate from the lithium-extracted ferrophosphate slag. The carbon content of the lithium-extracted ferrophosphate slag in this embodiment is 4.55 wt%. The method for decarbonizing the lithium-extracted ferrophosphate slag in this embodiment includes the following steps:

[0063] The lithium-extracting ferrophosphate slag is crushed into granular materials with a particle size of 1 mm. These granular materials are placed in a flotation cell, and water with a solid content of 40% is added to disperse the granular materials, resulting in a ferrophosphate slag dispersion. A magnetic field with a strength of 10 is applied to the bottom of the flotation cell (i.e., below the ferrophosphate slag dispersion). 6 The magnetic field of T;

[0064] A strong oxidizing agent is added to the bottom of the flotation cell containing the aforementioned phosphorus-iron slag dispersion to carry out an oxidative activation reaction. After the reaction is complete, an aromatic ether, a frother, and an inhibitor are added and stirred evenly to obtain an activated dispersion. The mass ratio of the strong oxidizing agent to the lithium-extracted phosphorus-iron slag is 1:0.8. The strong oxidizing agent is a mixed solution of dichromate and perchlorate in a 1:1 mass ratio, with a mass fraction of 85%. The oxidative activation reaction is carried out by stirring at 50°C for 2.5 hours. The aromatic ether is 0.05% of the mass of the lithium-extracted phosphorus-iron slag, and anisole is used. The frother is 0.05% of the mass of the lithium-extracted phosphorus-iron slag, and N-methylpyrrolidone is used. The inhibitor is 0.2% of the mass of the lithium-extracted phosphorus-iron slag, and sodium carbonate is used.

[0065] The collector and air were introduced together into the activated dispersion for flotation, resulting in solid-liquid separation to obtain a floating solid carbon layer and a settling decarbonized phosphorus-iron slag. The collector included a first collector and a second collector. The mass of the first collector was 0.2% of the mass of the phosphorus-iron slag in the activated dispersion, and the mass ratio of the first collector to the second collector was 1:1.7. The first collector was prepared by mixing citrate, surfactant, and sodium hydroxide in water and reacting at 80°C for 30 minutes. The mass ratio of citrate, sodium hydroxide, surfactant, and water was 4:1.3:1:2.5, and sodium stearate was used as the surfactant. The second collector was kerosene. Testing showed that the carbon content of the decarbonized phosphorus-iron slag in this embodiment was 0.16 wt%, and the carbon separation rate was 96.5%.

[0066] The method for preparing iron phosphate from lithium-extraction iron phosphate slag described in this embodiment includes the following steps:

[0067] The lithium-extracting phosphorus-iron slag was decarbonized according to the aforementioned method to obtain decarbonized phosphorus-iron slag.

[0068] Carbon-removed iron slag with 85% phosphoric acid was acid-leached. After solid-liquid separation, an acid leaching solution was obtained. Iron powder was added to the acid leaching solution, and the mixture was stirred for 1 hour. Solid-liquid separation was then performed to obtain a separated solution, which was passed through a macroporous strongly acidic cation exchange resin at a flow rate of 1 BV / h to obtain a pure iron phosphate solution. During acid leaching, H... + Fe in decarbonized phosphorus iron slag 3+ The molar ratio is 4:1; when iron powder is added, the molar amount of Fe in the iron powder is equal to the molar amount of Cu in the separation solution. 2+ Twice the molar amount.

[0069] The pH of the ferric phosphate solution was adjusted to 2.5 by adding ammonia dropwise, resulting in ferric phosphate precipitate. After solid-liquid separation, the precipitate was washed, dried, and dehydrated to obtain anhydrous ferric sulfate. Testing showed that the purity of the anhydrous ferric sulfate product in this embodiment was 99.7%, and the recovery rate of the ferric phosphate slag was 99.1%.

[0070] Comparative Example 1

[0071] This comparative example provides a method for preparing iron phosphate from lithium-extracted iron phosphate slag. Compared with Example 1, the lithium-extracted iron phosphate slag in this comparative example was not decarbonized, and the carbon content of the lithium-extracted iron phosphate slag in this comparative example is 4.55 wt%. The method for preparing iron phosphate from lithium-extracted iron phosphate slag in this comparative example includes the following steps:

[0072] The lithium-extracted ferric phosphate slag was acid-leached with 85% phosphoric acid. After solid-liquid separation, an acid leaching solution was obtained. Iron powder was added to the acid leaching solution, and the mixture was stirred for 2 hours. Solid-liquid separation was then performed to obtain a separated solution, which was passed through a macroporous strongly acidic cation exchange resin at a flow rate of 1 BV / h to obtain a pure ferric phosphate solution. During acid leaching, H... + Fe in decarbonized phosphorus iron slag 3+ The molar ratio is 3.5:1; when iron powder is added, the molar amount of Fe in the iron powder is equal to the molar amount of Cu in the separation solution. 2+ 1.5 times the molar amount.

[0073] The pH of the ferric phosphate solution was adjusted to 2 by adding ammonia dropwise, resulting in ferric phosphate precipitate. After solid-liquid separation, the precipitate was washed, dried, and dehydrated to obtain anhydrous ferric sulfate. Testing showed that the purity of the anhydrous ferric sulfate product in this comparative example was 84.2%, and the recovery rate of the ferric phosphate slag was 85.4%.

[0074] The following table shows the statistical data on carbon content, carbon content of decarbonized ferrophosphate slag, carbon separation rate, purity of anhydrous ferric sulfate, and recovery rate of ferrophosphate slag after lithium extraction in Examples 1-3 and Comparative Example 1:

[0075]

[0076] The beneficial effects of this disclosure are as follows:

[0077] 1. Deep removal of carbon impurities from ferrophosphate slag after lithium extraction was achieved. Specifically, a magnetic field was set below the ferrophosphate slag dispersion, causing ferric phosphate in the slag to be adsorbed below the dispersion under the influence of the magnetic field. This increased the difference in floatability between ferric phosphate and carbon particles in the ferrophosphate slag, ensuring that most of the carbon particles were dispersed above the ferric phosphate, achieving initial separation of carbon particles from ferric phosphate. Then, a strong oxidizing agent was introduced to oxidize and activate the carbon particles in the ferric phosphate, forming carbon-oxygen functional groups on the surface of the carbon particles adsorbed with ferric phosphate at the bottom of the tank. These carbon-oxygen functional groups can interact with the strongly polar oxygen atoms of the aromatic ether, promoting the separation of carbon particles from the ferrophosphate slag. Finally, the aromatic groups in the aromatic ether interact with the carbon particles... The π-bonded hydrophobic regions on the surface significantly enhance the hydrophobicity of the carbon particles. Inhibitors adsorb onto the surface of iron phosphate, increasing the hydrophilicity of the iron phosphate slag and further promoting the separation of carbon particles from the slag. Finally, a collector is introduced, which works synergistically with aromatic ethers, allowing it to spread efficiently on the surface of the carbon particles, further promoting separation. Under the synergistic effect of the aforementioned magnetic field, strong oxidizing agent, aromatic ether, inhibitor, and collector, the separation rate of carbon particles in the iron phosphate slag is significantly improved, thereby increasing the purity of the prepared iron phosphate. This solves the problem of high impurity content and poor product performance in the reprocessing of battery-grade iron phosphate from iron phosphate slag generated during the recycling of waste lithium iron phosphate batteries.

[0078] 2. The resource utilization of decarbonized phosphorus iron slag has been realized, and Cu, Al and anhydrous ferric phosphate products have been obtained from the decarbonized phosphorus iron slag. Specifically, the decarbonized phosphorus iron slag is acid-leached, and iron powder is added to the acid leaching solution. Copper in the acid leaching solution is removed by displacement reaction, and aluminum in the separation solution is removed by cation exchange resin to obtain a pure ferric phosphate solution.

[0079] 3. By limiting the particle size of the phosphate slag to greater than 20mm, some carbon particles are prevented from being encased inside the phosphate slag, thus ensuring the separation rate of carbon particles.

[0080] 4. By limiting the solid content of the phosphorus iron slag dispersion to 20% to 40%, the flotation effect of the phosphorus iron slag is guaranteed, avoiding low flotation efficiency due to a solid content of less than 20% and poor separation effect due to a solid content of more than 40%.

[0081] 5. By limiting the magnetic field strength to 10 4 T~10 6 T ensures that the magnetic field can increase the difference in floatability between the phosphorus-iron slag and carbon after lithium extraction, thus avoiding the problem of magnetic field strength being less than 10. 4 T results in a small increase in the difference in floatability between ferrophosphate slag and carbon, leading to insufficient separation of ferrophosphate slag and carbon particles during flotation and reducing carbon particle recovery rate; on the other hand, it avoids magnetic field strength greater than 10 6T, the accumulation of phosphorus-iron slag causes some carbon particles to be encapsulated within the accumulated phosphorus-iron slag, affecting the separation rate of carbon particles.

[0082] 6. By limiting the mass ratio of strong oxidizing activator to lithium-extracted phosphorus iron slag to (1:0.6) to (1:0.8), the carbon particles are ensured to be properly oxidized and activated. If the mass ratio of strong oxidizing activator to lithium-extracted phosphorus iron slag is less than 1:0.6, the oxidation and activation of carbon particles will be incomplete, affecting the subsequent carbon particle separation rate. If the mass ratio of strong oxidizing activator to lithium-extracted phosphorus iron slag is greater than 1:0.8, the amount of strong oxidizing activator used will be excessive, increasing costs, and the effect on carbon particle separation rate will be insignificant, resulting in low cost-effectiveness.

[0083] 7. By limiting the mass of aromatic ether to 0.01% to 0.05% of the mass of the lithium-extracted ferrophosphate slag, it is ensured that the aromatic ether can fully interact and bond with the carbon particle surface, thus guaranteeing the carbon particle separation rate. If the mass of aromatic ether accounts for less than 0.01% of the mass of the lithium-extracted ferrophosphate slag, the interaction and bonding between the aromatic ether and the carbon particle surface is insufficient, affecting the carbon particle separation rate. If the mass of aromatic ether accounts for more than 0.05% of the mass of the lithium-extracted ferrophosphate slag, the amount of aromatic ether used is excessive, which does not significantly improve the carbon particle separation rate and increases costs.

[0084] 8. By limiting the mass of the frother to 0.01% to 0.05% of the mass of the lithium-extracted phosphate slag, the amount of foam during flotation is ensured to be appropriate. If the mass of the frother accounts for less than 0.01% of the mass of the lithium-extracted phosphate slag, there will be too little foam and the separation effect of carbon particles will be poor. If the mass of the frother accounts for more than 0.05% of the mass of the lithium-extracted phosphate slag, there will be too much foam and the foam layer will be too thick, which will affect the separation rate of carbon particles.

[0085] 9. By limiting the mass of the inhibitor to 0.05% to 0.2% of the mass of the lithium-extracted ferrophosphate slag, sufficient coverage of the ferrophosphate slag surface by the inhibitor is ensured. If the mass of the inhibitor accounts for less than 0.05% of the mass of the lithium-extracted ferrophosphate slag, the coverage of the ferrophosphate slag surface by the inhibitor is insufficient, affecting the separation effect of carbon particles and ferrophosphate slag. If the mass of the inhibitor accounts for more than 0.2% of the mass of the lithium-extracted ferrophosphate slag, the amount of inhibitor used is too large, and the improvement of the separation rate of carbon particles is not significant, increasing costs.

[0086] 10. By mixing a water-soluble first collector and an oil-based second collector, and adding a surfactant to the water-soluble first collector, the dispersibility and adsorption performance of the collector at room temperature are improved, thereby increasing the collector's ability to collect carbon particles.

[0087] 11. By limiting the H+ in the acid during acid leaching + Fe in decarbonized phosphorus iron slag 3+The molar ratio is (3:1) to (4:1) to ensure that the ferric phosphate exists in a free form after acid leaching, which facilitates the subsequent copper removal and aluminum removal steps.

[0088] The embodiments described above are merely examples of several implementations of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this disclosure, and this disclosure also intends to include these modifications and variations.

Claims

1. A method for removing carbon from phosphorus-iron slag after lithium extraction, characterized in that, Includes the following steps: The lithium-extracted iron phosphate slag is dispersed in water to obtain an iron phosphate slag dispersion, and a magnetic field is applied below the iron phosphate slag dispersion. A strong oxidizing agent is added to the phosphorus iron slag dispersion to carry out an oxidative activation reaction. After the reaction is complete, an aromatic ether, a foaming agent, and an inhibitor are added and stirred evenly to obtain an activated dispersion. The aromatic ether includes one of anisole, phenethyl ether, and phenylpropyl ether. The collector and air are introduced into the activated dispersion for flotation, and solid-liquid separation is performed to obtain carbon-removed, phosphorus- and iron-removed slag.

2. The method for decarbonizing phosphorus-iron slag after lithium extraction according to claim 1, characterized in that, The particle size of the lithium-extracted phosphorus iron slag is <20mm, and the solid content of the phosphorus iron slag dispersion is 20%~40%.

3. The method for decarbonizing phosphorus-iron slag after lithium extraction according to claim 1, characterized in that, The strength of the magnetic field is 10. 4 T~10 6 T.

4. The method for decarbonizing phosphorus-iron slag after lithium extraction according to claim 1, characterized in that, The mass ratio of the strong oxidizing agent to the lithium-extracted phosphorus iron slag is (1:0.6) to (1:0.8). The strong oxidizing agent comprises a mixed solution of dichromate and perchlorate in a mass ratio of 1:1, and the mass fraction of the mixed solution is 85%.

5. The method for decarbonizing phosphorus-iron slag after lithium extraction according to claim 1, characterized in that, The method for carrying out the oxidation activation reaction is as follows: stirring at 50℃~70℃ for 0.5h~2.5h.

6. The method for decarbonizing phosphorus-iron slag after lithium extraction according to claim 1, characterized in that, The mass of the aromatic ether is 0.01% to 0.05% of the mass of the lithium-extracted ferrophosphate slag.

7. The method for decarbonizing phosphorus-iron slag after lithium extraction according to claim 1, characterized in that, The foaming agent is 0.01% to 0.05% of the mass of the lithium-extracted phosphorus-iron slag, and the foaming agent includes one of N-methylpyrrolidone and N,N-dimethylformamide.

8. The method for decarbonizing phosphorus-iron slag after lithium extraction according to claim 1, characterized in that, The mass of the inhibitor is 0.05% to 0.2% of the mass of the lithium-extracted ferrophosphate slag, and the inhibitor includes one of sodium carbonate, fluorosilicic acid, sodium tripolyphosphate, sodium hexametaphosphate, and sodium tartrate.

9. The method for decarbonizing phosphorus-iron slag after lithium extraction according to claim 1, characterized in that, The collector includes a first collector and a second collector. The first collector is prepared by mixing citrate, surfactant and sodium hydroxide in water and reacting at 40°C to 80°C for 30 to 60 minutes. The second collector is kerosene.

10. The method for decarbonizing phosphorus-iron slag after lithium extraction according to claim 9, characterized in that, The mass of the first collector is 0.03% to 0.2% of the mass of the phosphorus iron slag in the activated dispersion, and the mass ratio of the first collector to the second collector is (1:1.7) to (1:1.5).

11. The method for decarbonizing phosphorus-iron slag after lithium extraction according to claim 9, characterized in that, The mass ratio of the citrate, the sodium hydroxide, the surfactant, and the water is (3~4):(1.1~1.3):1:(1.5~2.5).

12. The method for decarbonizing phosphorus-iron slag after lithium extraction according to claim 9, characterized in that, The surfactant includes one of sodium oleate, sodium stearate, sodium dodecyl sulfate, dodecylamine, and sodium dodecylbenzene sulfonate.

13. A method for preparing ferric phosphate from lithium-extraction ferric phosphate slag, characterized in that, Includes the following steps: The lithium-extracting phosphorus-iron slag is decarbonized according to any one of claims 1 to 12 to obtain decarbonized phosphorus-iron slag. The decarbonized iron slag is acid-leached, and after solid-liquid separation, an acid leaching solution is obtained. Iron powder is added to the acid leaching solution, and after solid-liquid separation, a separation solution is obtained. A cation exchange resin is added to the separation solution to obtain an iron phosphate solution.

14. The method for preparing ferric phosphate from lithium-extraction ferric phosphate slag according to claim 13, characterized in that, When performing the acid leaching, the acid includes one of sulfuric acid, hydrochloric acid, and phosphoric acid.

15. The method for preparing ferric phosphate from lithium-extraction ferric phosphate slag according to claim 13, characterized in that, The acid contains H + Fe in the decarbonized phosphorus iron slag 3+ The molar ratio is (3:1) ~ (4:1).

16. The method for preparing ferric phosphate from lithium-extraction ferric phosphate slag according to claim 13, characterized in that, The molar amount of Fe in the iron powder is equal to the molar amount of Cu in the separation solution. 2+ One to two times the molar amount.

17. The method for preparing ferric phosphate from lithium-extraction ferric phosphate slag according to claim 13, characterized in that, It also includes the following steps: The pH of the ferric phosphate solution is adjusted to 1-2.5 to generate ferric phosphate precipitate. After solid-liquid separation, the precipitate is washed, dried, and dehydrated to obtain anhydrous ferric phosphate product.

Images