Method for preparing battery-grade iron phosphate by high-silicon high-calcium phosphorus iron slag step-by-step impurity removal

Abstract

The application discloses a method for preparing battery-grade iron phosphate from high-silicon and high-calcium phosphorus-iron slag through step-by-step impurity removal. The method comprises the following steps: S0, crushing the phosphorus-iron slag and then leaching the phosphorus-iron slag at room temperature with dilute acid; S1, mixing the material after the dilute acid pre-leaching with alkali liquor, and then performing solid-liquid separation and washing to obtain pre-silicon-removal material; S2, sorting by magnetic difference to obtain high-grade magnetic separation concentrate; S3, mixing the concentrate with phosphoric acid for leaching, adjusting the pH to remove aluminum and titanium impurities, adjusting the pH again to precipitate iron phosphate dihydrate; and S4, washing, drying and calcining the precipitate to obtain anhydrous battery-grade iron phosphate product. The method reduces the processing load of high-calcium raw materials through dilute acid pre-leaching, reduces the influence of siliceous impurities through alkaline pre-leaching, enriches iron and phosphorus components through wet-type weak magnetic separation, and effectively solves the problems of high-silicon and high-calcium phosphorus-iron slag, such as high difficulty in acid leaching treatment and difficulty in filtering silica gel, so that the prepared iron phosphate product has high purity and meets the battery-grade standard.

Description

Technical Field

[0001] This invention relates to the fields of chemical metallurgy and secondary resource utilization, specifically to a method for preparing battery-grade iron phosphate from high-silicon, high-calcium, phosphorus-iron slag through a cascaded impurity removal process. Background Technology

[0002] Iron phosphate slag is a solid byproduct produced during the production of yellow phosphorus or phosphate chemical processes, primarily composed of iron and phosphorus. The iron content is typically 40%–60%, the phosphorus content 15%–25%, and it also contains gangue impurities such as silicon (SiO2) 5%–15% and calcium (CaO) 3%–12%. High-silicon, high-calcium iron phosphate slag presents several problems when directly acid-leached due to its high impurity content and complex impurity morphologies (silicon exists as quartz or silicates, and calcium as calcium phosphate or calcium fluorophosphate): silicon forms silicate colloids under acidic conditions, leading to filtration difficulties and reduced iron-phosphorus yield; calcium recombines with phosphate ions during acid leaching to form calcium phosphate precipitate, interfering with the purity of the iron phosphate product; single-stage leaching struggles to achieve sufficient removal depth for all impurities, and the iron-phosphorus molar ratio of the product is difficult to control to battery-grade requirements (Fe / P≈0.96–1.0).

[0003] The prior art CN117401658A discloses a purification method for phosphorus iron slag after lithium extraction from waste lithium iron phosphate, which uses a mixture of reducing agent, acid and water to react and then perform solid-liquid separation. However, this method is aimed at phosphorus iron slag from lithium battery recycling systems, which has a different impurity profile, and does not consider the cascade treatment path of high silicon and high calcium systems.

[0004] Therefore, in order to address the problems of difficult silica gel filtration, interference from calcium impurities, and difficulty in controlling the iron-phosphorus ratio during the direct acid leaching process of high-silicon, high-calcium, and high-phosphorus iron slag, there is a need for a step-by-step treatment method that can pre-treat high-calcium raw materials, control siliceous impurities through alkaline pre-leaching, and prepare battery-grade iron phosphate through subsequent enrichment and phosphoric acid leaching purification. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for preparing battery-grade iron phosphate by cascaded impurity removal from high-silicon, high-calcium, phosphorus-iron slag.

[0006] Includes the following steps: S0 dilute acid pre-leaching: Crush the high-silicon, high-calcium, phosphorus-iron slag to a particle size ≤150μm, and leach it for 30 minutes at room temperature using an inorganic acid solution with a mass concentration of 5%~8% at a liquid-to-solid ratio of 2:1. S1 Alkaline pre-impregnation desilication: The material obtained in step S0 is mixed with an alkaline solution with a concentration of 50~150g / L at a liquid-solid ratio of 3:1~6:1. The mixture is stirred and reacted at 60~90℃ for 1~3 hours. The solid and liquid phases are separated and the solid phase is washed until it is neutral or the washing solution has a pH ≤ 9 to obtain the pre-desilication intermediate material. S2 Wet weak magnetic separation enrichment: The pre-desiliconized intermediate material obtained in step S1 is pulped and separated by wet weak magnetic separation. The magnetic field strength is controlled at 800~1500Gs to obtain magnetic concentrate with a total iron and phosphorus content of ≥78%. S3 Phosphoric acid leaching and two-stage pH purification: The magnetic concentrate obtained in step S2 is mixed with a phosphoric acid solution with a mass concentration of 20%~35% at a liquid-solid ratio of 2:1~4:1 and leached at 70~95℃ for 1~3 hours; after solid-liquid separation of the leaching solution, the pH is first adjusted to 1.5~2.5 to remove aluminum and titanium impurities, and then the pH is adjusted to 2.0~2.8 and aged at 80~95℃ for 2~4 hours to precipitate ferric phosphate dihydrate. S4 Post-processing: Wash and dry the precipitate obtained in step S3, and calcine it at 500~600℃ for 2~3 hours to obtain anhydrous battery-grade iron phosphate product.

[0007] Specifically, the CaO content in the high-silicon, high-calcium, phosphorus-iron slag is >8%.

[0008] Specifically, the alkaline solution in step S1 is a NaOH solution or a KOH solution.

[0009] Specifically, the pH adjuster used in step S3 is selected from ammonia, ammonium carbonate, or ammonium bicarbonate.

[0010] Specifically, the precipitate of ferric phosphate dihydrate precipitated in step S3 is separated into solid and liquid components, washed and dried, and then calcined at 500~600℃ to obtain anhydrous ferric phosphate product with a Fe / P molar ratio of 0.96~1.00.

[0011] It has the following beneficial effects: (1) The present invention sets the dilute acid pre-leaching before the alkaline pre-leaching, which is suitable for high-silicon, high-calcium, phosphorus-iron slag with high calcium content, and helps to reduce the impact of high-calcium raw materials on the subsequent alkaline pre-leaching and phosphoric acid leaching processes.

[0012] (2) The present invention limits the alkaline pre-impregnation step to pre-desilicon treatment to avoid the formation of silica colloids by silica impurities during the subsequent phosphoric acid leaching process, which would affect solid-liquid separation.

[0013] (3) In this invention, after alkaline pre-leaching, wet weak magnetic separation is used to enrich the iron and phosphorus components, so that the material entering the phosphoric acid leaching step has a higher iron and phosphorus grade, which is beneficial to reduce the influence of residual gangue impurities on phosphoric acid leaching and ferric phosphate dihydrate precipitation.

[0014] (4) The present invention adopts a combination of phosphoric acid leaching and two-stage pH purification to remove aluminum and titanium impurities first, and then age and precipitate iron phosphate dihydrate, which is beneficial to obtaining intermediate products that meet the requirements of subsequent battery-grade iron phosphate preparation. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0016] Figure 1 This is a flowchart of the method for preparing battery-grade iron phosphate from high-silicon, high-calcium, phosphorus-iron slag through a cascaded impurity removal process according to the present invention. Detailed Implementation

[0017] It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0018] The following detailed description of the implementation method of the present invention is in conjunction with the accompanying drawings. The description is only a partial embodiment and not all embodiments. For clarity, representations and descriptions unrelated to the present invention are omitted in the drawings and description.

[0019] To provide a clearer understanding of the technical features, objectives, and beneficial effects of this invention, the following detailed description of the technical solution is provided. Obviously, the described embodiments are only a portion of the embodiments of this invention, not all of them, and should not be construed as limiting the scope of implementation of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this invention.

[0020] Example 1 This embodiment is a specific implementation process of the method for preparing battery-grade iron phosphate from high-silicon, high-calcium, phosphorus iron slag through a cascaded impurity removal process according to the present invention.

[0021] In this embodiment, high-silicon, high-calcium, phosphorus-iron slag with a CaO content of 9.5% is taken and crushed to a particle size of ≤150μm.

[0022] In this embodiment, a 6% hydrochloric acid solution was used to leach the material at room temperature for 30 minutes with stirring, resulting in a liquid-to-solid ratio of 2:1, to obtain the material after dilute acid pre-soaking.

[0023] In this embodiment, the material pre-leached in dilute acid was added to a 100 g / L NaOH solution at a liquid-to-solid ratio of 4:1, and mechanically stirred for 2 hours at 80°C. After leaching, solid-liquid separation was performed, and the solid phase was washed with water until the pH of the washing solution was ≤9, yielding a pre-desiliconized intermediate material. The silicon-containing alkaline solution can be recycled by recovering NaOH through lime causticization.

[0024] In this embodiment, the pre-desiliconized intermediate material after washing is slurried to a mass concentration of 20% and then separated using wet weak magnetic separation with a magnetic field strength of 1200 Gs to obtain magnetic concentrate.

[0025] In this embodiment, a 30% phosphoric acid solution was added at a liquid-to-solid ratio of 3:1, and the solution was leached at 90°C for 2 hours. Iron and phosphorus dissolved to form a ferric dihydrogen phosphate / ferric phosphate solution. The filtrate was first adjusted to pH 2.0 with ammonia to remove Al and Ti precipitates. After solid-liquid separation, the pH was adjusted to 2.5, and the solution was aged at 90°C for 3 hours to precipitate FePO4·2H2O.

[0026] In this embodiment, the precipitate was washed with deionized water, dried at 110°C, and then calcined in a muffle furnace at 600°C for 3 hours to obtain anhydrous ferric phosphate product.

[0027] Example 2 This embodiment is another specific implementation process of the method for preparing battery-grade iron phosphate from high-silicon, high-calcium, phosphorus iron slag through a cascaded impurity removal process according to the present invention.

[0028] In this embodiment, 1000g of high-silicon, high-calcium, phosphorus-iron slag was taken, and the composition analysis was as follows: TFe 46.8%, P 19.8%, SiO2 8.5%, CaO 11.0%, Al2O3 2.8%, which was crushed to -100 mesh with a particle size ≤150μm.

[0029] In this embodiment, a 6% hydrochloric acid solution was used to leach the material at room temperature for 30 minutes with stirring, resulting in a liquid-to-solid ratio of 2:1, to obtain the material after dilute acid pre-soaking.

[0030] In this embodiment, a 100 g / L NaOH solution was added at a liquid-to-solid ratio of 4:1, and the mixture was mechanically stirred and leached at 80°C for 2 hours. After leaching, solid-liquid separation was performed, and the solid phase was washed with water until the pH of the washing solution was ≤9, yielding a pre-desiliconized intermediate material. The silicon-containing alkaline solution can be recycled by recovering NaOH through lime causticizing.

[0031] In this embodiment, the pre-desiliconized intermediate material after washing is slurried to a mass concentration of 20% and then separated by wet weak magnetic separation with the magnetic field strength controlled at 800~1500Gs to obtain a magnetic concentrate with a total iron and phosphorus content of ≥78%.

[0032] In this embodiment, a 30% phosphoric acid solution was added at a liquid-to-solid ratio of 3:1, and the solution was leached at 90°C for 2 hours. Iron and phosphorus dissolved to form a ferric dihydrogen phosphate / ferric phosphate solution. The filtrate was first adjusted to pH 2.0 with ammonia to remove Al and Ti precipitates. After solid-liquid separation, the pH was adjusted to 2.5, and the solution was aged at 90°C for 3 hours to precipitate FePO4·2H2O.

[0033] In this embodiment, the precipitate was washed with deionized water, dried at 110°C, and then calcined in a muffle furnace at 600°C for 3 hours. In this embodiment, the final product was a grayish-white powder with an Fe / P molar ratio of 0.97 and impurity contents of Na 32ppm, Ca 18ppm, Al 22ppm, and Si 35ppm, meeting the battery-grade iron phosphate standard.

[0034] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A method for preparing battery-grade iron phosphate from high-silicon, high-calcium, phosphorus-iron slag through a cascaded impurity removal process, characterized in that, Includes the following steps: S0 dilute acid pre-leaching: Crush the high-silicon, high-calcium, phosphorus-iron slag to a particle size ≤150μm, and leach it for 30 minutes at room temperature using an inorganic acid solution with a mass concentration of 5%~8% at a liquid-to-solid ratio of 2:

1. S1 Alkaline pre-impregnation desilication: The material obtained in step S0 is mixed with an alkaline solution with a concentration of 50~150g / L at a liquid-solid ratio of 3:1~6:

1. The mixture is stirred and reacted at 60~90℃ for 1~3 hours. The solid and liquid phases are separated and the solid phase is washed until it is neutral or the washing solution has a pH ≤ 9 to obtain the pre-desilication intermediate material. S2 Wet weak magnetic separation enrichment: The pre-desiliconized intermediate material obtained in step S1 is pulped and separated by wet weak magnetic separation. The magnetic field strength is controlled at 800~1500Gs to obtain magnetic concentrate with a total iron and phosphorus content of ≥78%. S3 Phosphoric acid leaching and two-stage pH purification: The magnetic concentrate obtained in step S2 is mixed with a phosphoric acid solution with a mass concentration of 20%~35% at a liquid-solid ratio of 2:1~4:1 and leached at 70~95℃ for 1~3 hours; after solid-liquid separation of the leachate, the pH is first adjusted to 1.5~2.5 to remove aluminum and titanium impurities, and then the pH is adjusted to 2.0~2.8 and aged at 80~95℃ for 2~4 hours to precipitate ferric phosphate dihydrate. S4 Post-processing: Wash and dry the precipitate obtained in step S3, and calcine it at 500~600℃ for 2~3 hours to obtain anhydrous battery-grade iron phosphate product.

2. The method for preparing battery-grade iron phosphate from high-silicon, high-calcium, phosphorus-iron slag through a cascaded impurity removal process according to claim 1, characterized in that: The high-silicon, high-calcium, phosphorus-iron slag contains >8% CaO.

3. The method for preparing battery-grade iron phosphate from high-silicon, high-calcium, phosphorus-iron slag through a cascaded impurity removal process according to claim 1, characterized in that: The alkaline solution in step S1 is either NaOH or KOH solution.

4. The method for preparing battery-grade iron phosphate from high-silicon, high-calcium, phosphorus-iron slag through a cascaded impurity removal process according to claim 1, characterized in that: The pH adjuster used in step S3 is selected from ammonia, ammonium carbonate, or ammonium bicarbonate.

5. The method for preparing battery-grade iron phosphate from high-silicon, high-calcium, phosphorus-iron slag through a cascaded impurity removal process according to claim 1, characterized in that: The precipitate of ferric phosphate dihydrate precipitated in step S3 is separated into solid and liquid components, washed and dried, and then calcined at 500~600℃ to obtain anhydrous ferric phosphate product with a Fe / P molar ratio of 0.96~1.00.

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