CN-121990614-A - Method for removing magnesium and calcium impurities in titanium white byproduct ferrous sulfate

CN121990614ACN 121990614 ACN121990614 ACN 121990614ACN-121990614-A

Abstract

The invention discloses a method for removing magnesium and calcium impurities in titanium white byproduct ferrous sulfate, and belongs to the technical field of battery material precursor purification. The method comprises the steps of dissolving titanium white byproduct ferrous sulfate, removing titanium from reduced iron powder to obtain ferrous sulfate pretreatment liquid, independently preparing and deeply washing to obtain a pure ferrous hydroxide wet filter cake with sodium content lower than 100 ppm, adding a fluoride ion source into the ferrous sulfate pretreatment liquid to obtain a fluoride-containing mixed liquid, adding the wet filter cake into the fluoride-containing mixed liquid to enable magnesium and calcium ions to form fluoride precipitates, carrying out solid-liquid separation to obtain ferrous sulfate purification liquid, and finally adding acid to stabilize the pH value to obtain a high-purity ferrous sulfate solution. The invention replaces the traditional alkali liquor with pure ferrous hydroxide, effectively removes magnesium and calcium impurities in a synergistic way, simultaneously avoids the introduction of new impurities such as sodium, potassium, ammonium and the like in principle, has simple process flow, low cost and high product purity.

Inventors

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Assignees

西南科技大学
惠州学院

Dates

Publication Date: 20260508
Application Date: 20251231

Claims (10)

1. The method for removing magnesium and calcium impurities in the titanium white byproduct ferrous sulfate is characterized by comprising the following steps of: S1, preparing and preprocessing raw material liquid, namely dissolving ferrous sulfate solid containing magnesium and/or calcium impurities into pure water to prepare a first ferrous sulfate solution, adding reduced iron powder into the first ferrous sulfate solution under the protection of inert gas to perform reduction and impurity removal reaction, and carrying out solid-liquid separation after the reaction is finished to obtain a ferrous sulfate preprocessing liquid; S2, preparing pure ferrous hydroxide, namely dripping sodium hydroxide solution into a part of second ferrous sulfate solution which is independently prepared under the protection of inert gas to generate ferrous hydroxide colloid, adding a flocculating agent into the ferrous hydroxide colloid to flocculate and precipitate the ferrous hydroxide, and obtaining a pure ferrous hydroxide wet filter cake with the sodium ion content lower than 100 ppm after solid-liquid separation and washing; S3, fluoridation and impurity removal, namely adding a fluoride ion source into the ferrous sulfate pretreatment liquid obtained in the step S1 under the protection of inert gas, wherein the ratio of the molar quantity of the fluoride ions in the fluoride ion source to the total molar quantity of the magnesium ions and the calcium ions in the ferrous sulfate pretreatment liquid is (2.0-2.65): 1, so as to obtain a fluorine-containing mixed liquid; S4, precipitating and separating, namely adding the pure ferrous hydroxide wet filter cake prepared in the step S2 into the fluorine-containing mixed solution prepared in the step S3 under the protection of inert gas, stirring for reaction, adjusting the pH value of a reaction system to 5.0-6.0, and performing solid-liquid separation to obtain a ferrous sulfate purified solution with magnesium and calcium removed; S5, stabilizing the product, namely adding acid into the ferrous sulfate purified solution obtained in the step S4 until the pH value of the solution is 1.5-2.5, and obtaining a stable high-purity ferrous sulfate solution.
2. The method for removing magnesium and calcium impurities from the titanium white byproduct ferrous sulfate according to claim 1, wherein the ferrous sulfate solid containing magnesium and/or calcium impurities is byproduct ferrous sulfate generated in the titanium white production process.
3. The method for removing magnesium and calcium impurities in the byproduct ferrous sulfate of titanium white according to claim 1, wherein in S1, the mass percentage concentration of iron in the first ferrous sulfate solution is 5.0 wt% -10.0 wt%.
4. The method for removing magnesium and calcium impurities in the titanium white byproduct ferrous sulfate according to claim 1, wherein in S1, the addition amount of the reduced iron powder is 0.3-1.5 wt% of the mass of the first ferrous sulfate solution, the temperature of the reduction impurity removal reaction is 70-85 ℃ and the time is 0.5-2 hours.
5. The method for removing magnesium and calcium impurities in the titanium white byproduct ferrous sulfate according to claim 1, wherein in S2, the molar ratio of NaOH contained in a sodium hydroxide solution to FeSO 4 contained in a second ferrous sulfate solution is (1.95-2.10): 1, the concentration of the sodium hydroxide solution is 8. 8 wt% -12. 12 wt% by mass, and the concentration of the second ferrous sulfate solution is 1.2% -6. 6 wt% by mass.
6. The method for removing magnesium and calcium impurities in the byproduct ferrous sulfate of titanium white according to claim 1, wherein in the S2, the flocculant is an anionic flocculant, and the addition amount of the flocculant is 0.15wt% of the mass of the ferrous hydroxide colloid.
7. The method for removing magnesium and calcium impurities in titanium white byproduct ferrous sulfate according to claim 1, wherein in S3, the fluoride ion source is hydrofluoric acid, and in S5, the acid is concentrated sulfuric acid.
8. The method for removing magnesium and calcium impurities in the byproduct ferrous sulfate of titanium white according to claim 1, wherein in S4, the pH of a reaction system is adjusted to 5.0-6.0 by controlling the addition amount of a ferrous hydroxide wet filter cake, and the stirring reaction time is 30 minutes to 2 hours.
9. The method for removing magnesium and calcium impurities in the titanium white byproduct ferrous sulfate according to claim 1, wherein the inert gas adopted for inert gas protection is nitrogen or argon.
10. The method for removing magnesium and calcium impurities in the byproduct ferrous sulfate of titanium white according to claim 1, wherein the concentration of magnesium ions in the purified ferrous sulfate solution obtained in the step S4 is lower than 200 ppm, the concentration of calcium ions is lower than 100ppm, and the concentrations of sodium ions, potassium ions and ammonium ions are lower than 100 ppm.

Description

Method for removing magnesium and calcium impurities in titanium white byproduct ferrous sulfate Technical Field The invention relates to the technical field of hydrometallurgy and battery material precursor purification, in particular to a method for removing magnesium and calcium impurities in titanium white byproduct ferrous sulfate. Background Ferrous sulfate is a key iron source for preparing lithium ion battery anode materials such as ferric phosphate, lithium iron phosphate and the like. At present, the sources of the titanium dioxide are mainly two, namely, the titanium dioxide is prepared by the reaction of high-purity metal iron powder and sulfuric acid, the purity is high but the cost is high, and the byproduct (hereinafter referred to as a titanium white byproduct ferrous sulfate) in the production process of the titanium dioxide has the advantages of high yield and low cost and has remarkable economic advantages. However, the titanium white byproduct ferrous sulfate contains various impurity elements such as titanium, manganese, chromium, vanadium, and magnesium (usually 4000-6000 ppm) and calcium in high concentration. These impurities, especially magnesium and calcium, can severely degrade the electrochemical properties, such as capacity, cycle life and rate capability, of the final lithium iron phosphate cathode material. In some high-end preparation processes such as a hydrothermal method and the like which are extremely sensitive to the purity of raw materials, the limitation on the content of impurities such as sodium, magnesium, calcium and the like is more strict, and the application of low-cost titanium white byproduct ferrous sulfate in the field of high added value is directly limited. For removal of magnesium and calcium impurities, the prior art is mainly based on the principle of formation of fluoride precipitates. Conventional methods typically add soluble fluorides (e.g., sodium fluoride, potassium fluoride) directly to the solution or use hydrofluoric acid in combination with alkaline agents such as sodium hydroxide, ammonia, and the like. However, these methods inevitably introduce new cationic impurities such as sodium (Na +), potassium (K +) or ammonium (NH 4+). The introduction of these foreign ions makes it difficult for the purified product to meet the ultra-high purity requirements of battery grade materials, particularly hydrothermal processes, on the raw materials. Therefore, developing a purification method which can be applied to the titanium white byproduct ferrous sulfate and can remove magnesium and calcium without introducing other impurity ions has become a key technical challenge of reducing the cost of battery materials and improving the resource utilization value. Disclosure of Invention The invention aims to overcome the defects of the prior art and provide a method for removing magnesium and calcium impurities in titanium white byproduct ferrous sulfate. According to the method, pure ferrous hydroxide is generated in situ in the system to serve as a pH regulator and a coprecipitation carrier, the pure ferrous hydroxide and fluorine ions are synergistic, efficient precipitation removal of magnesium and calcium impurities is achieved, any new cationic impurities such as sodium, potassium and ammonium are not additionally introduced in the whole process, and the final product is high in purity and particularly suitable for preparing battery-level high-purity ferrous sulfate. In order to achieve the above purpose, the technical scheme adopted by the invention is as follows: A method for removing magnesium and calcium impurities in titanium white byproduct ferrous sulfate comprises the following steps: S1, preparing and preprocessing raw material liquid, namely dissolving ferrous sulfate solid containing magnesium and/or calcium impurities into pure water to prepare a first ferrous sulfate solution, adding reduced iron powder into the first ferrous sulfate solution under the protection of inert gas to perform reduction and impurity removal reaction, and carrying out solid-liquid separation after the reaction is finished to obtain a ferrous sulfate preprocessing liquid; S2, preparing pure ferrous hydroxide, namely dripping sodium hydroxide solution into a part of second ferrous sulfate solution which is independently prepared under the protection of inert gas to generate ferrous hydroxide colloid, adding a flocculating agent into the ferrous hydroxide colloid to flocculate and precipitate the ferrous hydroxide, and obtaining a pure ferrous hydroxide wet filter cake with the sodium ion content lower than 100 ppm after solid-liquid separation and washing; S3, fluoridation and impurity removal, namely adding a fluoride ion source into the ferrous sulfate pretreatment liquid obtained in the step S1 under the protection of inert gas, wherein the ratio of the molar quantity of the fluoride ions in the fluoride ion source to the total molar quantity of the magnesium ion