Abstract:Spent lithium iron phosphate batteries form phosphorus iron slag after selective lithium extraction. When recovering phosphorus iron from this slag, there are generally problems such as difficulty in removing aluminum and high cost of aluminum removal. This article uses a mixture of sulfuric acid and hydrated iron sulfate to pre remove aluminum from phosphorus iron slag, investigates the influence of various parameters on the aluminum removal effect, analyzes the aluminum removal mechanism, and provides a comprehensive process flow that can reduce phosphorus iron loss. The pre aluminum removal method used in the experiment is technically feasible and effective. Under the conditions of a sulfuric acid concentration of 0.3mol/L, a mass ratio of hydrated iron sulfate to phosphorus iron slag of 20%, a reaction temperature of 95℃, and a reaction time of 1 hour, the one-time aluminum removal rate can reach 91.90%; The method of using sodium hydroxide to adjust the pH value of the liquid after aluminum removal can precipitate crude iron phosphate (with high aluminum content, which is then returned to the pre aluminum removal process). This comprehensive process does not lose much iron phosphate during aluminum removal, with a one-time aluminum removal efficiency of about 84%; The mixed agent can remove impurities such as Cu and Li from the phosphorus iron slag while removing aluminum. The content of Cu and Li in the phosphorus iron slag decreased from 0.095% and 0.056% to 0.0089% and 0.0012%, respectively; After aluminum removal, some of the iron hydroxide in the phosphorus iron slag is encapsulated by crystalline iron phosphate, making it difficult to effectively adjust the iron phosphorus ratio through aging. It needs to be dissolved in acid before synthesis. The comprehensive process of aluminum removal in this experiment has low cost, good effect, simple operation, and can effectively avoid the loss of phosphorus and iron. The final impurity removal liquid (wastewater) obtained can also be reused after simple treatment, with minimal environmental impact and obvious industrial advantages.
