Preparation of Doped Iron Phosphate by Acid Leaching Solution of a Low-grade Phosphate Iron Ore

Objective To address the environmental pollution caused by acid leaching of a low-grade phosphate iron ore, reduce the production cost of synthetic iron phosphate, and achieve comprehensive utilization of resources, Method doping-type iron phosphate was prepared by an acid leaching and co-precipitation method using low-grade phosphorite as the raw material and precursor of a lithium iron phosphate battery. The effects of different experimental parameters on the composition, morphology, and particle size of doped iron phosphate were systematically studied using XRD, SEM-EDS, particle size analysis, atomic absorption, and carbon sulfur analysis. ResultThe optimum acid leaching conditions were as follows: initial sulfuric acid concentration of 0.5 mol/L, acid leaching time of 30 min, stirring speed of 300 r/min, liquid-solid ratio of 4:1, and acid leaching temperature of 25 ℃. The optimum conditions for the synthesis of doped iron phosphate were a pH value of 2.0, phosphorus iron ratio of 1.5, reaction time of 240 min, and reaction temperature of 85 °C. The doped iron phosphate obtained after the calcination of the sample was evenly distributed without a large amount of agglomeration. After analyzing the SEM spectrum points, it is known that the product contains some doping elements, such as AlPO₄ in addition to FePO₄, and the particle size D50 of the sample after ball milling is 2.695 μm, which accords with the industry standard of battery-grade iron phosphate. After washing with citric acid 15 times, the sulfur content was < 0.04%. ConclusionDoped iron phosphate can be used as a precursor material for lithium iron phosphate batteries with a good electrochemical performance.