Selective Recovery of Valuable Components from Converter Steel Slag for Preparing Multidoped FePO4

A novel route for preparing multidoped FePO4, an excellent starting material for synthesis of multidoped LiFePO4 cathode materials for lithium ion batteries, by using converter steel slag as raw material is proposed in this study. The processes included selectively reclaiming Fe, Mn, Cr, and P from the slag in the form of a ferroalloy through a carbothermic process, reacting the ferroalloy with phosphoric acid and hydrogen peroxide solution to produce a precursor, and calcining the precursor to finally obtain the single-phase multidoped FePO4. Effects of the pH value of the reactive system on the constituents and structures of products are determined by XRF, XRD, and SEM analysis. The single-phase hexagonal multidoped FePO4 doped with 1.5-3.3 atom % (Mn+Cr) was obtained at pH = 3.0-4.0, where the molar ratios of (Fe+Mn+Cr) to P were tested to be close to 1. About 80 wt % Fe and Cr in the slag could be recovered and directly turned into the multidoped FePO4, and the control on recovery rate of Mn could be performed by adjusting the pH value of the precipitation system according to constituent demand of the final product. The results indicate that a feasible route for utilizing converter steel slag as substitutes for chemical reagents to prepare multidoped FePO4 has been offered.