FePO4 preparation and residue recycling by co-processing of steelmaking slag and steel pickling waste liquor: Comprehensive utilization of metallurgical wastes

To prepare FePO4 and to achieve resource utilization of metallurgical wastes, a collaborative treatment of P-bearing steelmaking slag and steel pickling waste liquor (SPWL) was proposed. The utilization of SPWL as a leachant for P separation from steelmaking slag facilitates P-removal residue recycling within steel plants, while also serving as a Fe source for the FePO4 preparation. In this study, the effects of synthetic SPWL with various Fe2+ (or Fe3+) contents and leaching parameters on the dissolution behavior of steelmaking slag were investigated. Moreover, the impacts of H2O2 oxidation and pH on the precipitation behavior of FePO4 from leachate were studied. It was found that increasing Fe2+ concentration in SPWL resulted in a marginal reduction in the P dissolution ratio; however, it was significantly influenced by the pH and solid/liquid ratio. Furthermore, the change in Fe3+ concentration within SPWL exhibited a conspicuous impact on the P dissolution ratio. After leaching, the residue containing massive Fe2O3, MgO, and MnO could be reused as a flux within the steelmaking process. The FePO4 precipitated predominantly at pH 2.0 similar to 3.0, and the crude FePO4 product containing 42.6 % Fe2O3 and 35.8 % P2O5 was obtained, providing a new solution for the utilization of metallurgical wastes.