Utilization of Waste Precipitated Iron Residues from Hydrometallurgy in Hydrogen-Based Ironmaking

Abstract Continued industrial electrification necessitates increased extraction of minerals and metals, resulting in substantial volumes of solid waste, such as precipitated iron residues. The scale of this waste generation can only be sufficiently valorized in equally large industries such as ironmaking. Promising processes using renewably sourced hydrogen (H 2 ) can eliminate ~ 7% of global CO 2 emissions during ironmaking for the steel industry. Using waste resources could generate a valuable alternative feedstock for the industry. Specifically, waste materials with high iron content such as precipitated iron residues (PIR), generated on the magnitude of ~ 100 Mt/y (dry Fe 2 O 3 -basis), are relevant. In this research, PIR was first synthesized and pelletized, before sintering in air and reduction with H 2 gas, simulating a vertical shaft furnace process. Blending of PIR with titanomagnetite ironsand resources from New Zealand was also performed in 2 – 20 wt% in pellets. Material characterization provided physical and chemical properties of the ironmaking materials and pellets. Results showed enhanced reduction kinetics achieved with increasing PIR content in pellets, although decreased sintered pellet compressive strength and undesirable sulphur content were also observed. A 5 wt% PIR blend in pellets was determined optimal, as it maintained pellet strength and kept sulphur levels within acceptable industrial limits. Subsequently, given the 2.6 Gt/y scale of iron ore processed at present and the ~ 100 Mt/y of PIR generated, a 5 wt% blend into conventional ores offers a viable alternative feedstock additive for ironmaking, while enhancing recycling in mineral processing. Graphical Abstract