Abstract
Basic oxygen furnace slag (BOFS) continues to be an enormous waste product of the steel industry with very low recycling rates and low value recycling methods. Due to the potential contained value, particularly iron oxide and calcium silicate minerals, there is interest in developing high value-added recycling methods that extract these components. The proposed method of H2 direct reduction and magnetic separation expands on previous research on BOFS valorization through the formation and extraction of metallic iron and calcium-silicate minerals. The tests to-date show that a maximum degree of reduction and metallization of 95% at temperatures ≥ 1000°C can be achieved. Kinetic modelling of reduction rate and dependency on H2 concentration and temperature is provided. The proposed single-stage magnetic separation produces a magnetic concentrate with Fe recovery and grade of 72% and 66% respectively with a 250-gauss field strength. The method also effectively separates contaminants from the magnetic concentrate such as sulphur, phosphorus, and vanadium. The non-magnetic tailings have a hydraulic dicalcium-silicate and total hydraulically active mineral content of 47% and 67% respectively and therefore has potential for use as a valuable supplementary cementitious material. An additional 600-gauss magnetic separation step can reduce the metallic iron content of the tailings from 8% to 0.6%. As compared to previous studies, the proposed method is relatively less energy and resource intensive, as it utilizes larger particle size, lower H2 concentration, and reduction time.