Optimisation of Metal Recovery From Metallurgical Residues Through Carbothermal Reduction: Experimental and Thermodynamic investigation

The de-fossilisation of industrial processes, particularly in the steel and cement sectors, accelerates structural changes in material flows. In Austria, the transition from blast furnaces to electric arc furnace steel production will significantly affect the availability and composition of industrial by-products, which are currently used to reduce the clinker factor in the cement industry. This study addresses the valorisation of electric arc furnace slag through carbothermal reduction experiments and thermodynamic calculations. A specially designed mixture was thermochemically treated in a laboratory-scale furnace under an inert atmosphere, followed by rapid cooling. The influence of target temperature, holding time and carbon addition on phase separation, reduction behaviour and the resulting metallic fraction was analysed. Water granulation was feasible for temperatures above 1400 °C. The chemical composition of the metal fraction shows iron contents above 80 wt% and varying degrees of chromium and manganese recovery, depending on process parameters. Longer holding times and higher temperatures led to improved manganese and chromium reduction and higher metal yield. The comparability of the metal fraction analysis with the thermodynamic calculation shows very good agreement for iron and carbon; for chromium and manganese, the trends with increasing temperature are also captured.