Selective Removal of Chromium from Carbon Steel Slag by Alkaline Roasting Followed by Water Leaching

Electric arc furnace (EAF) slag, a by-product generated during the refining of steel scrap in electric furnaces, is produced in large quantities and should be effectively used as a recycled resource. When EAF slag is considered for use as a cement raw material, the chromium compounds in EAF slag may pose environmental and regulatory concerns, necessitating effective removal strategies. In this study, the presence of chromium (Cr) compounds in carbon steel (CS) slag was investigated, and alkaline roasting followed by water leaching experiments were conducted to reduce the Cr concentration to a level suitable for use as a raw material in cement production. Cr in CS slag was mainly present in spinel phases bonded to other metals such as Fe and Mg. The Cr removal efficiency was influenced more strongly by the amount of NaOH added than by the roasting time. When the weight ratio of NaOH to CS slag 1 was roasted for 30 min, the Cr concentration in the leaching residue was reduced by more than 95%, whereas the Ca concentration showed relatively little change. Thermodynamic calculations and XRD analysis of the NaOH-roasted products indicated that the insoluble Cr in the CS slag was converted into soluble compounds. These results suggest that the application of the present process to CS slag may enable the development of applications beyond its conventional uses.