Recovery of Chromium from AOD-Converter Slags

Slags from the production of high-alloyed steel contain both chemically bound chromium (mainly as Cr(2)O(3)) in the mineral fraction and elemental chromium in the metallic remainders. Thermochemical post treatment of the slag in an electric arc furnace under reducing conditions enables the nearly complete recovery of the total amount of chromium in form of a metallic alloy. The best results were achieved by resistance melting (submerged electrodes) with addition of a reducing agent into the melt. The efficiencies of the reducing agents carbon, aluminium, silicon (as ferrosilicon) and silicon carbide were investigated and compared. As aluminium is the strongest reducing agent, it is less selective and reduces much more SiO(2) than Cr(2)O(3). While SiC shows only low reactivity because of its high thermal resistance, carbon and silicon had the highest reducing potentials: More than 97% of the chemically bound chromium can be recovered by application of these reducing agents. Due to the high temperature required for the reduction of the chromium compounds, the reduction of SiO(2) as an undesired side reaction cannot be avoided. However, compared with mechanical procedures that are limited to the recovery of the metallic remainders, the total chromium recovery can be significantly increased by the described reductive melting procedure.