Reduction of chromium ore by recycled silicon cutting sludge waste with carbon addition

A basic study on the feasibility of producing ferrochrome (silicon) alloys using Si sludge waste collected from the silicon ingot cutting process was carried out, and the effects of the addition of carbon components, reaction time, and reaction temperature on the silicothermic reduction of chromium ore by Si sludge were studied. The cordierite (Mg₂Al₄Si₅O₁₈) phase was generated in the slag, and the Fe–Cr(–Si)–C alloy was formed by the silicothermic reduction. Moreover, the addition of carbon powder lowered the reduction initiating temperature, and the reduction ratio based on the oxygen content was evaluated at around 68–88% at 1573 K, which increased with an increase in carbon. However, it was difficult to find a significant difference in the reduction behavior in response to increasing the holding time. The reduced ferrochrome (Fe–Cr) metal alloy droplets coalesced more intensively with an increase in reduction temperature, and for manufacturing the Fe–Cr alloy, it is estimated that a temperature of 1773 K or higher is required for good separation of the slag and the metal. Furthermore, the metallization ratio was defined, and higher values are evaluated for Fe than for Cr.