Carbothermic reduction of domestic chromites

Abstract

Maximizing minerals recovery from domestic resources and minimizing the energy requirements of mineral processing constitute two goals of the Bureau of Mines, U.S. Department of the Interior. Accordingly, the Bureau has determined that coal char is generally the preferred reductant among commercially available carbonaceous materials in laboratory scale reduction experiments in argon between 1100 and 1500°C on a domestic metallurgical grade chromite with respect to the degree of reduction and metallization. For a domestic high iron chromite, coal char is preferred between 1100 and 1300°C, whereas metallurgical coke is the reductant of choice at 1400 and 1500°C. Both domestic chromites display generally similar reduction characteristics. The degrees of reduction and metallization are proportional to the time and/or temperature used and generally the rate of reduction is greatest during the first 15 min. The high iron chromite is more easily reduced, especially at the higher temperatures. Relatively simple kinetic equations cannot adequately describe the reduction mechanism for both chromites. The reduction may be nucleation controlled, especially under conditions of interest to commercial operations. The results could be used as a guideline for prereducing domestic chromites for subsequent smelting operations.