The Effect of Manganese Ore Iron Content on Carbothermic Reduction Rates at Low Temperatures

Abstract

Extensive studies on the carbothermic reduction of manganese ores from the Kalahari Manganese Field (KMF) in South Africa illustrated an increase in reduction rates with increased iron content in the ore (as oxides). This observation is most noticeable in stage two reduction, ranging from approximately 33% to 70% reduction at temperatures of 1200°C - 1350°C. These studies illustrated the complex mineralogy changes which occur as the ore reduction process proceeds. Manganese ore reduction is complex at intermediate reaction temperatures of 1100°C - 1400°C due to the formation of liquid oxide and/or alloy phases in varying phase proportions and distributions. The results prompt the question: how important is increased iron content in manganese ores in setting low temperature ore reduction rates, both for manganese ores of different mineralogy, and also within the same type of manganese ore? This important aspect is explored in this work by considering both literature evidence and reporting results from simplified experiments which simulate increased iron content in MnO-Fe-C mixtures. The MnO-Fe-C mixtures serve as a simplified reaction system because liquid oxide formation is excluded, allowing the work to be focused on alloy phase formation and its effect on MnO reduction. Furthermore, the results illustrate how the MnO reduction rate equation may be updated to incorporate the effect of manganese ore iron content.