The role of metallic iron in low temperature carbothermic reduction of MnO : phase chemistry and thermodynamic analysis

Abstract

Manganese ore reduction is quite complex at intermediate reaction temperatures of 1100–1400 C due to the formation of liquid oxide and/or alloy phases in varying phase proportions and distributions. Evidence in the literature shows that MnO reduction rates are higher for manganese ores of higher iron mineral content. This is due to a lowering of the manganese activity in the presence of iron and carbon in the alloy. Consequently, the minimum required temperature for carbothermic reduction of MnO is lowered. The simplification of the complex ore reduction system is achieved by reacting pure MnO with carbon instead of using gangue-containing ore. The effect of variation in the %C in the alloy product has not been well quantified in previous works. Here the complete alloy phase analyses are used to clarify the role of metallic iron added to MnO-Fe-C compressed pellets reacted at 1100 and 1200 C. The phase chemistry analyses show that the alloy compositions follow a polynomial curve in %Mn vs. %C plots, with alloy phase compositions formed internal to the MnO particles containing lower %Mn (<50%) and lower %C (<6%) vs. alloy phase compositions formed external to the MnO particles at 60–71% Mn and 6–10% C. Most of the Mn-Fe-C alloy areas internal to the MnO particles are liquid at 1200 C. Thermodynamic analysis shows that the low-temperature reduction (1200 C) of MnO in the presence of metallic iron is possibly due to lowered Mn activity in the product alloy Mn-Fe-C alloy and reduction via CO.