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.
