Manganese Ore Reduction with CO gas or CO-CO2 gas Mixture: Studies on properties and reduction of manganese ores-II

Authors studied on manganese ore reduction with CO gas or CO-CO2 gas mixture by the method of thermal balance analysis, and then discussed its reducibility with mineral composition. (1) Reducibility decreases in the next order: i. e. MnO2 ore, burnt ore of MnCO3 (manganese low oxide ores such as α-Mn2O3 or Mn3O4 etc.) and manganese silicate ore. It is plain enough that every ore is reduced to MnO with CO gas. (2) There is scarcely any difference in reducibility with CO gas among all MnO2 phases i. e. cryptomelane, pyrolusite, γ-MnO2 and birnessite. Only, MnO2 transforms to reduced state (till Mn3O4) through mere thermal decomposition simultaneously with reduction by CO gas. Therefore, authors support the general reasoning that easily thermal-decomposable and incomplete crystalline γ-MnO is most reactive. (3) Under low temperature reduction, the obtained MnO is unstable in the air after cooling in CO gas flow. Meanwhile it is shown that through reduction at above 700°C, the obtained MnO is rather stable in the air after cooling. X-ray diffraction shows that this phenomenon is due to crystalline structure. (4) During manganese are reduction with CO gas, carbon deposition is observed in certain ores; especially in high iron-content ores this tendency is remarkable. (5) On the basis of above results, some discussions are made on refining furnace reaction and preliminary reduction.