A study on the carbonization and alloying process of MnO2 by methane-hydrogen gas mixture in the presence of Fe2O3

Abstract

Carbonization of pure MnO2 by CH4-H2 gas mixture with various CH4/(CH4+H2) molar ratios in the temperature range of 900–1250°C had been performed in our previous work. This study further investigated the carbonization and alloying process of MnO2 by CH4-H2 gas mixture in the presence of Fe2O3 at 900–1300°C using XRD, optical microstructure, SEM-EDS and phase diagram analyses. Carbonization test of pure Fe2O3 was also conducted to understand the effect of Fe2O3 on the carbonization of MnO2 more explicitly. It was found that Fe2O3 could be carbonized to Fe3C at 900–1150°C. The Fe2O3 briquettes began to melt at 1100°C and a large amount of Fe-C melts appeared as the temperature went up to 1150°C. When the MnO2+25 wt%Fe2O3 briquettes were reduced at 900–1000°C in CH4-H2 gas mixture, the Fe2O3 was preferentially carbonized to Fe-C phase while the MnO2 was only reduced to MnO. The formation of Fe-C phase was beneficial to the carbonization of MnO since the carbonization temperature of MnO can decrease from 1100°C to 1000°C. The carbonization degree of MnO was dramatically accelerated over 1100°C due to the transformation of Fe-C phase from solid state to melts. Morphology analysis indicated that the MnO core was wrapped by the shell of Fe-C melts. The alloying process of Mn-Fe-C was conducted through the elements migration of Fe and Mn between the core and shell. At 1300°C, the Mn-Fe-C alloy turned to melt and aggregated since the highest melting temperature of the Mn-C-25 wt% Fe system was only 1274°C. Finally, a ferromanganese crude alloy with 68–72wt% Mn, 20–25wt% Fe and 6.0–8.0wt% C was obtained when the MnO2+25wt% Fe2O3 briquettes were carbonized by CH4-H2 gas mixture at 1300°C for 60min.