Reaction equilibria in the production of manganese ferroalloys

A laboratory investigation has been carried out to determine slag/metal and slag/metal/gas equilibria relevant to production of manganese ferroalloys. The metal phase was normally composed of MnSi-C_sat alloys, but in some experiments, the alloys contained up to 15 wt pct Fe. Different slag systems were used: MnO-SiO₂, MnO-SiO₂-CaO, MnO-SiO₂-Al₂O₃, and quaternary MnO-SiO₂-CaO-Al₂O₃ with fixed CaO/Al₂O₃ weight ratios of 1.5 and 3. The experiments were normally made in CO gas atmosphere at temperatures ranging from 1450 °C to 1600 °C. The results give comprehensive information about equilibrium relations.Partial andcomplete equilibria are illustrated in equilibrium diagrams. Partial equilibrium is a situation in which equilibrium is established with respect to certain variables but not to others, in this case, between slag and metal but not with the gas phase. The effect of temperature was found to be of minor importance for the partial slag/metal equilibrium, whereas the complete slag/metal/gas equilibrium is considerably influenced by both temperature and CO pressure. As expected, increasing temperature and decreasing CO pressure will reduce the equilibrium MnO content of slags. The influence of alumina addition to the slag phase and of iron to the metal phase is also discussed.