S. E. Olsen

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-Csat 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.

Kinetic Modelling of MnO Reduction from Manganese Ore

Abstract This paper analyzes the results of MnO reduction from manganese ore and ferromanganese slag obtained at NTNU (Trondheim) and UNSW (Sydney). Manganese ore upon melting consists of two phases: solid MnO phase which may be a pure MnO oxide or a MnO-MgO solid solution and liquid slag. The process of manganese ore reduction includes MnO phase dissolution into the molten slag and MnO reduction from the slag. It is suggested that the reduction rate of MnO is controlled by the intrinsic kinetic step. The proposed kinetic model takes into account changes in the interfacial area and manganese oxide activity in the slag in the course of reduction. The kinetic model is used to examine effects of temperature, ore composition, CO partial pressure, coke size and reaction time on the extent of MnO reduction. Kinetic constraints in electric furnace and blast furnace ferromanganese making are also discussed.