State of Reactions in Silicomanganese Smelting Process

Abstract

Recent studies by Safarian et al. and Kim show that carbothermic smelting processes for SiMn alloys proceed by multiple reactions consisting of oxidation of carbon, simultaneous reduction of MnO and SiO2 species, and distribution of Mn and Si elements between slag and alloy. A consideration of reaction equilibrium shows that the smelting reaction system is described by the reaction of carbon oxidation and that of distribution of Mn and Si. The distribution reaction with respect to SiMn alloy and slag is described by the following, 2(MnO) + [Si] = 2[Mn] + (SiO2), where oxide species in parenthesis indicate in solution of slag and elements in square brackets in solution of carbon saturated SiMn alloy. The present investigation of chemical analyses of alloy and slag taken from laboratory experiment by Swinbourne et al. and industrial smelting operation shows that the distribution reaction system is univariant for carbon saturated SiMn alloy, and the distribution reaction equilibrium is specified with temperature. As it is driven by reducing reactions, the distribution reaction equilibrium is established as either chemically or electrochemically depending on the characteristic of reducing reactions. For smelting of SiMn alloy with the standard grade composition, the chemical equilibrium is established at 1600 oC. At temperatures lower than 1600 oC, carbon at the interface of alloy and slag is oxidized by free oxygen ion, O2-, in slag at the gas phase pressure of PCO = 1 atm, and the electrochemical equilibrium is attained.