Effect of Slag Foaming on the Reduction of Iron Oxide in Molten Slag by Graphite.

Abstract

A kinetic study has been made on the reduction of iron oxide in molten slag, held in an alumina crucible under argon gas atmosphere, with graphite, cylindrical in shape. The composition of the primary slag was 20.5%Li2O-38.4%CaO-41.1%SiO2 (molar ratio=1:1:1). The initial concentration of iron oxide was changed between 3% and 12.5%. The experimental temperature was 1300°C. The rotation speed of the graphite cylinder was varied from zero to 1900 rpm. The reaction rate was largely affected by slag foaming. At higher FeO concentrations, the apparent rate constant was almost independent of the mechanical stirring. At lower concentrations, the effect of the rotation on the apparent rate constant was found to be small at lower speeds but tended to become larger at higher speeds. This was an indication that the melt was strongly agitated by CO gas bubble evolution. The effect of foaming is taken into account by introducing gas holdup factor into ordinary (foam-free) kinetic equations. Values of the mass transfer coefficient of oxygen in the molten slag, calculated by applying the penetration theory, are close to those of the apparent rate constant, measured experimentally. This implies that the rate of the reduction is controlled predominantly by the mass transfer in the slag phase.