Partial slag solidification within an ilmenite smelter

Abstract

Within ilmenite smelters, the slag is at a temperature just above its liquidus (because the furnace operates with a slag freeze lining), and the metal bath is at a temperature which is approximately 150°C lower than the slag temperature. As a result, solidification of the slag in contact with the metal is expected, and was indeed detected with sounding bars in operating furnaces. Samples of the solidified layer were obtained from a DC ilmenite smelter which had cooled with its contents intact. Analysis showed parts of the layer to be close to anosovite (Ti3O5) in composition; in all cases, the solid contained much less FeO than the primary pseudobrookite which forms during bulk slag solidification after tapping. Equilibrium calculations show that these compositions can result from reaction of initially FeO-rich pseudobrookite with dissolved carbon in the metal bath. The presence of this layer of near-anosovite material in the furnace has possible implications for settling of metal and for the furnace energy balance; the latter was explored with thermodynamic calculations.