Feasibility study of HIsmelt smelting of vanadium–titanium magnetite based on slag viscosity: influence of slag chemistry on its fluidity

Abstract

Vanadium–titanium magnetite (VTM) is a symbiotic composite mineral composed of iron, vanadium, titanium and other metals and has high comprehensive utilisation value. HIsmelt smelting reduction is a flexible and environmentally friendly ironmaking process that can cope with complex raw material conditions and is a feasible process for smelting VTM. However, the presence of a large amount of TiO₂ will make the slag sticky and difficult to tap. In this article, the viscosities of the slag generated in the smelting of various proportion of VTM and Australian PB fines were measured by using the rotating cylinder method. Meanwhile, SEM-EDS were used to determine the crystalline phase in the slag and verified with the Factsage thermodynamic calculation results. In addition, the solid phases formation during the titanium-containing slag cooling were observed in situ by using a confocal laser scanning microscope. The experimental results show that increasing the TiO₂ content in slag will reduce the viscosity of the liquid slag, but will also increase the critical-viscosity temperature (Tcv) of its viscosity–temperature curve and hence reduce the operability of high titanium slag. When the slag basicity is 1.2, the TiO₂ content ranging from 6% to 40% can meet the operating requirements of HIsmelt. An increase in basicity will reduce the slag viscosity and Tcv. When the TiO₂ content is 30% and 40%, the slag basicity should be maintained at 1.2. For high titanium slag, the perovskite precipitated at high temperatures floats on the slag surface, hence has little impact on the slag viscosity. However, as the temperature decreases, the precipitated pseudobrookite suspends in the slag and leads to a sharp increase in slag viscosity. Therefore, the operating temperature should be controlled to be above 1450 °C during HIsmelt smelting of VTM to ensure the fluidity of the slag.