Interaction of New Zealand Ironsand and Flux Materials

Abstract

New Zealand ironsand is mined for steel production. Its composition approximates that of titanomagnetite (Fe_3-xTi_xO₄) containing about 60 wt% iron and 8 wt% titania. The ironsand provides an alternative source of iron to conventional iron ores. Its addition into a sinter blend is an established method of utilisation in ironmaking. Knowledge of the interaction between ironsand and flux materials during sintering is helpful to understand the sintering mechanism of titanomagnetite. In this study, two-layer interaction couples between ironsand and flux materials (CaO, MgO and dolomite) were prepared and sintered in an atmosphere of pO₂ = 0.5 kPa in the temperature range of 1200–1300°C for different times. When the ironsand was sintered with MgO, Mg²⁺ ions significantly diffused into the lattice of ironsand, which stabilised the system of FeO_x–MgO and hindered the assimilation of ironsand particles. During the sintering of ironsand with CaO, a reaction zone consisting of perovskite and calcium ferrite formed between the two layers. In comparison, a reaction zone consisting of perovskite, MgO–FeO solid solution and calcium ferrite occurred during the sintering of ironsand with dolomite. Increasing sintering temperature significantly enhanced the penetration of calcium ferrite into the dolomite layer; whereas the perovskite phase and MgO–FeO solid solution remained at higher sintering temperatures due to their relatively high melting points.