Investigation of Molten Salt Phase Formation during Alkali Roasting of Titaniferous Minerals with Sodium and Potassium Hydroxide

The benefit of alkali roasting over existing processes is that it minimises waste and energy consumption compared with the current methods for the beneficiation of titaniferous minerals. Previous studies on the liquid phase formation during alkali roasting of titaniferous minerals were based on the use of Na2CO3, whereas this study focuses on the oxidative roasting of ilmenite with either NaOH or KOH, using different alkali to mineral ratios, in air at 1,000 °C. This work attempts to characterise the alkali-rich liquid phase formed during roasting and determine its impact on the physical chemistry of roasting. Phase equilibria of the Na/K-Fe-Ti-O systems were calculated and compared with experimental results. Samples roasted with NaOH demonstrated segregation of Ti and Fe oxides, but only Ti-K–Fe–O ternary compound were present in products treated with KOH. The presence of the liquid phase at the reaction interface adversely affects the oxygen diffusion during roasting, which has influence on the products formed.