Kinetics of Na₂O evaporation from CaO–Al₂O₃–SiO₂–MgO–TiO₂–Na₂O slags

Abstract

The present work is carried out to study the evaporation of Na2O from CaO–Al2O3–SiO2–TiO2–MgO–Na2O slags with high basicity and high alumina in the temperature range of 1500–1560°C. The ratio of evaporation was determined by monitoring the Na2O content change of the slag melt under isothermal reduction conditions. The results show that the evaporation ratio increases with increasing the temperature. Higher basicity and increasing concentrations of Na2O, Al2O3 are also found to increase the evaporation ratio of Na2O, while MgO addition only slightly enhances the evaporation ratio. With TiO2 content increasing, the evaporation ratio first increases and then decreases. The evaporation rate of Na2O appears to be controlled by chemical reaction at the slag/gas interface in the beginning, followed by a mixed reaction-mass transfer regime, and finally a liquid-phase mass transport step. The apparent activation energy is 134.74 kJ mol−1 for the chemical reaction regime and 268.53 kJ mol−1 for the liquid-phase mass diffusion step.