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.

Keywords:

• CaO–Al₂O₃–SiO₂–TiO₂–MgO–Na₂O slags
• Na₂O evaporation
• Kinetics
• Chemical reaction step
• Liquid-phase mass diffusion step

Acknowledgements

Financial supports from National Natural Science Foundation of China [51174100] and from Natural Science Foundation of Jiangxi province [2010GZC0058] as well as Jiangxi Provincial Department of education funded projects [GJJ10474] are gratefully acknowledged.