Mathematical model of the dissolution process of alumina particles in the Hall-Héroult process

Dissolution performance of alumina is one of the important indicators in the process of aluminum electrolysis. Clarifying the dynamic dissolution process of alumina is important to improve the current efficiency of aluminum electrolysis. A semi-analytical mathematical model was developed to describe the freezing, melting and dissolution processes of alumina particles and the time duration for each stage. This model is based on the heat and mass transport mechanism of moisture containing porous media, with the conservation of thermal energy and mass. The effects of moisture in the pores and the gas phase on the heat conductivity of the particles, as well as the effect of chemical reactions on the heat processes between particles and shells were investigated. Dimensionless method was employed and the expression for size change was derived. The result shows that the freezing and melting stages are mainly affected by superheat, and the shortest time required for particle dissolution when the Stefan number is 0.045. Time of the dissolution stage accounted for 71.1% of the total dissolution time, while the time of the freezing stage and melting stage accounted for 9.3% and 19.6% of the total time