The Formation and Dissolution of Crust Upon Alumina Addition into Cryolite Electrolyte

The properties of the alumina agglomerate/crust formed upon smelting grade alumina feeding and the corresponding dissolution rates in cryolite electrolyte were studied using a suspended weighing device. A series of experiments was designed to investigate the dissolution rate of the crust at various temperatures and the effects of initial alumina concentration in the electrolyte on the formation process and properties of the crust. Initial results showed that under experimental non-stirring conditions, a large proportion as high as 54–64% of the fed alumina participated in the formation of the crust upon feeding at 1233–1238 K (960–965°C). The dissolution rate of the crust decreased greatly with the increase of initial alumina concentration and the decrease of operating temperature. The mass of the crust increased significantly at high initial alumina concentrations and decreased temperature, while the alumina content of the crust showed a slight decreasing trend. Other parameters of the crust such as volume density and gas-filling fraction were also measured. The influence of physical stirring on alumina dissolution rate was also discussed.