Modelling the dissolution of alumina powder in cryolite

Alumina dissolution in cryolite is a complex process at elevated temperatures. However, it is desirable to have a simple model for predictive purposes. In this study, several models for the dissolution of alumina powder in cryolite were formulated and compared with experimental results obtained using modified fast linear sweep voltammetry. As a first approximation the alumina was assumed to be smooth spheres which decrease in size as dissolution proceeds. The models were based on rate control by either first order chemical reaction at the alumina surface, heat transfer, or diffusion. The shape of the curves generated gave a reasonable fit to experimental data but the heat transfer and diffusion models appear to be the best. It is certain that these models can be used to correlate the experimental data on dissolution. It is envisioned that the actual mechanism may be a combination of both heat transfer and diffusion control. The models developed may also be applicable to other systems involving dissolving particles.