Flotation of alumina on the surface of the electrolyte in an aluminum electrolysis cell

A model of flotation was developed and applied to alumina in the aluminum electrolysis cell. The conditions of flotation for alumina on the cryolitic bath surface were determined for disc and sphere geometries. The contact angle between alumina and cryolitic bath, which had not been found in the literature, was measured and it was found to be around 30 deg. Experiments with compressed alumina discs on the cryolitic bath surface were conducted, and the results were compared to the model. The experiments showed how impurities on the bath surface influence the flotation; and how a slight asymmetry in the system may accelerate sinking

Validation of the gravimetric method to properly follow alumina dissolution in cryolitic bath

Alumina dissolution is now one of the greatest concerns about Hall-Héroult process optimization. To tackle alumina dissolution kinetics, a gravimetric method was developed. This method follows the apparent weight of an alumina sample while immersed in a cryolitic bath. Then, from the weight over time curve, it is possible to identify the forces acting on the sample especially the change of gravity and buoyancy forces. The experimental results obtained by this method were compared to four other values: namely the data found in the literature, values computed with a CFD model, the total mass loss of alumina disc samples over time and finally to a sample boundary displacement method. The boundary displacement and the CFD model have also demonstrated the strong dependence of the dissolution rate on the convection pattern around the sample