Behaviour of aluminium oxide in KF-AlF3-Al2O3 melts and suspensions

Abstract

The article addresses the properties of melts and alumina suspensions based on the molten KF-AlF3-Al2O3 system, the kinetics of alumina dissolution and the rheological properties that determine the sedimentation stability. The study of such suspensions has become topical due to the prospects of their use as electrolytes in the production of aluminium using carbon-free anodes. The effects of the temperature, the particle size and the phase composition of the dispersed material and its volume fraction in the suspension on the dissolution kinetics and the sedimentation velocity are studied. The experiments were carried out over the melts with cryolite ratios 1.3 and 1.5 in the range of 750–850 °C. Three different types of aluminium oxide were used. The Reynolds numbers for sedimentation have indicated the Stokesian regime. Typical alumina dissolution rates were in the range of 0.028–0.167 g kg-1 s-1, which is close to the values reported previously. Sedimentation velocities were in the range of (0.05–3.61)∙10-2 m/s, which is several times higher than those obtained previously for ϕ = 0.24–0.32 at 700 °C. It is shown that mechanical activation of alumina increases the performance of the suspension in terms of the sedimentation stability and the dissolution rate increasing.