Effect of the content of the α-phase and granulometric composition on the dissolution rate of alumina in cryolite-alumina melts

Abstract

The rate and mechanism of dissolution alumina in a cryolite-alumina melt were determined starting from the results of a measurement of the dissolution rate, visual observations, and investigations of alumina agglomerates using an electron microscope. In the experiments, alumina samples delivered by different suppliers and differing in phase and granulometric compositions were dissolved. It is established that the dissolution rate of alumina decreases with the increase in the contents of α-Al2O3 and −45-μm fraction, as well as of the starting concentration of Al2O3 in the electrolyte. The particles >150 μm in size and alumina, in which their amount reaches 31%, dissolved slower than alumina containing the −45-μm fraction. Photographs of agglomerates forming after charging alumina and images of their microstructure are presented. The data on the dissolution rate are interpreted based on the behavior of the alumina charge in electrolyte, which is associated with recrystallization γ-Al2O3 → α-Al2O3 and with the formation of the network consisting of interlacing α-Al2O3 plates.