On the mechanisms of alumina dissolution with relevance to point feeding aluminum cells

Abstract

The dissolution of alumina in cryolite melts was studied in a laboratory apparatus intended to simulate the conditions in industrial cells with point feeding. Rapid dissolution is achieved if (1) a large proportion of the batch of alumina added is dispersed in the bath upon addition, and (2) the agglomerates which form, disintegrate quickly. Bubbling of gas through the melt increased the dissolution rate by promoting the dispersion of alumina grains as well as breaking up the agglomerates. Preheating of the alumina also resulted in faster dissolution, mainly due to effective dispersion of the alumina grains. High superheat of the bath enhanced the dissolution rate of the agglomerates. Measurements on a point fed industrial cell showed that the dissolution rate of the alumina decreased when the feeding hole was plugged compared to the situation when the feeding hole stayed open.