Laboratory tests have been conducted in order to study the behaviour of alumina immediately after addition to the bath. Primary (virgin) alumina and secondary (reacted) alumina from different producers have been tested. The effect of bath composition, bath temperature and preheat of the alumina on the dissolution rate was studied.
The rate of dissolution increased when the alumina was preheated. Addition of LiF to the bath also increased the dissolution rate. In these laboratory tests larger differences were found between primary and secondary alumina of the same origin than between the different primary aluminas. The secondary alumina showed less tendency to form lumps and dissolved faster than the corresponding primary alumina.
It is believed that the difference in dissolution rate between the various aluminas mainly is determined by their tendency to form lumps when they come in contact with the bath.