Further studies of alumina dissolution under conditions similar to cell operation

Abstract

Previous studies (1) have highlighted that thermal effects, method of addition and the dispersion of alumina (which is aided by the release of volatiles, for example) are all important. However, those studies were unable to derive quantitative assessment of the relative importance of the various structural properties of alumina versus cell operating variables. The earlier apparatus has been modified by incorporating a fibre optic cable, variable feeder design and modified stirring for control of mass transfer thus increasing sensitivity. After determining the importance of electrolyte superheat, its velocity, the alumina concentration and method of addition, the experimental conditions could be adjusted for a fast dissolution regime for normal alumina. This has enabled the importance of selected physical or structural properties of alumina to be determined. The results show that the most important structural properties are those effecting the flowability (or flow funnel time), the particle size (favouring coarse material) and loss on ignition. The BET surface area is also important, but this is interrelated to loss on ignition generally. While structural properties can change the dissolution time, the magnitude of dissolution time is influenced more by operating conditions.