Oxide Sensor Measurements and Simultaneous Optical Observations During Dissolution of Alumina in Cryolite Melt

Faster dissolution of alumina is one of the key challenges for improvement of the energy efficiency and production rate increase of Hall-Héroult electrolysis cells. To obtain a faster dissolution, a better knowledge of the phenomena involved in the alumina dissolution process becomes important. In this work, an alumina sensor based on the electromotive force principle was applied to measure the concentration of dissolved alumina in a cryolite-based melt from the addition of the alumina throughout the entire dissolution process. Simultaneously, the dissolution process was video recorded. The measurements were performed in a quartz crucible and alumina was added in 1 wt% subsequent additions. Three different industrial aluminas were tested. The general working principle of the sensor was studied, and the information extracted from the video recordings was used to explain the sensor results as well as the general dissolution phenomena. The total dissolution time found based on the sensor results and video recording was compared for different alumina concentrations. The influence of stirring of the melt was also studied.KeywordsAlumina dissolutionElectrochemical sensorSee-through cell