Cartography and Chemical Composition of the Different Deposits in the Hall-Heroult Process

The formation of solid deposits on the cathode surface is problematic for the performance of the electrolysis cell (cathode voltage drop, cell stability, cell life). Furthermore, its mechanism is still not well understood. Although alumina feeding is tightly controlled in industrial cells, the formation of solid deposits is still observed at the interface between the cathode block and aluminum. In order to understand the formation mechanisms and reduce the occurrence of solid deposits, many samples taken from different positions of the interface were analyzed for both the industrial and laboratory electrolysis cells. The effect of the alumina feeding rate and the impact of a thermal gradient on the composition of the deposits were also evaluated. The analysis of industrial and experimental samples demonstrated a concentration gradient of Al₂O₃ and AlF₃ within the deposits implying a variation in the liquidus temperature of the deposit. This study provides insight into the mechanisms responsible for the formation of solid deposits at the cathode surface.