Formation mechanism and redissolution of cathode deposits and their influences on the cathodic voltage drop (CVD) in aluminum electrolysis process

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The production of aluminum is based on different technologies, which are all the variants of the Hall-Heroult process. From 1900 to 2011, global production of aluminum increased from 8000 (t) to 45 million (t). In Canada, about 3 million (t) is annually produced. The Hall-Heroult process can be summarized as follows: the alumina is initially dissolved in a bath containing of molten cryolite at temperature between 940 and 980 ° C. Aluminum is then produced at the bottom of the electrolysis cell after applying about 300 kA current. This method requires a cell made of materials resistant to chemical, thermal and mechanical degradation. Since 1886, several technological advances have led to significant improvements of the process. However, the energy consumption remains high (14 000 kWh/t of aluminum), and a better understanding of the phenomena involved is required in order to further improve the energy efficiency. Our project aims to understand the formation of deposits observed at the cathodic surface during the cell operation. These deposits affect the electrical resistance of the cathode resulting in an increase of the cathodic voltage drop (CVD). More specifically, this project is to study the parameters affecting the formation of such deposits on the cathodic surface which significantly influence the energy consumption for aluminum production. In this regard, the role of different grades of the cathode, re-dissolution of deposits already formed on the cathodic surface during the electrolysis process as well as the role of thermal evolution following cell start-up on the deposit formation will be studied in this project.