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

铝的生产基于不同的技术，这些技术都是霍尔-赫鲁特工艺的变体。从1900年到2011年，全球铝产量从8000吨增加到4500万吨。在加拿大，年产量约为300万吨。霍尔-赫鲁特过程可概括如下：氧化铝首先在940至980℃的冰晶石熔池中溶解，然后在施加约300kA的电流后在电解槽底部生产铝。这种方法需要一个由耐化学、热和机械降解的材料制成的电池。自1886年以来，几项技术进步导致了这一过程的重大改进。然而，能源消耗仍然很高(14000千瓦时/吨铝)，需要更好地了解所涉及的现象，以进一步提高能源效率。 我们的项目旨在了解在电池运行期间在阴极表面观察到的沉积物的形成。这些沉积会影响阴极的电阻，导致阴极压降(CVD)的增加。更具体地说，本项目是研究影响阴极表面此类沉积物形成的参数，这些参数对铝生产的能源消耗有显著影响。在这方面，本项目将研究不同等级的阴极的作用，在电解过程中阴极表面已经形成的沉积物的再溶解，以及电池启动后的热演变对沉积物形成的作用。

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.