Mechanism of transport between the anode-bath interface and the active bubble generation sites in hall-héroult cells

Abstract

During the last decades, many efforts were spent to investigate different aspects of the Hall-Héroult process in order to improve its design and operation. However, many questions remain unanswered due to the complexity of the process and the hostile environment. One of the still unclarified questions is the mechanism of the transport of CO/CO2 gas between the active electrolysis sites and the bubble-evolving anode pores. Generally, during electrolysis in aqueous systems, the generated gas is dissolved and transported through the electrolyte, especially when the anode is impermeable. However, the solubility of CO2 in the molten cryolite is poor and the anodes, used in aluminum industry, are highly porous. In this paper, different mechanisms of the CO/CO2 transport between the gas generating anode - bath interface and the bubble releasing sites are examined. The majority of the anode gas seems to be transported through a thin superficial layer of the porous anodes, while transport via the molten bath and gas adsorption by the anodes plays a secondary role.