Abstract
An accurate knowledge of the interfacial tension between liquid aluminium and cryolitic melts is critical to better understand the process parameters influencing the current efficiency in electrolysis cells. In principle, the interfacial tension can be predicted from the surface tension of liquid aluminium, cryolitic melts and their adhesion energy. In industrial electrolysis cells, liquid aluminium contains several impurities (Na, Si, Fe, V, O, …) for which the concentration is modulated by the current density and the thermochemical and electrochemical reactions between aluminium and cryolitic melts, strongly impacting the surface tension of the liquid metal and therefore the interfacial tension. The aim of this paper is to present a predictive model describing the interfacial tension between the liquid aluminium pad and cryolitic melts taking into account the thermochemical and electrochemical reactions within industrial electrolysis cells, depending on the current density. The impurity concentrations within the metal pad are calculated from the cryolitic melt compositions and the current density. The presence of Na and O, even if just a few ppm, may drastically decrease the surface tension of the liquid pad. As no experimental data is available for Al-Na-O system, it has been predicted based on a theoretical approach. Overall, the predicted interfacial tension with the proposed model is in good agreement with the different experimental datasets reported in the literature. A mapping of interfacial tension as a function of electrolyte composition, temperature and current density is proposed. Lastly, based on the proposed interfacial tension model, the probability of precipitation of undissolved alumina particles at the bottom of the cells and its impact upon the current efficiency is discussed.
Published Version
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