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Sixth International Conference on Molten Salt Chemistry and Technology Thermodynamic investigations into low temperature electrolytesM. Somerville, L. Zhang and S. Jahanshahi G K Williams Cooperative Centre for Extractive Metallurgy CSIRO Division of Minerals Box 312, Clayton South, VIC, Australia, 3169 Fax: 61 3 9562 8919 Email; michael.somerville@minerals.csiro.au Abstract Many advantages are available if the liquidus temperature of Aluminium cell (Hall-Heroult) electrolyte and hence operating temperature could be reduced. In particular an improvement in current efficiency can be expected. A number of disadvantages can also be expected if the operating temperature is lowered including lower electrical conductivity, and lower alumina solubility. The addition of aluminium fluoride to cryolite has the greatest effect at lowering liquidus temperature while lithium fluoride can be used to increase electrical conductivity. A thermodynamic investigation into the Na3AlF6-AlF3-LiF and Na3AlF6-AlF3-LiF-Al2O3 systems was conducted as part of a wider investigations into some of the physiochemical properties of low temperature electrolytes for aluminium production. In this paper results from an experimental and thermodynamic modelling program are presented. The experimental work involved measuring the liquidus temperature of the Na3AlF6-AlF3-LiF-Al2O3 system. A modified thermal analysis technique was used to determine the precipitation of a primary phase after the addition of seed material to a melt of known composition. The thermodynamic modelling utilised the IRSID adaptation of Kapoor and Fromberg’s cell model to describe the liquid phases and the compound energy model was used to describe the solid phases in the Na3AlF6-AlF3-LiF system. |
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