Study on Liquidus Temperature of NaF-KF-LiF-AlF3 System with Low Cryolite Ratio

Development of an energy-efficient method for aluminum manufacturing is the current research trend in the aluminum electrolysis industry. A low-temperature electrolysis process is an appropriate choice for aluminum electrolysis. The NaF-KF-LiF-AlF3 system with its low cryolite ratio may be a suitable candidate electrolyte system because of its reduced liquidus temperature. In this paper, the liquidus temperature of NaF-KF-LiF-AlF3 system with cryolite ratios of 1.3 and 1.4 is investigated via the cooling curve method and the differential thermal analysis method. The effects of both potassium fluoride and lithium fluoride on the NaF-KF-LiF-AlF3 system are studied. The liquidus curves of systems containing potassium fluoride and lithium fluoride are different and depend on the KF/(NaF+KF+LiF) and LiF/(NaF+KF+LiF) ratios. Part of the (NaF-LiF-AlF3)-KF pseudo-binary phase diagram with fixed LiF concentration is plotted according to the data of liquidus temperature and the compositions of the phase diagram containing potassium fluoride and lithium fluoride with a cryolite ratio of 1.3 are analyzed. The change trend of the compositions is similar to the NaF-KF-AlF3 system with a low cryolite ratio. LiF hardly participate in the formation of the compounds at equilibrium state except for the fact that chiolite is the main composition of molten salt.