KF-NaF-AlF3 System: Liquidus Temperature and Phase Transition

The development of low-temperature aluminum electrolysis makes it possible to reduce energy consumption and greenhouse gas emissions. The KF-NaF-AlF 3 -based electrolyte is a promising low-temperature electrolyte for aluminum reduction. The liquidus temperatures of KF-NaF-AlF 3 electrolytes with a total cryolite ratio (CR t ) fixed at 1.3–2.0, and with different concentrations of NaF (with a step change of 5 mol.%), were investigated by the cooling curve method. The results showed that the liquidus temperature of KF-NaF-AlF 3 mixtures increases with the increase of the CR t , which has a bigger influence on the liquidus temperature than the traditional NaF-AlF 3 electrolyte currently used in aluminum smelters. When the content of NaF is 10–20 mol.%, the curves of the liquidus temperature vs. NaF content reach a peak. When the NaF content ranges from 30 to 40 mol.%, the liquidus temperature is relatively low (695–900°C). The precipitated order of the compounds in molten KF-NaF-AlF 3 electrolytes with a CR t of 1.3 is as follows: K 2 NaAlF 6 (or K 3 AlF 6 ) → Na 3 Al 5 F 14  → K 2 NaAl 3 F 12  → KAlF 4 .