KF-NaF-AlF3 System: Liquidus Temperature and Phase Transition
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The development of low-temperature aluminum electrolysis makes it possible to reduce energy consumption and greenhouse gas emissions. The KF-NaF-AlF3-based electrolyte is a promising low-temperature electrolyte for aluminum reduction. The liquidus temperatures of KF-NaF-AlF3 electrolytes with a total cryolite ratio (CRt) 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-AlF3 mixtures increases with the increase of the CRt, which has a bigger influence on the liquidus temperature than the traditional NaF-AlF3 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-AlF3 electrolytes with a CRt of 1.3 is as follows: K2NaAlF6 (or K3AlF6) → Na3Al5F14 → K2NaAl3F12 → KAlF4.
The financial support from NSFC (Project 51764032), State Key Laboratory of Complex Nonferrous Metal Resources Cleaning Utilization in Yunnan Province (Project KKPT201652009), the Program for Innovative Research Team in University of Ministry of Education of China (No. IRT_17R48), and the Program for Innovative research team in university of Yunnan province (No. 201808) are acknowledged.
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