Abstract:
The conventional technology for aluminum production uses consumable carbon anodes evolving CO and CO2. The high energy and material consumption, as well as the significant greenhouse emission encouraged the industry and researchers to pursue innovative technologies for aluminum production. Recently, a new low-temperature process based on electrolysis of low-melted potassium and potassium-sodium cryolites became a subject of interest: decreasing the operating temperature can decrease energy costs and reduce material corrosion, electrolyte evaporation, aluminum solubility in electrolyte, and alkali metal content in the aluminum product. Besides, the low-temperature electrolytic bath allows implementation of oxygen-evolving inert anodes and wetted cathodes that result in significant energy and environment benefits for aluminum production. The basic physical-chemical properties (liquidus temperature, electrical conductivity, density, and alumina solubility) of the mixed potassium-sodium cryolites (KF-NaF-AlF3) with cryolite ratio (CR) 1.3-1.5 containing LiF and CaF2 additions were measured and described by overall regression equations. The KF-AlF3 and KF-NaF (12-15 wt%)-AlF3 melts with CR=1.3-1.5 have the liquidus temperature below 800°C, and the alumina solubility over 4.5 wt% in the 700-800°C temperature range. The LiF additions in amount of not more than 3 wt% are optional to improve the electrical conductivity. The presence of CaF2 in electrolyte is not desirable. Based on obtained data the prospective electrolyte compositions can be chosen for low-temperature aluminum electrolysis.
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