Study On The Electrical Conductivity Of NaF-KF-LiF-AlF₃ Electrolyte Melts For Aluminum Electrolysis

High-energy and high (greenhouse gas) emissions are seriously restricting for the sustainable development of aluminum industry.Low-temperature electrolytic aluminum to achieve an important way of saving energy and reducing consumption, low temperature, high Al₂O₃ concentration and high electrical conductivity electrolyte development is key to the success of the technology.Papers with financial support from national "863 Program" and Chalco for the development of low-temperature electrolytic technology, upgrading the existing aluminum industries, through the combination of literature research and the basis of preliminary studies, select the NaF-KF-LiF-AlF₃ aluminum electrolyte system, studied alkali metal fluoride single and binary KF-AlF₃ melt temperature, the composition of the impact of change on the electrical conductivity of the law, as well as the melt overheated electrolyte aluminum industry, the CR and additives on the electrical conductivity of the melt; On this basis, the further study of the NaF-KF-LiF-AlF₃ multicomponent molten salt electrolyte electrical conductivity and the relationship between temperature and composition, access to the following major findings:.(1) Single-alkali metal fluoride LiF, NaF and KF, respectively, the electrical conductivity activation energy for 93.11,104.57 and 140.45 kJ / mol, higher temperature 10℃, respectively, the corresponding molten salt conductivity increase 0.0532 S·cm^-1, 0.0267 S·cm^-1 and 0.0314 S·cm^-1. At the same temperature by the molten salt in the cation radius, LiF, NaF and KF conductivity ratio of approximately 2.5:1.26:1. By the ionic bond strength of different effects to the same temperature electrical conductivity of K₃AlF₆ is much smaller than Na₃AlF₆, the ratio of about 1.647:1.(2)For low CR (CR＜2.3) electrolyte aluminum, CR increased 0.1 than the electrical conductivity increased by about 0.1 S·cm^-1; and the CR of 2.3 -2.8, the changes of electrical conductivity fluctuations in molten salt the gap was only 0.1-0.2S·cm^-1; superheat increased by 10℃, its electrical conductivity can be increased by about 0.05S·cm^-1. 1-5% in the range of LiF electrolyte aluminum industry to add capacity for each additional lwt%, the same melt temperature electrical conductivity increased by about 0.024 S·cm^-1; when alternative KF increased from 0 to 26%, the electrolyte electrical conductivity from 2.02 S·cm^-1 decreased to 1.6 S·cm^-1, all alternative NaF with KF, the melt electrical conductivity of 1.24 S·cm^-1.(3) Access to the primary crystal temperature range of 890-920℃in a variety of NaF-KF-LiF-AlF₃ multi-component electrolyte composition, electrolyte aluminum industry with the current compared to Al₂O₃ melt dissolved in comparable or improved performance , while the electrical conductivity increased by 5-10%. Also identified the primary crystal temperature range of 800-850℃of the NaF-KF-LiF-AlF₃ multi-component electrolyte composition: KF content of 8.0%, LiF content <11%, when 860℃, electrical conductivity> 1.6S·cm^-1. Through non-linear fitting of experimental data obtained a correlation coefficient of 0.9551, with an average error of 0.123 S·cm^-1 of the NaF-KF-LiF-AlF₃ electrical conductivity electrolyte system calculated empirical formula:κ=7.167-2.457NaF-2.457KF-6.768LiF-2.104AlF₃-3.923NaF²+3.795KF²+10.442 LiF²-6.083AlF₃²-7.741(CaF₂+MgF₂+Al₂O₃)-7.469(T/1200) +8.756(T/1200)²Where: NaF for 0-50wt.%, KF for 0-50wt.% LiF for 0-50wt.%, AlF₃ for 30-40wt.%, CaF₂ for 0-5 wt.%, MgF₂ for 0-5wt.% , Al₂O₃ for 0-5wt.%, electrolyte temperature T for the 750-1000℃。...