Electrolyte viscosity and solid phase formation during aluminium electrolysis

Abstract

This paper presents experimental data on the dependence on alumina and calcium fluoride concentrations of the viscosity of the industrial electrolytes NaF-AlF3-CaF2-Al2O3 with cryolite ratios (CR) of 2.1, 2.3, 2.5 in the temperature range 1243–1293 K. The temperature dependence of the formation of a solid phase on the graphite crucible wall in cryolite-alumina electrolyte during aluminium electrolysis was studied in a laboratory-scale electrolytic cell. The viscosity of the industrial electrolytes was found to depend more on the temperature and cryolite ratio than on the alumina concentration in the melt. A long period of electrolysis with controlled solid phase formation on the cell wall was carried out, with a constant electrolyte composition (CR = 2.4), a calcium fluoride concentration of 5 wt% and an alumina content of 4.0 wt%. The formation of a stable solid phase layer on the graphite crucible wall was found to depend on the electrolysis temperature. A correlation was observed between the formation of a solid under the influence of temperature and the viscosity of the melt.