Liquidus temperatures of Na3AlF6-AlF3-CaF2-KF-LiF-Al2O3 melts

Abstract

Temperatures for the primary crystallization of Na3AlF6-AlF3-CaF2-KF-LiF-Al2O3 system adopted in aluminum electrolysis process were determined by thermal analysis. An empirical equation was derived to describe the liquidus temperatures for the primary crystallization of this multicomponent electrolyte system: t/?=1011 + 0.7w(AlF3) - 0.232w(AlF3)2 - 7.65w(Al2O3) + 0.523w(Al2O3)2 - 8.96w(LiF) + 0.043w(LiF)2 - 3.32w(KF) - 0.12w(KF)2 - 3.28w(CaF2) +0.037w(CaF2)2 + 0.091w(AlF3)w(LiF) + 0.074w(AlF3)w(KF) + 0.084w(AlF3)w(CaF2) - 0.27w(Al2O3)w(LiF), where w(AlF3) denotes the mass fraction of excess aluminum fluoride with respect to cryolite. While w(Al2O3) ranges from 2% to 4%, w(LiF), w(KF) and w(CaF2) from 0 to 7%, and the molar ratio of NaF/AlF3 from 2.2 to 3.

The Behavior of Additives LiF, MgF2 and KF on Current Efficiency in Aluminium Electrolysis

“…The reduction of the liquidus temperatures of the electrolyte is 2.8°C to 4.0°C by 1% KF and 8°C to 9°C by 1% LiF, respectively, dependent on other components. 21 The use of additives (LiF, KF) as well as an increase of the AlF 3 excess allows decreasing the liquidus temperature of the cryolite melts dramatically. Some metal diffuses from the aluminum pad into the molten bath.…”