LIQUIDUS TEMPERATURES FOR PRIMARY CRYSTALLIZATION OF CRYOLITE IN MOLTEN-SALT SYSTEMS OF INTEREST FOR ALUMINUM ELECTROLYSIS

Temperatures for primary crystallization of Na(3)A1F(6) in multicompon ent electrolyte systems of interest for the aluminum electrolysis proc ess were determined by thermal analysis. The results are presented as binary and quasibinary diagrams and discussed in view of the literatur e data. An empirical equation describing liquidus temperatures for pri mary crystallization of Na(3)A1F(6) was derived: t/(degrees C) = 1011 + 0.05[AlF3] - 0.13[AIF(3)](2.2) - 3.45[CaF2]/1 + 0.0173[CaF2] +0.124[ CaF2] . [AlF3] - 0.00542 ([CaF2] . [AlF3])(1.5) - 7.93[Al2O3]/1 + 0.93 6[Al2O3] - 0.0017[Al2O3](2) - 0.0023[AlF3] . [Al2O3] - 8.90[LiF]/1 + 0 .0047[LiF] + 0.0010[AlF3](2) - 3.95[MgF2] - 3.95[KF] where t is the te mperature in degree Celsius and the square brackets denote the weight percent of components in the system Na(3)A1F(6)-A1F(3)-CaF2-A1(2)O(3)- LiF-MgF2-KF. The composition limitations are [A1F3] approximate to [Ca F2] approximate to [LiF] < 20 wt pct, [MgF2] approximate to [KF] < 5 w t pct, and [A1(2)O(3)] up to saturation.