Alumina solubility in molten salt systems of interest for aluminum electrolysis and related phase diagram data

The solubility of alumina in molten Na sub 3 AlF sub 6 containing various amounts of AlF sub 3 , CaF sub 2 , and LiF was determined by measuring the weight loss of a rotating sintered corundum disc. The results were fitted to the following empirical expression: [Al sub 2 O sub 3 ] sub sat =A(t/1000) exp n where A=11.9-0.062[AlF sub 3 ]-0.0031[AlF sub 3 ] exp 2 -0.50[LiF]-0.20[CaF sub 2 ]-0.30 [MgF sub 2 ]+42[LiF]mult[AlF sub 3 ]/2000 + [LiF]mult[AlF sub 3 ] B=4.8-0.048[AlF sub 3 ] + 2.2[LiF] exp 1.5 /10 + [LiF] + 0.001[AlF sub 3 ] exp 3 where the square brackets denote weight percent of components in the system Na sub 3 AlF sub 6 -Al sub 2 O sub 3 (sat)-AlF sub 3 -CaF sub 2 -MgF sub 2 -LiF and t is the temperature in degrees Celsius. The standard deviation between the equation and the experimental points in the temperature range from 1050 deg C to about 850 deg C was found to be 0.29 wt.% Al sub 2 O sub 3 . A series of revised phase diagram data of interest for aluminum electrolysis was derived based on the present work and recently published data for primary crystallization of Na sub 3 AlF sub 6 in the same systems.