SOLUBILITY OF AGCL IN MOLTEN NACL-ALCL3 AND KCL-ALCL3

Measurements of AgCl solubility (in mol fraction units) in molten NaCl -AlCl3 and KCl-AlCl3 were determined by an electromotive force techniq ue. For the NaCl-AlCl3 experiments, the temperature was maintained at 448 K and the composition of the solvent varied from X(AlCl3)solvent = 0.500 to X(AlCl3)solvent = 0.530. There was a compositional dependenc e of the AgCl solubilities with a minimum near the equimolar solvent c omposition. The minimum solubility in mol fraction of AgCl was 5.75 x 10(-3) at X(AlCl3)solvent = 0.505. The true solubility produce for AgC l at 448 K was calculated to be 7.35 x 10(-9). The magnitude of the so lubility product is primarily related to the fact that the standard fr ee energy of formation of NaAlCl4 from NaCl and AlCl3 is about 67 kJ m ol-1 more negative than the corresponding free energy for AgAlCl4 (i.e ., AgAlCl4 is unstable). In basic and in somewhat acidic melts, the so lubility is related to the formation of the associated ionic species s uch as AgCl, AgCl2-, AgCl32-, and AgCl43-. From our measurements, the formation constant of AgCl at 448 K, K11, was 1.36 x 10(6). Further, t he specific bond free energy for the associated complex AgCl, DELTAA11 , has been calculated as -47.5 kJ mol-1. For the KCl-AlCl3 experiments , the composition was maintained at the equimolar and the temperature varied in the range 518 to 583 K. The AgCl solubility increases from 4 .32 x 10(-3) at 518 K to 6.85 x 10(-3) at 583 K. The apparent heat of solution was 17.68 kJ mol-1 for this temperature range.