Solubility Products of Metal Sulfides in Molten Salts Measurements and Calculations for Iron Sulfide in the Eutectic Composition

An electrochemical titration technique is used to determine the solubilities of and the solubility products of in the molten eutectic composition in the temperature range from 673° to 773°K. The solubility products of are, on an ion fraction basis, , , and at 673°, 723°, and 773°K, respectively. These values are in good agreement with values calculated a priori from an exact thermodynamic cycle; at 723°K, we deduce a value of −38.36 kcal mole−1 (or −160.50 kJ mole−1) for , as compared with an experimentally derived value of −38.50 kcal mole−1 (or −161.11 kJ mole−1). During the operation of the cells at relatively high sulfide compositions, the complex phases (≡X phase) and (≡J phase) are formed, as established by x‐ray and metallographic analyses. A discussion of their chemical stability in the electrolyte in the temperature range of this study is presented. A moderate change in the activities of and can influence the formation of the J phase.