Sulfide and sulfate solid solubility in lime, magnesia, and calcined dolomite: Part II. free energy of formation of magnesium sulfate.

The free energy of formation of magnesium sulfate and its solubility in magnesia have been determined. The salient feature of the results is that trace amounts of calcium impurity in magnesia noticeably lower the dissociation temperature and pressure of magnesium sulfate. A high-purity magnesia, which was prepared by oxidation of a high-purity magnesium, was used to determine the equilibrium constant for the formation of MgSO. The sulfate solubil-ity In magnesia saturated with MgSO was found to be higher than that in lime saturated with CaSO. At 1100°C, CaSO and CaS form in calcined dolomite at SO partial pressures higher than those in pure CaO. From these findings it is estimated that at MgO saturation the ac-tivity coefficient relative to CaO is about 0.8. [ABSTRACT FROM AUTHOR]