A thermodynamic study of the Mg2+, Zn2+vertical bar vertical bar SO42--H2Osystem at 25 degrees C

The phase diagram of the Mg2+, Zn2+ \\ SO42--H2O system at 25 degreesC was studied by isothermally removing supersaturation. The activity of water in the homogeneous legion of the system was determined by the isopiestic metho d. The literature data on the Gibbs energy of formation of MgxZn1-xSO4. 7H( 2)O solid solutions were analyzed. The discrepancies between these data wer e shown to be caused by the inconsistency of the experimental solubility da ta on binary and ternary systems on the one hand and an incorrect use of th e "third component" method on the other. The Gibbs energies of formation of solid solutions and the phase diagram of the system were correctly calcula ted.