The measurement of sulfate mineral solubilities in the NaKCaClSO _{4}H _{2}O system at temperatures of 100, 150 and 200°C
Abstract
At T > 100°C development of thermodynamic models suffers from missing experimental data, particularly for solubilities of sulfate minerals in mixed solutions. Solubilities in Na ^{+}K ^{+}Ca ^{2+}Cl ^{}SO _{4}^{2}/H _{2}O subsystems were investigated at 150, 200°C and at selected compositions at 100°C. The apparatus used to examine solidliquid phase equilibria under hydrothermal conditions has been described. In the system NaClCaSO _{4}H _{2}O the missing anhydrite (CaSO _{4}) solubilities at high NaCl concentrations up to halite saturation have been determined. In the system Na _{2}SO _{4}CaSO _{4}H _{2}O the observed glauberite (Na _{2}SO _{4} · CaSO _{4}) solubility is higher than that predicted by the high temperature model of Greenberg and Møller (1989), especially at 200°C. At high salt concentrations, solubilities of both anhydrite and glauberite increase with increasing temperature. Stability fields of the minerals syngenite (K _{2}SO _{4} · CaSO _{4} · H _{2}O) and goergeyite (K _{2}SO _{4} · 5 CaSO _{4} · H _{2}O) were determined, and a new phase was found at 200°C in the K _{2}SO _{4}CaSO _{4}H _{2}O system. Chemical and single crystal structure analysis give the formula K _{2}SO _{4} · CaSO _{4}. The structure is isostructural with palmierite (K _{2}SO _{4} · PbSO _{4}). The glaserite ("3 K _{2}SO _{4} · Na _{2}SO _{4}") appears as solid solution in the system Na _{2}SO _{4}K _{2}SO _{4}H _{2}O. Its solubility and stoichiometry was determined as a function of solution composition.
 Publication:

Geochimica et Cosmochimica Acta
 Pub Date:
 January 2004
 DOI:
 10.1016/S00167037(03)002151
 Bibcode:
 2004GeCoA..68..307F