EQUATIONS OF STATE FOR SOLID NACL-KCL AND SATURATED LIQUID NACL-KCL-H2O

The equilibrium between the solid solution of NaCl-KCl and the ternary liquid NaCl-KCl-H2O is both scientifically interesting and geological ly important. Equations of the Margules type have been derived for the two phases that accurately reproduce the extensive array of published measurements, together with recent measurements of Chou for the liqui dus of the ternary and the solidus of the NaCl-KCl binary. The range o f validity of the equations extends to 1200 K, to 5 kbar, but for the aqueous system it is limited to compositions on the salt saturation su rface. Of particular interest is the transition in the liquid-solid eq uilibrium of the ternary from the pattern at high temperatures where t he solid is a solution of composition near that of the liquid to that at lower temperatures where the solid is nearly pure NaCl or KCl. The phase compositions for anhydrous NaCl-KCl are consistent with the heat of mixing data of Hersh and Kleppa and yield a new expression for the entropy of mixing.