Solid-liquid equilibria in the quaternary system NaCl-KCl-NH4Cl-H2O

The mixture parameters of the mole-fraction model of Pitzer-Sinionson-Clegg pertaining to the aqueous salt pair NH4Cl + KCl were obtained by fitting the semi-empirical equations to the solid-liquid distribution data measured for KCl and NH4Cl, at 293, 313 and 333 K, as well as to experimental solubilities of NaCl in the quaternary system NaCl + KCl + NH4Cl + H2O. The fitted parameters and the solid-liquid equilibria (SLE) data were used to estimate the activity coefficients of KCl and NH4Cl in the Solid phases, thus allowing the calculation of the eutonic points of the discontinuous series of solid solutions precipitated from aqueous solutions containing both chlorides.