Thermodynamic mixing properties of nepheline-kalsilite crystalline solutions

Abstract

A solution calorimetric investigation has been carried out on two nepheline-kalsilite ion-exchange series, each consisting of 13 members. Dissolutions were performed at 50°C in 20.1 wt% HF under isoperibolic conditions. Heats of solution varied linearly with K/Na ratio for both sodium-rich nephelines and all kalsilites, interpreted as ideal thermodynamic behavior. Potassic nephelines, however, exhibited positive enthalpies of K-Na mixing associated with the entry of K+1 into relatively small Na sites; [ ]Si substitution was found to have very significant effects on the heats of solution of these minerals, and vacancies associated with both the latter substitution and with the substitution of Ca+2 in the alkali sites were found to increase substantially enthalpies of K-Na mixing and also to increase the critical temperature of the solvus. -from Authors