Solubility of NaF and Li₂CO₃ salts of the 2nd type in supercritical water and solutions of aqueous electrolytes (NaCl, Na₂WO₄, and Li₂SO₄)

Abstract

Experimental studies of binary and ternary water-salt systems containing NaF or Li₂CO₃ demonstrate that these salts belong to compounds of the 2nd type. The compounds are characterized by a negative temperature coefficient of salt solubility in water, critical phenomena in salt-saturated aqueous solutions, and a wide region of fluid equilibria, with supercritical fluid solutions being homogeneous within this region at any pressure. However, the behavior of these two salts of the 2nd type is different from that of alkali metals sulfates and carbonates, which is complicated by the immiscibility phenomena in stable and metastable states. It is concluded that the immiscibility phenomena in the hydrothermal binary systems with NaF and Li₂CO₃ are absent, while the second critical Q end-point appears in solid saturated solutions at a very high temperature and pressure (above 500°C and 150 MPa, correspondingly).