Key words: water-salt systems, supercritical fluids, immiscibility of liquid phases, salt solubility, phase diagrams
General features of the phase behavior of systems "water-salt" of different types in sub- and supercritical conditions are analyzed. Type 1 systems are characterized by the increasing solubility of non-volatile component (salt) at rising temperature, whereas in type 2 systems the solubility decreases. An existence of homogeneous unsaturated fluid and of fluid equilibrium with solid salt components at temperatures above the critical temperature of water at any pressures is a distinguishing feature of water-salt systems of type 2. An appearance of supercritical fluid in the systems of type 1 is observed only above the critical temperature of salt. Review of available experimental data permits to establish both the general features of salt solubility behavior in binary systems of various types and some distinctive properties of hydrothermal solubility of the salts of type 2 in aqueous solutions of type 1 salts. Special attention is paid to the processes of heterogenization of supercritical fluid saturated with the salts of type 2 when the salt of type 1 is added and to an influence of immiscibility phenomena, which are common in the hydrothermal salt solutions on fluid phase heterogenization.