Aqueous inorganic phase equilibria at high temperatures: some experimental, theoretical, and applied aspects

Experimental studies generally performed at this laboratory on the solubility of particular salts and oxides in dilute and concentrated aqueous solutions of electrolytes at temperatures up to 400°C are presented. The techniques used are described. Some of this work applies an extended Debye-HUckel equation as a function of the ionic strength of the solution at the high temperatures. From the variation with temperature of a particular ionization or solubility equilibrium obtained from the studies, ther— modynamic functions at infinite dilution of electrolyte are calculated. The studies describe solubility behavior of sulfate salts in exhibiting retrograde solubilities with increasing temperature. But some 2-2 sulfate salts, like magnesium or nickel sulfates, hydrolytically precipitate oxy— sulfates or hydroxides in nearly neutral solutions at about 200°C. Other sulfate, fluoride, and phosphate salts form two liquid phases at temperatures of 250—400°C at saturated vapor pressures. The solubility behavior of quartz and amorphous silica in salt solutions is reviewed. Some liquid—vapor critical phenomena are also presented. The studies are shown to apply to several fields such as water desalination, power plant steam generator chemistry, geochemistry, and chemical oceanography of deep ocean hot springs.