An Experimental Study of $${\text{ZrF}}_{6}^{{2 - }}$$ Stability in Hydrothermal Solutions at 90–255°C

Abstract

Abstract—The solubility of fluorite in HCl and HF solutions with a variable concentration of Zr at 90, 155, 205, and 255°C and the pressure of saturated water vapor is investigated. It is shown that the solubility of fluorite increases with zirconium concentration. The free energies of the $${\text{ZrF}}_{6}^{{2 - }}$$ complex determined from the experimental data using OptimA software were used to calculate the dissociation constants of the $${\text{ZrF}}_{6}^{{2 - }}$$ = Zr4+ + 6F– reaction. The pK values were 29.86 ± 0.13, 34.03 ± 0.062, 38.28 ± 0.033, 40.94 ± 0.079 at 90, 155, 205, and 255°C (saturated water vapor pressure).