Experimental study of ZrF<sub>6</sub><sup>2–</sup> stability in hydrothermal solutions at 90–255 ᵒC

Abstract

The solubility of fluorite in HCl and HF solutions with a variable concentration of Zr at 90, 155, 205 and 255 ᵒC and the pressure of saturated water vapor were investigated. The results showed that the solubility of fluorite increases with increasing concentration of zirconium. Using the OptimA program, the free energies of the ZrF62– complex were determined from the experimental data, from which the dissociation constants of the reaction ZrF62– =Zr4+ + 6F- were calculated. 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 ᵒС (saturated water vapor pressure).