Experimental study of fluorite solubility in acidic solutions as a method for boron fluoride complexes studying

Fluorite solubility in HCl and HF solutions with varied concentrations of boric acid was studied at 81, 155, and 208°C and saturated vapor pressure. Our experimental results demonstrate that fluorite solubility increases with increasing B(OH)3 concentration, and this was interpreted as the formation of the BF3OH–complex (Ryss, 1956). The experimental data were used to determine, using the OptimA software, the free energies of formation of HF°(aq) and, which were then used to calculate the constants of the reactions HF = H+ + F– (1) and B(OH)3(aq) + 2H+ + 3 F– (2). The pK 1 values are 3.71 ± 0.013, 4.28 ± 0.015, and 4.89 ± 0.017 and pK 2 13.60 ± 0.02, 13.99 ± 0.02, and 14.95 ± 0.03 at saturated vapor pressure and 81, 155, and 208°C, respectively.