Chemical speciation of aqueous hydrogen fluoride at various temperatures from 298.15 K to 353.15 K

Abstract

The chemical speciation of aqueous hydrofluoric acid solutions was investigated at various temperatures. The experimental results and calculations were carried out to study a qualitative and quantitative speciation of the system HF-H2O. Literature review of thermodynamic and speciation studies of aqueous hydrogen fluoride were reported and revealed some deficiencies at various temperatures. The dissociation of HF in the aqueous solution is not complete, which exhibits a concentration-dependent stoichiometric coefficient and directly influences the thermodynamic properties. Neglecting this concentration dependence leads to erroneous osmotic coefficients for solutions of weak electrolytes. The water activities of the HF-H2O system were measured within the molality range from 0.10 mol kg−1 to 6.00 mol kg−1 at different temperatures from 298.15 K to 353.15 K using the hygrometric method. From these measurements, on the basis of the fluorine 19F nuclear magnetic resonance and the chemical equilibriums, the qualitative and quantitative speciation aqueous hydrofluoric acid solutions were performed respectively. The deployed approach was developed based on ion interaction model to describe the behavior of HF aqueous solutions, considering a polyelectrolyte system HF−H−F−HF2−H2F3−H2O. The calculated species HF(aq), H+, F−, HF2− and H2F3−were determined at various temperatures. From the complementary techniques and the developed model, the results reflect the present species and allow describing the behavior of hydrofluoric acid aqueous solutions.