Solubility of Malladrite Na2SiF6 and K2SiF6 in aqueous solutions

The water activities of binary solutions Na2SiF6-H2O and K2SiF6-H2O are measured from dilution to saturation using the hygrometric method at temperature 353 K. From these experimental data, the activity coefficients of solute were calculated using parameters of ionic interaction model. These coefficients are used to predict the solubility products of the K°sp, the free energy ΔG°diss of dissolution and also the characterization of the precipitated phases to saturation of the system containing Na2SiF6 or K2SiF6. The analyzed of solid phase obtained from saturated solution is made by Xray- diffraction.