Experimental-computational approach for elucidating the dissolution behavior of potassium phosphates in near- and supercritical water

The present work investigates the solubility of dipotassium and monopotassium phosphate in near- and supercritical water. The highest solubilities exceeded 100 mmol kg⁻¹ at 633.15 K and 30 MPa, the lowest temperature and highest pressure conditions examined, while at 723.15 K and 19 MPa, the lowest solubilities were observed for approximately 0.2 mmol kg⁻¹and 0.001 mmol kg⁻¹. For potassium phosphates, increasing density and decreasing temperature monotonically increased their solubility. Three semi-empirical models were employed to correlate the measured solubility data. Enthalpy model and ionization model were demonstrated to provide the highest accuracies for correlating the experimental solubility of di- and monopotassium phosphate, respectively. The chemical equilibrium reactions facilitating the dissolution and precipitation of potassium phosphates were assessed by theoretical calculations via R-HKF equations of state. Calculations by the R-HKF EOS indicated that precipitation was thermodynamically favored under all conditions, however, increasing temperature and water density promoted the dissolution and hydrolysis of potassium phosphates.