Water Activities and Equilibrium Phase Behavior for the Binary K3PO4(aq), K2SO4(aq) and the Ternary K3PO4 + K2SO4 + H2O Systems at Various Temperatures from 298.15 to 353.15 K

Abstract

Thermodynamic properties of the aqueous binary and ternary potassium phosphate or/and sulfate solutions were studied at various temperatures from 298.15 to 353.15 K. The water activity measurements for the binary K2SO4(aq), K3PO4(aq) and the ternary K3PO4 + K2SO4 + H2O systems were performed from dilute to saturated solution using the hygrometric method. The modeling approach based on the ion interaction model was developed to evaluate the thermodynamic properties. From these measurements of phosphate and sulfate salts, the ion-interaction parameters β(0), β(1), and C ϕ in binary solutions were determined at various temperatures, and used to calculate the osmotic and activity coefficients of these aqueous solutions. The water activity of mixed salts solutions and related properties such as osmotic and activity coefficients are reported at four different temperatures. The osmotic coefficients and binary parameters were used to evaluate the mixing parameters $$ \theta_{{{\text{PO}}_{ 4} , {\text{SO}}_{ 4} }} $$ and $$ \psi_{{{\text{K,PO}}_{ 4} , {\text{SO}}_{ 4} }} $$ in the mixed K3PO4 + K2SO4 + H2O solutions. The solubility measurements of the binary systems were carried out for K2SO4(s) and K3PO4(s) from 298.15 to 353.15 K, up to mmax(K3PO4(s)) = 8.90 mol·kg−1 and mmax(K2SO4(s)) = 1.20 mol·kg−1 at 353.15 K, respectively. The thermodynamic characteristics, solubility products $$ K_{\text{SP}}^{^\circ } $$ and the excess Gibbs energies of K2SO4(aq) and K3PO4(aq) are also reported.