Experimental and theoretical studies on thermodynamic activities of binaries ferric and magnesium chlorides in aqueous solutions at various temperatures

Abstract

The investigation of the thermodynamic properties of binary systems of ferric and magnesium chlorides in aqueous solutions was reported at various temperatures using both the hygrometric method and thermodynamic modeling. Water activities were measured over a molality range of 0.100 up to $m_{\text{max}\left(\text{FeC}{l}_3\right)}=$ 2.500 $\text{mol}·k{g}^{-1}$ and to $m_{\text{max}\left(\text{MgC}{l}_2\right)}=$(5.798, 6.090, 6.394, and 6.839) $\text{mol}·k{g}^{-1}$at temperatures from 298.15 K to 353.15 K, respectively. From the new measurements, the osmotic coefficients of water were evaluated and compared with the existing literature data at ambient temperature. These coefficients were treated at various temperatures using established thermodynamic models of the Pitzer, Filippov–Charykov–Rumyantsev, extended ion interaction, and Clegg–Pitzer–Brimblecombe. The relevant properties of ferric and magnesium electrolyte solutions were determined in the temperature range. Indeed, the parameterizations of $\text{FeC}{l}_3\left(\text{aq}\right)$ and $\text{MgC}{l}_2\left(\text{aq}\right)$ were evaluated and employed for the computation of solute activity and osmotic coefficients. Based on literature emf data for $\text{MgC}{l}_2\left(\text{aq}\right)$ at a temperature of 298.15 K, the consistency of the activity coefficients was evaluated using an adequate model, and an excellent description of the prediction activity coefficients is obtained by the extended ion interaction model. Then, the recommended activity coefficients were given at various temperatures by extending this procedure. An experimental investigation was also carried out to evaluate the solubility equilibrium of $\text{MgC}{l}_2$ in aqueous solutions at different temperatures. The solubility product and standard Gibbs energies of dissolution and formation were also calculated at different temperatures and compared with those existing in the literature.