Use of the Bromley equation for the analysis of ionic equilibria in mixed ferric and ferrous chloride solutions at 25 °C

The ionic equilibria in the mixed ferric and ferrous chloride solution were analyzed by considering the complex formation reactions as well as the mass and charge balance equations. The activity coefficients of the ions were calculated using the Bromley equation. The equilibrium constants for the formation of ferrous complexes were determined from the reported thermodynamic data. The interaction parameters of the ferric species were estimated from the reported values of FeCl3 in an HCl solution. By applying the ionic equilibria, the speciation of the ferric and ferrous species with the composition was obtained. The predicted pH values of the FeCl3-FeCl2-HCl-H2O system agreed well with the measured values at 25 degrees C in the ionic strength range of up to 9.34 m.