Study and modeling of the liquid–solid equilibrium of the KCl–KNO3–HCl–H2O system at 283.15 K

In this work, the liquid-solid equilibrium of the KCl-KNO3-HCl-H2O system at 283.15 K was investigated. To calculate the solubility product constants of KCl and KNO3 in HCl solution, the Pitzer equation was used to calculate the activity coefficient of the ionic species in aqueous solution. In addition, the thermodynamic model with the Pitzer equation was constructed to regress the temperature coefficient parameters for HCl and HNO3. The calculation and prediction of the KCl-KNO3-HCl-H2O system using the results of the regression confirmed that the regression was successful and the Pitzer equation was suitable. For the reaction KCl(s)+HNO3 -> KNO3(s) + HCl, the equilibrium constant K can be obtained from the solubility product constants of KCl and KNO3. Eutectic points for the KCl-KNO3-HCl-H2O system were also predicted. These equilibrium data could be expressed by the triangular phase diagram. The process of the reaction to produce KNO3 could be explained through this triangular phase.