Formation Process and Solid–Liquid Phase Equilibrium of Cs(Cl, Br) Solid Solutions in Aqueous Solution

To investigate the formation process of cesium in a system where chlorine and bromine coexist, as well as the laws governing solid–liquid phase equilibrium, this paper conducts a multiscale study of the CsCl–CsBr–H2O ternary system at 298.15 K. First, the formation process of Cs(Cl, Br) solid solutions was investigated through long-term experiments, while molecular dynamics simulations were employed to examine the coordination and migration of ions at different stages of the reaction. Building on this, the isothermal dissolution equilibrium method was used to systematically determine the stable phase equilibrium relationships in this system and to plot a phase diagram; furthermore, various solid-state characterization analyses were performed on the equilibrium solid phase. Finally, utilizing the thermodynamic data obtained from the experiments, the Pitzer model was parametrized to calculate the solubility of this solid solution system, which was then compared with the experimental results. This research provides a theoretical basis for understanding and predicting the precipitation behavior of cesium in systems where chlorine and bromine coexist.