Phase Equilibrium of the RbCl–RbBr–H ₂ O System at 298.15 K and Molecular Dynamics Simulations of MCl–MBr–H ₂ O (M = Li ⁺ , Na ⁺ , K ⁺ , Rb ⁺ , NH ₄ ⁺ )

This study addresses the unclear crystallization behavior of rubidium in chlorobromine coexisting brine systems through experimental and simulation approaches. First, the phase equilibrium data of the ternary system RbCl–RbBr–H2O at 298.15 K were determined using the isothermal dissolution equilibrium method, and the corresponding phase diagram was constructed. The solid phase was characterized by XRD and SEM-EDS, and solubility was theoretically calculated and validated using the Pitzer model. To further elucidate the solid-solution formation behavior of rubidium in chlorobromine coexisting brine systems at the microscopic level, molecular dynamics simulations were performed. Combined with the previously reported phase diagrams of MCl–MBr–H2O systems (M = Li+, Na+, K+, NH4+), the radial distribution functions, coordination numbers, and mean square displacements of different systems were systematically analyzed to examine the differences in ionic hydration structures and migration behavior. From macroscopic phase equilibria to microscopic ion dynamics, this study systematically clarifies the common patterns of formation of continuous solid solutions in chlorobromine coexisting brine systems.