Dissolution‐Controlled Phase Separation of Cs ⁺ /Rb ⁺ in High‐Salinity Brines via All‐Inorganic Prussian Blue Analogs

The similar physicochemical properties of alkali metal elements make the co‐enrichment and precise separation of Cs + and Rb + in complex brine systems highly challenging. Here, an all‐inorganic strategy is proposed, which achieves efficient enrichment and precise separation of Cs + and Rb + in high‐salt systems by constructing Sr 2+ /Ba 2+ ‐based Prussian blue analogs. Two super‐sized precipitates, CsRb‐SrFC, and CsRb‐BaFC (particle sizes up to ∼5 and ∼15 μm), were successfully synthesized, significantly simplifying the complex solid–liquid separation process of traditional fine particles. Both systems exhibit rapid reaction kinetics (completed within 5 min) and efficient enrichment performance across a wide pH range (2–13). The Sr 2+ system shows maximum recovery rates of 96.08% for Cs + and 66.20% for Rb + , whereas the Ba 2+ system demonstrates stronger affinity for Rb + ( R Rb = 70.92%, R Cs = 56.26%). More importantly, CsRb‐SrFC achieves phase‐selective separation through dissolution differentiation, where water washing induces Rb + dissolution into the liquid phase, whereas Cs + remains fixed in the solid phase, enabling precise acquisition of pure Cs 2 CO 3 (purity ∼98%) through solid–liquid interfacial phase separation. Furthermore, dynamic separation experiments maintain stable and rapid ion‐specific separation characteristics (separation factor SF Cs/Rb = 353.82). This all‐inorganic process combines green economy with engineering applicability, providing theoretical support and technical pathways for targeted recovery and high‐value utilization of Cs + /Rb + resources in complex brine systems.