pH‐Controlled Switch over Coadsorption and Separation for Mixed Cs⁺ and Sr²⁺ by an Acid‐Resistant Potassium Thioantimonate

Abstract Switchable coadsorption and separation for elimination/partitioning of Cs⁺ and Sr²⁺ is achieved by pH‐controlled ion exchange using a potassium thioantimonate K₂Sb₄S₇·2H₂O (SbS‐1K) with fantastic pH durability from diluted NaOH (pH 12) to concentrated HCl (3 m). At pH 6, SbS‐1K exhibits ultrafast adsorption kinetics (R ≈ 90% in 2 min for Cs⁺ and 20 min for Sr²⁺) and high removal rates (R ≈ 98–99%) at equilibrium for both Cs⁺ and Sr²⁺. At pH 2, the Sr²⁺ adsorption is inhibited by H⁺ with a great loss in R^Sr to 11.18%, whereas the R^Cs remains at 96.99%, contributing to a top‐ranked separation factor SF_Cs/Sr of 256. The SbS‐1K‐filled ion exchange column can be switched between the eliminating (R^Cs > 99.91%; R^Sr > 98.19%) and separating (R^Cs > 98.99%; R^Sr ≈ 0±3%) modes for treating continuous flow with a variation from pH 6 to pH 2 or vice versa. The SbS‐1K/PTFE membrane exhibits coadsorption and separation effects for filtration of low concentrated mixed Cs⁺ and Sr²⁺ solution (1 ppm for each), even at an ultrafast vacuum filtration speed (30 mL min^–1). Combined with easy synthesis and high β/γ irradiation resistance, SbS‐1K represents a new‐concept bifunctional exchanger with discriminating intelligence for equipment innovation.