Unveiling the adsorption behavior and mass transfer mechanism of Rb+ and Cs+ adsorption on FeMn-MOF

•FeMn-MOF with different particle size and specific surface area were prepared.•The structure, performance difference and related mechanism of different FeMn-MOF were clarified.•The adsorption properties of small particles and 2D FeMn-MOF were significantly improved.•The ion exchange process and migration mode were analyzed in detail by using MD simulation method. The development of efficient adsorbents is essential for utilizing low-grade liquid rubidium (Rb) and cesium (Cs) resources, which is often hindered by unclear adsorption mechanisms. In this study, a metal–organic framework (MOF) adsorbent with a Prussian blue structure, named FeMn-MOF, was designed and synthesized. The FeMn-MOF materials were processed into small particles with varying sizes and specific surface areas, and into two-dimensional (2D) FeMn-MOF using ball milling and exfoliation methods. Characterization and adsorption experiments demonstrated the excellent adsorption properties of Rb+ and Cs+. The results indicate that the adsorption rate and capacity are significantly influenced by the particle size and specific surface area, wherein smaller particles and 2D FeMn-MOF exhibiting superior performance. Additionally, molecular dynamics simulations at the microscopic level revealed that ion exchange occurs at the adsorption interface, which limits the actual adsorption capacity. During the adsorption process, Rb+ and Cs+ undergo partial dehydration from the bulk phase to the adsorption interface; however, even after partial dehydration, the hydrated ions retain a relatively large radius, hindering their entry into the internal framework. This work paves the way for developing advanced adsorbents with large surface areas to enhance adsorption performance, providing valuable insights and a theoretical foundation for the separation and extraction of Rb and Cs resources from salt lakes.