Effects of NH₄⁺, K⁺, Mg²⁺, and Ca²⁺ on the Cesium Adsorption/Desorption in Binding Sites of Vermiculitized Biotite

The reversibility of cesium adsorption in contaminated soil is largely dependent on its interaction with micaceous minerals, which may be greatly influenced by various cations. Herein, we systematically investigated the effects of NH₄⁺, K⁺, Mg²⁺, and Ca²⁺ on the adsorption/desorption of Cs⁺ into different binding sites of vermiculitized biotite (VB). Original VB was initially saturated by NH₄⁺, K⁺, or Mg²⁺ we then evaluated the adsorption of Cs⁺ on three treated VBs, and the desorption by extraction with NH₄⁺, K⁺, Mg²⁺, or Ca²⁺ was further evaluated. Our structural analysis and Cs⁺ extractability determinations showed that NH₄⁺ and K⁺ both collapsed the interlayers of VB, resulting in the dominant adsorption of Cs⁺ to external surface sites on which Cs⁺ was readily extracted by NH₄⁺, K⁺, Mg²⁺, or Ca²⁺ irrespective of their species, whereas Mg²⁺ maintained the VB with expanded interlayers, leading to the overwhelming adsorption of Cs⁺ in collapsed interlayer sites on which the Cs⁺ desorption was difficult and varied significantly by the cations used in extraction. The order of Cs⁺ extraction ability from the collapsed interlayers was K⁺ ≫ Mg²⁺ ≈ Ca²⁺ ≫ NH₄⁺. These results could provide important insights into Cs migration in soil and its decontamination for soil remediation.