Enhanced cesium removal from clay minerals using surfactant-assisted capacitive deionization

Cesium (Cs + ) is strongly retained by clay minerals, particularly within the interlayers of 2:1-type clays, making its removal from contaminated soils challenging. We hypothesised that coupling capacitive deionization (CDI) with cationic surfactant intercalation would produce a synergistic effect, whereby surfactant-induced interlayer expansion increases accessibility to strongly bound Cs + , which can then be mobilised and extracted by the applied electric field, enabling more rapid and efficient desorption than either technique alone. To test this, Cs-loaded kaolinite and montmorillonite were prepared at low (5%) and saturated (100%) loadings, and their desorption behaviour studied under surfactant-only washing, CDI-only treatment, and the combined CDI–surfactant approach, with systematic variation of surfactant type, concentration, and treatment duration. Structural and compositional changes were characterised using SEM–EDX and XRD, and Cs partitioning assessed through sequential extraction. The combined process delivered markedly superior performance, achieving >90% Cs + removal within 1 h for both clay types, including fully saturated montmorillonite, far exceeding the efficiencies of either CDI alone or 24 h surfactant washing. XRD confirmed substantial interlayer expansion in montmorillonite upon surfactant intercalation, whilst CDI enhanced ion mobility and enabled access to strongly bound interlayer Cs + . The integrated approach also required up to 50% less surfactant to attain maximum desorption, demonstrating a strong synergistic effect between surfactant-induced structural modification and electric-field-driven ion extraction. These findings validate the hypothesis and establish CDI-assisted surfactant intercalation as a promising and scalable strategy for the remediation of Cs-contaminated soils. • CDI–surfactant coupling achieves >90% Cs removal from clays within 1 h. • Electric-field-driven ion migration accelerates desorption of interlayer-bound Cs + . • Up to 50% reduction in surfactant usage achieved without loss of removal efficiency.