Simultaneous cesium desorption and surfactant degradation from montmorillonite by coupled capacitive deionization-electro-oxidation.

Abstract

Remediation of cesium-contaminated clay minerals is difficult because Cs+ is strongly retained within collapsed interlayer spaces. Cationic surfactants can promote Cs+ release, but residual surfactant creates a secondary pollution risk requiring post-treatment. Here, a coupled capacitive deionization-electro-oxidation (CDI-EO) system using a boron-doped diamond (BDD) anode and activated carbon cathode was developed for one-step Cs+ desorption and in situ surfactant degradation from Cs-saturated montmorillonite (0.95 mmol g-1, 85% of cation exchange capacity, CEC). Electrochemical degradation of dodecyltrimethylammonium bromide (DTAB) was first optimised in a static electrolytic cell, reaching ∼96% degradation at 150 mA cm-2 after 12 h for a DTAB loading of 0.5 × CEC. These conditions (150 mA cm-2, 0.4 M Na2SO4, pH 7) were then applied in a recirculating flow-by CDI cell at 20 mL min-1. Within 6 h, DTAB degradation reached 84-89% and Cs+ desorption up to ∼89%, with maximum Cs+ release within 1 h due to surfactant-induced interlayer expansion and electric-field-driven ion extraction. XRD showed interlayer contraction to 1.22-1.25 nm after treatment, confirming effective surfactant removal from the clay structure. Over five consecutive cycles, Cs+ desorption remained ∼70% and surfactant degradation exceeded 80%, demonstrating sustained treatment performance. Electrical energy consumption was 129-140 kWh kg-1 clay for the dilute laboratory batches studied, and the electrosorption capacity of the unmodified AC cathode is identified as the bottleneck for net Cs⁺ capture. The integrated CDI-EO process therefore provides a simplified single-step route for radionuclide-contaminated clay remediation, simultaneously combining decontamination and surfactant removal while avoiding a separate post-treatment stage for disposal.

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