(446f) Remediating Contaminated Land on Nuclear Sites

In the UK, the Sellafield nuclear site has entered a phase of waste management and decommissioning. As part of the decommissioning plan, the site operator will begin to remediate contaminated land on and around the facility to avoid its unnecessary long-term storage as waste. The current research explores the design and use of surfactants to increase the decontamination factor of expandable and non-expandable clays. The study has evaluated the use of cationic surfactants (alkyl ammonium ions) ranging from carbon chain length of 8 to 22 with head groups of methyl, ethyl and propyl for the desorption of Cs⁺ from different clay minerals. The decontamination study revealed very good removal of Cs⁺ (⁓98%) from non-expandable clay (kaolinite) using C-22 surfactant. However, decontamination decreased to 70-75% for the expandable clay minerals due to interlayer collapse with Cs⁺ adsorbed. Through appropriate design of the surfactant molecule, the intercalation of surfactant led to an expansion of the clay interlayer which improved Cs⁺ mobility and increased desorption to ⁓83.8% and 79.5% for montmorillonite and vermiculite, respectively. The two-phase kinetic model revealed that the desorption of Cs⁺ from expandable clay minerals was fast for phase 1 (A1 ⁓40%) within t1 47 min, which accounted for the outer-sphere complexes, while slow for phase 2 (A2 ⁓13%) with t2 219 min, attributed to the tightly bound exchangeable ions. However, approximately ⁓18% of adsorbed Cs⁺ was found to be non-exchangeable for desorption due to immobility and fixation in interlayers/FES/hexagon pockets. To enhance desorption performance of the synthesized surfactant, hydrogen peroxide (H₂O₂) was used as an enhancing agent (H₂O₂ catalyzed surface Fe present in clays) and increased the ion-exchange due to its decomposition in interlayers, increasing Cs⁺ desorption from expandable clay minerals to ⁓90%.