“…Due to isomorphic substitutions in the octahedral and tetrahedral sheets, a net negative charge is established in the structure; this charge is balanced through cation adsorption, usually in the interlayer spaces, which results in a high cation exchange capacity (CEC) (Bergaya et al, 2006). In addition to the adsorption of mono-and divalent cations such as Na + , K + , and Ca 2+ , smectite can also adsorb trivalent elements (e.g., trivalent rare earth elements (REE 3+ ) and trivalent actinides), as has been shown in several studies (Takahashi et al, 1998;Stumpf et al, 2001;Bradbury and Baeysns, 2002;Coppin et al, 2002;Stumpf et al, 2002;Coppin et al, 2003;Stumpf et al, 2004;Rabung et al, 2005;Brandt et al, 2007;Tan et al, 2010). Due to these and other features, smectites are used as geochemical barriers in different contexts including secondary barriers for deep nuclear waste disposal (Pusch, 1998), where smectites are employed to adsorb actinide trivalent cations.…”