title: Analysis of the improvement of selenite retention in smectite by adding alumina nanoparticles.
abstract: Smectite clay is used as barrier for hazardous waste retention and confinement. It is a powerful material to retain cations, but less effective for retaining anionic species like selenite. This study shows that the addition of a small percentage of γ-Al2O3nanoparticles to smectite significantly improves selenite sorption. γ-Al2O3nanoparticles provide high surface area and positively charged surface sites within a wide range of pH, since their point of zero charge is at pH8-9. An addition of 20wt% of γ-Al2O3to smectite is sufficient to approach the sorption capacity of pure alumina. To analyze the sorption behavior of the smectite/oxide mixtures, a nonelectrostatic surface complexation model was considered, accounting for the surface complexation of HSeO3-and SeO32-, the anion competition, and the formation of surface ternary complexes with major cations present in the solution. Selenite sorption in mixtures was satisfactorily described with the surface parameters and complexation constants defined for the pure systems, accounting only for the mixture weight fractions. Sorption in mixtures was additive despite the particle heteroaggregation observed in previous stability studies carried out on smectite/γ-Al2O3mixtures.
authors: CIEMAT, Department of Environment, Avenida Complutense 40, CP 28040, Madrid, Spain. Electronic address: natalia.mayordomo@ciemat.es.
authors: Natalia
authors: N
authors: Mayordomo
authors: CIEMAT, Department of Environment, Avenida Complutense 40, CP 28040, Madrid, Spain.
authors: Ursula
authors: U
authors: Alonso
authors: CIEMAT, Department of Environment, Avenida Complutense 40, CP 28040, Madrid, Spain.
authors: Tiziana
authors: T
authors: Missana
keywords: Alumina; Mixtures; Selenite; Smectite; Sorption modeling