Selenite sorption onto goethite: isotherm and ion-competitive studies, and effect of pH on sorption kinetics

Sorption of oxyanions onto ferric oxyhydroxides’ surfaces is naturally occurring process with advantageous implications in remediation of contaminated waters or management of landfills. Therefore, this paper provides information on selenite sorption onto goethite, which is one of the most common oxyhydroxides in the environment. Our results showed that selenite sorption was well described by the pseudo-second-order kinetic model, as well as by Langmuir isotherm. This suggests chemisorption as a rate-controlling step and formation of selenite monolayer on goethite surface with relatively high 83.8 µmol g−1 maximum sorption capacity at pH 3, which was determined for initial selenite concentration in the range of 45–550 µmol L−1 in 0.5 g L−1 (m/v) goethite suspension. The Mössbauer analysis revealed only marginal structural changes in goethite during sorption. Our results also showed that pH significantly affects the overall sorption rate constant with the highest values at the acidic region. Study on competitive sorption behaviour highlighted significant influence of phosphate on selenite sorption. There was no competition for sorption positions with excessive concentrations of sulphate and chloride ions. However, equimolar concentrations of sulphate and chloride led to changes in selenite sorption efficiency. Our results showed that selenite sorption onto goethite is a viable method for selenite removal and, thus, goethite can be successfully applied as a component in commercial composite sorbents or in geochemical barriers.