Influence of Ca–Na–Cl physicochemical solution properties on the adsorption of Se(-II) onto granite and MX-80 bentonite

Abstract

The adsorption behaviour of Se(-II) onto granite and MX-80 bentonite in Ca–Na–Cl solutions has been studied utilizing adsorption experiments and surface complexation modelling. Adsorption kinetic experiments allude to steady-state adsorption periods after 7 days for granite and 14 days for MX-80 bentonite. Batch adsorption experiments were carried out to determine the influence that the physicochemical solution properties would have on Se(-II) adsorption behaviour. Adsorption of Se(-II) onto granite and MX-80 bentonite follows the trend of anionic adsorption, with a decrease in Rd values as the solution pH increased. There is also an ionic strength influence on the adsorption of Se(-II) onto granite with a decrease in the Rd value as the ionic strength increased. This effect is not found when observing Se(-II) adsorption onto MX-80 bentonite. Final experiments with a representative groundwater, determined that the adsorption of Se(-II) onto granite and MX-80 bentonite returned Rd values of (1.80 ± 0.10) m3∙kg−1 and (0.47 ± 0.38) m3∙kg−1, respectively. In support of the experiments, a surface complexation modelling approach has been employed to simulate the adsorption of Se(-II) onto granite and MX-80 bentonite, where it was determined that two different surface complexes, ≡S_Se−and ≡SOH2+_H2Se were capable of simulating Se(-II) adsorption behaviour.