Superior capability of MgAl2O4 for selenite removal from contaminated groundwater during its reconstruction of layered double hydroxides

In this study, MgAl2O4 (cLDHs) with a typical spinel structure was synthesized by calcination of Mg/Al layered double hydroxides (LDHs) and was used as adsorbent for selenite (IV) removal from contaminated groundwater. Based on XRD, SEM/TEM and XPS analysis, the layered structure of LDHs was completely destroyed after calcination and pure bimetal oxides with flakiness structure was obtained. Compared with Mg/Al LDHs (66.89 mg/g), MgAl2O4 (cLDHs) exhibited an excellent selenite removal performance and the maximum adsorption capacity of selenite was 179.59 mg/g. The results indicated that Freundlich isotherm model is suitable to describe the adsorption equilibrium of selenite by cLDHs and the selenite adsorption also followed pseudo-second-order kinetics. Moreover, the influence solution pH and co-existed anion on the selenite by cLDHs was also investigated in detail. According all the experimental results, the removal mechanism of selenite was further discussed. Besides the surface adsorption and ion exchange by LDHs, most of selenite were removed by the intercalation into the interlayer region during the reconstruction process.