Abstract:In this study, montmorillonite-goethite and montmorillonite-ferrihydrite complexes were synthesized, and batch adsorption experiments combined with various spectroscopies were applied to investigate the binding behaviors and mechanisms of tungsten (WO42-). The results showed that iron oxides could form heterogeneous and fine particles on the surface of montmorillonite, the order of adsorption capacity for tungsten was montmorillonite-ferrihydrite>montmorillonite-goethite complexes> montmorillonite, and the adsorption decreased with increasing pH; In situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy showed that outer-sphere complexes were formed on montmorillonite surface, whereas inner-sphere complexes (Fe-O-W) were formed on montmorillonite-iron oxide complexes. Moreover, tungsten polymerization occured at low pH on iron oxide surface; X-ray photoelectron spectroscopy (XPS) further showed that FeOH groups participate in the binding of tungsten on montmorillonite-iron oxide complexes. In conclusion, the coating of iron oxide on phyllosilicates could enhance tungsten retention, transform tungsten species from outer-sphere to inner-sphere complexes, as well as facilitated the formation of polymeric tungstate, which provided significant guidance for predicting the mobility, bioavailability, and fate of tungsten in soil.