蒙脱石-氧化铁二元复合胶体吸附钨的研究

本研究选取代表性层状硅酸盐蒙脱石，两种代表性氧化铁(水铁矿、针铁矿)，合成蒙脱石-水铁矿、蒙脱石-针铁矿二元复合体，通过宏观吸附以及光谱学技术探究钨(WO₄^2-)在蒙脱石-氧化铁复合体上的吸附行为和潜在机制。结果表明：氧化铁紧密覆盖在蒙脱石表面，使表面颗粒更加细小；钨的吸附量随pH升高而降低，3种吸附剂对钨吸附量大小顺序为：蒙脱石-水铁矿>蒙脱石-针铁矿>蒙脱石；原位红外光谱实验表明，钨在蒙脱石表面主要以外圈络合物形式存在，而在蒙脱石-氧化铁复合体上形成内圈络合物(Fe-O-W)，且在低pH时，形成聚合态钨；X-射线光电子能谱进一步表明，针铁矿和水铁矿表面铁羟基参与了钨的络合反应。本研究证实，氧化铁覆盖不仅增大蒙脱石对钨的吸附量，而且使钨由外圈络合物形态转变为内圈络合态，进一步生成聚合态钨。研究结果对预测钨在土壤中的迁移转化、生物有效性和归宿有重要指导意义。

Adsorption of Tungsten by Montmorillonite-Iron oxide Binary Complex

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 (WO₄^2-). 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.