Gräfe Markus, Singh Balwant, Balasubramanian Mahalingam
Faculty of Agriculture, Food & Natural Resources, The University of Sydney, Sydney, NSW 2006, Australia.
J Colloid Interface Sci. 2007 Nov 1;315(1):21-32. doi: 10.1016/j.jcis.2007.05.022. Epub 2007 Aug 21.
Little spectroscopic evidence exists in the literature describing the surface complexation of cadmium (Cd) and lead (Pb) on kaolinite, the dominant clay mineral present in highly weathered soils of tropical and humid climates. X-ray absorption fine structure (XAFS) spectroscopy data at the Cd K and Pb L(III) edges were collected on Cd- and Pb-sorbed kaolinite samples and compared to a suite of reference materials including Pb and Cd sorbed on amorphous (am-)gibbsite. Cadmium formed dominantly (>75%) outer sphere complexes on kaolinite and a small fraction of CdOHCl complexes. In contrast Cd adsorbed as an inner sphere complex on gibbsite, suggesting that the Si tetrahedral sheet hindered Cd sorption to the Al octahedral sheet on kaolinite. Lead formed polymeric complexes, which bonded to kaolinite via edge sharing with surface Al octahedra. Two distinct Pb-Al edge-sharing distances on am-gibbsite, as opposed to one on kaolinite, suggested a similar steric hindrance effect for the surface complexation of polymeric Pb complexes on kaolinite. The results of this study show that the Si tetrahedral sheet limited the surface complexation of Cd and Pb on kaolinite, elevating kaolinite's permanent negative charge properties in retaining these heavy metals at its surface.
在文献中，几乎没有光谱证据描述镉（Cd）和铅（Pb）在高岭石上的表面络合情况，高岭石是热带和湿润气候高度风化土壤中存在的主要粘土矿物。在吸附了Cd和Pb的高岭石样品上收集了Cd K边和Pb L(III)边的X射线吸收精细结构（XAFS）光谱数据，并与一组参考材料进行了比较，这些参考材料包括吸附在无定形（am-）三水铝石上的Pb和Cd。镉在高岭石上主要形成（>75%）外层络合物以及一小部分CdOHCl络合物。相比之下，镉以内层络合物的形式吸附在三水铝石上，这表明硅四面体片层阻碍了镉在高岭石上吸附到铝八面体片层上。铅形成了聚合络合物，通过与表面铝八面体的边共享与高岭石结合。在无定形三水铝石上有两种不同的Pb-Al边共享距离，而在高岭石上只有一种，这表明聚合铅络合物在高岭石上的表面络合存在类似的空间位阻效应。这项研究的结果表明，硅四面体片层限制了镉和铅在高岭石上的表面络合，提高了高岭石在其表面保留这些重金属的永久负电荷特性。
