Abstract
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 LIII 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.
| Original language | English |
|---|---|
| Pages (from-to) | 21-32 |
| Number of pages | 12 |
| Journal | Journal of Colloid and Interface Science |
| Volume | 315 |
| Issue number | 1 |
| DOIs | |
| State | Published - Nov 1 2007 |
| Externally published | Yes |
Funding
The authors gratefully acknowledge the help of Prashant Srivastava and Navdeep Kaur for the preparation of the Pb- and Cd-sorbed kaolinite samples and various Pb and Cd reference materials, respectively. This work was performed in part at the Australian National Beamline Facility with support from the Australian Synchrotron Research Program (03/04-AB-26, 03/04-GUP-01), which is funded by the Commonwealth of Australia under the Major National Research Facilities Program. We gratefully acknowledge the help from Garry Foran at the ANBF and Steven Heald at XOR/PNC-CAT for help with the collection of XAFS data. Use of XOR/PNC facilities at the Advanced Photon Source, and research at these facilities, are supported by the U.S. Department of Energy, Basic Energy Sciences, a major facilities access grant from NSERC, the University of Washington, Simon Fraser University, the Pacific Northwest National Laboratory and the Advanced Photon Source. Use of the Advanced Photon Source is also supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract DE-AC02-06CH11357.
Keywords
- Adsorption
- EXAFS spectroscopy
- Gibbsite
- Polynuclear complexes
- Steric hindrance
- Surface structure