Spectroscopic evidence for the formation of mixed-cation hydroxide phases upon metal sorption on clays and aluminum oxides
- Univ. of Delaware, Newark, DE (United States). Dept. of Plant and Soil Sciences
- Brookhaven National Lab., Upton, NY (United States)
Retention of heavy metal ions on soil mineral surfaces is an important process for maintaining environmental quality. The present study examines the kinetics and mechanisms of Ni(II) sorption onto pyrophyllite, kaolinite, gibbsite, and montmorillonite. Ni sorption reactions were initially fast (15--40% of the initial Ni was removed within the first hour). Thereafter, the rate of sorption decreased significantly. X-ray absorption fine structure (XAFS) spectroscopy was used to determine the local structural environment of Ni(II). Data analysis reveals the presence of polynuclear Ni surface complexes. Ni-Ni bond distances (3.00--3.03 {angstrom}) were distinctly shorter than in Ni(OH){sub 2}(s) (3.09 {angstrom}). The authors propose that the reduction of the Ni-Ni distances is caused by the formation of mixed Ni/Al hydroxide phases. They suspect that the release of Al into solution is the rate-determining step for the formation of mixed Ni/Al hydroxide-like phases in this study. The study demonstrates that mixed Ni/Al hydroxide-like compounds can form when Ni is introduced into a suitable environment in which there is a source of hydrolyzed species of Al. Thus, the formation of mixed-cation hydroxide compounds should be considered when conducting metal sorption experiments, modeling metal surface complexation, determining speciation, and assessing the risk of the migration of contaminants in polluted sites.
- OSTI ID:
- 438901
- Journal Information:
- Journal of Colloid and Interface Science, Vol. 186, Issue 1; Other Information: PBD: 1 Feb 1997
- Country of Publication:
- United States
- Language:
- English
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