title: EXAFS study of Zn sorption mechanisms on montmorillonite.
abstract: Extended X-ray absorption fine structure (EXAFS) analysis of zinc sorption on montmorillonite showed that different types of surface complexes or surface precipitates were formed depending on the reaction time. With an initial zinc concentration of 10(-3) M at neutral pH, zinc remained octahedrally coordinated with about six oxygen atoms at Zn-O bond distances of 2.02-2.07 A for up to six months. For samples aged up to 11 days, the Zn-Zn contribution in the second shell suggested formation of multinuclear surface complexes or surface precipitates. For samples aged 20 days and more, Zn-Zn and Zn-Si contributions in the second shell suggested formation of mixed metal coprecipitates such as a Zn phyllosilicate-like phase. Formation of these mixed metal solids probably accounts for the slow continuous sorption reaction at aging times exceeding 20 days. Sequestration of Zn in mixed metal precipitates and the stability of these phases can reduce the concentration, mobility, and toxicity of Zn in soils or sediments.
authors.affiliation: Department of Chemical and Environmental Engineering, Illinois Institute of Technology, Chicago, Illinois 60616, USA.
authors.forename: Shinwoo
authors.initials: S
authors.lastname: Lee
authors.forename: Paul R
authors.initials: PR
authors.lastname: Anderson
authors.forename: Grant B
authors.initials: GB
authors.lastname: Bunker
authors.forename: Cahit
authors.initials: C
authors.lastname: Karanfil
mesh_terms: D000327:Adsorption; D000538:Aluminum Silicates / Q000737:chemistry*; D011232:Chemical Precipitation; D004577:Electron Probe Microanalysis; D005583:Fourier Analysis; D015032:Zinc / Q000737:chemistry*
chemical_list: D000538:Aluminum Silicates; D015032:Zinc