Structure and stability of Cd[sup 2+] surface complexes on ferric oxides; 1: Results from EXAFS spectroscopy

In the environment, such different processes as transport and availability of contaminants in soils, scavenging and release of trace elements in water cycles, wastewater treatment, and groundwater protection are intimately correlated with interfacial chemical reactions. Extended X-ray absorption fin...

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Bibliographic Details
Published in:Journal of colloid and interface science 1994-11, Vol.168:1
Main Authors: Spadini, L., Manceau, A., Charlet, L., Schindler, P.W.
Format: Article
Language:English
Subjects:
540220 - Environment, Terrestrial- Chemicals Monitoring & Transport- (1990-)
ABSORPTION SPECTROSCOPY
ADSORPTION
CADMIUM COMPLEXES
CHALCOGENIDES
COMPLEXES
CRYSTAL STRUCTURE
ENVIRONMENTAL SCIENCES
GOETHITE
IRON COMPOUNDS
IRON OXIDES
MINERALS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PHASE STUDIES
SORPTION
SORPTIVE PROPERTIES
SPECTROSCOPY
SURFACE PROPERTIES
TRANSITION ELEMENT COMPOUNDS
X-RAY SPECTROSCOPY
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Summary:In the environment, such different processes as transport and availability of contaminants in soils, scavenging and release of trace elements in water cycles, wastewater treatment, and groundwater protection are intimately correlated with interfacial chemical reactions. Extended X-ray absorption fine structure (EXAFS) spectroscopy has been used to study the adsorption and coprecipitation mechanism of Cd(II) on hydrous ferric oxide (HFO) and [alpha]-FeOOH (goethite) in aqueous solutions. Fe and Cd K-edge EXAFS spectra of a coprecipitated [alpha]-(Cd[sub 0.005]Fe[sub 0.995]) OOH phase are similar which indicates that both cations have the same structural environment and, hence, that Cd substitutes for Fe within the [alpha]-FeOOH lattice. At low coverage, Cd atoms mainly sorb at the termination of goethite chains on (001) planes by sharing edges and corners with surface Fe octahedra. At medium and high surface loading, Cd atoms sorb along chains on (hk0) planes where they share mainly C with Fe octahedra. As a consequence, crystallographic planes of goethite, and thus surface sites, do not appear to have the same affinity for Cd and it is demonstrated that the number of bonds between the sorbate and the sorbent is at a maximum on high affinity surface sites. On HFO, Cd-Fe distances are similar to those found for goethite but the number of nearest and next-nearest Fe cations is independent of solution parameters. This result indicates that the high affinity to low affinity surface site density ratio is much higher on HFO than on goethite and it is shown that this finding is fully consistent with the structure of ferrihydrite.
ISSN:0021-9797
1095-7103
DOI:10.1006/jcis.1994.1395