Sorption of metal ions on clay minerals. 1: Polarized EXAFS evidence for the adsorption of Co on the edges of hectorite particles

Journal Article · Thu Jul 01 04:00:00 EDT 1999 · Journal of Colloid and Interface Science

DOI:https://doi.org/10.1006/jcis.1999.6253· OSTI ID:362072

Schlegel, M L; Manceau, A; Charlet, L ^[1]; Chateigner, D ^[2]

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1. Univ. of Grenoble (France). Environmental Geochemistry Group
2. Univ. du Maine, Le Mans (France). Lab. de Physique de l`Etat Condense

The local structural environment of Co sorbed on hectorite (a magnesian smectite) has been investigated by polarized EXAFS (P-EXAFS) spectroscopy on a self-supporting film of Co-sorbed hectorite. This sorption sample was prepared by contacting Co and hectorite at pH 6.5 and at high ionic strength (0.3 M NaNO{sub 3}) to favor pH-dependent sorption reaction over cation exchange. A self-supporting film was elaborated after 120 h of reacting time, when apparent quasi-equilibrium conditions were attained. The half-width at half maximum of the orientation distribution of c* axis of individual clay platelets off the film normal was determined by quantitative texture analysis, and found to be equal to 18.9{degree}. Co K-edge P-EXAFS spectra were recorded at angles between the incident beam and the film normal equal to 0, 35, 50, and 60{degree}; the 90{degree} spectrum was obtained by extrapolation. Spectral analysis led to the identification of the two nearest cationic subshells containing 1.6 {+-} 0.4 Mg at 3.03 {angstrom} and 2.3 {+-} 0.5 Si at 3.27 {angstrom}. These distances are respectively characteristic of edge-sharing linkages between Mg and Co octahedra and of corner-sharing linkages between Co octahedra and Si tetrahedra, as in clay structures. The angular dependence of the Co-Mg and Co-Si contributions indicates that Co-Mg pairs are oriented parallel to the film plane, whereas Co-Si pairs are not. These results are interpreted by the formation of Co inner-sphere mononuclear surface complexes located at the edges of hectorite platelets, in the continuity of the (Mg, Li) octahedral sheet.

• OSTI ID: 362072
• Journal Information: Journal of Colloid and Interface Science, Journal Name: Journal of Colloid and Interface Science Journal Issue: 1 Vol. 215; ISSN 0021-9797; ISSN JCISA5
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
ADSORPTION
COBALT
CRYSTAL STRUCTURE
ENVIRONMENTAL TRANSPORT
MONTMORILLONITE
SORPTIVE PROPERTIES