Studies of the nature of Cu{sup 2+} and Pb{sup 2+} binding sites in soil humic substances using x-ray absorption spectroscopy
- Univ. of Wisconsin, Madison, WI (United States)
We have investigated the binding environments of Cu{sup 2+} and Pb{sup 2+} complexed by soil humic substances using synchrotron-based X-ray absorption spectroscopy. With the assistance of bond network analysis, analysis of X-ray absorption near edge structure (XANES) and radial structure functions derived from extended X-ray absorption fine structure (EXAFS) spectra of Cu-humate at pH 4, 5, and 6 yielded a tetragonally-distorted octahedral binding environment for Cu with 4 O atoms at an average distance of 1.94 {angstrom}, 20 atoms at an average distance of 2.02 {angstrom}, and 4 C atoms at an average distance of 3.13 {angstrom}. Analysis of Pb-humate samples at pH 4, 5, and 6 yielded 4 O atoms at average distances between 2.46 {angstrom} to 2.32 {angstrom} and 2 C atoms at an average distance of 3.26 {angstrom} for Pb. We interpret the presence of C atoms in the second atomic shell of the metal binding site as evidence that both C{sup 2+} and Pb{sup 2+} form innersphere complexes with soil humic substances. Within the pH range 4-6, there is no significant change in the structure of the binding sites for either Cu or Pb. 65 refs., 8 figs., 5 tabs.
- OSTI ID:
- 576338
- Journal Information:
- Geochimica et Cosmochimica Acta, Vol. 61, Issue 11; Other Information: PBD: Jun 1997
- Country of Publication:
- United States
- Language:
- English
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