Differentiation between adsorbed and precipitated sulphate in soils and at micro-sites of soil aggregates by sulphurK-edge XANES

Autor: J. Prietzel, Murielle Salomé, A. Herre, D. Eichert, Juergen Thieme
Rok vydání: 2008
Předmět:
Zdroj: European Journal of Soil Science. 59:730-743
ISSN: 1365-2389
1351-0754
DOI: 10.1111/j.1365-2389.2008.01034.x
Popis: To investigate the potential of synchrotron-based X-ray Absorption Near-Edge Structure spectroscopy (XANES) at the sulphur (S) K-edge for a discrimination of adsorbed and precipitated sulphate in soils and soil particles, XANES spectra of ionic sulphate compounds and Al/Fe hydroxy sulphate minerals were compared with spectra of SO 4 2- adsorbed to ferrihydrite, goethite, haematite, gibbsite or allophane. Ionic sulphate and hydroxy sulphate precipitates had broader white-lines (WL) at 2482.5 eV (full width at half maximum (FWHM) of edge-normalized spectra, 2.4-4.2 eV; Al hydroxy sulphates, 3.0 eV) than SO 4 2- adsorbed to Al/Fe oxyhydroxides or allophane (FWHM, 1.8-2.4 eV). The ratio of the white-line (WL) height to the height of the post-edge feature at 2499 eV (WL/PEF) was larger for SO 4 2- adsorbed to Al/Fe oxyhydroxides or allophane (8.1-11.9) than for Al/Fe hydroxy sulphates and ionic sulphates (3.9-5.7). The WL/PEF ratio of edge-normalized S K-edge XANES spectra can be used to distinguish adsorbed from precipitated SO 4 2- in soils and also at microsites of soil particles. The contribution of adsorbed and precipitated SO 4 2- to the total SO 4 2- pool can be roughly quantified. Adsorbed ester sulphate may result in overestimation of precipitated SO 4 2- . The spectra of most soils could be fitted by linear combination fitting (LCF), yielding a similar partitioning between adsorbed and precipitated SO 4 2- as an evaluation of the WL/PEF ratio. The SO 4 2- pool of German forest soils on silicate parent material in most cases was strongly dominated by adsorbed SO 4 2- ; however, in three German forest soils subject to elevated atmospheric S deposition, a considerable portion of the SO 4 2- pool was precipitated SO 4 2- , most likely Al hydroxy sulphate. The same is true for Nicaraguan Eutric and Vitric Andosols subject to high volcanogenic S input. In the subsoil of the Vitric Andosol, adsorbed SO 4 2- and Al hydroxy sulphate coexist on a micron scale.
Databáze: OpenAIRE
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