Fe
L-, S
L-, and O
K-edge X-ray absorption spectra of natural monoclinic and hexagonal pyrrhotites, Fe
1-xS, and arsenopyrite, FeAsS, have been measured and compared with the spectra of minerals oxidized in air and treated in aqueous acidic solutions, as well as with the previous XPS studies. The Fe
L-edge X-ray absorption near-edge structure (XANES) of vacuum-cleaved pyrrhotites showed the presence of, aside from high-spin Fe
2+, small quantity of Fe
3+, which was higher for a monoclinic mineral. The spectra of the essentially metal-depleted surfaces produced by the non-oxidative and oxidative acidic leaching of pyrrhotites exhibit substantially enhanced contributions of Fe
3+ and a form of high-spin Fe
2+ with the energy of the 3d orbitals increased by 0.3–0.8 eV; low-spin Fe
2+ was not confidently distinguished, owing probably to its rapid oxidation. The changes in the S
L-edge spectra reflect the emergence of Fe
3+ and reduced density of S s–Fe 4s antibonding states. The Fe
L-edge XANES of arsenopyrite shows almost unsplit
eg band of singlet Fe
2+ along with minor contributions attributable to high-spin Fe
2+ and Fe
3+. Iron retains the low-spin state in the sulphur-excessive layer formed by the oxidative leaching in 0.4 M ferric chloride and ferric sulphate acidic solutions. The S
L-edge XANES of arsenopyrite leached in the ferric chloride, but not ferric sulphate, solution has considerably decreased pre-edge maxima, indicating the lesser admixture of S s states to Fe 3d orbitals in the reacted surface layer. The ferric nitrate treatment produces Fe
3+ species and sulphur in oxidation state between +2 and +4.
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