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A Raman spectroscopic study of bukovskýite Fe2(AsO4)(SO4)(OH)· 7H2O, a mineral phase with a significant role in arsenic migration



The Raman spectrum of bukovskýite [Fe3+2(OH)(SO4)(AsO4)· 7H2O] has been studied and compared with that of an amorphous gel containing specifically Fe, As and S, which is understood to be an intermediate product in the formation of bukovskýite. The observed bands are assigned to the stretching and bending vibrations of (SO4)2− and (AsO4)3− units, stretching and bending vibrations and vibrational modes of hydrogen-bonded water molecules, stretching and bending vibrations of hydrogen-bonded (OH) ions and Fe3+[BOND](O,OH) units. The approximate range of O[BOND]H···O hydrogen bond lengths was inferred from the Raman spectra. Raman spectra of crystalline bukovskýite and of the amorphous gel differ in that the bukovskýite spectrum is more complex, the observed bands are sharp and the degenerate bands of (SO4)2− and (AsO4)3− are split and more intense. Lower wavenumbers of δ H2O bending vibrations in the spectrum of the amorphous gel may indicate the presence of weaker hydrogen bonds compared to those in bukovskýite. Copyright © 2011 John Wiley & Sons, Ltd.

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