Original paper

Effect of oxygen sharing on the white line of S K-edge XANES spectra of sulphate minerals

Figueiredo, Maria; Ondinada Silva, Teresa; Pereira,


Sulphur occurs under a diversity of formal oxidation states being simultaneously an essential plant nutrient and an environmental pollutant. Intermediate formal valences between 6+ (sulphate) and 4+ (sulphite) were assigned by previous authors in soil colloids by X-ray absorption spectroscopy; a search for similar electronic states was undertaken by analyzing near-edge details preceding the strong white line of S 1s XANES spectra in well crystallized sulphates depending on the structural arrangement. Sulphate minerals illustrating a variety of sharing degrees of oxygen anions between tetrahedral groups [SO4] and transition metal cations, ranging from non-bonded, isolated tetrahedra to fully shared oxygen anions, were selected for the spectroscopic study. Differences in details appearing at the shoulder of the intense white line of fully oxidized sulphur were successfully correlated with the crystal structural features of these model minerals, showing that intermediate valence states of sulphur resulting from the sharing of oxygen anions may be also present in crystalline sulphates.


sulphatessulphurxaneswhite linepre-edge