Chemical forms of sulfur in geological and archeological asphaltenes from Middle East, France, and Spain determined by sulfur K- and L-edge X-ray absorption near-edge structure spectroscopy

Asphaltene samples extracted from archeological and geological bitumens fro m the Middle East, France, and Spain were studied by sulfur K- and L-edge X -ray absorption near-edge structure (XANES) spectroscopy in combination wit h isotopic analyses (delta(13)C and delta D). Within each series, the sampl es were genetically related by their delta(13)C values. The gross and eleme ntal composition and the delta D values were used to characterize the weath ering state of the samples. Sulfur K- and L-edge XANES results show that in all the samples, dibenzothiophenes are the dominant forms of sulfur. In th e least oxidized asphaltenes, minor species include disulfides, alkyl and a ryl sulfides, and sulfoxides. With increasing alteration the proportion of oxidized sulfur (sulfoxides, sulfones, sulfonates and sulfates) increases, whereas the disulfide and sulfide content decreases. This evolution is obse rved in all the series, regardless of the origin of the asphaltenes. This w ork illustrates the advantages of XANES spectroscopy as a selective probe f or determining sulfur speciation in natural samples. It also shows that S K - and L-edge XANES spectroscopy are complementary for identifying the oxidi zed and reduced forms of sulfur, respectively. Copyright (C) 1999 Elsevier Science Ltd.