Fe and S K-edge XAS determination of iron-sulfur species present in a range of acid sulfate soils: Effects of particle size and concentration on quantitative XANES determinations

Acid sulfate soils (ASS) are soils and soft sediments in which sulfuric acid may be produced from iron sulfides or have been produced leaving iron oxyhydroxysulfates in amounts that have a long lasting effect on soil characteristics. If soil material is exposed to rotting vegetation or other reducing material, the Fe-oxyhydroxysulfates can be bacterially reduced to sulfides including disulfides (pyrite and marcasite), and Monosulfidic Black Ooze (MBO) a poorly characterised material known to be a mixture of iron sulfides (especially mackinawite) and organic matter. The chemistry of these environments is strongly affected by Fe and S cycling processes and herein we have sought to identify key differences in environments that occur as a function of Fe and S concentration. In addition to our chemical results, we have found that the effects of particle size on self absorption in natural sediments play an important role in the spectroscopic identification of the relative proportions of different species present.