Assessing the size-dependent chemical speciation of soil particles using electron probe X-ray microanalysis.

Soils of the Pereemnaya river catchment, East Siberia, Russia, characterized by high percentage of particles under 10 µm size and the almost total absence of clay minerals, were studied using ultra-thin window electron probe X-ray microanalysis (EPMA). Three subfractions – 10–5 µm, 1–5 µm and <1 µm were distinguished within <10 µm fraction on the basis of mineralogical composition and chemistry peculiarities. Besides the single particles characterization, the bulk chemistry of specified subfractions and their contributions to the bulk soil chemistry were evaluated. It was shown that concentrations of alkali and alkaline-earth metals within <10 µm fraction increased in the row (5–10 µm) < (1–5 µm) < (<1 µm). The presence of two mica types – low-Fe and rich-Fe – was detected in all the subfractions. Being compared with the soil bulk chemistry, the data obtained for fraction <10 µm show that this fraction is the major source of alkali and alkaline-earth metals and consequently the main contributor to element release due to weathering. [ABSTRACT FROM AUTHOR]