EXAFS and XANES study of arsenic in contaminated soil

Historical mining, processing and refinement of arsenic in purpose built calciners in Cornwall, UK, have resulted in extremely high contamination of soils with arsenic in some localized areas. The x-ray absorption spectroscopic methods XANES (x-ray absorption near-edge structure) and EXAFS (extended x-ray absorption fine structure) were used to retrieve arsenic molecular information, i.e. oxidation state and local structure around As atoms, in the soil from a calciner ' s residue dump near Camborne (which contained 8.82 wt% arsenic) and identify the most abundant modes of As bonding. The results show that arsenic is predominantly in pentavalent form, tetrahedrally bound to oxygen atoms in the first coordination sphere. Fe and Al atoms are found in the next neighbour coordination shells around As. The As-Fe and As-Al distances and coordination numbers strongly suggest that arsenate in the soil is present in two forms, viz. as amorphous or poorly crystalline hydrous oxides of Fe (most likely FeAsO4) and adsorbed on aluminium (hydr)oxides or aluminosilicates such as clay. Copyright (c) 2005 John Wiley & Sons, Ltd.