Arsenic, Iron and Organic Matter in Quaternary Aquifer Sediments from Western Hetao Basin, Inner Mongolia

To investigate geochemical and mineralogical features of sediments from aquifers containing high levels of dissolved arsenic (As) in western Hetao Basin, Inner Mongolia, sediment samples were collected for XRD (X-ray diffraction), amorphous Fe/Mn oxides, and humic/fulvic acid analyses, in addition to As determination. In the study area, the total As contents in the sediments were in the range 5.3-28.8 mg/kg; while that associated with humic substances in the range 4-9 mg/kg, accounting for 26%-47% of the total As. The results of XRD analysis suggest that clay and silt contain certain small amounts of iron oxides minerals, such as ferrihydrite, hematite and goethite, whereas have higher As and Fe2O3 contents. Up to one third of As in the sediments could be extracted by ammonium oxalate, and high As contents were generally found in organic-rich clay or silty clay samples with high FA/HA ratio. As is strongly associated with humic substances and Fe oxyhydroxides, which may be the major sink and source of As in the aquifer sediments.