Environmental Geochemistry of Sediments in Endemic Arseniasis at Western Hetao Plain

Arsenic and As-bearing solid phases in sediments was studied to provide a further evidence for researches of enrichment mechanism of arsenic at western Hetao Plain. The content of arsenic in 23 core sediment samples varies from 7.7 to 34.6 mg/Kg, with great value in clay and mild clay layer. The obvious positive relationship in content between Fe₂O₃, Mn, Sb, B, V and As indicates that the distribution of arsenic in the sediments may be related to Fe and Mn oxides, and mobilization of Sb, B and V may be affected by similar geochemical processes as that of As. Sequential extraction show that in addition to recalcitrant mineral phase dissolved by acid, the major forms of arsenic in the sediment are strongly adsorbed As, followed by As coprecipitated with amorphous Fe oxyhydroxides, As coprecipitated with acid volatile sulfide (AVS), carbonates, Mn oxides, and very amorphous Fe oxyhydroxides. The release of arsenic from the sediment is mainly affected by the competition of phosphate absorption and reductive dissolution of iron hydroxide.