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Arsenic Speciation: Involvement in Evaluation of Environmental Impact Caused by Mine Wastes

Roussel, Christophe, Bril, Hubert, Fernandez, Angel
Journal of environmental quality 2000 v.29 no.1 pp. 182-188
arsenic, chemical speciation, pH, redox potential, pollution control, mine spoil
Since large areas have been contaminated by arsenic-rich industrial and mining by-products in several countries, knowledge of arsenic (As) behavior in soils and water is of major concern for reclamation of polluted sites and evaluation of environmental risk. Cheni's tailings (France) contains average concentrations up to 7000 mg kg As and was listed by the authority as an important potentially pollutant site. Because As speciation determines its mobility, it was investigated in surface and ground waters of the site and a study of the solid As-bearing phase was performed on suspended particulate material (SPM). Results of sequential extraction, carried out on the SPM collected in drainage waters, show that most of total extracted As (78%) and Fe (77%) is bound to an iron hydrous oxide phase, which was determined to be lepidocrocite (γ-FeOOH) by x-ray diffraction and infrared spectrometry. Particulate material was >220 times more concentrated than dissolved As. Conditions for the stability of dissolved (<0.45 µm) arsenite [As(III)] and arsenate [As(V)] are discussed on the basis of thermodynamical data and field measurements of pH and redox potentials. The theoretical stability of As(V) corresponds to a large association between As and particulate material, and large amounts of the metalloid are released in solution when As-rich particles come from oxidized ground waters to moderately reduced conditions. These results are important for evaluating, modeling, and rehabilitating As-polluted sites.