Friday, 14 July 2006

Study of the Speciation and Distribution of Arsenic in a Particularly Polluted Soil in Villa de la Paz, San Luís Potosí, México.

M. Elena García1, Norma Gascón O.1, Luisa Ma. Flores-Velez1, Sonia Soriano1, and Nadia V. Martínez-Villegas2. (1) Universidad Autónoma de San Luís Potosí, Manuel Nava , Zona Universitaria, San Luis Potosi, Mexico, (2) Universidad Autónoma de San Luis Potosí, Manuel Nava, Zona Universitaria, San Luis Potosí, Mexico

The mining industry in Mexico continues to be an important industry in Mexican economy. Due to its high production significant problems of pollution are found in soils adjacent to the mines. High concentrations of total As have been found in superficial soils of the mining area of Villa de la Paz (S.L.P., Mexico), probably generated by acid mine drainage of tailings deposed over soils near the concentration plant. This work deals with the speciation and distribution of As(III) and As(V) in a particularly polluted site in the mining area of Villa de la Paz, San Luis Potosi, Mexico. Soil sampling was carried out in 4 points, 3 in the polluted site area and a reference soil (not polluted) 2 km far from this area. Arsenic mobility and transport in the environment are strongly influenced by its associations with solid phases in soils and sediments. Four methods were carried out to study this site: single step and sequential chemical extractions, cathodic stripping voltammetry with square wave and leaching tests in columns. Chemical extractions were adapted to extract As coming from pyrite tailings. Five steps are proposed in the arsenic distribution: water soluble (Norm ASTM 3987), strongly adsorbed (NaH2PO4), coprecipitated with amorphous iron oxyhydroxides (NH4C2O4/H2C2O4), coprecipitated with crystalline iron oxyhydroxides (Na3C6H5O7/Na2S2O4) and arsenic oxides and coprecipitated with silicates (HNO3, HClO4, HF). Total Arsenic was measured by atomic absorption spectroscopy. Arsenic was determined as As(III) and As(V) by cathodic stripping voltammetry on hanging mercury drop electrode in conjunction with the use of square wave in arsenic soluble extracts. A leaching method was also developed by column test to simulate the leaching of inorganic components from powdered and granular materials in an aerobic environment.

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