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SPECIAL SECTION: ZNS'03 VADOSE ZONE RESEARCH

Adsorption–Desorption of Arsenate in Three Spanish Soils

^a Instituto Tecnológico Agrario de Castilla y León, Ctra. de Burgos, Km. 119, 47014 Valladolid, Spain
^b Dep. de Ingeniería Química, Universidad de Valladolid, Prado de la Magdalena s/n, 47005 Valladolid, Spain
^* Corresponding author (jabenedi{at}iq.uva.es)

Received 22 June 2004.

Adsorption–desorption processes of As in agricultural soils are of great importance because of the risk of entry of this contaminant into the food chain, As(V) being the main form of As in well-aerated environments. This study presents the dynamics of the adsorption of As(V) in three agricultural soils (Xerochrept, Xerofluvent, and Xerorthent) with loamy sand, sandy clay loam, and clay textures, respectively. Initially obtained kinetic data showed a relatively rapid first adsorption stage reaching pseudoequilibrium within a few hours. The adsorption–desorption isotherms revealed the presence of an unrecoverable fraction of As linked to the soil, which was further supported by a strong hysteresis subsequently observed in the desorption process. The temperature showed a relatively small effect on the isotherm within 10 to 25°C, although a decrease in the fraction of sorbed As(V) was found at 40°C as expected for an exothermic process. Finally, the effects of other ions typically present in productive agricultural systems were evaluated by quantifying their effects on the As(V) adsorption isotherm. The presence of phosphates significantly decreased the adsorption of As, thus increasing its bioavailability, while nitrate had the opposite effect. The presence of chlorides and sulfates did not present similar significant effects. Values obtained from modeling the sorption experiments in this study can provide a basis for the use of solute transport simulation models. Further application of such models will allow the establishment of future production strategies in zones having elevated As content in irrigation water.

Abbreviations: As(V), arsenate • As(III), arsenite • CEC, cation exchange capacity • XRD, X-ray diffraction