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TECHNICAL REPORTS

Heavy Metals in the Environment

Desorption Kinetics of Arsenate from Kaolinite as Influenced by pH

M. Quaghebeur^a,b,*, A. Rate^a, Z. Rengel^a, and C. Hinz^a

^a Soil Science and Plant Nutrition, School of Earth and Geographical Sciences, University of Western Australia, 35 Stirling Highway, Crawley WA 6009, Australia
^b Current address: Flemish Institute for Technological Research (Vito), Boeretang 200, BE-2400 Mol, Belgium

^* Corresponding author (mieke.quaghebeur{at}vito.be)

Received for publication January 29, 2004. Arsenic is highly toxic and therefore represents a potential threat to the environment and human health. The mobility and bioavailability of arsenic in soil is mostly controlled by adsorption and desorption reactions. Even though adsorption and traditional batch desorption experiments provide information about the environmental fate of As, the equilibrium conditions imposed in these studies would usually not be reached in the natural environment. Flow-through desorption techniques, where the desorbed species are removed from the substrate, can therefore be used to provide information about the rate and mechanisms of As desorption. The effect of pH on As adsorption reactions is relatively well understood; however, desorption of As and the effect of pH on As desorption remain unexplored. Desorption of As(V) (the most dominant arsenic species in aerated soils) was therefore investigated using batch and flow-through desorption experiments. Traditional batch desorption experiments underestimated the desorption rate of As(V) from kaolinite. The pH had a large effect on the amount of As(V) desorbed from kaolinite, with both an increase and a decrease in pH (from the initial pH 6.4) enhancing As(V) desorption. Modeling desorption over time revealed that the pH can influence As(V) desorption over extended periods of time.

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This Issue in Journal of Environmental Quality

JEQ 2005 34: 403-407. [Full Text]