Journal
WATER AIR AND SOIL POLLUTION
Volume 215, Issue 1-4, Pages 573-584Publisher
SPRINGER INTERNATIONAL PUBLISHING AG
DOI: 10.1007/s11270-010-0500-3
Keywords
Adsorption; Aquatic chemistry; Clay mineral; Low molecular weight (LMW) organic acids; Particle; Phyllosilicates; Soil; Ternary surface complex
Funding
- US Department of Energy (DOE) Office of Biological and Environmental Research as part of the Science Focus Area at Oak Ridge National Laboratory (ORNL)
- College of Arts and Sciences at Tennessee Tech University
- DOE [DE-AC05-00OR22725]
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Sorption and desorption of Hg(II) on clay minerals can impact the biogeochemical cycle and bio-uptake of Hg in the environment. We studied the kinetics of the desorption of Hg(II) from kaolinite as affected by oxalate and cysteine, representing the ligands with carboxylic and thiol groups of different affinities for Hg(II). The effects of pH (3, 5, and 7), ligand concentration (0.25 and 1.0 mM), and temperature (15A degrees C, 25A degrees C, and 35A degrees C) on the Hg(II) desorption were investigated through desorption kinetics. Our study showed that the Hg(II) desorption was pH dependent. In the absence of any organic ligand, > 90% of the previously adsorbed Hg(II) desorbed at pH 3 within 2 h, compared to < 10% at pH 7. Similar results were observed in the presence of oxalate, showing that it hardly affected the Hg(II) desorption. Cysteine inhibited the Hg(II) desorption significantly at all the pH tested, especially in the first 80 min with the desorption less than 20%, but the inhibition of the desorption appeared to be less prominent afterwards. The effect of the ligand concentration on the Hg(II) desorption was small, especially in the presence of oxalate. The effect of temperature on the Hg(II) desorption was nearly insignificant. The effect of the organic acids on the Hg(II) sorption and desorption is explained by the formation of the ternary surface complexes involving the mineral, ligand, and Hg(II). The competition for Hg(II) between the cysteine molecules adsorbed on the particle surfaces and in the solution phase probably can also affect the Hg(II) desorption.
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