| Abstract
| - Mercury is an environmental contaminant of global concern. The reduction of oxidized mercury species (HgII) by organic acids to elemental mercury (Hg0) is significant for understanding the cycling of mercury between the atmosphere and aqueous systems. This study focused on the reduction of HgII by small, semivolatile dicarboxylic acids (C2−C4). The reaction kinetics was studied using cold vapor atomic fluorescence spectroscopy (CVAFS), and the products of the reaction were analyzed using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and nuclear magnetic resonance (NMR) spectrometry. The effects of light, dissolved oxygen and chloride ion on reaction rates were also investigated. The highest reaction rates were observed in systems free of both oxygen and chloride ion with the second-order apparent rate constants of 1.2 × 104, 4.9 × 103, and 2.8 × 103 (L·mol−1·s−1) for oxalic, malonic, and succinic acids at pH 3.0 and T = 296 ± 2 K, respectively. The photoreduction of HgII was mediated by the complexes formed between HgII and dicarboxylic acids, and the identified products were Hg0, hydroxycarboxylic acids and monocarboxylic acids. Our results also indicated that the presence of chloride ion significantly reduced the reduction rate by competing with the complexation of HgII with dicarboxylic acids, while dissolved oxygen retarded the production of Hg0 by involving in the reoxidation of reduced Hg species to HgII. Based on our experimental results, a tentative mechanism is proposed and the potential environmental implications are discussed.
- The kinetic data and product identification are obtained for the reduction of HgII by dicarboxylic acids (C2−C4), of which the tentative mechanism is proposed.
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