Aqueous Photochemistry of Mercury with Organic Acids

To understand the dynamic chemical changes of mercury taking place in atmospheric water, a more detailed knowledge of the reactions of mercury with organic acids must be obtained. The rate of the above chemical reactions with different Hg(II) species is especially essential for understanding the dominant pathway of mercury transformation in the atmosphere. The objective of this research is to study the rate of photochemical reactions of dissolved divalent mercury with organic acids such as oxalate, acetate, and formate, which are abundant in atmospheric water. Laboratory photochemical experiments with simulated sunlight were conducted to assess the role of homogeneous photochemistry in changing the redox states of mercury in atmospheric water. It is observed that Hg(II) is readily reduced by hydroperoxyl radicals produced by the photolysis of oxalate. The second-order rate constant for the Hg(II)-hydroperoxyl radical reaction was found to be 1.7 x 10⁴ M^-1 s^-1 when no chloride is present and 1.1 x 10⁴ M^-1 s^-1 when chloride is present in the system. Modeling of mercury speciation has been performed using MICROQL equilibrium software.