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Title: Redox cycling of mercury mediated by bromine/iron: Environmental implications
Authors: WANG ZHI
Keywords: Redox, Mercury, Bromine, Iron.
Issue Date: 17-May-2004
Citation: WANG ZHI (2004-05-17). Redox cycling of mercury mediated by bromine/iron: Environmental implications. ScholarBank@NUS Repository.
Abstract: The special characteristics of mercury, such as, long range atmospheric transport, its transformation between species, biomagnification, and neurotoxin make it as a pollutant of global concern. The chemical processes take place in the atmosphere and water systems are closely linked the transformations of mercury. Therefore, the environmental implications by the redox cycling of mercury mediated by bromine and iron are well investigated in this study.The second order rate constants at room temperature (20~230C) for the Hg0(aq)-Br2, Hg0(aq)- HOBr and Hg0(aq)-OBr- are determined to be 0.196 A? 0.03 M-1s-1, 0.279 A? 0.02 M-1s-1 and 0.273 A? 0.04 M-1s-1, respectively. Such slow rate constants also mean that the important atmospheric a??sinka?? for mercury is not caused by aqueous bromine, but gaseous bromine. The backward reaction between aqueous elemental mercury and ferric iron was found to proceed extremely slowly with the second-order rate constant of 0.73 A? 0.29 M-1s-1. The forward reaction between divalent mercury and ferrous iron was found to be light-catalyzed. The enhancement of the forward reaction rate is achieved by three main factors, e. g. low pH value, high concentrations of the ferrous iron; the presence of short wavelengths (in the UV range of sunlight) and high light intensity catalyze the rate of the forward reaction.
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