[Influence of light wavelength and intensity on the reduction of divalent mercury in aquatic system]

Laboratory experiments were conducted to investigate the photo-reduction of HgCI2, under various light wavelengths and intensities. The whole process was tracked by changing Hg0 concentrations in argon and Hg0 flux was calculated for qualitative and quantitative analysis; the rate order was determined by both differential and integral methods. The principal results indicated: Higher mercury emission flux was observed under shorter light wavelength and stronger intensity, which shows the important role of photoenergy in the reaction. The degree of mercury reduction was determined by radiation wavelength and intensity, and it was also influenced by solution volume and the flow rate of carrier gas. Under different light conditions, Hg0 concentrations in argon all increased at the beginning and decreased after a specific time period, since the main reactions in rising period were the photo-reduction of Hg2+ and the emission of Hg0 while the reaction in decreasing period was the emission of Hg0 only. The rate order under visible light was the first order while it was the second order under UVA and UVB, which attributes to the fact that coordination complex has certain light absorption band, which is related with the available light wavelength provided by experimental lamps.