Lawrence Berkeley National Laboratory

Accurate oxidation rate constants of mercury gas are needed for determining its dispersion and lifetime in the atmosphere. They would also help in developing a technology for the control of mercury emissions from coal-fired power plants. However, it is difficult to establish the accurate rate constants primarily due to the fact that mercury easily adsorbs on solid surface and its reactions can be catalyzed by the surface. We have demonstrated a procedure that allows the determination of gas phase, surface-induced, and photo-induced contributions in the kinetic study of the oxidation of mercury by chlorine gas. The kinetics was studied using reactors with various surface to volume ratios. The effect of the surface and the photo irradiation on the reaction was taken into consideration. The pressure dependent study revealed that the gas phase oxidation was a three-body collision process. The third order rate constant was determined to be 7.5(?0.2)?10-39 mL2 molecules-2s-1 with N2 as the third body at 297?1?K. The surface induced reaction on quartz window was second order and the rate constant was 2.7?10-17 mL2 molecules-1 cm-2 sec. Meanwhile, the 253.7 nm photon employed for mercury detection was found to accelerate the reaction. The utilization efficiency of 253.7 nm photon for Hg0 oxidation was 6.7?10-4 molecules photon-1 under the conditions employed in this study.