Influence of HCl on oxidation of gaseous elemental mercury by dielectric barrier discharge process

Abstract

The influence of HCl on the oxidation of gaseous elemental mercury (Hg 0) has been investigated using a dielectric barrier discharge (DBD) plasma process, where the temperature of the plasma reactor and the composition of gas mixtures of HCl, H 2O, NO, and O 2 in N 2 balance have been varied. We observe that Cl atoms and Cl 2 molecules, created by the DBD process, play important roles in the oxidation of Hg 0 to HgCl 2. The addition of H 2O to the gas mixture of HCl in N 2 accelerates the oxidation of Hg 0, although no appreciable effect of H 2O alone on the oxidation of Hg 0 has been observed. The increase of the reaction temperature in the presence of HCl results in the reduction of Hg 0 oxidation efficiency probably due to the deterioration of the heterogeneous chemical reaction of Hg 0 with chlorinated species on the reactor wall. The presence of NO shows an inhibitory effect on the oxidation of Hg 0 under DBD of 16% O 2 in N 2, indicating that NO acts as an O and O 3 scavenger. At the composition of Hg 0 (280 μg m −3), HCl (25 ppm), NO (204 ppm), O 2 (16%) and N 2 (balance) and temperature 90 °C, we obtain the nearly complete oxidation of Hg 0 at a specific energy density of 8 J l −1. These results lead us to suggest that the DBD process can be viable for the treatment of mercury released from coal-fired power plants.