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, H2O, 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 HgCl2. The addition of H2O to the gas mixture of HCl in N-2 accelerates the oxidation of Hg-0, although no appreciable effect of H2O 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 He (280 mu g m(-3)), HCl (25 ppm), NO (204 ppm), O-2 (16%) and N-2 (balance) and temperature 90 degrees 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. (C) 2008 Elsevier Ltd. All rights reserved.