Removal mechanism of elemental mercury by using non-thermal plasma

Abstract

The removal mechanism of elementary mercury (Hg 0) by non-thermal plasma (NTP) has been investigated, where dielectric barrier discharge and O 3 injection methods as oxidation techniques are employed, together with the analysis of mercury species deposited on the reactor surface using temperature-programmed desorption and dissociation (TPDD) and scanning electron microscopy–energy dispersive spectroscopy. The removal of Hg 0 by NTP is found to be time-dependent and proceed through three domains; the Hg 0 concentration just slightly decreases as soon as NTP is initiated and then becomes constant for several minutes (Region 1), thereafter starts to decrease rapidly for 1 h (Region 2) and, after passing fall-off region, very slowly decreases for about 4 h (Region 3). The deposited mercury species on the reactor surface were conglomerated like islands, rather than dispersed uniformly, and their ratio of Hg 0 to O composition is observed to be 1:2. Additionally, the new peak in TPDD spectra observed in the region of 260–380 °C is proposed as HgO 3. These results lead us to conclude that the deposited mercury species by NTP have extra O atoms to oxidize the adsorbed Hg 0, resulting in the acceleration of removal rate as the oxidation of Hg 0 proceeds.