Professor, Graduate Institute of Environmental Engineering, National Taiwan University

Speech Title: Removal of Liquid-Phase Hg from Actual Seawater Flue Gas Desulfurization Wastewater of a Coal-Burning Power Plant by Using Sulfurized Activated Carbon

Abstract: Mercury (Hg) emitted from combustion sources, such as coal-fired power plants (CFPPs), poses a risk to the public health and the environment. Control of Hg emissions could be achieved by using conventional air pollution control devices pre-equipped in the CFPPs. Among the available technologies, seawater flue gas desulfurization (SFGD) system has raised great awareness. SFGD in principle utilizes the natural alkalinity of seawater to neutralize SO₂, as well as co-benefit control of dissolved Hg. A great concern thus aroused if the Hg-containing wastewater is directly discharge into the ocean environment without proper treatment.

In this study, a series of batch experiments were conducted to obtain the optimal adsorption conditions for removing Hg2+ from SFGD system by using sulfurized activated carbon (SAC), which is highly effective in adsorption of Hg pollutants because of its suitable physical and chemical properties. SAC was prepared by using raw activated carbon (AC) impregnated with elemental sulfur at 400 °C. The total surface area and sulfur content of SAC was approximately 765 m2/g and 5.8wt%, respectively. At low initial Hg concentration, significant difference between the removal efficiency of SAC and AC was not observed. When the initial concentration reached 4723 ng/L, the Hg adsorption capacity of SAC increased with increasing initial Hg concentration whereas that of AC decreased. Hg removal efficiency at pH 7 and 8 was also shown to be slightly higher than that in an acid seawater condition. In addition, the zero point of charge (ZPC) of SAC was found to occur in seawater at pH 0.6, implying that Hg2+ adsorption by SAC was favorable in the test pH range of 2-8. Furthermore, thermodynamic parameter calculation concluded that △H°= 53.3 kJ/mole, △S°= 0.221 kJ/mole, and △G≒ -17.1 kJ/mole, indicating that Hg adsorption by SAC is endothermic and spontaneous.