| dc.description.abstract | Mercury (Hg) is one of the hazardous metals for animals, plants and human beings and has been listed as the first priority toxic substance in the world. In this study, the mercury-contaminated soil was collected from An-shun site in Tainan and was sieved to remove the branches, rocks and bricks for experimental tests. Thermal desorption is experimentally evaluated for the effectiveness in removing Hg from contaminated soil, because it has advantages including high treatment capacity and high removal efficiency. First of all, the experimental tests were conducted with a batch-type laboratory-scale thermal desorption system. In order to evaluate and compare the removal efficiencies, the experimental tests were performed at different operating conditions including temperature and the type of carrier gas. The results indicate that when the operating temperature is above 500oC, the Hg content of the treated soil concentration is below the Taiwan EPA criteria (20 mg/kg) and Hg removal efficiency increases with increasing temperature. The continuous thermal desorption system was operated at 500, 600, 700 and 750oC, while the treating capacity was controlled at 2, 2.5 and 3 kg/hr (retention time: 33 min, 26 min and 22 min), respectively. The results show that the removal efficiency reaches 97.88% at the operating temperature of 700oC and the residual concentration in treated soil could also meet the criteria of 20 mg/kg. Finally, in order to avoid the secondary pollution, a series of air pollution control devices (APCD) consisting of a baghouse, a quench tower and a multilayer activated carbon adsorption bed are designed and adopted. Experimental results indicate that the baghouse could effectively remove 99% particulate matter and reduce the loading of subsequent APCDs. The quench tower could not only condense the water vapor but also capture the Hg and its compounds, with significant accumulation of mercury drop in the chilled water. As the off gas passes through the activated carbon adsorption bed, mercury concentration in off-gas is well below the emission standard promulgated by Taiwan EPA (50 μg/m3). Results obtained from activated carbon adsorption test indicate that the replacement of AC beds should be maintained at 1 layer/day to ensure the Hg concentration in off gas meet the emission standard of 50 μg/Nm3. | en_US |