Study On Enhancements For Mercury-contaminated Soils Remediation By Thermal Desorption Technology

Mercury is one of the most severe environmental pollutants due to its Persistence, potent neurotoxin, and the consequent accumulation in the food chain. The threat of such kind of pollutant in soil has been paid more attention at recent years. Thermal desorption is a physical process which uses either direct or indirect heat exchange to vaporize and/or volatize contaminants from soil. Typical mercury-contaminated soil samples were treated with thermal desorption process to investigate the removal of mercury speciations. Current thermal desorption methods for remediating mercury contaminated soil are expensive due to high treating temperature, In this study, relatively low temperature thermal desorption for mercury contaminated soil treatment with different additives were investigated.The experimental results indicated that thermal desorption could effectively remove mercury from the soil. After the treatment, the major mercury speciation in the soil was found to be the chloroazotic acid soluble mercury, which causes little environmental risk. Transformation may happen between different mercury speciations. Low temperature with long-time treatment can not only reduce the risk of Hg in soil, but also help for soil to restore farmland tillage. High removal rate of mercury from soil can be obtained with FeCl3 as an additive during thermal desorption process, while with lower temperature and less time. The addition of FeCl3 at 150 times of the mole concentration of mercury in soil would be needed to effectively remove Hg from contaminated soils. The parameters were further optimized to thermal treated at 450? for 20 min. With the addition of FeCl3, the mercury content of contaminated soil could be reduced to less than the limit of Environmental quality standard for soils of China at relatively low temperature and short time. High removal rate of mercury from soil can also be obtained with EDTA, oxalic acid, citric acid as an additive during thermal desorption process, while with lower temperature and less time. The addition of organic acids at 5.3 times of the mole concentration of mercury was the optimized parameter.