Hydrothermal Treatment of Incineration Fly Ash: Factors Affecting Dioxin Decomposition and Mechanism Involved

摘要

The factors affecting decomposition of PCDD/Fs contained in incineration fly ash during hydrothermal process was investigated. Experimental results indicated that additives, temperature, pretreatment and cooling procedure as well as reaction time are the most important factors affecting decomposition of dioxin contained in the incineration fly ash, especially temperature is the most important. To reach the decomposition rate of dioxins more than 80% by I-TEQ, the temperature should reach 290 °C. Effects of additives were influenced by pretreatment and reaction temperature. With help of a Gaussian 3.0 software, computational quantum chemistry was adopted to investigate the mechanism of dioxin decomposition involved with hydro-thermal process from point view of energy change profile. Investigation showed that the most toxic 2378-TCDD was also the most difficult congener to be decomposed and re-synthesized due to the highest potential energy barriers related with it. The calculation results also explained decomposition behaviors of other congeners during hydrothermal process and changes of some congeners concentration related to different cooling procedures.