Research progress on formation characteristics and inhibition mechanism of dioxins during direct thermal desorption of soil

Abstract

Based on the existing researches related to thermal desorption technology and dioxins, this paper provides a comprehensive review on the technological process, influencing factors of dioxins formation, and the mechanisms and measures of dioxins inhibition during the direct thermal desorption remediation of organic contaminated soil. Firstly, dioxins may be produced during different technological processes: dioxins present in contaminated soil are desorbed by heating; the organic pollutants in soil undergo molecular deconstruction and recombination, thus causing the generation of dioxins during the heating process of rotary kiln; dioxins are generated by heterogeneous catalytic reactions (including precursor and de-novo synthesis reactions) at each cooling stage in the exhaust gas purification process. Secondly, thermal desorption process parameters can also affect dioxins formation, such as heating temperature, heating time, flowing rate of carrier gas, reaction atmosphere and so on. Thirdly, the presence of metal compounds, water, carbon and chlorine source in contaminated soil can catalyze the formation of dioxins. Additionally, the characteristics of site pollution also have a certain impact on dioxins production. The addition of alkaline, sulfur, ammonium/nitrogen or sulfur-nitrogen containing compounds can inhibit the formation of dioxins during thermal desorption. At the end of the paper, the challenges of dioxin inhibition during thermal desorption are summarized, including the unclear chemical transformation mechanisms of various pollutants, the development of high-efficiency and practical inhibitors, etc. In addition, some future research directions are prospected.