Behavior of dioxin during thermal remediation in the zone combustion process

In the previous study, a new process concept for the thermal remediation of particulate/powder materials contaminated by polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) has been verified. It leads to removal efficiencies of more than 99.9% in the soil contaminated by PCDD/Fs in terms of toxicity equivalent quantity (TEQ). However, details of the reactions and phenomena during the process, i.e., decomposition, vaporization, reformation and trap of PCDD/Fs and their relating compounds, have not sufficiently been clarified yet. The present study aims to examine experimentally the transport and fate of PCDD/Fs in the process. In the experiment, a laboratory-scale process simulator and a soil sample preliminary mixed with octachlorinated dibenzo-p-dioxin spiked by carbon-13 isotope (C-13-OCDD) were used. The distribution of C-13-OCDD in the soil bed during the process was measured by applying a quench technique that rapidly cools-down the bed. Further, the total amount of C-13-OCDD discharged with outlet gas was measured. Using the obtained data, mass balance of C-13-OCDD in the process was estimated. The results show that about 99% of C-13-OCDD preliminary admixed with the soil was decomposed rather than released to the outlet gas. Only a trace amount of C-13-OCDD remained in the treated soil. In addition, a very small amount of other congeners having the C-13-cycles was detected in the treated soil and outlet gas although its TEQ values are not significant. These were probably formed by dechlorination reactions occurring in the process. (C) 2002 Elsevier Science Ltd. All rights reserved.