Abstract
Toxic species such as dioxins and heavy metals released from incinerators have become a serious issue that Japan has been confronted with. Since they are concentrated especially in fly ash, supplemental treatment systems to detoxificate them are usually required. If the regulation of these species shifts to that by total emission in future, they will need to be removed from fly ash by some method such as thermal treatment and chemical extraction. The present study was aimed at establishing a technique to treat these species (dioxins, zinc and lead) in fly ash at a high temperature (>500 oC) by adding chemicals while preventing the sintering of fly ash. Based on the hypothesis that calcium chloride in fly ash results in the sintering, sodium hydroxide (NaOH), mullite and coal fly ash were chosen as additives to scavenge chlorine from fly ash. The fly ash samples with additive were heated up to a given temperature (400 to 1000 oC) for a given time, followed by various analyses for the determination of chemical and physical structure of the treated fly ash as well as the quantification of the volatilized heavy metals and the remaining dioxins. As a result, we found that CaClOH plays a key role in the sintering, and that the additives studied in this work are effective for the decomposition of CaClOH so as to suppress the sintering of treated fly ash, and these other than NaOH enhanced dioxins decomposition and heavy metal volatilization from fly ash.
