Change in Chemical Form of Copper in Fly Ash at Temperatures Suitable for Dioxin Formation

Understanding the mechanisms involved in the formation of dioxins in fly ash is necessary in the control of dioxin emission. Dioxins are secondarily formed in a post-combustion zone, which is considered to occur primarily on and in fly ash, as first described by Stiegltiz and Vogg [1]. According to many studies, copper compounds are regarded as influential catalysts that generate large amounts of dioxins in heat experiments involving model fly ash. Nevertheless, only limited information on the chemical forms of copper or their changes in real fly ash is available in the literature. Previously, we investigated the chemical forms of copper in eight types of real fly ash before heating experiments using XANES [2]. However, to understand the exact formation mechanism, it is necessary to study the reaction that takes place with Cu compounds during the heating of fly ash. Here, we conducted in situ XANES experiments using real fly ash. Real fly ash was sampled from a bag filter in a normal stoker-type municipal solid-waste incinerator (MSWI). The measured copper, chlorine, and total organic carbon levels were 2600 mg/kg, 14%, and 1.5%, respectively. The direct speciation of copper in fly ash was examined using XANES with an in situ cell (see Fig. 1) at beamline BL01B1. The heating procedure and atmospheric conditions are shown in Fig. 2. The spectra were collected in a fluorescence mode using a 19-element Ge solid-state detector with a Si(111) monochromator. Species have also been distinguished using the linear combination fit (LCF) technique, in which the spectra of known reference species are fitted to the spectrum of an unknown sample.