Chemical states of trace elements in sewage sludge incineration ash by using x-ray absorption fine structure

In this study, the chemical states of chromium (Cr), arsenic (As), and selenium (Se) in sewage sludge incineration ash were determined by X-ray absorption fine structure (XAFS) spectroscopy. Sewage sludge incineration ash was sampled from several facilities, and XAFS measurements were carried out with a beam line BL01B1 at the SPring-8 facility. Cr K-edge X-ray absorption near-edge structure (XANES) spectra suggested that Cr compounds were predominantly speciated as Cr(III) and the fraction of Cr(VI) was very minor. Compared to the reference materials, Cr XANES spectra of the incineration ashes were similar to those of FeCr₂O₄, Cr(OH)₃, and CaCr₂O₄. As K-edge XANES spectra indicated that As(V) compounds were present in incineration ashes. Because the chemical state of As in sewage sludge was As^3 + in our previous study, we speculated that the chemical state of As changed into As(V) during the incineration process. According to Se K-edge XANES spectra, Se compounds were predominantly Se(IV), and a slight difference was observed in the chemical states amongst facilities using inorganic or organic coagulants in the dewatering process.