Tracking of arsenics during the thermal stabilization of an AsH3 scrubber sludge
Toxic arsenics in an AsH3 scrubber sludge were thermally stabilized in the temperature range of 973–1,373 K. To better understand how the high-temperature treatments can stabilize arsenics in the sludge, their synchrotron X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra of arsenics were determined. It is found that the reduced arsenic leachability may be associated with the formation of As2O5 (51–59%) and embedded As(V) within the Ca3(PO4)2 matrix (41–49%) in the stabilized sludge. In addition, the As-O bond distances in the stabilized As2O5 are much less than that of normal As2O5 by 0.05–0.07 Å. The shorter As-O bond distances accompanied with the higher bonding energy also have a contribution to the thermal stabilization of arsenics.