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 Ca ₃(PO₄)₂ matrix (41-49%) in the stabilized sludge. In addition, the As-O bond distances in the stabilized As ₂O₅ are much less than that of normal As₂O ₅ 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.