XAS study of chromium in thermally cured mixture of clay and Cr-containing plating sludge

Chromium oxide and clay are two important refractory ingredients. This study mixed with clay an industrial hazardous electroplating sludge that contained Cr(OH)(3), followed by thermal curing at 900 or 1100 degrees C for 4 h. Synchrotron-based X-ray absorption spectroscopy (XAS) was used to investigate the change of electronic property of chromium in samples. XANES spectra show that chromium in the mixture thermally cured at 1100 degrees C is virtually non-Cr(OH)(3) Cr(III), whilst there is considerable fraction of Cr(VI) in that cured at 900 degrees C. The ingredients in clay enhanced the chemical reduction of Cr(VI) into Cr(III), as indicated by the relatively smaller pre-edge peak in the mixture XANES when in comparison with the raw sludge. For the raw plating sludge heated at 1100 degrees C, its pre-edge peak position shifts to lower photon energy by approximately 1.0 eV, as compared with that at 900 degrees C. This indicates that chromium in the 1100 degrees C heated sludge might have a lesser oxidation state, probably in a form of Cr(V). The intensity of the white band is greater in the Cr XANES spectra from the sample heated at 1100 degrees C than that heated at 900 degrees C. (c) 2005 Elsevier B.V. All rights reserved.