Structure and thermal stability of toxic chromium(VI) species doped onto TiO(2) powders through heat treatment.

Chromium(VI)-containing sorbents in the form of sludge or solid residue from treatment processes are often landfilled or used as fill materials, therefore the long-term stability of metal binding is important. The reduction of Cr(VI)-Cr(III) through heat treatment may be a useful detoxification method. After heating at 500, 900, 1000, and 1100 degrees C for 4h, the transformation of chemical states of chromium on 105 degrees C-dried, 7.9% Cr(VI)-doped TiO(2) powders was studied on the basis of surface area measurements, scanning electron microscopy (SEM) images, X-ray diffraction (XRD), and extended X-ray absorption fine structure (EXAFS) spectra. It was shown that Cr(VI) was reduced to Cr(III) in the Cr(VI)-doped samples after heating within 500-900 degrees C. The present results also suggested that the chromium octahedral was bridged to the titanium tetrahedral and was incorporated in TiO(2) minerals formed after 1000 degrees C treatment.