Abstract
μ-XRF, XAFS and μ-XAFS spectroscopies were implemented in order to investigate the effect of thermal annealing on the stability of a vitrified tannery waste. The two dimensional μ-XRF scans disclose the presence of Cr-rich and depleted regions where both Cr(III) and Cr(VI) are present. However the polymerization of the Cr-O-Cr chains is different in these two distinct regions. More specifically, the μ-XANES and μ-EXAFS results reveal that in the Cr-rich inclusions, the Cr(in)O6 belong to Cr2O3, while in the Cr-depleted regions, different linkages among the Cr(III)O6 octahedra are detected. The percentage of the different type of polymeric structure around Cr(III) in the two distinct regions was assessed using Cr-K- EXAFS and XANES spectroscopies. It is revealed that upon thermal annealing the number of Cr(VI) ions is preserved and participate in the formation of the glass matrix. Even though Cr(III) is a glass modifier, the local coordination of the Cr(III)-octahedra changes upon thermal treatment. The presence of Cr(VI) suggests the limited capacity of the vitrification process to inhibit Cr(III) oxidation, however, Cr(VI) is safely trapped into both the glass and glass- ceramic matrix.
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