Thermal detoxification and bloating of chromium(VI) with bentonite

This study stabilizes and bloats Cr(VI)-sorbed bentonite by heating at high temperature. Cr leaching decreases with increasing temperatures. Heating the sample at 1100 °C results in a non-detectable Cr concentration in the leachate, equivalent to a Cr leaching percent less than 0.001% (i.e., Cr TCLP concentration <0.018 mg of Cr L−1 of leachate). Morphology observed with a scanning electron microscopy indicates the occurrence of sintering of the sample heated at 1100 °C. The heated samples also show the occurrence of a vesicant process at 1100 °C. X-ray absorption spectroscopy results indicate that heating at 500 °C for 4 h can convert approximately 87% Cr(VI) into Cr(III) that is negligibly toxic; Cr2O3 was detected to be the most abundant Cr species. After heating at higher temperatures, namely 900–1100 °C, almost all doped Cr(VI) is reduced to Cr(III) as inferred from the height of the pre-edge peak of XANES spectra and/or from XANES simulation.