Novel highly reactive and regenerable carbon/iron composites prepared from tar and hematite for the reduction of Cr(VI) contaminant

Abstract

Highly reactive carbon/Fe composites were prepared from tar used as a carbon source, and hematite (α-Fe2O3), a widespread naturally available iron oxide. Tar was impregnated on hematite and thermally treated under N2 atmosphere. Mössbauer, powder X-ray diffraction and magnetization data suggested that treatment at 400 and 600 °C produced only magnetite (Fe3O4) whereas at 800 °C mainly metallic iron (Fe0) was produced. Raman, TG and XRD analyses of the different composites revealed the presence of amorphous and graphitic carbon highly dispersed on the iron oxide surface. The composites obtained at 800 °C were very efficient in reducing aqueous Cr(VI), as CrO42−, even compared to finely ground commercial Fe0. XPS and Mössbauer data showed that after five consecutive reuses, the composites deactivated, due to the surface oxidation of Fe0. A simple treatment at 800 °C completely regenerated the composite by reducing Fe3+ species allowing several reuses.