Enhanced reduction and adsorption of hexavalent chromium by palladium and silicon rich biochar supported nanoscale zero-valent iron.

The potential of silicon-rich biochar and Pd were evaluated for the enhanced removal of Cr(VI) in solution by nanoscale zero-valent iron (nZVI) composites. The composition and structures of the nZVI, RS700-supported nZVI, and Pd-doped samples were analyzed by scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy before and after reaction with Cr(VI). The amount of Cr(VI) removed by nZVI-RS700-Pd was considerably greater than the removal by nZVI, nZVI-Pd, or nZVI-RS700. This was mainly due to the enhanced reduction and adsorption of Cr(VI) by silicon-rich biochar and Pd. Silicon and Pd promoted the reduction of Cr(VI) due to the Fe0 crystallinity in the nZVI structures. The significantly decreased removal of Cr(VI) by the silicon-removed sample (nZVI-RS700 (-Si)) further confirmed that silicon played a significant role in the removal of Cr(VI). Cr(VI) adsorption was enhanced by the dispersion and adsorption of RS700. Following the reaction of RS700-supported nZVI with Cr(VI), ferrous chromite (FeCr2O4) was observed on the nZVI-RS700 composite surface. The formation of FeCr2O4 can be attributed to the reduction of Cr(VI) by the nZVI and coprecipitation of chromium oxide with iron on the RS700 surface. Therefore, nZVI-RS700-Pd is a potential remediation reagent that can be used to effectively treat Cr(VI)-contaminated groundwater.