Single-step removal of Hexavalent chromium and phenol using meso zerovalent iron

Abstract

Novel meso-zero valent iron (mZVI) was investigated for treating complex wastewater containing toxic heavy metal Cr6+ and organic compound phenol. This study is first of its kind illustrating coupled removal in single-step with H2O2 playing a major role as an oxidant and reductant. The mechanism involved was electron transfer from Fe0/2+ to Cr6+ resulting in Fe2+/3+ which in turn was consumed for phenol oxidation returning as Fe2+ into the system for further Cr6+ reduction. While comparing, single-step simultaneous removal of Cr6+ and phenol showed better performance in terms of pollutant removal, Fe2+/3+ recurrent reaction and precipitation generation, double-tep sequential removal performed better in iron active-corrosion time. It was also observed that the entire redox cycle of Cr6+-Cr3+-Cr6+ was reusable for co-contaminant phenol degradation at all pH with the recurrence of Fe2+-Fe3+-Fe2+. The proposed technique was checked for its viability in a single batch reactor and the complex chemistry of the reactions are unfolded by conducting chemical speciation and mass balance study at every stage of reaction. The unique functioning of mZVI was proven with micro-analysis of ZVI's surface and compared with granular ZVI, cZVI. The results obtained from this study open the door for a safer and cleaner single treatment system in removing both toxic heavy metals and organic compounds from contaminated surface water, groundwater and many such industrial effluents.