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

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 Fe^0/2+ to Cr⁶⁺ resulting in Fe^2+/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, Fe^2+/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.