Series Removal of Heavy Metal and Aromatic Compound from Contaminated Groundwater Using Zero-Valent Iron (ZVI)

Abstract

In this study, it is proposed to couple the two processes, i.e. phenol oxidation and chromium reduction. During this coupling process, it is hypothesized that the ferric iron generated from the chromium reduction process acts as the electron acceptor and catalyst for the Fenton’s phenol oxidation process. The Ferrous iron formed from the Fenton reactions during phenol oxidation can be reused for the chromium reduction, and thus the iron can be made to recycle between the two reactions changing back and forth between ferrous and ferric forms. Two sizes of iron, millimetre and micron, were used in this experiment, and their optimum dosages were about 2 g/l and 20 mg/L, respectively; Cr(VI) concentration was maintained as 2 ppm and phenol concentration was about 5 ppm throughout this experiment. In case of mmZVI, 100% Cr(VI) removal was taken place at 7 h and considering mZVI, it was about 6 h, respectively. H₂O₂ was optimized as 1.5 ml for mmZVI and 1 ml for mZVI. Using mmZVI with 1.5 ml H₂O₂, for pH 4, 7 and 10, the reaction time required for the complete removal was 60, 150 and 270 min. Using mZVI with 1 ml H₂O₂, it was about 90, 240 and 390 min for pH 4, 7 and 10, respectively, series removal of phenol and Cr(VI) started with phenol reduction, and this experiment was continued for three cycles. It was also observed that the time taken for Cr(VI) reduction gets decreased in the series removal system than the individual system. The phenol oxidation process which converted some of the Fe³⁺ to Fe²⁺ sustained the chromium reduction for a longer time. The Cr(VI) reduction oxidizes Fe⁰ to Fe²⁺/Fe³⁺ and thus enabling the phenol oxidation. This cycles the iron between the two processes and sustains the barrier wall and expected to increase its lifespan.