Effect of pH on Reduction of Nitrobenzene in Groundwater by Zero-Valent Iron

The effects of different pH values on the reduction of nitrobenzene (NB or ArNO₂) by zero-valent iron (ZVI) were studied in groundwater through batch experiments. The concentrations of NB and its reduction product aniline were determined during the process of reaction. The changes in the reduction rates for nitrobenzene, the quantities of aniline formed, and the reaction kinetics during the reduction by ZVI were examined and analyzed at different pH values. Experimental results showed that nitrobenzene in groundwater could be reductively degraded effectively by ZVI. The optimum pH for the reduction was found to be 3.0 within the tested pH range of 3.0 to 12.0. The pH value tended to increase gradually with the progress of reduction reaction. At various pH values, the reduction of nitrobenzene by ZVI followed pseudo-first-order kinetics, and the observed kinetic constant k_obs increased with decreasing pH. Both the reduction rate of nitrobenzene and the formation of aniline decreased with increasing pH. According to UV spectral and GC-MS analyses, aniline was the final reaction product of NB when reduced by zero-valent iron.