Polarographic studies of zero valent iron as a reductant for remediation of nitroaromatics in the environment

Zero valent iron as a reactive barrier material has garnered considerable a ttention over the past few years because it is relatively inexpensive, abun dant, harmless to the environment and effective in reducing organic contami nants. The redox process requires adsorption of the organic contaminant ont o the Fe surface, where protonation and electron transfer occur. In this st udy, nitrobenzene reduction by Fe was investigated using differential pulse polarography. This technique was employed because it is able to simultaneo usly monitor the disappearance of nitrobenzene and the appearance of Fe2+. Initial studies focused on the efficiency and reaction kinetics as a functi on of the Fe surface pretreatment. The presence of a pH dependent induction period in the reduction of nitrobenzene using stored Fe was observed. Deta iled secondary experiments were also performed using freshly prepared Fe, w hich was washed with the reaction medium buffer to eliminate solvent effect s. Since oxygen is an important factor in iron corrosion, the effect of oxy gen on the efficiency of reduction of nitrobenzene was studied by comparing the reaction kinetics of aerated and de-aerated solutions at pH 6 and 7. F urthermore, the adsorptivity of Fe towards anions, intermediate surface spe cies, and organic contaminants, was investigated to elucidate the multiface ted role of the buffer. These studies proved informative, despite the fact that oxygen, mass transfer, and colloidal iron (II) limited our ability to access information about crucial mechanistic details on the chemical proces ses controlling the reduction of organic compounds at the Fe surface. (C) 2 001 Elsevier Science B.V. All rights reserved.