KINETICS OF NITROAROMATIC REDUCTION ON GRANULAR IRON IN RECIRCULATINGBATCH EXPERIMENTS

Granular iron has been determined to be a potentially useful reductant for the removal of common organic contaminants from groundwater. This research is aimed at improving our understanding of the processes tha t control the reactivity and longevity of the iron particles when they are used for groundwater treatment. A suite of nitroaromatic compound s (NACs) including 4-chloronitrobenzene (4CINB), 4-acetylnitrobenzene (4AcNB), nitrobenzene, 2-methylnitrobenzene (2MeNB), and 2,4,6-trinitr otoluene (TNT) was used to investigate granular iron reactivity in ano xic pH 10, 0.008 M KNO3 solution. Master Builder's brand of granular i ron with a surface area of about 1 m(2)/g was used in all experiments. The NACs were reduced rapidly to anilines that were found to sorb rea sonably strongly to the solid particles and to interfere with the redu ction of NACs. The granular iron was found to lose reactivity quite ra pidly over the first few days of exposure and then more slowly over th e next several months. Reactivity loss due to reversibly sorbed produc ts was minimized by flushing the system with background electrolyte be tween experiments. Competition experiments with binary mixtures of 4CI NB and each one of the other NACs were performed to investigate relati ve affinities of these compounds for the solid surface. Despite the ov erall loss in reactivity observed for the granular iron, the relative rare constants in the competition experiments appeared to remain const ant in time.