Effect Of Slag (Iron Oxide)/Fe～(2+) On Nitrobenzene Reduction

Nitrobenzene is a common toxic organic pollution that can be found in surfacewater and ground water. Nitrobenzene has stable chemical property and can restrainmicrobial metabolism. When microbial treatment is not sufficient, non-biologicaltreatment becomes necessary. This thesis tried to use slag with Fe²⁺ to reducenitrobenzene. It also analyzed several influence factors, and discussed the mechanismof this reaction.In order to secure experimental data, this paper first established a measurementmethod that could determine nitrobenzene and its degradation productssimultaneously. Although GC was recommended by reference, liquid-liquidextract-GC was strongly affected by several pre-treatment factors. It was also unableto detect an intermediate product—hydroxyaniline, while HPLC could avoid theseinfluences and was preferred to organic analysis.Research on slag/Fe²⁺ system found that, due to the chemical composition ofslag, slag leach liquor was strongly alkaline, so adding Fe²⁺ into slag slurry wouldgenerate dark-green floc—Fe(OH)₂, which could completely reduce nitrobenzene inless than 1h. The reaction rate could be slowed when pH＜6.5 and Fe(OH)₂ generationwas avoid. Under this condition, it was found that slag had a strong adsorption effecton Fe²⁺ and the whole system could reduce nitrobenzene according to the followingpath: nitrobenzene→nitrosobenzene→hydroxyaniline→aniline. This reduction couldbe well described by pseudo-first order model. Under mild acid condition, reducingthe amount of slag would decelerate reaction. High concentration of Fe²⁺ wouldincrease the amount of H^-, which would also lead to the deceleration of the reaction.By increasing nitrobenzene dose, the kinetic rate constant could be decreased.Under the same experiment condition, several effective factors were alsoinvestigated. Enhancing hydraulics condition, pH and environmental temperaturecould greatly increase the reaction rate constant. Long time wash of slag would causethe loss of surface active spot, and slow the adsorption rate of Fe²⁺ and reduction rateof nitrobenzene. Some competition factors were also investigated. Dissolved oxygen could compete with nitrobenzene as electron donors. Phosphor could compete withnitrobenzene for active spot, while humic acid would first compete with nitrobenzene,but also slowly reduce oxidized Fe³⁺ to Fe²⁺, and enhance the reduction reaction. Cu²⁺could hinder the adsorption of Fe²⁺ onto slag surface, which would slow the reaction.4-nitrochlorobenzene would not effect nitrobenzene's reduction, but would beretarded by nitrobenzene.Different minerals have been used to substitute slag. When pH＜5, hematite,goethite and magnetite/Fe²⁺ had no reduction effect on nitrobenzene. When pH＞6.3,magnetite/Fe²⁺ represented a surface-bonded reduction effect on nitrobenzene. Thebatch experiment of blast furnace slag, zeolite, shale, dolomite and gravel showedthat only blast furnace slag and modified dolomite had reduction effect onnitrobenzene. But none of Fe₃O₄, blast furnace slag, and modified dolomite had afaster reaction rate than slag on nitrobenzene.In the end, a mechanism discussion of slag/Fe²⁺ reaction was proposed. Both Caand FeO in slag could contribute to nitrobenzene reduction. Combined with these twopossible mechanisms, slag was an excellent material to bind with Fe²⁺ together fornitrobenzene reduction. Using slag/Fe²⁺ system to treat environmental nitrobenzenewas theoretically and practically feasible.