| Abstrakt: |
There is a widespread interest in understanding the reactivity of organic pollutants in reducing systems. The reductive transformation of 4-cyanonitrobenzene (4-CNB) was examined in batch suspensions of goethite (a-FeOOH) and ascorbic acid from pH 6–8. Experimental results demonstrate that ascorbic acid promotes the reductive dissolution of goethite, which in turn, facilitates the reductive transformation of 4-CNB at all pH values examined. 4-CNB transformation rates are dependent on ascorbic acid concentration, oxide loading, and pH. In goethite suspensions, both ferric oxide dissolution and ferrous iron adsorption occur simultaneously. Generally, reductive transformation of 4-CNB by ferrous iron in suspensions of geothite and ascorbic acid would be unlikely at neutral pH because this condition is less favorable for the reductive dissolution of ferric oxides, although favorable for Fe(II) adsorption. However, we find that neutral pH values provide suitable conditions for the reductive dissolution of goethite and the subsequent transformation of 4-CNB by adsorbed Fe(II). Goethite suspensions in which the pH was pre-equilibrated at pH 4, and then increased to pH 6, 7, or 8, were more effective at producing increased Fe(II) concentrations and resulted in faster transformations of 4-CNB. The results of this study provide evidence that naturally occurring organic acids play an indirect role in the transformation of reducible organic pollutants. |
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