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Remediating TNT-contaminated water and soil by Fenton oxidation
Abstract
Past disposal practices at munitions production facilities have generated numerous acres of TNT-contaminated soil. We determined the potential of the Fenton reagent (Fe$\sp{2+}$ and H$\rm\sb2O\sb2$) to remediate TNT contamination in water, aqueous extracts of soil, and soil-water slurries. The effects of H$\rm\sb2O\sb2$ and Fe$\sp{2+}$ concentrations, solution pH, temperature, and initial TNT concentration on transformation and mineralization rates were evaluated. Complete destruction of TNT was achieved by 24-h Fenton oxidation in the dark, coinciding with 40 to 60% mineralization. Subsequent exposure to visible light (400-1000 nm) resulted in greater than 90% mineralization. We observed generation of 2,4,6-trinitrobenzoic acid and 1,3,5-trinitrobenzene within 15 min following Fenton oxidation. This indicates that initial TNT destruction likely occurs by methyl group oxidation and decarboxylation. Further destruction involves nitro moiety removal with ring hydroxylation and cleavage, as evidenced by the stoichiometric recovery of TNT-nitrogen as NO$\sbsp{-}{3}$ and production of oxalic acid as the primary C-containing end product. Upon exposure to light, Fe(II) was regenerated and oxalic acid produced from $\sp{14}$C-TNT oxidation disappeared. Similar observations were made when $\sp{14}$C-oxalic acid was the starting substrate. Ultraviolet irradiation significantly increased the destruction rates of TNT and other nitrotoluenes by Fenton oxidation. Fenton oxidation was also effective in destroying TNT in aqueous extracts of contaminated soil and soil-water slurries but higher H$\rm\sb2O\sb2$ and Fe$\sp{2+}$ concentrations were required to achieve the transformation and mineralization rates observed in pure solution. Greater TNT destruction in soil slurry was achieved when temperature was increased $(45\sp\circ$C), the Fenton reagent was incrementally added, and soil-slurry pH lowered. Soluble organic matter and clay had varying effects on TNT transformation rates.
Subject Area
Environmental science|Soil sciences|Agricultural chemicals
Recommended Citation
Li, Zhengming, "Remediating TNT-contaminated water and soil by Fenton oxidation" (1996). ETD collection for University of Nebraska-Lincoln. AAI9628239.
https://digitalcommons.unl.edu/dissertations/AAI9628239