Fenton oxidation of 2,4,6-trinitrotoluene in contaminated soil slurries

Numerous acres of soil are contaminated with trinitrotoluene (TNT) at sites where munitions were formerly manufactured, stored, or demilitarized. Our objective was to determine the potential for remediating TNT-contaminated soil by direct Fenton oxidation of contaminated soil slurries. The Fenton reagent (Fe²⁺ + H₂O₂) effectively oxidized TNT in a soil slurry (1:5 w/v soil:H₂O) containing 4200 mg TNT kg^-1, but TNT destruction was affected by temperature, dissolved organic matter (DOM), and clay mineralogy. Greater TNT destruction occurred at 45°C than 23°C and when the Fenton reagent was added sequentially rather than in a single-batch addition. Experiments performed with aqueous TNT indicated little effect of DOM on total TNT destruction within 24 h, but transformation rates were affected. While the TNT transformation rate was increased by fulvic acid (20 mg C L^-1), destruction rates were similar in humic acid solution and pure H₂O. Although both humic and fulvic acid were shown to reduce Fe(III) to Fe(II), more Fe(II) was regenerated in the presence of fulvic acid and may explain the higher TNT destruction rate. TNT mineralization rate was not greatly affected by fulvic or humic acid in the treatment solution. Small amounts of Ca²⁺- montmorillonite (0.1-1.0% w/v) also increased the TNT transformation rate. Adsorption of Fe(III) and TNT by montmorillonite may have enhanced Fenton oxidation of the TNT near the montmorillonite surface. In contrast, kaolinite had little affinity for TNT or Fe(III) and TNT transformation rate decreased as kaolinite concentration was increased from 0.1 to 2.0% (w/v). Although temperature, soil, and solution variables affected the efficiency of TNT destruction, our results indicate that Fenton oxidation is an effective abiotic treatment for remediating TNT-contaminated soils.