Oxidation of 2,4,6-trinitrotoluene in the presence of different iron-bearing minerals at neutral pH

Herein, TNT oxidation by Fenton-like systems in the presence of naturally occurring iron-bearing minerals was investigated in aqueous suspension at neutral pH. TNT degradation pseudo-first-order rate constant's (ksurf) values were found to be: 3.75 × 10−4 L m−2 min−1 > 2.55 × 10−4 L m−2 min−1 > 1 × 10−4 L m−2 min−1 > 1 × 10−6 L m−2 min−1 for pyrite, green rust, magnetite and goethite, respectively. Degradation efficiency was correlated with the increasing Fe(II) content in the mineral structure. Similar behavior was observed in more complex systems, including iron-coated quartz and iron-doped clays. Particularly, magnetite, Fe3O4 (mixed ferrous–ferric oxides), was efficient to promote Fenton-like reactions at pH 7 and its catalytic activity was preserved when incorporated into mineral assemblages with silica quartz or clay. For magnetite-bearing mineral systems, the addition of a non-toxic iron chelatant, carboxy-methyl-cyclodextrin (CMCD), improved TNT mineralization by a factor of 3. This increase in oxidation yield could in part be explained by the increased iron dissolution rate prompting higher Fenton's reaction efficiency. Consequently, CMCD might be used as an alternative to toxic iron chelating agents such as EDTA and NTA in in situ chemical oxidation (ISCO) processes for contaminated soil remediation.