Abiotic transformation of hexahydro-1,3,5-trinitro-1,3,5-triazine by fell bound to magnetite

RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), a nitramine explosive, is often found as a subsurface contaminant at military installations. Though biological transformations of RDX are often reported, abiotic studies in a defined medium are uncommon. The work reported here was initiated to investigate the transformation of RDX by ferrous iron (Fe-II) associated with a mineral surface. RDX is transformed by Fe-II in aqueous suspensions of magnetite (Fe3O4). Negligible transformation of RDX occurred when it was exposed to Fe-II or magnetite alone. The sequential nitroso reduction products (MNX, DNX, and TNX) were observed as intermediates. NH4+, N2O, and HCHO were stable products of the transformation. Experiments with radiolabeled RDX indicate that 90% of the carbon end products remained in solution and that negligible mineralization occurred. Rates of RDX transformation measured for a range of initial Fe-II concentrations and solution pH values indicate that greater amounts of adsorbed Fe-II result in faster transformation rates. As pH increases, more Fe-II adsorbs and k(obs) increases. The degradation of RDX by FeII- magnetite suspensions indicates a possible remedial option that could be employed in natural and engineered environments where iron oxides are abundant and ferrous iron is present.