Abiotic transformation of hexahydro-1,3,5-trinitro-1,3,5-triazine by Fe(II) 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 Fe(II)-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.