| Abstract
| - RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) and HMX(octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) are cyclicnitramines ((CH2NNO2)n; n = 3 or 4, respectively) widely usedas energetic chemicals. Their extensive use led to wideenvironmental contamination. In contrast to RDX, HMX tendsto accumulate in soils due to its unique recalcitrance. Inthe present study, we investigated the potential of zerovalentiron (ZVI) to transform HMX under anoxic conditions.HMX underwent a rapid transformation when added in well-mixed anoxic ZVI−H2O batch systems to ultimatelyproduce formaldehyde (HCHO), ammonium (NH4+), hydrazine(NH2NH2), and nitrous oxide (N2O). Time course experimentsshowed that the mechanism of HMX transformationoccurred through at least two initial reactions. One reactioninvolved the sequential reduction of N−NO2 groups tothe five nitroso products (1NO−HMX, cis-2NO−HMX, trans-2NO−HMX, 3NO−HMX, and 4NO−HMX). Another impliedring cleavage from either HMX or 1NO−HMX asdemonstrated by the observation of methylenedinitramine(NH(NO2)CH2NH(NO2)) and another intermediate thatwas tentatively identified as (NH(NO2)CH2N(NO)CH2NH(NO2)) or its isomer (NH(NO)CH2N(NO2)CH2NH(NO2)). Thisis the first study that demonstrates transformation of HMXby ZVI to significant amounts of NH2NH2 and HCHO.Both toxic products seemed to persist under reductiveconditions, thereby suggesting that the ultimate fate of thesechemicals, particularly hydrazine, should be understoodprior to using zerovalent iron to remediate cyclic nitramines.
|
