The chemical oxidant permanganate (MnO4-) has been shown to effectively transform hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) at both the laboratory and field scales. We treated RDX with MnO4 - with the objective of quantifying the effects of pH and temperature on destruction kinetics and determining reaction rates. A nitrogen mass balance and the distribution of reaction products were used to provide insight into reaction mechanisms. Kinetic experiments (at pH ∼ 7, 25 °C) verified that RDX-MnO4- reaction was first-order with respect to MnO4- and initial RDX concentration (second-order rate: 4.2 × 10-5 M-1 s-1). Batch experiments showed that choice of quenching agents (MnSO4, MnCO3, and H2O2) influenced sample pH and product distribution. When MnCO3 was used as a quenching agent, the pH of the RDX-MnO 4- solution was relatively unchanged and N2O and NO3- constituted 94% of the N-containing products after 80% of the RDX was transformed. On the basis of the preponderance of N2O produced under neutral pH (molar ratio N2O/NO 3 ∼ 5:1), no strong pH effect on RDX-MnO4- reaction rates, a lower activation energy than the hydrolysis pathway, and previous literature on MnO4- oxidation of amines, we propose that RDX-MnO4- reaction involves direct oxidation of the methylene group (hydride abstraction), followed by hydrolysis of the resulting imides, and decarboxylation of the resulting carboxylic acids to form N2O, CO2, and H2O.
ASJC Scopus subject areas
- Environmental Chemistry