Transformation of Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by Permanganate

Abstract

IntroductionHexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a common groundwater contaminant at numerous military sites where munitions were either formulated, manufactured, or used in military exercises. Permanganate (MnO 4 − ) is an oxidant commonly used with in situ chemical oxidation (ISCO) and has been widely accepted for treating chlorinated ethenes. Past research has shown that MnO 4 − preferentially attacks compounds with carbon−carbon double bonds, aldehyde groups, or hydroxyl groups and is attracted to the electron-rich region of chlorinated alkenes.(1) Although RDX possesses none of these characteristics, laboratory studies performed by Adam et al.(2) showed that MnO 4 − could effectively transform and mineralize RDX (i.e., ~87% recovered as 14 CO 2 ). Moreover, a pilotscale demonstration at the Nebraska Ordnance Plant further supported MnO 4 − as a possible in situ treatment for RDX-contaminated groundwater.(3) Despite demonstrating efficacy in removing RDX from tainted waters, the reaction rates and mechanisms by which MnO 4 − transforms RDX (and other explosives) have not been thoroughly studied.(4) While a carbon mass balance of the RDX−MnO 4 − reaction has been observed,(2) a similar nitrogen mass balance for this reaction has not been reported.One analytical challenge to identifying degradation products in a MnO 4 − matrix is that the solution is highly colored (i.e., purple), so colorimetric and UV detection techniques are not possible unless samples are quenched to remove MnO 4 − before analysis. However, the choice of quenching agent may influence pH or product distribution and further complicates understanding the RDX−MnO 4 − reaction mechanism.The transformation of RDX by various treatments has revealed several possible reaction pathways. These include direct ring cleavage, nitro-group reduction, concerted decomposition, and N-denitration.(5-12) While intermediates produced by some of these pathways are fleeting and difficult to mea- AbstractThe chemical oxidant permanganate (MnO 4 − ) 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 MnO 4 − 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−MnO 4 − reaction was first-order with respect to MnO 4 − and initial RDX concentration (second-order rate: 4.2 × 10 −5 M −1 s −1 ). Batch experiments showed that choice of quenching agents (MnSO 4 , MnCO 3 , and H 2 O 2 ) influenced sample pH and product distribution. When MnCO 3 was used as a quenching agent, the pH of the RDX−MnO 4 − solution was relatively unchanged and N 2 O and NO 3 − constituted 94% of the N-containing products after 80% of the RDX was transformed. On the basis of the preponderance of N 2 O produced under neutral pH (molar ratio N 2 O/...

A transition in the spatially integrated reaction rate of bimolecular reaction-diffusion systems

“… k = 4.2 × 10 −5 lit/mol/s, m = 2, n = 1 [ Chokejaroenrat et al ., ], p = q = 1 for all the reactions.…”

Using slow-release permanganate candles to remediate PAH-contaminated water

“…To prevent PAH volatilization during centrifugation and analysis, sample collection protocol maintained a ratio of 50% aqueous sample to 50% organic solvent (methanol for phenanthrene; acetonitrile for PAH syringe experiments). At each sampling, 0.7 mL of sample was placed into a 1.5-mL centrifuge vial and then mixed with 0.7 mL methanol or acetonitrile and 20 L manganese sulfate solution (0.1 g mL −1 ) to quench the reaction [30]. For control samples, 20 L H 2 O was used in place of manganese sulfate to maintain the dilution factor across all samples.…”

Permanganate oxidation of diclofenac: The pH-dependent reaction kinetics and a ring-opening mechanism

“…In addition to CBZ, the degradation kinetics and mechanisms between Mn(VII) and three other widely used antibiotics were investigated, where the apparent second-order rate constants were reported to be 0.61 ± 0.02 M À1 s À1 (ciprofloxacin), 1.6 ± 0.1 M À1 s À1 (trimethoprim) and 3.6 ± 0.1 M À1 s À1 (lincomycin) at pH 7 and 25°C (Hu et al, 2010(Hu et al, , 2011. Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), a common groundwater contaminant, can be effectively transformed by Mn(VII) at both laboratory and field conditions, with a second-order rate constant 4.6 Â 10 À5 M À1 s À1 at pH 7 and 25°C (Chokejaroenrat et al, 2011). Jiang et al (2009) examined the oxidation of triclosan in aqueous solution at pH 5-9 and clarified the important roles of ligands during the oxidation process.…”