Effect of adsorption to elemental iron on the transformation of 2,4,6‐trinitrotoluene and hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine in solution

Abstract

Abstract-The effect of adsorption to elemental iron on the reductive transformation of 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (royal demolition explosive [RDX]) in aqueous solution was studied with scrap iron and high-purity iron. In batch experiments with the same total iron surface area and a mixing rate of 100 rpm, TNT and RDX were removed from the solution within 30 min. With high-purity iron, adsorbed TNT was reduced to 2,4,6-triaminotoluene (TAT) rapidly, with little accumulation of intermediates at the surface. With scrap iron, the extent of adsorption of TNT and its daughter products was more significant and reduction of these adsorbed molecules to TAT was slower. Distribution of the intermediates indicated that the reaction with scrap iron occurred primarily through reduction of the ortho nitro group. Kinetic analysis suggests that mass transfer or adsorption of TNT controlled the overall rate of TNT reduction to TAT with pure iron, whereas with scrap iron, the rate of TAT formation was probably limited by other processes. Compared to TNT, transformation of adsorbed RDX was more rapid and less affected by iron type. The RDX was reduced to an unidentified, water-soluble intermediate and , which accounted for ap-ϩ NH 4 proximately 50% of the RDX nitrogen. No total organic carbon reduction was observed before and after RDX transformation with scrap iron.

Effects of operational parameters and common ions on the reduction of 2,4-dinitrotoluene by scrap copper-modified cast iron

“…6 Effects of Na 2 CO 3 on 2,4-DNT reduction (a), pH variation profiles (b), the reduction products and mass balance (c) and the repeated use of CMCI (d, e) at 100 mg L −1 of 2,4-DNT, pH 7, 0.25 % mass ratio (Cu:Fe), and 200 g L −1 scrap cast iron the iron surface. Similar results (Oh et al 2002) are also reported for the reduction of 2,4,6-trinitrotoluene with highpurity iron, in which the adsorption of dinitro and mononitro intermediates are minimal throughout the reaction. Therefore, the formation of precipitates can be a potential mechanism of CO 3 2− , in which the products of reduction are strongly adsorbed, thereby decreasing the observed efficiency in the current study.…”

Fate and Transport of 2,4,6-Trinitrotoluene in Loams at a Former Explosives Factory

“…Results indicate that there may be impedance to further 2ADNT degradation at this site, with preferential onward reaction of 4ADNT to form 2,4DANT. A similar product distribution was reported by Oh et al (2002) for reductive transformation experiments involving scrap iron, which they described as having high carbon content.…”

“…Sustainable biogeochemical cycles have been postulated for abiotic degradation involving iron (Hofstetter et al, 1999), suggesting ferrous-ferric iron cycling would be inexhaustible under highly reducing conditions; however, given the close proximity of results we cannot make any definitive suggestions on specific abiotic transformation mechanisms operative at the study area. Referring back to the concurrent Fe, TNT and TP contaminant peak discussed in the source zone characterization section, it has been commonly reported in laboratory studies that an increased elemental iron or Fe(II) content correlates to increased TNT transformation Downloaded by [University of Connecticut] at 09:58 09 October 2014 rates via direct enhancement of abiotic transformation, where Fe acts as an electron donor in ferrous-ferric iron cycling (Hofstetter et al, 1999;Oh et al, 2002;Hofstetter et al, 2003). Abiotic testwork indicates, however, that transformation rates are low at the study sites, reiterating that the observed product distribution is more likely a function of mobility.…”

“…As a result, the last few decades have seen significant advances in the understanding of fate and transport processes affecting TNT in the environment, though many aspects still remain relatively poorly understood compared to other compounds such as hydrocarbons or pesticides. Research and development into TNT's fate has focused upon specific process level mechanisms under idealized laboratory conditions (Pennington and Patrick, 1990;Comfort et al, 1995;Spain, 1995;Haderlein and Schwarzenbach, 1995;Duan et al, 1998;Myers et al, 1998;Sheremata et al, 1999;Eschenbach et al, 2001;Oh et al, 2002;Hofstetter, Schwarzenbach, and Haderlein, 2003), the heterogeneous distribution of contaminants at the field scale including sampling and analysis techniques (Jenkins et al, 1997;Thiboutot et al, 2002), or remediation concepts and technologies (Carpenter et al, 1978;Kaplan and Kaplan, 1982;Williams et al, 1992;Funk et al, 1993;Boopathy et al, 1994;Thompson et al, 1998;Bhadra et al, 1999;Siciliano and Greer, 2000). Through integration of the complimentary aspects of in situ contaminant occurrence data, and laboratory scale adsorption and microcosm experiments designed to closely represent in situ conditions (using native soils and bacteria, and field collected contaminants), we aimed to quantify natural attenuation rates of TNT within two test loams for wider applicability, while also discussing fate and transport of TNT and TPs at the study areas.…”

Soils contaminated with explosives: Environmental fate and evaluation of state-of-the-art remediation processes (IUPAC Technical Report)

“…More than 95 % of the 14 C lost, however, was recovered from the Fe 0 surface through a series of extraction and oxidation procedures. Oh et al [352] treated RDX with scrap iron and high-purity iron under anaerobic conditions. They observed that RDX was readily transformed by both iron sources with no appreciable build-up of identifiable degradates.…”