Degradation of energetic compounds using an integrated elemental iron: Fenton process

Application of zero-valent iron was investigated to develop a cost-effective pink water treatment process. We hypothesized that an iron reduction process may rapidly remove the explosives and enhance the rate and extent of subsequent oxidation processes. In batch experiments, 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (Royal Demolition Explosive, RDX) were completely removed from the solutions within 30 min. With scrap iron, the extent of adsorption of TNT and its products was more significant and reduction of these adsorbed molecules to TAT was slower. Compared to TNT, transformation of adsorbed RDX was more rapid and less affected by iron type. The mechanism and pathway via which 2,4-dinitrotoluene (DNT) was reductively transformed with elemental iron was investigated. Experiments were conducted using two-compartment dialysis cells where DNT and pure iron powder were separated by a graphite sheet. Graphite-mediated, indirect reduction of DNT occurred primarily through reduction of the ortho nitro group to form 2A4NT, whereas DNT reduction at iron (hydr/oxide) surface occurred via para nitro reduction to give 4A2NT. The kinetics and pathway of nitroglycerin reduction with elemental iron was investigated by batch experiments. Nitroglycerin was reduced stepwise via 1,2- and 1,3-dinitroglycerins (DNGs), and 1- and 2-mononitroglycerins (MNGs) to glycerol. Each of these reduction steps released NO₂−, which was subsequently reduced to NH₄+. Nitroglycerin was reduced to glycerol mainly via 1,2-DNG/1,3-DNG and 1-MNG. The effect of reductive treatment with elemental iron on the rate and extent of mineralization by Fenton oxidation was studied for TNT and RDX using a completely-stirred tank reactor (CSTR). Iron pretreatment enhanced the extent of TOC removal by approximately 20% and 60% for TNT and RDX, respectively. Complete TOC removal was achieved for TNT and RDX solutions with iron pretreatment under optimal conditions. The bench-scale iron treatment-Fenton oxidation integrated system showed more than 95% TOC removal for TNT and RDX solutions under optimal conditions. The integrated system removed approximately 85% of TOC in pink water from the Iowa Army ammunition plant. These results suggest that the sequential iron treatment-Fenton oxidation process may be a viable technology for pink water treatment.