Degradation of RDX using granular iron and nickel-plated granular iron

Abstract

Using granular iron (Fe) and nickel-plated iron (Ni/Fe), this paper examines the effectiveness of these two types of reactive materials for the treatment of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), a common groundwater and soil contaminant at military facilities. RDX degraded very rapidly in the presence of both Fe and Ni/Fe in column and batch experiments. Enhancement by Ni/Fe did not prove to be effective as the half-lives of RDX ranged from 3 to 24 seconds and 3 to 11 seconds in the Fe and Ni/Fe columns, respectively. Reaction vessel experiments and estimation of the mass transfer coefficient in the column indicated that reaction kinetics was mass transfer limited. Detailed analyses of reaction intermediates and products suggest that RDX degradation proceeds through direct electron transfer processes and following to the same pathways in the presence of Fe and Ni/Fe. The formation of carbon-containing products, including formaldehyde (up to 60%), CO2 (up to 45%) and formic acid (1%) and the nitrogen containing products of ammonium (up to 48%) and N2O (up to 13%), provides convincing evidence that RDX was completely decomposed to non-toxic end products. CO2, previously reported to form only in biological or Fe-microbial combined systems, was detected as one of the main C-bearing end product. Therefore, this study shows that Fe is an effective material for remediating groundwater and industrial effluents containing RDX; and the use of additional enhancement, either biological or with Ni catalyst, does not provide additional advantages.