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TECHNICAL REPORTS

Organic Compounds in the Environment

Remediating Munitions-Contaminated Soil with Zerovalent Iron and Cationic Surfactants

School of Natural Resources, University of Nebraska–Lincoln, 256 Keim Hall, Lincoln, NE 68583-0915

^* Corresponding author (scomfort{at}unl.edu).

Received for publication May 8, 2003. Soils contaminated from military operations often contain mixtures of HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine), RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), and TNT (2,4,6-trinitrotoluene) rather than a single explosive. Differences among explosives in solubility and reactivity make developing a single remediation treatment difficult. When Fe⁰ was used to treat a munitions-contaminated soil, we observed high rates of destruction for RDX and TNT (98%) but not HMX. Our objective was to determine if HMX destruction by Fe⁰ could be enhanced by increasing HMX solubility by physical (temperature) or chemical (surfactants) means. To determine electron acceptor preference, we treated RDX and HMX with Fe⁰ in homogeneous solutions and binary mixtures. Increasing aqueous temperature (20 to 55°C) increased HMX solubility (2 to 22 mg L^–1) but did not increase destruction by Fe⁰ in a contaminated soil slurry that also contained RDX and TNT. Batch experiments using equal molar concentrations of RDX and HMX demonstrated that RDX was preferentially reduced over HMX by Fe⁰. By testing various surfactants, we found that the cationic surfactants (HDTMA [hexadecyltrimethylammonium bromide], didecyl, and didodecyl) were most effective in increasing HMX concentration in solution. Didecyl and HDTMA were also found to be highly effective in facilitating the transformation of HMX by Fe⁰. Using HDTMA or didecyl solutions (3%, w/v) containing solid-phase HMX, we observed that 100% of the added HMX was transformed by Fe⁰ in the didecyl matrix and 60% in the HDTMA matrix. These results indicate that cationic surfactants can increase HMX solubility and facilitate Fe⁰–mediated transformation kinetics but HMX destruction rates will be slowed when RDX is present.

Abbreviations: CMC, critical micelle concentration • HDTMA, hexadecyltrimethylammonium bromide • HE, high explosives • HMX, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine • HPLC, high performance liquid chromatography • LANL, Los Alamos National Laboratory • LUMO, lowest unoccupied molecular orbital • RDX, hexahydro-1,3,5-trinitro-1,3,5-triazine • TNT, 2,4,6-trinitrotoluene

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This Issue in Journal of Environmental Quality

JEQ 2004 33: 1177-1182. [Full Text]