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Remediating munitions-contaminated soil and water with zerovalent iron and surfactants
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. 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, and didecyl) were most effective in increasing HMX concentration in solution. Result showed that Fe0 + 2% didecyl was most effective in removing high explosives from Los Alamos National Laboratory soil. Equilibrium concentrations of didecyl were slightly above the critical micelle concentration (CIVIC) when added to the soil slurry at 2% (w/v). Pretreating Fe0 with didecyl was superior to using Fe0 alone, or mixing Fe0 and didecyl together, in removing HMX from aqueous solution, but not as effective as Fe0 + didecyl when solid-phase HMX was present. Reseeding experiments in which HMX was added intermittently to the batch reactor to mimic dissolution of solid phase HMX showed that Fe 0 pretreated with didecyl was highly reactive but reaction rates were not sustained. We conclude that didecyl can enhance HMX destruction by Fe 0 and is optimized when concentrations are below the CMC so that only patchy or mono surfactant layers form on the iron surface. We determined the toxicity of munitions residues produced after treatment with Fe0 and didecyl. High toxicity was observed when Fe0 + didecyl were added to soil slurry containing HMX and RDX. We found that the main source of the toxicity was didecyl rather than explosives and their products. To reduce didecyl toxicity and promote biodegradation, we treated activated carbon with Fe0 + didecyl in soil slurry. Results indicated that activated carbon can reduce toxicity and decrease didecyl concentrations to more acceptable levels for biodegradation. Activated carbon may be useful as a secondary treatment. ^
Agriculture, Soil Science|Environmental Sciences|Engineering, Environmental
Park, Jeong, "Remediating munitions-contaminated soil and water with zerovalent iron and surfactants" (2004). ETD collection for University of Nebraska - Lincoln. AAI3126961.