Pilot-scale treatment of RDX-contaminated soil with zerovalent iron

Soils in Technical Area 16 at Los Alamos National Laboratory (LANL) are severely contaminated from past explosives testing and research. Our objective was to conduct laboratory and pilot-scale experiments to determine if zerovalent iron (Fe-0) could effectively transform RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) in two LANL soils that differed in physicochemical properties (Soils A and B). Laboratory tests indicated that Soil A was highly alkaline and needed to be acidified [with H2SO4, Al-2(SO4)(3), or CH3COOH] before Fe-0 could transform RDX. Pilot-scale experiments were performed by mixing Fe-0 and contaminated soil (70 kg), and acidifying amendments with a high-speed mixer that was a one-sixth replica of a field-scale unit. Soils were kept unsaturated (soil water content = 0.30-0.34 kg kg(-1)) and sampled with time (0-120 d). While adding CH3COOH improved the effectiveness of Fe-0 to remove RDX in Soil A (98% destruction), CH3COOH had a negative effect in Soil B. We believe that this difference is a result of high concentrations of organic matter and Ba. Adding CH3COOH to Soil B lowered pH and facilitated Ba release from BaSO4 or BaCO3, which decreased Fe-0 performance by promoting flocculation of humic material on the iron. Despite problems encountered with CH3COOH, pilot-scale treatment of Soil B (12 100 mg RDX kg(-1)) with Fe-0 or Fe-0 + Al-2(SO4)(3) showed high RDX destruction (96-98%). This indicates that RDX-contaminated soil can he remediated at the field scale with Fe-0 and soil-specific problems (i.e., alkalinity, high organic matter or Ba) can he overcome by adjustments to the Fe-0 treatment.