Patrick J. Shea

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 (Fe⁰) 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, Al₂(SO₄)₃, or CH₃COOH] before Fe⁰ could transform RDX. Pilot‐scale experiments were performed by mixing Fe⁰ 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 Fe⁰ 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 Fe⁰ performance by promoting flocculation of humic material on the iron. Despite problems encountered with CH₃COOH, pilot‐scale treatment of Soil B (12100 mg RDX kg⁻¹) with Fe⁰ or Fe⁰ + Al₂(SO₄)₃ showed high RDX destruction (96–98%). This indicates that RDX‐contaminated soil can be remediated at the field scale with Fe⁰ and soil‐specific problems (i.e., alkalinity, high organic matter or Ba) can be overcome by adjustments to the Fe⁰ treatment.

Activated carbon can be used to decrease 2,4,6‐trinitrotoluene (TNT) toxicity and promote bioremediation of highly contaminated soil. Adding activated carbon at 0.25, 0.75, and 1.0% (w/w) to Sharpsbu...

Atrazine is the most widely used herbicide in the U.S. and has been detected in surface water and groundwater. Technologies are needed for onsite and in situ remediation of water and soil containing atrazine. We investigated the potential of using fine-grained, zero-valent iron (Fe⁰) to remove atrazine and promote its degradation in contaminated water and soil. Atrazine loss from aqueous solution increased with increasing Fe⁰concentration (w/v). Agitating 20 μg¹⁴C-ring-labeled atrazine L⁻¹with 10% Fe⁰(w/v) removed 92% of the¹⁴C from solution within 48 h. Only about 4% of the¹⁴C lost from solution was extractable from the iron with 3 mM CaCl₂(readily available pool), 81% was extractable with CH₃CN (potentially available pool), and 11% was unextractable residues. A companion experiment indicated that most of the¹⁴C extracted from the iron with 3 mM CaCl₂after the 48-h Fe⁰treatment was unaltered atrazine, while the CH₃CN extract contained approximately 33% atrazine and 48% was unidentified atrazine transformation products. Treating a highly contaminated solution (20 mg atrazine L⁻¹) with 20% Fe⁰(w/v) removed 88% of the¹⁴C (added as¹⁴C-ring-labeled atrazine) from solution within 48 h. Deethylatrazine was the main atrazine transformation product detected in solution after treatment, but small amounts of deisopropylatrazine, didealkylatrazine, and hydroxyatrazine were also found. Treating Sharpsburg surface soil containing 1 mg atrazine kg⁻¹with Fe⁰(2%, w/w) increased atrazine mineralization from 4.1 to 11.2% after 120 d. Pyrite (4% FeS₂, w/w) also increased atrazine mineralization in surface soil, but was less effective in the presence of NO₃⁻or SO₄²⁻(100 mg kg⁻¹soil). Adding 2% Fe⁰(w/w) and 100 mg NO₃⁻kg⁻¹to contaminated subsurface soil increased atrazine mineralization from 0.4 to 8.2% within 120 d, and unextractable residues increased from 4.6 to 9.8%. These results indicate iron can sorb atrazine and promote its transformation in water and soil.