Jeffrey L. Davis

Lime Treatment of Explosives-Contaminated Soil from Munitions Plants and Firing Ranges

Microcosms were prepared using soils from munitions plants and active firing ranges and treated with hydrated lime. The presence of particulate explosives and co-contaminants, and the concentration of soil total organic carbon (TOC) on the alkaline hydrolysis reaction were studied. Trinitrobenzene (TNB) and dinitrobenzene (DNB) were sensitive to alkaline hydrolysis under these experimental conditions. The TNT metabolites, 2A- and 4A-DNT, were also removed, although more slowly than the parent compound, and the reaction required a higher pH (>12). RDX retention in the soil was proportional to the TOC content. The degradation intermediates of the alkaline hydrolysis reaction partitioned in the soil matrix in a manner similar to the parent. Solid particles of explosives are also degraded by alkaline hydrolysis. RDX and HMX exhibited 74 and 57% removal, respectively, in 21 days. TNT, as whole and broken grains, showed 83 and 99.9% removal in 21 days, respectively. The propellants, 2,4- and 2,6-DNT, were insensitive to alkaline hydrolysis. Alkaline hydrolysis is an inexpensive and effective means of reducing the varied explosives contamination.

Sorption of 2,4,6-Trinitrotoluene to Natural Soils Before and After Hydrogen Peroxide Application

Abstract Laboratory batch sorption experiments were conducted to investigate the impact of hydrogen peroxide (H2O2) pre-application on post-sorptive behavior of 2,4,6-trinitrotoluene (TNT) in different natural soils (average soil, high Fe soil, and high pH soil). After H2O2 application, the values of Freundlich coefficient Kf were increased by ∼ 160% for the average and high pH soils and by ∼ 120% for the high Fe soil, showing that the soils became more favorable for TNT sorption after H2O2 application. Nonlinearity in terms of the Freundlich exponent n was increased by ∼ 40% for the average and high pH soils and by ∼ 30% for the high Fe soil, showing greater sorption affinity of TNT for the oxidized soils at lower TNT concentrations and also implying greater TNT availability for transport at high concentrations. The increase in sorption extent for the H2O2-oxidized soils was presumably attributed to the oxygen-induced enhancement in the sorption capacity of the soils and the more dominant contribution of clay minerals to sorption. Therefore, enhanced sorption following H2O2 application may inhibit the subsequent formation of a TNT plume after either source zone remediation or plume remediation using H2O2 such as Fenton oxidation.

Electrolytic Alkaline Decomposition of a Munition Constituent (RDX) Contaminated Groundwater

Combined use of electrolysis and alkaline hydrolysis is explored for in-situ decomposition of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in laboratory experiments with simulated groundwater. Alkaline medium generated by water electrolysis at the cathode under direct electric currents will develop a permeable alkaline barrier for in-situ decomposition of RDX. Pseudo-first order transformation rate coefficients were developed from alkaline hydrolysis and electrolytic batch experiments for RDX decomposition with time. The results provided a target pH of 12 and a current density of 1 mA/cm 2 for treatment of RDX under groundwater flow column experiment. The results from the one-dimensional sand-filled alkaline hydrolysis columns (5-cm ID) were used to develop reaction rate coefficients used in designing a large scale-up one-dimensional column to test the electrolytic generation of hydroxide (10-cm ID). The rate coefficient from the 5-cm alkaline columns (0.46 per hr) was used to calculate a column length (160 cm) for complete removal of RDX and its nitroso-substituted products under groundwater flow rate of 30 cm/day. Effluent RDX concentrations from the 10-cm scale-up column (4,000 µg/L influent) were less than 0.1 µg/L for 36 days of treatment. The study concludes that cathodes placed at the down-gradient of groundwater RDX plume can perform as an effective permeable alkaline hydrolysis barrier for decomposition of RDX to levels below EPA drinking water advisory limits.

Direct Electrolytic Reduction of Energetic Compounds (hexahydro-1,3,5-trinitro-1,3,5-triazine and 2,4,6-trinitrotoluene) in Groundwater

Electrolytic reactive barriers (e-barriers) consist of closely spaced permeable electrodes installed across a groundwater contaminant plume in a permeable reactive barrier format. Application of sufficient potential to the electrodes results in sequential oxidation and reduction of the target contaminant. The objective of this study was to quantify the mass distribution of compounds produced during sequential electrolytic oxidation and reduction of ordinance related compounds (ORCs) in a laboratory analog to an e-barrier. In this study, a series of column tests were conducted using RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) and TNT (2,4,6-trinitrotoluene) as representative ORCs. The experimental setup consisted of a plexiglass column packed with quart-feldspar sand to simulate aquifer conditions. A single set of porous electrodes consisting of expanded titanium-mixed metal oxide mesh was placed at the midpoint of the soil column as a one-dimensional analog to an e-barrier. Constant current of 20 mA (variable voltage) was applied to the electrode set. Initial studies involved quantification of reaction products using unlabeled RDX and TNT. The results indicated approximately 70% of the influent concentration was transformed, in one pass, through sequential oxidation-reduction for both contaminants. Following the unlabeled studies, 14 C labeled ORCs were introduced to conduct the mass balance. An activity balance of up to 95.5% was achieved for both 14 C-RDX and 14 C-TNT. For both contaminants, approximately 21% of the influent activity was mineralized to 14 CO 2 . The proportion of the initial activity in the dissolved fraction was different for the two test contaminants. Approximately 30% of the initial 14 C-RDX was recovered as unreacted in the dissolved phase. The balance of the 14 C-RDX was recovered as non-volatile, non-nitroso transformation products. None of the 14 C-RDX was sorbed to the column sand packing. For 14 C-TNT approximately 51% of the initial activity was recovered in the dissolved phase, the majority of which was unreacted TNT. The balance of the 14 C-TNT was either sorbed to the sand packing (approximately 23.7 %) or dissolved/mineralized as unidentified ring cleavage products (4.5%).