Sorption of High Explosives to Water‐Dispersible Clay: Influence of Organic Carbon, Aluminosilicate Clay, and Extractable Iron

Abstract

Explosives in soils can present environmental problems for military installations. Fine, mobile particles represent the most reactive fraction of the soil and, therefore, are expected to adsorb explosives and potentially facilitate their transport. Th e objective of this study was to determine the relative signifi cance of phyllosilicate clay, organic matter, and two forms of extractable iron in adsorption of 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by the colloidal water-dispersible clay (WDC) fraction of the soil. Th e WDC fraction of two mineral and one organic soil was separated and then treated to remove organic carbon (OC) and several forms of iron (Fe o , oxalate extractable, and Fe d , dithionite-citrate extractable). Adsorption coeffi cients were determined for whole soils, untreated, and treated WDC. For mineral soils, adsorption of TNT and RDX on the WDC was greater than on the whole soil. Th e presence of OC increased explosives sorption by WDC. When OC was removed, iron interfered with TNT sorption. In the presence of OC, removal of Fe o decreased RDX adsorption and increased TNT adsorption indicating diff erent adsorption mechanisms. Organic carbon was a more signifi cant indicator of explosives adsorption by WDC than clays or iron oxides and hydroxides. Th erefore, OC is the most likely medium for facilitated transport of TNT and RDX. P revious research has demonstrated contamination of livefi re training ranges with residues of high explosives (HE) . Anticipation of the extent to which migration of HE occurs is vital to assessments of contamination behavior/transport and appropriate range management. Specifi cally, 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) are common HE that have been detected on live-fi re ranges and due to their dissimilar chemical structure are expected to exhibit diff erent behavior in the environment. Previous studies of adsorption by soils and transport of explosives in solution phase (review by Pennington and Brannon, 2002) indicated signifi cant adsorption of TNT relative to much less adsorption of RDX. Th erefore TNT tends to be a sediment contaminant, and RDX tends to be leached further down in the soil profi le and is a common groundwater contaminant. Th e aspect of HE fate that was not studied previously is transport in association with mineral and organic colloidal material. However, signifi cant contribution of colloids to transport of several other contaminants has been demonstrated (de Jonge et al., 2004). Strong adsorption of TNT to dissolved organic carbon (DOC) (K DOC = 41-68 mL g C −1 ) observed by Eriksson et al. (2004) suggests that colloid-facilitated transport may be contributing to TNT movement. Sorption of High Explosives toTh e clay-sized (colloidal) fraction of the soil consists of silica, iron, aluminum, manganese, titanium oxides and hydroxides, phyllosilicate minerals, and organic compounds. Th e portion of clay that can be mobilized by water is operationally defi ned as water-...

Batch soil adsorption and column transport studies of 2,4-dinitroanisole (DNAN) in soils

“…Our estimated mean log K OC (K d normalized to OC) for DNAN was 2.24 ± 0.20, a value similar to one estimated for DNAN by Hawari et al (2015) (2.45 ± 0.16), but also to values for TNT in soils (2.48-3.04) (US Department of Health and Human Services, 1995) and in water dispersible clay extracted from soils (2.65 ± 0.28) (Dontsova et al, 2009). The low variability of K OC values as well as their consistent decrease with decrease in log K ow implies that DNAN adsorbs to OC through hydrophobic interactions.…”

“…Comparing these coefficients to TNT adsorption coefficients for Plymouth and Catlin soils showed higher adsorption of DNAN in Plymouth soil (K d of 4.4 L kg −1 for DNAN and 0.63-1.6 L kg −1 for TNT depending on the method used) (Dontsova et al, 2006) but less adsorption of DNAN in the Catlin soil (TNT K d 17.9 L kg − 1 vs. DNAN K d 6.1 L kg − 1 ) (Dontsova et al, 2009). The Freundlich parameters were closer for the two compounds for the Catlin soil (K f = 45.6, n = 0.57 for DNAN and K f = 32.67, n = 0.60 for TNT) (Dontsova et al, 2009). Hawari et al (2015) demonstrated a link between solubility, octanol-water partition coefficient (K ow ), and K OC for DNAN, for several its transformation products, and for TNT.…”

“…In general, organic carbon is often the best predictor of adsorption behavior of organic compounds, particularly non-ionic ones like DNAN (e.g., Site, 2001). However, TNT is adsorbed by both OC and phyllosilicate clays (Haderlein et al, 1996;Dontsova et al, 2009) suggesting that DNAN may also be adsorbed by clays. This was confirmed by Linker et al (2015).…”

Column transport studies of 3-nitro-1,2,4-triazol-5-one (NTO) in soils

“…They were a subset of eleven soils used for NTO batch adsorption and transformation studies by Mark et al (2016). Some of these soils had been used previously in studies of explosive and propellant formulation constituents (Dontsova et al, 2006(Dontsova et al, , 2007(Dontsova et al, , 2009a(Dontsova et al, , 2009bTaylor et al, 2012). As the same soils were used in batch and saturated flow studies we were able to compare determined parameters to verify if the previously observed processes were responsible for NTO attenuation.…”

The stability of TNT, RDX and PETN in simulated post-explosion soils: Implications of sample preparation for analysis

“…In addition to microbial-based attenuation, explosives may undergo adsorption to many potential sorbents within a soil matrix, such as organic carbon, microorganisms, humic material, and surfaces present in the clay fraction of soils [1,10,14,15,19,26,30,37,39,40]. TNT [39,41] and RDX [19] have both been reported to undergo adsorption to organic carbon in soil.…”