ADSORPTION-DESORPTION OF 2, 4, 6-TRINITROTOLUENE AND HEXAHYDRO-1, 3, 5-TRINITRO-1, 3, 5-TRIAZINE IN SOILS

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Abstract
We studied the adsorption-desorption behavior of TNT (2, 4, 6-trinitrotoluene) and RDX (hexahydro-1, 3, 5-trinitro-1, 3, 5-triazine) in a bentonite/sand reference material (Swy-1 montmorillonite clay mixed with acidwashed sand) and two selected soils (Norwood and Kolin). Release of TNT, RDX, and other compounds from a contaminated soil obtained from the Louisiana Army Ammunition Plant (AAP) site was also investigated. The kinetics of TNT and RDX retention were measured using batch methods for a range of input concentrations. For RDX, the adsorption isotherms were distinctly linear. The TNT adsorption isotherm for bentonite/sand mixture appeared linear and was described equally well using linear, Freundlich, Langmuir, and a modified Langmuir model. For the Norwood and Kolin soils, TNT adsorption isotherms exhibited distinct nonlinearity and the Freundlich model provided the best fit. As indicated by the Kd values, TNT exhibited stronger retention or affinity to all soils and the bentonite/sand mixture than for RDX. The RDX retention data indicated little time-dependent behavior. The TNT retention data indicated a continued decrease in TNT concentration with time in the Norwood and Kolin soils. This was possibly caused by the formation and subsequent adsorption of transformation products because transformation products, such as amino nitro toluene compounds, were identified during batch experiments. For the bentonite/sand mixture, TNT retention was rapid initially and reached apparent equilibrium within 1 day. Unlike Kolin and Norwood soils, there was no hysteretic behavior of TNT adsorption-desorption by the bentonite/sand mixture and a mass balance suggested fully reversible retention mechanisms. © Williams & Wilkins 1995. All Rights Reserved.

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