Measure and Model Dissolution of Explosive Compounds TNT, RDX, and HMX under Continuous Flow Conditions

Chao Wang ¹, Mark E. Fuller ², Volha Lazouskaya ^1,2, Charles Schaefer ², Jeffrey L. Caplan ^1,3, Yan Jin ^{1 *}

¹ Department of Plant and Soil Sciences, University of Delaware, Newark, Delaware, 19716, USA; ² Shaw Environmental, Inc., 17 Princess Road, Lawrenceville, New Jersey, 08648, USA; ³ Delaware Biotechnology Institute, University of Delaware, Newark, Delaware, 19716, USA

^*Corresponding author: Yan Jin, Phone: (302)-831-6962; Fax: (302)-831-0605; Email: yjin@udel.edu.

Abstract

Explosive compounds of 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro -1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) are the most common contaminants around active military firing ranges. Dissolution of TNT, RDX, and HMX from their mixed solid-phase energetic residues is usually the first step prior to their entry and spreading in the subsurface environment. Nevertheless, dissolution of individual TNT, RDX, and HMX under continuous flow conditions has not been well investigated. The present study applied spectral confocal microscopy to observe and quantify the dissolution of microscale crystals (<100 µm) of TNT, RDX, and HMX in a micromodel channel. A dissolution model was thereafter developed and applied to describe the change of radius, surface area, volume, and specific surface area of the energetic crystals as a function of time. The results indicated that the model, which incorporated a retardation term that takes into account the unexposed surface area due to attachment to channel surfaces, well described the dissolution processes. In contrast, the model without the retardation term could not capture the measurements at the late stage of TNT dissolution. Fitting of the model to experimental measurements allowed estimation of mass transfer constants and dissolution rates. This study highlights the importance of the retardation term in the dissolution model and illustrates the utility of the newly developed spectral imaging method for investigating the mass transfer of TNT, RDX, and HMX.