Dissolution of explosive compounds TNT, RDX, and HMX under continuous flow conditions

Area of Science:

• Environmental Science
• Chemical Engineering
• Geochemistry

Background:

• 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 prevalent contaminants at military firing ranges.
• Understanding the dissolution of these energetic materials is crucial for predicting their subsurface transport and environmental fate.
• Previous investigations have not sufficiently explored the continuous flow dissolution dynamics of individual TNT, RDX, and HMX.

Purpose of the Study:

• To investigate and quantify the dissolution behavior of TNT, RDX, and HMX crystals under continuous flow conditions.
• To develop and validate dissolution models that accurately describe the changes in crystal size, surface area, and volume over time.
• To assess the significance of surface area in direct contact with channel surfaces (resistance term) on dissolution modeling.

Main Methods:

• Utilized spectral confocal microscopy to observe and quantify the dissolution of TNT, RDX, and HMX crystals (<100 μm) within micromodel channels.
• Developed dissolution models to track changes in crystal radii, surface areas, volumes, and specific surface areas as a function of time.
• Compared model performance with and without a resistance term to evaluate its impact on dissolution dynamics.

Main Results:

• A dissolution model incorporating a resistance term, accounting for surface area not exposed to flow, accurately described the observed dissolution processes.
• The model without the resistance term failed to capture late-stage TNT dissolution data.
• Model-fitted mass transfer coefficients were consistent with previously reported values, validating the approach.

Conclusions:

• The inclusion of a resistance term is critical for accurately modeling the dissolution of TNT, RDX, and HMX in subsurface environments.
• Spectral confocal microscopy provides a powerful tool for quantifying mass transfer during contaminant dissolution.
• This study enhances the understanding of contaminant transport dynamics from military firing ranges.