Tailored PCM That Serves as Reactive Adsorbent to Promote Simultaneous Adsorption and Hydrolysis of MC

High concentrations of munitions constituents (MC) residues, including legacy and insensitive high explosives (IHE), are commonly found in soil at Department of Defense(DoD) testing and training ranges, posing a significant safety threat to personnel. Many IHE are highly water-soluble and can easily migrate from soil to water. Consequently, IHEs may represent a significant source of contamination to ground and surface waters at DoD ranges. Therefore, there is a pressing need to maximize the sorption of legacy explosives and IHE, minimize their transport from DoD sites, and promote their decay whenever possible. This project will address this urgent need by developing technologies for simultaneously adsorbing and destroying MC residues. The central objective of this project is to design and optimize pyrogenic carbonaceous matter (PCM) in ways that facilitate the retention and/or hydrolysis of legacy explosives and IHE that are of concern at DoD sites. The project will use a combined experimental and computational approach.

The project will tailor carbon amendments, PCM (e.g. activated carbon and biochar), to serve the dual purpose of effectively concentrating MC and hydroxide ions on PCM surfaces, thereby promoting a reaction that leads to MC degradation. For explosives that are not prone to hydrolysis, PCM will be modified to increase PCM affinity for these compounds. Because coupled interfacial processes are likely to be involved, computational modeling will be used to aid in the design of experiments and the interpretation of results. Computational modeling can also help identify the structural features of PCM that facilitate hydrolysis and adsorption, thereby providing guidance for the tailoring of carbons. Four tasks will be performed to achieve the central objective: (1) identify the key structural characteristics of legacy explosives and IHE that make them susceptible to adsorption and/or PCM-facilitated hydrolysis, (2) tailor the surface characteristics of PCM to enhance the adsorption and hydrolysis of MC, (3) apply computational chemistry to both provide a mechanistic understanding of PCM-facilitated hydrolysis and guide the optimization of PCM toward achieving the dual function of MC adsorption and hydrolysis, and (4) assess the effectiveness of optimized PCM as soil amendments toward MC mixtures.

Historically, carbonaceous amendments have been used to remove contaminants from the aqueous phase by sorption and/or complexation, but not to bring about their degradation. There is evidence that carbons not only adsorb, but also catalyze the hydrolysis of some MC. This project will advance the field, first, by identifying structural features of both the MC and the carbons that will facilitate hydrolysis, and second, by developing tailored carbons that will accelerate hydrolysis. The combined approach of experimentation and computational modeling will allow the project to gain a fundamental understanding of this novel surface process, which has the potential of transforming the field of MC remediation. The end product will be an optimized PCM that is inexpensive and easy to deploy. When applied as amendments on DoD ranges, PCM can maximize the sorption/degradation of legacy explosives and IHE, minimize the transport of such explosives, and therefore mitigate their harmful impact on the environment. The tailored PCM can also be used for treatment at the source of contamination. The knowledge generated from this project may also lead to the development of effective technologies for treating MC in wastewaters from manufacturing facilities. (Anticipated Project Completion - 2024)

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