New insensitive high explosives (IHE), which are fire/shock resistant components of insensitive munitions, pose great challenges to conventional explosives manufacturing wastewater treatment processes and require advanced methods to effectively and efficiently mineralize these recalcitrant pollutants. Oxidation processes that utilize the fundamental techniques of Fenton chemistry optimized to overcome the limitations inherent to this method are vital to provide efficient degradation of these pollutants while maintaining cost-effectiveness and scalability. In this manner, optimizing the use of heterogeneous catalysts and in-situ generated H2O2 to degrade IHEs is proposed. From a heterogeneous catalyst optimization perspective, varying the surface chemistry of activated carbon for use as a catalyst removes precipitation complications associated with utilizing traditional iron species in Fenton chemistry while introducing possible adsorption/regeneration capabilities if combined in a novel electrochemical system. Comparing various additives and surface chemistry modifications, raw activated carbon doped with 5% MnO2 in the presence of H2O2 realized a high concentration of hydroxyl radical formation while maintaining low cost and relative ease of synthesis. This AC-Mn5 catalyst performed effectively over a wide pH range and in the presence of varying H2O2 concentrations with a sufficient effective lifetime. In-situ generation of H2O2 removes the logistical and economic constraints associated with external H2O2, with hydrophobic carbon electrodes utilizing generated gaseous O2 as efficient and economic materials for this internal generation. In a novel flow-through reactor, gaseous O2 is generated on a titanium/mixed metal oxide anode with subsequent H2O2 electrogeneration on a hydrophobic microporous-layered carbon cloth cathode. This reactor electrogenerates sufficient H2O2 concentrations at an optimized current intensity and over a wide range of flow rates, influent pH values, and through multiple iterations. Coupling these two optimization methods realizes the production of highly oxidative hydroxyl radicals by Fenton-like catalysis of electrogenerated H2O2 on the surface of an MnO2-doped activated carbon catalyst. This method incorporates electrochemically induced oxidation of munitions while maintaining cost-effectiveness and scalability. It is anticipated this platform holds great promises to eliminate analogous contaminants.

Optimizing Fenton-like oxidation of legacy munitions/insensitive high explosives utilizing a cost-effective MnO2-doped activated carbon catalyst in the presence of electrochemically generated H2O2

ACS Fall 2021

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