Degradation of dissolved RDX, NQ, and DNAN by cathodic processes in an electrochemical flow-through reactor

Abstract

Both legacy munitions compounds (e.g., RDX) and new insensitive high explosives (e.g. DNAN, NQ) are being manufactured and utilized concurrently, and there exists a need for wastewater treatment systems that are able to degrade both classes of explosives. Electrochemical systems offer treatment possibilities using inexpensive materials and no chemical additions. Electrochemically induced removal of RDX, NQ, and DNAN were separately studied within an electrochemical plug flow reactor hosting a stainless steel (SS) cathode and downstream Ti/MMO anode. Varying wire mesh cathodes and operating conditions were evaluated in an effort to identify the optimal cathode material, to determine the relative contributions of cathodically-induced removal processes, to shorten time to steady-state removal conditions, and to find practical ranges of operating conditions. Applied current allowed the cathode to support munitions removal mainly by direct reduction at the cathode surface, and the secondary reactions of cathodically-induced alkaline hydrolysis and catalytic hydrogenation by adsorbed H on Ni-containing cathode surfaces might contribute to some munitions degradation. The optimal cathode material was identified as SS grade 316, possibly due to its superior Ni content and lack of corrosion protection coating. Higher current, longer cathode length, and smaller mesh pore sizes resulted in slightly greater removal extents and shorter acclimation times to steady state removal conditions, but there are practical upper limits to these properties. Higher Ni content within SS improved RDX and NQ removal but does not affect DNAN removal. Prolonged use of SS grade 316 showed no debilitating changes in electrical performance or chemical content.