Both legacy munitions compounds and new insensitive high explosives are being manufactured and utilized concurrently, and a need now exists for water treatment systems that are able to degrade both classes of explosives.  Electrochemical systems offer the possibility to degrade all types of explosives due to their ability to host redox reactions that are easy to control through low-power voltage and current settings capable to be sustained in long-term operation.  More recently, stainless steel has been evaluated as a cost-effective alternative electrode material, and it is a widely available material in various compositions, mesh sizes, and weaves.  The goal of this work is to understand the cathodic processes for electrochemically induced removal of RDX, NQ, and DNAN within an electrochemical plug flow reactor. Stainless steel and nickel wire meshes were evaluated as cathodes, and the operating conditions were optimized to enhance munitions removal and to shorten time to steady-state.   Applied current allowed the cathode to support munitions removal by direct reduction at the cathode surface, catholically-induced alkaline hydrolysis, and catalytic hydrogenation on Ni-containing cathode surfaces. The applied current reduces RDX, NQ, and DNAN mainly by direct electron transfer, and higher current gives slightly greater removal extent and shorter acclimation time to steady state.  More available cathode surface area improves RDX removal extent, but differences in wire diameter had no significant effect on removal percentage. The optimal cathode material for RDX removal was found to be stainless steel 316 grade, mesh size 80, of any wire diameter. Higher nickel percentage within stainless steel improves RDX and NQ removal but does not affect DNAN removal.  As for alkaline hydrolysis, RDX, NQ, and DNAN could be degraded at pH greater than 12, and reaction order appeared to be first order with respect to hydroxide concentration for RDX and DNAN, but for NQ the reaction order was 0.5. RDX removal through the entire cathode could be modeled as first order decay, and similar rate coefficients were observed at different flow rates, which allows for a simple relationship between flow rate, detention time, and reaction rates.

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

ACS Spring Meeting 2021

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