Cathodic electrochemical degradation of legacy (HMX, RDX, TNT) and insensitive (NTO, NQ, DNAN) munitions constituents

Abstract

This research evaluated the cathodic electrochemical treatment of wastewater contaminated with energetic compounds, including “legacy” explosives octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), hexahydro-1,3,5-trinitro-s-triazine (RDX), and trinitrotoluene (TNT), as well as compounds insensitive munitions constituents, including 3-nitro-1,2,4-triazol-5-one (NTO), nitroguanidine (NQ), 2,4-dinitroanisole (DNAN). Rate constants and transformation products observed using electrochemical degradation performed under constant voltage (4 V) and constant current (0.5 A), as well as degradation via alkaline hydrolysis, were compared. Electrochemical degradation rate constants for all the energetics were greater than rate constants measured during alkaline hydrolysis. Degradation rate constants for individual energetics were generally similar to those observed in a mixture of all six compounds, with the exception of TNT (0.41 vs. 1.08 h^-1). Many of the transformation products detected (e.g., HCHO, dinitrophenol (DNP), NH₄⁺) evidenced further electrochemical degradation, but remained as residuals during alkaline hydrolysis. Utilizing ¹³C/¹⁵N labeled parent compounds, varying degrees of mineralization to ¹³CO₂ and ¹⁵N₂O were confirmed for RDX, NTO, and DNAN. The calculated electrical energy per order of removal (E_EO) was generally lower under constant voltage compared to constant current conditions, and ranged from 2 Wh/L for TNT to 10 Wh/L for NTO. These results provide proof-of-concept data for cathodic electrochemical treatment of mixed energetics wastewater.