Kinetics of the alkaline hydrolysis of high explosives RDX and HMX in aqueous solution and adsorbed to activated carbon

Aqueous alkaline hydrolysis of bulk quantities and wastewater contaminated with high explosives is a promising technology for treatment and disposal of the worldwide surplus of munitions. We investigated the hydrolysis kinetics of the high explosives hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) for temperatures ranging from 50 to 80 degrees C and in the pH range from 10 to 12. The experimental data were described using a pseudo-first-order model with subsequent calculation of second-order rate constants from experiments with excess hydroxide concentration. The temperature dependency of the rate constants was evaluated using the Arrhenius model. The activation energies were determined to be E(RDX) = 99.9 +/- 1.9 kJ mol(-1) and E(HMX) = 111.9 +/- 0.8 kJ mol(-1). The rate of HMX hydrolysis is much slower than the rate of RDX hydrolysis and may become rate limiting in the treatment of RDX/HMX mixtures. The alkaline hydrolysis of RDX yields 1.6 M NO2-, 1.5 M HCOO-, 0.1 M CH3COO-, 1.1 M HCHO (11), 0.9 M NH3, 1.1 M N2O, and 0.34 M N-2 per mol of RDX hydrolyzed. Acetate ion (CH3COO-) is a previously unknown end product of the alkaline hydrolysis of RDX. A mass balance showed a recovery of 94% carbon and 90% nitrogen. During GC/MS analysis of the end products, no further unknown products could be found. In batch desorption studies, it was also shown that RDX-laden activated carbon can be regenerated using alkaline hydrolysis (T = 80 degrees C, pH 12) and that the desorption of the hydrolysis products is complete.