Simultaneous adsorption and hydrolysis of insensitive munition compounds by pyrogenic carbonaceous matter (PCM) and functionalized PCM in soils

Abstract

Military training with insensitive munitions (IM) deposits a large amount of post-detonation residues on range soils that may contaminate groundwater. This study investigated the effectiveness of pyrogenic carbonaceous matter (PCM) and functionalized PCM as a soil amendment to retain and transform IM compounds (e.g., 5-nitro-1,2-dihydro-3H-1,2,4-triazin-3-one (NTO), nitroguanidine (NQ), and 2,4-dinitroanisole (DNAN)). Initial hydrolysis tests showed quaternary ammonium (QA)-modified PCM accelerated NQ hydrolysis, while NTO formed charge-assisted hydrogen bonds with PCM's surface groups instead of hydrolyzing. We amended three soils with a subset of PCM materials and monitored the removal of NTO, NQ, and DNAN under varying pH conditions (i.e., 8.0, 10.0, and 12.0) and amendment dosages (i.e., 0, 2, 3, and 5 % (w)) in batch reactors. We also assessed the reactivity and reusability of the best-performing PCM by consecutive addition of IM post-detonation residues. Our results indicate that PCM can significantly enhance the removal of NTO, NQ, and DNAN in soils by 50–300-fold compared to soil controls, and QA-modified activated carbon (AC) performed the best. Increasing pH from 8.0 to 10.0 enhanced the DNAN hydrolysis with PCM, whereas NQ hydrolysis only occurred at pH 12.0. However, increasing PCM dosage from 2 % to 5 % (w) did not significantly increase the removal of NTO, NQ, and DNAN. QA-modified AC maintained its reactivity over three consecutive additions of IM post-detonation residues at pH 10.0, with an average NTO and NQ removal of 98.8 ± 0.6 % and 84.2 ± 3.2 %, respectively, and DNAN decay of 55.3 ± 2.9 %. Overall, our findings highlight the effectiveness of the functionalized PCM in simultaneously retaining and transforming IM compounds, providing a strategy for using reactive amendment in-situ to sustain military operation and mitigate pollution.