Treatment of the insensitive munitions compound, 3-nitro-1,2,4-triazol-5-one (NTO), in flow-through columns packed with zero-valent iron

The need for effective technologies to remediate the insensitive munitions compound 3-nitro-1,2,4-triazol-5-one (NTO) is emerging due to the increasing use by the US Army and environmental concerns about the toxicity and aqueous mobility of NTO. Reductive treatment is essential for the complete degradation of NTO to environmentally safe products. The objective of this study is to investigate the feasibility of applying zero-valent iron (ZVI) in a continuous-flow packed bed reactor as an effective NTO remediation technology. The ZVI-packed columns treated an acidic influent (pH 3.0) or a circumneutral influent (pH 6.0) for 6 months (ca. 11,000 pore volumes, PVs). Both columns effectively reduced NTO to the amine product, 3-amino-1,2,4-triazol-5-one (ATO). The column treating the pH-3.0 influent exhibited prolonged longevity in reducing NTO, treating 11-fold more PVs than the column treating pH-6.0 influent until the breakthrough point (defined as when 85% of NTO was removed). The exhausted columns (defined as when only 10% of NTO was removed) regained the NTO reducing capacity by reactivation using 1 M HCl, fully removing NTO. After the experiment, solid-phase analysis of the packed-bed material showed that ZVI was oxidized to iron (oxyhydr)oxide minerals such as magnetite, lepidocrocite, and goethite during NTO treatment. This is the first report on the reduction of NTO and the concomitant oxidation of ZVI in continuous-flow column experiments. The evidence indicates that treatment in a ZVI-packed bed reactor is an effective approach for the removal of NTO.

Automated summary

This study investigated the feasibility of using zero-valent iron (ZVI) in a continuous-flow packed bed reactor for the effective remediation of 3-nitro-1,2,4-triazol-5-one (NTO). The ZVI-packed columns successfully reduced NTO to a safe product and the column treating acidic influent showed better performance than the column treating neutral influent. Reactivation using 1 M HCl restored the exhausted columns' NTO reducing capacity.