Iron(II) monosulfide (FeS) minerals reductively transform the insensitive munitions compounds 2,4-dinitroanisole (DNAN) and 3-nitro-1,2,4-triazol-5-one (NTO)

• Published in: Chemosphere (Oxford) 2021-12, Vol.285 (C), p.131409-131409, Article 131409
• Main Authors: Menezes, Osmar, Yu, Youngjae, Root, Robert A., Gavazza, Savia, Chorover, Jon, Sierra-Alvarez, Reyes, Field, Jim A.
• Format: Article
• Language: English
• Subjects: INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Insensitive high explosive; Mackinawite; Nitro-heterocyclic; Nitroaromatic; Pyrrhotite; Troilite
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2021.131409

As military applications of the insensitive munitions compounds (IMCs) 2,4-dinitroanisole (DNAN) and 3-nitro-1,2,4-triazol-5-one (NTO) increase, there is a growing need to understand their environmental fate and to develop remediation strategies to mitigate their impacts. Iron (II) monosulfide (FeS) minerals are abundant in freshwater and marine sediments, marshes, and hydrothermal environments. This study shows that FeS solids can reduce DNAN and NTO to their corresponding amines under anoxic ambient conditions. The reactions between IMCs and the FeS minerals were surface-mediated since they did not occur when only dissolved Fe2+(aq) and S2−(aq) were present. Mackinawite, a tetragonal FeS with a layered structure, reduced DNAN mainly to 2-methoxy-5-nitroaniline (MENA), which in turn was partially reduced to 2-4-diaminoanisole (DAAN). The layered structure of mackinawite provided intercalation sites likely responsible for partial adsorption of MENA and DAAN. Mackinawite entirely reduced NTO to 3-amino-1,2,4-triazol-5-one (ATO). The reduction of IMCs showed concurrent oxidation of mackinawite to goethite and elemental sulfur. A commercial FeS product, composed mainly of pyrrhotite and troilite, reduced DNAN to DAAN and NTO to ATO. At pH 6.5, DNAN and NTO transformation rates were 667 and 912 μmol h−1 m−2, respectively, on the mackinawite surface and 417 and 1344 μmol h−1 m−2, respectively, on the commercial FeS surface. This is the first report of the reduction of a nitro-heterocyclic compound (NTO) by FeS minerals. The evidence indicates that DNAN and NTO can be rapidly transformed to their succeeding amines in anoxic subsurface environments and aquatic sediments rich in FeS minerals. [Display omitted] •FeS minerals tested were mackinawite and a commercial FeS (pyrrhotite and troilite).•FeS minerals reduced DNAN to DAAN (MENA as intermediate) and NTO to ATO.•Mackinawite adsorbed MENA and DAAN partially.•Mackinawite oxidation products were goethite and elemental sulfur.•The mineral surfaces mediated the reactions.