Degradation and fate of 2,4-dinitroanisole (DNAN) and its intermediates treated with Mg/Cu bimetal: Surface examination with XAS, DFT, and LDI-MS

A novel Mg-based bimetal reagent (Mg/Cu) was used as an enhanced reductive system to degrade insensitive munition 2,4-dinitroanisole (DNAN), a contaminant found in energetic-laden waste. Degradation of DNAN was significantly impacted by dissolved oxygen and studied in anoxic and oxic bimetal systems (i.e., purging with N₂, air, or O₂ gas). Degradation occurred through sequential nitroreduction: first one nitro group was reduced (ortho or para) to form short-lived intermediates 2-amino-4-nitroanisole or 4-amino-2-nitroanisole (2-ANAN or 4-ANAN), and then subsequent reduction of the other nitro group formed 2,4-diaminoanisole (DAAN). The nitro-amino intermediates demonstrated regioselective reduction in the ortho position to 2-ANAN; Regioselectivity was also impacted by the anoxic/oxic environment. Under O₂-purging DNAN degradation rate was slightly enhanced, but most notably O₂ significantly accelerated DAAN generation. DAAN also further degraded only in the oxygenated Mg/Cu system. Adsorption of DNAN byproducts to the reagent occurred regardless of anoxic/oxic condition, resulting in a partition of carbon mass between the adsorbed phase (27%-35%) and dissolved phase (59%-72%). Additional surface techniques were applied to investigate contaminant interaction with Cu. Density functional theory (DFT) calculations identified preferential adsorption structures for DNAN on Cu with binding through two O atoms of one or both nitro groups. X-ray absorption spectroscopy (XAS) measurements determined the oxidation state of catalytic metal Cu and formation of a Cu-O-N bond during treatment. Laser desorption ionization mass spectrometry (LDI-MS) measurements also identified intermediate 2-ANAN adsorbed to the bimetal surface.

Determining degradation kinetics, byproducts and toxicity for the reductive treatment of Nitroguanidine (NQ) by magnesium-based bimetal Mg/Cu

Energetic-laden process water from industrial munition facilities can be treated by zero-valent metals (ZVMs) or zero-valent iron (ZVI) to remove residual energetics. This reduction-based treatment is significantly enhanced with the addition of a secondary catalytic metal (i.e. forming a bimetal reagent). The reagent is further enhanced by using a more reductive base metal, such as Mg. In this work, the reductive degradation of nitroguanidine (NQ) in aqueous solutions by Mg/Cu bimetal is investigated. Two initial pH conditions (unadjusted and pH 2.7) were studied. Under unadjusted initial pH conditions, 90% of NQ degraded within 30 min reaction time. After 150 min, NQ degradation generated a suite of products including guanidine (44%), cyanamide (31%), formamide (15%), aminoguanidine (AQ) (6%), urea (2%) and cyanoguanidine (0.03%), leading to 100.0% carbon closure when accounting for residual NQ. The experimentally-derived degradation reaction pathway consisted of two parallel reactions: nitroreduction led to formation of AQ with further degradation to urea, cyanamide and formamide, or reductive cleavage of the N-N bond led to guanidine formation. Toxicological assessments indicated only cyanamide and AQ were toxic to S. obliquus at certain concentrations. A lowered initial pH promoted AQ transformation to benign formamide, thus reducing toxicity and complexity of products.

Characterization of Mg-based bimetal treatment of insensitive munition 2,4-dinitroanisole

The manufacturing of insensitive munition 2,4-dinitroanisole (DNAN) generates waste streams that require treatment. DNAN has been treated previously with zero-valent iron (ZVI) and Fe-based bimetals. Use of Mg-based bimetals offers certain advantages including potential higher reactivity and relative insensitivity to pH conditions. This work reports preliminary findings of DNAN degradation by three Mg-based bimetals: Mg/Cu, Mg/Ni, and Mg/Zn. Treatment of DNAN by all three bimetals is highly effective in aqueous solutions (> 89% removal) and wastewater (> 91% removal) in comparison with treatment solely with zero-valent magnesium (ZVMg; 35% removal). Investigation of reaction byproducts supports a partial degradation pathway involving reduction of the ortho or para nitro to amino group, leading to 2-amino-4-nitroanisole (2-ANAN) and 4-amino-2-nitroanisole (4-ANAN). Further reduction of the second nitro group leads to 2,4-diaminoanisole (DAAN). These byproducts are detected in small quantities in the aqueous phase. Carbon mass balance analysis suggests near-complete closure (91%) with 12.4 and 78.4% of the total organic carbon (TOC) distributed in the aqueous and mineral bimetal phases, respectively. Post-treatment surface mineral phase analysis indicates Mg(OH)₂ as the main oxidized species; oxide formation does not appear to impair treatment.

Dechlorination of polychlorinated biphenyls, naphthalenes and dibenzo-p-dioxins by magnesium/palladium bimetallic particles

The contamination of sediments with polychlorinated organics such as polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (Dioxins) and polychlorinated naphthalenes (PCNs) remains a significant problem in many rivers, harbors, and estuarine areas in the US and around the world. In this work, rapid dechlorination of PCBs, PCNs, and Dioxins by palladium - coated magnesium (0.01% by weight Pd) has been demonstrated in pure solvent systems (10% methanol in distilled water). This reaction was investigated with the goal of developing it as a future sediment treatment method. More than 90% of the initial single PCB congeners BZ 3 and 170 were removed in 1 to 10 minutes and about 58% of the total initial Arochlor 1260 was removed in 4 minutes. The removal of single Dioxin and PCN congeners also occurred rapidly resulting in a 69 to 95% reduction in 30 minutes. Rapid removal of biphenyl, the expected degradation end product for PCBs, was also observed (80% removal in 5 minutes). Experiments conducted with Arochlor 1260 and biphenyl did not identify significant volatile fractions. A significant amount of PCBs were extracted from the filtered Mg/Pd material suggesting that PCBs first adsorb to the surface of the bimetal and then dechlorination occurs; lesser chlorinated congeners and biphenyl were also found adsorbed to the Mg/Pd material. Experiments conducted with single PCB congeners BZ 194 and 204 demonstrated the formation of lower - chlorinated PCB congeners, indicating that dechlorination was occurring. A stepwise dechlorination process was suggested in which chlorines in the ortho position were removed last.