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

• Published in: Journal of hazardous materials 2022-02, Vol.423 (Pt A), p.126943-126943, Article 126943
• Main Authors: Mai, A., Hadnagy, E., Abraham, J., Terracciano, A., Zheng, Z., Smolinski, B., Koutsospyros, A., Christodoulatos, C.
• Format: Article
• Language: English
• Subjects: Aquatic toxicity; Bimetallic; Byproducts; Guanidines - toxicity; Iron; Kinetics; Magnesium; Reductive degradation; Water Pollutants, Chemical - toxicity
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2021.126943

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. [Display omitted] •Nitroguanidine (NQ) underwent rapid reductive degradation by a novel Mg-based bimetallic reagent.•Bimetal reagent utilized unconventional metal, Mg, with reduction catalyzed by Cu.•Comprehensive analysis of by- and end-products and a reaction pathway led to complete carbon closure.•Byproduct toxicity was determined with microalgae strain S. obliquus.•Reaction pathway and treated effluent toxicity can be controlled with pH.