Kinetics of Reductive Degradation of 2,4-dinitroanisole (DNAN) Using Mg-Based Bimetals

Abstract

Technology advancements and modern use of explosives have led to the development of insensitive munitions such as 2,4-dinitroanisole (DNAN). Treatment systems using zero-valent iron (ZVI) and Fe-based bimetals are well-known, however, Mg-based bimetals can be advantageous over iron because of the more negative reduction potential and relative insensitivity to pH conditions. This work reports on the use of ZVMg and Mg-bimetals (Mg/Cu, Mg/Ni, Mg/Zn) to treat pure compound aqueous solutions and wastewater containing DNAN. Kinetic experiments were carried out in bench-scale batch reactors at unadjusted initial pH, 0.5% solids-to-liquid ratio (S/L), and 10:1 Mg to catalytic metal ratio. The results, modelled with a pseudo-first order kinetic expression, are used to determine reaction rate constants via nonlinear regression. For pure DNAN aqueous solutions, the pseudo-first order kinetic rate constants are 0.119, 0.102, 0.020, and 0.009 min−1 for Mg/Cu, Mg/Zn, Mg/Ni, and ZVMg, respectively. Reaction rate constants for DNAN wastewater are 0.114, 0.046, and 0.021 min−1 for Mg/Cu, Mg/Zn and Mg/Ni, respectively. Parametric studies investigated the impact of catalytic metal, reagent dose, and initial pH on DNAN degradation. Reagent dose levels tested were 0.25, 0.50 and 0.75% S/L. Initial pH, lowered with acetic acid (pH range 3.3–4.0), significantly enhanced reaction rates of all bimetal pairs and ZVMg yielding half-lives between 0.7–1.4 min. The bimetal pair showing the fastest kinetics at unadjusted initial pH, Mg/Cu, was characterized in constant temperature experiments. Under identical conditions (unadjusted initial pH, 0.5% S/L, 10:1 Mg: Cu), the activation energy of DNAN degradation by Mg/Cu is 8.47 kJ/mol.