Degradation of TNT, RDX, and HMX Explosive Wastewaters Using Zero-Valent Iron Nanoparticles

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Abstract

The high-energy explosives 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and the high melting explosive octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) are common groundwater contaminants at active and abandoned munitions production facilities causing serious environmental problems. A highly efficient and environmentally friendly method was developed for the treatment of the explosives-contaminated wastewaters using zero-valent iron nanoparticles (ZVINs). ZVINs with diameters of 20–50 nm and specific surface areas of 42.56 m2 g−1 were synthesized by the co-precipitation method. The explosives degradation reaction is expressed to be of pseudo first-order and the kinetic reaction parameters are calculated based on different initial concentrations of TNT, RDX, and HMX. In addition, by comparison of the field emission scanning electron microscopy (FE-SEM) images for the fresh and reacted ZVINs, it was apparent that the ZVINs were oxidized and aggregated to form Fe3O4 nanoparticles as a result of the chemical reaction. The X-ray diffraction (XRD) and X-ray absorption near edge structure (XANES) measurements confirmed that the ZVINs corrosion primarily occurred due to the formation of Fe3O4. Furthermore, the postulated reaction kinetics in different concentrations of TNT, RDX, and HMX, showed that the rate of TNT removal was higher than RDX and HMX. Furthermore, by-products obtained after degradation of TNT (long-chain alkanes/methylamine) and RDX/HMX (formaldehyde/methanol/hydrazine/dimethyl hydrazine) were determined by LC/MS/MS, respectively. The high reaction rate and significant removal efficiencies suggest that ZVINs might be suitable and powerful materials for an in-situ degradation of explosive polluted wastewaters.

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