Effects of transition-metal ions on the reduction of N-nitrosodimethylamine in water by zinc

The influencing factors, products and mechanism of N -nitrosodimethylamine (NDMA) reduction by zinc (Zn) in the presence of transition-metal ions (Mn 2+ , Co 2+ and Ni 2+ ), were investigated. The NDMA removal by Zn was significantly improved by them, and the promoting effect of Co 2+ and Ni 2+ were better than Mn 2+ . With the decrease of pH values and dissolved oxygen concentrations, the removals of NDMA were enhanced in all reaction systems. NDMA was mainly reduced to unsymmetrical dimethylhydrazine (UDMH) in Zn and Zn/Mn 2+ systems. It was mainly reduced to dimethylamine (DMA) and ammonium (NH 4 + ) in Zn/Co 2+ and Zn/Ni 2+ systems. There were undetected products in all reaction systems. Catalytic hydrogenation was the main mechanism, and active hydrogen atom was the main active species. The presence of Mn 2+ , Co 2+ and Ni 2+ promoted the corrosion of Zn and changed the surface morphology of Zn. The formation of type I film on Zn surface was promoted in the presence of Co 2+ and Ni 2+ , which was conducive to the continuous corrosion of Zn and hydrogen generation. While type II film which would inhibit the corrosion of Zn formed on Zn surface in the presence of Mn 2+ . MnO 2 , Co 3 O 4 and Ni(OH) 2 were formed in Zn/Mn 2+ , Zn/Co 2+ and Zn/Ni 2+ systems, respectively. They would facilitate more generation of active hydrogen atoms.