Reductive treatment characteristics of nitrate by metallic iron in aquaticsolution

Metallic iron was selected as a new reductant for chemical reductive remova l of nitrate from water in this study. The effect of pH on the reduction ra te and products of nitrate was investigated with a fixed dosage of iron pow der (size: 80 mesh) of 12 mol-Fe-mol-N-1 under acidic (pH = 2-5) and aerobi c conditions. The reduction of nitrate by metallic iron was a pseudo-first order reaction under our experimental conditions. The reduction rate of nit rate was increased with decreasing pH of the reaction solution, and the pse udo-first order reaction rate constants were 0.49, 0.40, 0.05 and 0.01 h(-1 ) at pH = 2, 3, 4 and 5, respectively. The reduction products of nitrate we re ammonia and nitrogen gas, and their yields were strongly affected by pH. The yields of nitrogen gas were 30, 31 and 45% at pH = 3, 4 and 5, respect ively, but no formation of nitrogen was found at pH = 2. It was also demons trated that the indirect reduction of nitrate by hydrogen generated from th e reaction between proton and metallic iron may be a major mechanism for th e reduction of nitrate under the experimental conditions.