Reductive Treatment Characteristics of Nitrate by Metallic Iron in Aquatic Solution

Abstract

Metallic iron was selected as a new reductant for chemical reductive removal of nitrate from water in this study. The effect of pH on the reduction rate and products of nitrate was investigated with a fixed dosage of iron powder (size: 80 mesh) of 12 mol-Fe·mol-N^-1 under acidic (pH = 2-5) and aerobic conditions. The reduction of nitrate by metallic iron was a pseudo-first order reaction under our experimental conditions. The reduction rate of nitrate was increased with decreasing pH of the reaction solution, and the pseudo-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 were 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, respectively, but no formation of nitrogen was found at pH = 2. It was also demonstrated that the indirect reduction of nitrate by hydrogen generated from the reaction between proton and metallic iron may be a major mechanism for the reduction of nitrate under the experimental conditions.