Effect of pH on the reduction of nitrite in water by metallic iron

Chemical reduction is an alternative technique to remove nitrogen oxides from contaminated groundwater and closed-surface water body. Metallic iron was employed as a reductant for the reduction of nitrite in water in this study. The effect of pH on the rate and products of nitrite reduction was investigated with a fixed dosage of metallic iron powder (12 mol-Fe/mol-N, size of the powder: 80 mesh). The reduction of nitrite by metallic iron was a pseudo-zero-order reaction under the experimental conditions. The reduction rate of nitrite was increased with decreasing the pH of reaction solution, and the pseudo-zero-order reaction rate constants were 180, 130, 60, 15, 10, and 1 mM/h at pH = 2, 3, 4, 5, 6, and 7, respectively. The reduction products of nitrite were nitrogen gas and ammonium. The yields of nitrogen gas from nitrite reduction were 0.63, 0.74, 0.81, 0.87, 0.92, and 0.98 as molar ratios of nitrogen atom at pH =2, 3, 4, 5, 6, and 7, respectively. Neutral condition enhanced the formation of nitrogen gas from nitrite reduction.