Enhanced reduction of nitrate by zero-valent iron at elevated temperatures

Kinetics of nitrate reduction by zero-valent iron at elevated temperatures was studied through batch and column experiments. It was hypothesized that under increased solution temperatures, the zero-valent iron may accelerate the reduction of nitrate by overcoming the activation energy barrier to nitrate reduction. The results of the batch experiment showed the synergistic effects of elevated temperature (75 degrees C) and a buffered condition (pH 7.4 with 0.1 M HEPES) to enhance the rate of nitrate reduction by zero-valent iron from 0.072 +/- 0.006 h(-1) ((0.35 +/- 0.03) x 10(-4) L m(-2) h(-1)) at room temperature to 1.39 +/- 0.23 h(-1) ((1.03 +/- 0.07) x 10-3 L m(-2) h(-1)). Complete nitrate removal was obtained in a Fe(0) column after 30 min under both buffered and unbuffered conditions at 75 degrees C. These results indicate that a temperature increase could overcome the energy barrier. We suggest that an iron reduction process at moderately elevated temperature (50-75 degrees C) may be a suitable method for removing nitrate from industrial discharges. (C) 2007 Elsevier B.V. All rights reserved.