Kinetics of reductive denitrification by nanoscale zero-valent iron

Zero-valent iron powder (Fe⁰) has been determined to be potentially useful for the removal of nitrate in the water environment. This research is aimed at subjecting the kinetics of denitrification by nanoscale Fe⁰ to an analysis of factors affecting the chemical denitrification of nitrate. Nanoscale iron particles with a diameter in the range of 1-100 nm, which are characterized by the large BET specific surface area to mass ratio (31.4 m²/g), removed mostly 50, 100, 200, and 400 mg/l of nitrate within a period of 30 min with little intermediates. Compared with microscale (75-150 μm) Fe⁰, endproduct is not ammonia but N₂ gas. Kinetics analysis from batch studies revealed that the denitrification reaction with nanoscale Fe₀ appeared to be a pseudo first-order with respect to substrate and the observed reaction rate constant (k(obs)) varied with iron content at a relatively low degree of application. The effects of mixing intensity (rpm) on the denitrification rate suggest that the denitrification appears to be coupled with oxidative dissolution of iron through a largely mass transport- limited surface reaction (< 40 rpm). (C) 2000 Elsevier Science Ltd.