title: Kinetics of nitrate, nitrite, and Cr(VI) reduction by iron metal.
abstract: The kinetics of nitrate, nitrite, and Cr(VI) reduction by three types of iron metal (Fe0) were studied in batch reactors for a range of Fe0 surface area concentrations and solution pH values (5.5-9.0). At pH 7.0, there was only a modest difference (2-4x) in first-order rate coefficients (k(obs)) for each contaminant among the three Fe0 types investigated (Fisher, Peerless, and Connelly). The k(obs) values at pH 7.0 for both nitrite and Cr(VI) reduction were first-order with respect to Fe0 surface area concentration, and average surface area normalized rate coefficients (kSA) of 9.0 x 10(-3) and 2.2 x 10(-1) L m(-2) h(-1) were determined for nitrite and Cr(VI), respectively. Unlike nitrite and Cr(VI), Fe0 surface area concentration had little effect on rates of nitrate reduction (with the exception of Connelly Fe0, which reduced nitrate at slower rates at higher Fe0 surface areas). The rates of nitrate, nitrite, and Cr(VI) reduction by Fisher Fe0 decreased with increasing pH with apparent reaction orders of 0.49 +/- 0.04 for nitrate, 0.61 +/- 0.02 for nitrite, and 0.72 +/- 0.07 for Cr(VI). Buffer type had minimal effects on reduction rates, indicating that pH was primarily responsible for the differences in rate. At high pH values, Cr(VI) reduction ceased after a short time period, and negligible nitrite reduction was observed over 48 h.
authors.affiliation: Department of Civil and Environmental Engineering, University of Iowa, Iowa City 52242, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Alowitz
authors.forename: Michelle M
authors.initials: MM
authors.lastname: Scherer
mesh_terms: D002274:Carcinogens, Environmental / Q000737:chemistry*; D002857:Chromium / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D009566:Nitrates / Q000737:chemistry; D009573:Nitrites / Q000737:chemistry; D010084:Oxidation-Reduction
chemical_list: D002274:Carcinogens, Environmental; D009566:Nitrates; D009573:Nitrites; D002857:Chromium; C074702:chromium hexavalent ion; D007501:Iron