title: Mass transport effects on the kinetics of nitrobenzene reduction by iron metal.
abstract: To evaluate the importance of external mass transport on the overall rates of contaminant reduction by iron metal (Fe0), we have compared measured rates of surface reaction for nitrobenzene (ArNO2) to estimated rates of external mass transport in a permeable reactive barrier (PRB). The rate of surface reaction was measured at a polished Fe0 rotating disk electrode (RDE) in an electrochemical cell, and the rate of mass transport was estimated from a correlation for mass transport in packed-bed reactors. The kinetics of ArNO2 reduction were studied in pH 8.4 borate buffer at a potential below which an oxide film would form. The cathodic current measured in this system was dependent on the electrode rotation rate, and the measured first-order heterogeneous rate coefficient for surface reaction [krxn = (1.7 +/- 0.2) x 10(-3) cm s-1] was about 10 times faster than the first-order mass transport rate coefficient (kmt approximately 2 x 10(-4) cm s-1) estimated for PRBs. The similarity between rates of surface reaction and mass transport suggest that it may be important to consider mass transport processes in the design of PRBs for contaminants such as nitroaromatics that are highly reactive with Fe0.
authors.affiliation: Department of Civil and Environmental Engineering, University of Iowa, Iowa City, Iowa 52242-1527, USA. michelle-scherer@uiowa.edu
authors.forename: M M
authors.initials: MM
authors.lastname: Scherer
authors.forename: K M
authors.initials: KM
authors.lastname: Johnson
authors.forename: J C
authors.initials: JC
authors.lastname: Westall
authors.forename: P G
authors.initials: PG
authors.lastname: Tratnyek
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004787:Environmental Pollution / Q000517:prevention & control; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D009578:Nitrobenzenes / Q000737:chemistry*; D010084:Oxidation-Reduction; D012997:Solvents / Q000737:chemistry
chemical_list: D009578:Nitrobenzenes; D012997:Solvents; D007501:Iron; C036077:nitrobenzene