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EFFECT OF REDOX ZONATION ON THE REDUCTIVE TRANSFORMATION OF P-CYANONITROBENZENE IN A LABORATORY SEDIMENT COLUMN
Citation:
Simon, R., D Colon, C L. TebesStevens, AND E J. Weber. EFFECT OF REDOX ZONATION ON THE REDUCTIVE TRANSFORMATION OF P-CYANONITROBENZENE IN A LABORATORY SEDIMENT COLUMN. ENVIRONMENTAL SCIENCE & TECHNOLOGY 34(17):3617-3622, (2000).
Impact/Purpose:
Elucidate and model the underlying processes (physical, chemical, enzymatic, biological, and geochemical) that describe the species-specific transformation and transport of organic contaminants and nutrients in environmental and biological systems. Develop and integrate chemical behavior parameterization models (e.g., SPARC), chemical-process models, and ecosystem-characterization models into reactive-transport models.
Description:
The reductive transformation of a model compound, p-cyanonitrobenzene (pCNB), was investigated in a laboratory sediment column that had been characterized with respect to redox zonation. Characterization of the redox zones was assessed by measurement of the solution phase concentrations of NO3-, NO2-, Mn(ll), Fe(ll), and SO42-. Monitoring iron concentrations over time showed that the redox zones were not under steady-state conditions. The iron-reducing zone migrated in the direction of the flow at an initial rate of about 0.2 cm per pore volume resulting in more oxidizing conditions with time, pCNB was rapidly reduced at the head of the column to p-cyano-N-hydroxylaniline (pCNH), which was reduced further to
p-cyanoaniline (pCNA) in the iron-reducing zone. The same reaction-product distribution was observed in batch experiments with Fe(ll)/goethite. Modeling of the column reaction kinetics demonstrated, however, that reduction of pCNB occurred at least an order of magnitude faster on the column than predicted by reaction parameters from the batch experiment. Aging of the
column had a significant effect on the reduction kinetics of pCNB. After elution of 240 pore volumes, pCNB underwent facile reduction directly to pCNA under nitrate-reducing conditions suggesting a change in reaction mechanism from a chemical to a biological process. After elution of 283 pore volumes, the column was completely oxic, and reduction of pCNB was no longer observed.