A Generalized-Rate Model for Describing and Scaling Redox Kinetics in Sediments Containing Variable Redox-Reactive Materials.

This study developed a generalized modeling approach for describing and scaling redox reactions from reactive components to the sediments and their assemblages, using Cr(VI) reduction as an example. Batch experiments were performed to characterize the rates of Cr(VI) reduction in four Fe(II)-containing sediments and their assemblages. The experimental data were first used to calibrate a generalized-rate model of Cr(VI) reduction with generic rate parameters. The generalized-rate model was then used to describe the kinetics of Cr(VI) reduction in the sediment assemblages by linearly scaling the rate parameters from the individual sediments. Via comparison with the experimental results, this study found that the generalized-rate model with generic rate parameters can describe Cr(VI) reduction in individual sediments and their assemblages with different redox reactivity toward Cr(VI) reduction. The sediment-associated Fe(II) and its reactivity were found to be the key variables in the generalized model for describing the Cr(VI) reduction in the studied sediments. A three-step extraction method was subsequently developed to estimate the rate-specific Fe(II) pools that can facilitate the application of the scaling approach in field systems.