Influence of Iron Oxide Inclusion Shape on CoII/IIIEDTA Reactive Transport through Spatially Heterogeneous Sediment

Authors

James E. Szecsody, Pacific Northwest National LaboratoryFollow
Ashley Chilakapati, Pacific Northwest National Laboratory
John M. Zachara, Pacific Northwest National LaboratoryFollow
Amanda Garvin, Pacific Northwest National Laboratory

Date of this Version

1998

Citation

WATER RESOURCES RESEARCH, VOL. 34, NO. 10, PAGES 2501-2514, OCTOBER 1998

Abstract

Multisolute reactive transport was investigated in chemically heterogeneous systems to determine the influence of the shapes of the reactive heterogeneities (iron oxide inclusions) by comparison of two-dimensional heterogeneous experiments with spatially averaged models that had differing inclusion characterization. Eleven reactions were considered in this system, starting with absorption of the initial solute (Co^IIEDTA) to Fe oxides, followed by two competing surface reactions: oxidation forming Co^IIIEDTA and Fe dissolution forming Fe^IIIEDTA and Co2+. Spatial moments of the eight mobile species were compared between data and models. One spatially averaged model (homogenous equivalent), which incorporated inclusion mass only, significantly under predicted oxidation (up to 74%), the influence of reaction kinetics, and species retardation. In contrast, the ensemble average model (incorporating inclusion mass and length) well predicted speciation, retardation, and skewness. This large difference in prediction between two spatially averaging models was caused by the lack of incorporation of contact time of solutes with iron oxides in the homogenous equivalent model and the importance of the contact time with the differing timescales of reactions.