Abstract
Oxidation of Co(II)EDTA2- to Co(III)EDTA- by manganese and iron hydrous oxide minerals enhances the transport of 60Co in subsurface environments. Until now, reduction of the oxidant MnO2 has not been identified in hydrodynamic systems, leaving the fate and transport mechanisms involving 60Co in natural environments unresolved. We investigated the transport of Co(II)EDTA2- through packed beds of β-MnO2 and identified the reaction mechanism using a novel hydrodynamic flow cell coupled with X-ray absorption near edge structure (XANES) spectroscopy. Using this technique we are able to determine both solution and solid-phase species of cobalt and manganese in real-time. Co(II)EDTA2- is produced while Mn(IV) is reduced to Mn(III) which forms an α-Mn2O3 layer on pyrolusite. This layer passivates the surface after an initial reaction period and ultimately limits the production of Co(III)EDTA-. As a consequence, the enhanced transport of 60Co by oxidative processes may be diminished by continual exposure to pyrolusite--an advantage from an environmental quality perspective. It has also been clarified that Mn(III) is formed rather than Mn(II) resulting in formation of a stable trivalent manganese solid (α-Mn2O3).
| Original language | English |
|---|---|
| Pages (from-to) | 3049-3057 |
| Number of pages | 9 |
| Journal | Geochimica et Cosmochimica Acta |
| Volume | 63 |
| Issue number | 19-20 |
| DOIs | |
| State | Published - Oct 1999 |
Funding
This research was funded by the Laboratory Directed Research and Development Program of the Oak Ridge National Laboratory and the Subsurface Science Program of the Office of Biological and Environmental Research, U.S. Department of Energy, under contract DE-AC05-96OR22464 with Lockheed Martin Energy Corporation. The authors appreciate the efforts of Dr. Frank Wobber, the contract officer for the Department of Energy, who partially supported this work. We also gratefully acknowledge the staff and scientists at the Stanford Synchrotron Radiation Laboratory (SSRL) for their help in conducting the XANES analyses. SSRL is operated by the Department of Energy, Office of Basic Energy Sciences. The SSRL Biotechnology Program is supported by the National Institutes of Health, National Center for Research Resources, Biomedical Technology Program, and by the Department of Energy, Office of Biological and Environmental Research. We would also like to thank three anonymous reviewers and the Associate Editor for their helpful comments which greatly improved this manuscript.