Abstract
The structure and Mn(III) concentration of birnessite dictate its reactivity and can be changed by birnessite partial reduction, but effects of pH and reductant/birnessite ratios on the changes by reduction remain unclear. We found that the two factors strongly affect the structure of birnessite (δ-MnO2) and its Mn(III) content during its reduction by fulvic acid (FA) at pH 4-8 and FA/solid mass ratios of 0.01-10 under anoxic conditions over 600 h. During the reduction, the structure of δ-MnO2 is increasingly accumulated with both Mn(III) and Mn(II) but much more with Mn(III) at pH 8, whereas the accumulated Mn is mainly Mn(II) with little Mn(III) at pH 4 and 6. Mn(III) accumulation, either in layers or over vacancies, is stronger at higher FA/solid ratios. At FA/solid ratios ≥1 and pH 6 and 8, additional hausmannite and MnOOH phases form. The altered birnessite favorably adsorbs FA because of the structural accumulation of Mn(II, III). Like during microbially mediated oxidative precipitation of birnessite, the dynamic changes during its reduction are ascribed to the birnessite-Mn(II) redox reactions. Our work suggests low reactivity of birnessite coexisting with organic matter and severe decline of its reactivity by partial reduction in alkaline environment.
| Original language | English |
|---|---|
| Pages (from-to) | 1844-1853 |
| Number of pages | 10 |
| Journal | Environmental Science and Technology |
| Volume | 52 |
| Issue number | 4 |
| DOIs | |
| State | Published - Feb 20 2018 |
| Externally published | Yes |
Funding
This work was supported by the U.S. National Science Foundation under Grant EAR-1529937. We acknowledge beamline scientists Olaf J. Borkiewicz, Kevin A. Beyer, and Karena W. Chapman at beamline 11-ID-B and John Katsoudas and Carlo Segre at beamline 10-BM-B at APS for their technical assistance in data collection. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. This work was supported by the U.S. National Science Foundation under Grant EAR-1529937. We acknowledge beamline scientists Olaf J. Borkiewicz, Kevin A. Beyer, and Karena W. Chapman at beamline 11-ID-B and John Katsoudas and Carlo Segre at beamline 10-BM-B at APS for their technical assistance in data collection. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We thank four anonymous reviewers and Associate Editor T. David Waite for constructive comments and suggestions.
| Funders | Funder number |
|---|---|
| Advanced Photon Source | |
| DOE Office of Science | |
| Office of Science User Facility operated | |
| U.S. National Science Foundation | EAR-1529937 |
| U.S. Department of Energy | |
| Office of Science | |
| Argonne National Laboratory | DE-AC02-06CH11357 |