Abstract
Manganese (Mn) oxides have a high surface area and redox potential that facilitate sorption and/or oxidation of organic carbon (OC), but their role in regulating soil C storage is relatively unexplored. Small OC compounds with distinct structures were reacted with Mn(III/IV)-oxides to investigate the effects of OC/Mn molar ratios on Mn-OC interaction mechanisms. Dissolved and solid-phase OC and Mn were measured to quantify the OC sorption to and/or the redox reaction with Mn-oxides. Mineral transformation was evaluated using X-ray diffraction and X-ray absorption spectroscopy. Higher OC/Mn ratios resulted in higher sorption and/or redox transformation; however, interaction mechanisms differed at low or high OC/Mn ratios for some OC. Citrate, pyruvate, ascorbate, and catechol induced Mn-oxide dissolution. The average oxidation state of Mn in the solid phase did not change during the reaction with citrate, suggesting ligand-promoted mineral dissolution, but decreased significantly during reactions with the other compounds, suggesting reductive dissolution mechanisms. Phthalate primarily sorbed on Mn-oxides with no detectable formation of redox products. Mn-OC interactions led primarily to C loss through OC oxidation into inorganic C, except phthalate, which was predominantly immobilized in the solid phase. Together, these results provided detailed fundamental insights into reactions happening at organo-mineral interfaces in soils.
| Original language | English |
|---|---|
| Pages (from-to) | 741-750 |
| Number of pages | 10 |
| Journal | Environmental Science and Technology |
| Volume | 57 |
| Issue number | 1 |
| DOIs | |
| State | Published - Jan 10 2023 |
Funding
This work was sponsored by the Laboratory-Directed Research and Development Program of the Oak Ridge National Laboratory (ORNL), managed by UT-Battelle, LCC for the US Department of Energy (DOE) under contract DE-AC05-00OR22725, project number 9958, by the ORNL Critical Interfaces Science Focus Area sponsored by the DOE Office of Science Biological and Environmental Research Program, and by the US Department of Agriculture-National Institute of Food and Agriculture (USDA-NIFA), Hatch project NC02898. The authors would like to acknowledge Xiangping Yin, Jana Phillips, and Geoff Schwaner (ORNL) for assistance with DOC and total solid C content analysis and Xiaoyan Sun (NC State University) for assistance with NMR analysis. This research used resources at Beamline 12-BM of the Advanced Photon Source, a user facility operated for the US DOE Office of Science by the Argonne National Laboratory under contract DE-AC02-06CH11357. This work was performed in part by the Molecular Education, Technology and Research Innovation Center at the NC State University, which is supported by the State of North Carolina.
Keywords
- Mn−OC interaction mechanisms
- OC immobilization
- OC oxidation
- OC/Mn molar ratio
- phase transformation