Rhodochrosite conversion to Mn (oxyhydr)oxides significantly affects the fate and transport of various substances in the environment. We examined rhodochrosite oxidation by dissolved oxygen and the oxidation product formation with an emphasis on the effects of goethite substrate. Without goethite, rhodochrosite oxidation was slow as no detectable change was observed for 28 d with microscopic and spectroscopic analyses, except a minor change in X-ray diffraction. Interestingly, by contrast, it was greatly accelerated and completed in 7 d in the presence of goethite, resulting in the heteroepitaxial growth of groutite (α-MnOOH)-like Mn oxides on the goethite (α-FeOOH) tip surfaces. The formation of this secondary Mn oxide likely induced the acidification of the microenvironment in the vicinity of rhodochrosite particles and thereby promoted their dissolution. Subsequently, their oxidative conversion to the Mn oxide was expedited by the surface catalyzed Mn(II) oxidation on the goethite tip. Our results revealed that goethite as a foreign substrate imparts a decisive control on not only the rate but also the type of the reaction product of rhodochrosite oxidation. This study presents a new insight into the geochemical roles of foreign particles on the dynamics of redox-sensitive solid phases in the environment.
|Number of pages||9|
|Journal||Environmental Science and Technology|
|Publication status||Published - 2021 Nov 2|
Bibliographical noteFunding Information:
This manuscript was prepared in honor of Professor James Morgan. During his postdoc at Caltech, it was G.L.’s great honor to discuss and chat with him who always inspired young researchers with his characteristic big and benevolent smile. This research was supported by a National Research Foundation of Korea (NRF) grant funded by the Korean Government (NRF-2020R1A2C2010089). We thank Sungsik Lee at the X-ray Science Division for the beamlines of the Advanced Photon Source, Argonne National Laboratory for the aid of XAFS analysis at the beamline 12-BM-B of the APS, 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 also thank the Pohang Accelerator Laboratory for beamtime on the 7D beamline and Haesung Jung in the School of Civil, Environmental, and Chemical Engineering at Changwon National University, Korea for the XAFS database for groutite. Three anonymous reviewers are appreciated, and our manuscript has been substantially improved by their comments and suggestions. The support of the Hydrogeology Laboratory and the Institute for High-pressure Mineral Physics and Chemistry at Yonsei University for providing ICP-OES and XRD facilities, respectively, for our sample analyses is also appreciated.
© 2021 The Authors. Published by American Chemical Society
All Science Journal Classification (ASJC) codes
- Environmental Chemistry