Reduction of Hg(II) by Fe(II)-Bearing Smectite Clay Minerals
Abstract
Aluminosilicate clay minerals are often a major component of soils and sediments and many of these clays contain structural Fe (e.g., smectites and illites). Structural Fe(III) in smectite clays is redox active and can be reduced to Fe(II) by biotic and abiotic processes. Fe(II)-bearing minerals such as magnetite and green rust can reduce Hg(II) to Hg(0); however, the ability of other environmentally relevant Fe(II) phases, such as structural Fe(II) in smectite clays, to reduce Hg(II) is largely undetermined. We conducted experiments examining the potential for reduction of Hg(II) by smectite clay minerals containing 0–25 wt% Fe. Fe(III) in the clays (SYn-1 synthetic mica-montmorillonite, SWy-2 montmorillonite, NAu-1 and NAu-2 nontronite, and a nontronite from Cheney, Washington (CWN)) was reduced to Fe(II) using the citrate-bicarbonate-dithionite method. Experiments were initiated by adding 500 µM Hg(II) to reduced clay suspensions (4 g clay L⁻¹) buffered at pH 7.2 in 20 mM 3-morpholinopropane-1-sulfonic acid (MOPS). The potential for Hg(II) reduction in the presence of chloride (0–10 mM) and at pH 5–9 was examined in the presence of reduced NAu-1. Analysis of the samples by Hg LIII-edge X-ray absorption fine structure (XAFS) spectroscopy indicated little to no reduction of Hg(II) by SYn-1 (0% Fe), while reduction of Hg(II) to Hg(0) was observed in the presence of reduced SWy-2, NAu-1, NAu-2, and CWN (2.8–24.8% Fe). Hg(II) was reduced to Hg(0) by NAu-1 at all pH and chloride concentrations examined. These results suggest that Fe(II)-bearing smectite clays may contribute to Hg(II) reduction in suboxic/anoxic soils and sediments.
Additional Information
© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). Received: 28 October 2020; Accepted: 25 November 2020; Published: 1 December 2020. We thank the MRCAT beamline staff for assistance during data collection at the synchrotron and the four anonymous reviewers for their thoughtful comments. Research under the Wetlands Hydrobiogeochemistry Scientific Focus Area (SFA) at Argonne National Laboratory was supported by the Subsurface Biogeochemical Research Program, Office of Biological and Environmental Research (BER), Office of Science, U.S. Department of Energy (DOE), under contract DE-AC02-06CH11357. MRCAT/EnviroCAT operations are supported by DOE and the member institutions. Use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357. Argonne National Laboratory is a U.S. Department of Energy laboratory managed by UChicago Argonne, LLC. Author Contributions: Conceptualization E.J.O.; formal analysis M.I.B.; funding acquisition M.I.B., K.M.K., and E.J.O.; Investigation M.I.B., K.M.K., E.J.O., and K.O.T.; Project administration E.J.O.; Visualization M.I.B.; writing—original draft M.I.B. and E.J.O.; and writing—review and editing M.I.B., K.M.K., E.J.O., and K.O.T. All authors have read and agreed to the published version of the manuscript. The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.Attached Files
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- Eprint ID
- 107008
- Resolver ID
- CaltechAUTHORS:20201210-100246643
- DE-AC02-06CH11357
- Department of Energy (DOE)
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2020-12-10Created from EPrint's datestamp field
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2021-11-16Created from EPrint's last_modified field