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Coupled Transformation of Humic Substances and Redox Cycling Iron in Clay Minerals & Environmental Implications

Zuo, Hongyan
http://rave.ohiolink.edu/etdc/view?acc_num=miami1595579176346292

Abstract Details

2020, Doctor of Philosophy, Miami University, Geology and Environmental Earth Science.
Despite common co-presence of clay minerals, humic substances, and microbes, the role of humic substances in iron-redox cycling in Fe-bearing clay minerals has not been well-studied. Past research has focused on biological reduction of aqueous Fe(III) and structural Fe(III) in oxides, but the importance of structural Fe in phyllosilicates is only recently studied. However, the effect of humic substances on the rate and the mechanism of the reaction under different conditions, and subsequent mineralogical transformation are still poorly known. The objective of the first research was to investigate the mutual interaction between clay mineral nontronite (NAu-2) and humic acid (HA) and fulvic acid (FA), in the presence of a metal-reducing bacterium Shewanella putrefaciens CN32. The results of this study show that the electron shuttling role of clay-sorbed humic substances strongly depends on the type of electron donors (lactate versus H2). As a result of electron shutting, humic substances underwent partial transformation to amino acids and other compounds. This study highlights a need for using naturally present H2 as a relevant electron donor to study the electron shuttling function of humic substances and the importance of understanding coupled Fe-C biogeochemical processes in natural environment. The objective of the second research was to determine the role of natural HS as electron donor when coupled with reduction of Fe(III) in an iron-rich smectite, nontronite (NAu-2), with and without an iron-reducing bacterium (DIRB), Shewanella putrefaciens CN32. The results showed that natural HS served as electron donor to abiotically reduce Fe(III) in nontronite, and as electron shuttle to enhance Fe(III) bioreduction by S. putrefaciens. A unique set of secondary minerals, including talc, illite, silica, zeolite, albite, ilmenite, and ferrihydrite formed as a result of reduction. The results highlight the importance of coupled C and Fe biogeochemical transformations and have implications for nutrient cycling and contaminant migration in the environment. The objective of the third study is to test the pathways that may be possible to promote clay mineral reactions under ambient condition. The results showed that nontronite transformation products included kaolinite, talc, albite, quartz, goethite, and zeolite, with kaolinite as a transient phase. And it also showed the presence of more humic acids would destabilize the kaolinite phase. Humic acid-stimulated clay mineral transformation was achieved via a combination of dissolution/re-crystallization mechanism. Nontronite transformation to silicate minerals followed the order of 1:1 layered (kaolinite) - 2:1 layered (talc) - framework (albite).
Hailiang Dong (Advisor)
Richard Edelmann (Committee Member)
Mark Krekeler (Committee Member)
Zhanfei Liu (Committee Member)
David L. Tierney (Committee Member)
134 p.
Geology

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Citations

  • Zuo, H. (2020). Coupled Transformation of Humic Substances and Redox Cycling Iron in Clay Minerals & Environmental Implications [Doctoral dissertation, Miami University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=miami1595579176346292

    APA Style (7th edition)

  • Zuo, Hongyan. Coupled Transformation of Humic Substances and Redox Cycling Iron in Clay Minerals & Environmental Implications . 2020. Miami University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=miami1595579176346292.

    MLA Style (8th edition)

  • Zuo, Hongyan. "Coupled Transformation of Humic Substances and Redox Cycling Iron in Clay Minerals & Environmental Implications ." Doctoral dissertation, Miami University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=miami1595579176346292

    Chicago Manual of Style (17th edition)

miami1595579176346292
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This open access ETD is published by Miami University and OhioLINK.