COLLEGE OF SCIENCES

SCHOOL OF EARTH AND ATMOSPHERIC SCIENCES

EAS Ph.D. Defense

Shiliang Zhao

March 28, 2018

11:30 AM

Earth and Atmospheric Sciences

Ford Environmental Science & Technology (ES&T)311 Ferst Drive, ES&TAtlanta, GA 30332-0340Web: eas.gatech.edu

ES&T

L1114

Title:Effects of metal impurity on the structure and reactivity of manganese oxides

Committee members: Dr. Yuanzhi Tang (advisor), Dr. Martial Taillerfert, Dr. Chris Reinhard, Dr. Jennifer Glass, and Dr. MengqiangZhu( University of Wyoming)

Abstract: Mnoxides are among the most ubiquitous and reactive mineral phases in natural environments and significantly influence the cycles of essential elements such as C and N, as well as the transport and fate of a wide range of metals. The structure and reactivity of Mnoxides were extensively studied but most of these studies used pure Mnoxide minerals, which are barely found in real geological or engineering settings. Considering the prevalent interactions between metal cations and growing Mnoxide phases in the natural environments, more understanding is needed about the effects of metal impurity on the structure and reactivity of Mnoxides. Zn is least compatible in Mnoxide layers among the heavy metals commonly associated with Mnoxides (Co, Ni, Cu, Fe, Zn), and probably could cause greatest structure modifications in Mnoxides when coprecipitated, according to previous studies. The overall goal of this study is to systematically explore the effects of Zn coprecipitationon the structure, reactivity and transformation of biotic and abiotic Mnoxides, and compare with the effects of Zn adsorption. We combined a suite of complementary techniques that are capable of probing mineral surface properties, morphology, and structure orders at various ranges, including BET surface area analysis, zeta-potential measurements, Zn and MnX-ray absorption spectroscopy (XAS), X-ray diffraction (XRD), pair distribution function (PDF) analysis of X-ray total scattering, and high resolution transmission electron microscopy (HRTEM). Significant Mnoxide structural modifications by Zn coprecipitationwere observed such as decreased particle size, increased average oxidations state and increased vacancy site density. Controlled laboratory adsorption experiments were conducted (e.g. sorption isotherm, kinetics and pH edge experiments) using Cd(II) as a cation probe while AsO43-and PO43-as anion probes, to investigate the effects of Zn coprecipitationon the sorptiveproperty of Mnoxides, based on the structure modification observed. The kinetics and pathways of Mn(II) induced reductive Mnoxide transformation were conducted to investigate the long-term stability of Zn coprecipitatedMnoxides. The different sorptiveand redox reactivity of Zn coprecipitatedfrom pure Mnoxides suggests that the roles of Mnoxides in regulating nutrients, metals, and organic contaminants fate and transport, as well as Mnbiogeochemical cycles itself, should be re-visited by considering the impacts of metal impurity.