Iron and Mercury: Solid-Water Interfacial Processes and Contaminant Transformation

Anh Pham (Ph.D.) Department of Civil and Environmental Engineering, Duke University

13 February 2014 at 10:30

Location: JHE 326H




The transformation of contaminants in the environment is often controlled by processes that occur at the solid-water interface, many of which are currently not well understood due to the heterogeneity and complexity of this interface. In this talk, I will discuss how the use of techniques, including analytical chemistry, microscopy, and spectroscopy, has allowed us to gain new insights into factors that control the transformation of various contaminants in water, soils and sediments.

In the first part, I will discuss how redox reactions between hydrogen peroxide (H2O2) and iron minerals can be utilized for in situ treatment of contaminated groundwater and soil. When injected into the subsurface, H2O2 interacts with iron minerals and is activated into hydroxyl radical (•OH), a highly reactive oxidant that can oxidize a wide range of organic contaminants. This remediation technology is simple and easy to deploy, but its use is often limited by the low •OH yield and short lifetime of H2O2 in the subsurface. By coupling kinetic studies of the complex radical chain reactions with surface characterization techniques, we have demonstrated the role of the surface properties of iron minerals in the activation of H2O2, and identified approaches for increasing the efficiency of the technology.

The second part of the presentation will discuss how geochemical processes such as precipitation, dissolution, and biotransformation control the fate and toxicity of mercury. Mercury (Hg) has been recognized as a global contaminant. While all forms of Hg are toxic, it is monomethylmercury (MeHg) (i.e., a neurotoxin produced by Hg-methylating microorganisms) that has raised the biggest concerns. By using synchrotron-based techniques, such as Small Angle X-ray Scattering (SAXS) and Extended X-ray Absorption Fine Spectroscopy (EXAFS), combined with a Hg-methylation bioassay, we have elucidated how the precipitation and dissolution of HgS minerals control Hg biotransformation. Our findings help better predict MeHg production, and have important implications for remediation and management of Hg- contaminated ecosystems.

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