Hannah Veldhuizen

Antimony Isotopes as Redox Proxies:

This research focuses on the use of antimony stable isotopes to determine the fractionation associated with geomicrobiological cycling of Sb(V) and Sb(III). Stable isotope ratios of elements in the environment can provide valuable information on sources and processes such as redox transformations, precipitation, and adsorption. For example, if a decrease in Sb concentrations over space or time is identified in a groundwater plume, the cause could be dilution with clean water, adsorption onto solids, or precipitation by reduction. An accompanying isotope measurement could qualitatively identify reduction as the cause of the decreased Sb concentration. This work provides important fundamental knowledge of a major driver of Sb isotope variation in nature and will be used as Sb isotopes are developed for use in modern environmental monitoring efforts and as a proxy for paleo-redox conditions.

Mobilization of Redox Active Elements in Coal Ash during Redox Fluctuations:

Coal ash is a waste product of burning coal that is stored in landfills or coal ash waste ponds. When coal ash comes into contact with water by infiltration of rainwater or direct contact with groundwater, toxic elements such as arsenic and selenium leach into the surrounding water. When these toxic elements are released into the environment they impact humans and wildlife by exceeding safe standards for water. Fluctuating redox conditions can control the mobility of toxic elements by making some elements mobile in oxic conditions while other elements are mobile in anoxic conditions. Variation in redox conditions is driven by the presence of oxygen in natural environments where oxygen-rich (oxic) and oxygen-poor (anoxic) both exist. The goal of this research is to determine the influence that repeated fluctuations of oxic and anoxic conditions have on the mobility of toxic elements in laboratory coal ash leaching experiments. Over a series of repeated oscillations in redox conditions, dissolved redox active elements may be reversibly adsorbed, reversibly sequestered by precipitation, or irreversibly sequestered by precipitation.