Dalton Seminar Series: Long-Term in Situ Behaviour of Biogenic Uraninite in Alluvial Aquifer
|Starts:||12:00 30 Sep 2015|
|Ends:||13:00 30 Sep 2015|
|What is it:||Seminar|
|Organiser:||Dalton Nuclear Institute|
|Who is it for:||University staff, Current University students|
|Speaker:||Dr. Harish Veeramani|
Uranium is a subsurface contaminant of concern at several countries worldwide. Under oxic conditions, uranium exists predominantly in the hexavalent (U(VI)) form often as aqueous uranyl carbonate complexes. Under anoxic conditions, it exists in the tetravalent form (U(IV)) which generally precipitates as a sparingly soluble mineral, uraninite (UO2). Due to its low solubility, most remediation strategies aim at reducing U(VI) to U(IV)/UO2 as an in situ waste form in the subsurface. Although U(VI) can be reduced to UO2, enzymatically/biologically (via the action of microbes) and abiotically (via Fe(II) and sulfide-bearing minerals, sorbed Fe(II) species), the process is reversible in the presence of oxidizing agents such as dissolved oxygen (DO), nitrate, nitrite and manganese oxides. Uraninite oxidation is therefore expected to be of broad and acute scientific importance to fate and transport of uranium in contaminated aquifers. The success of a remediation strategy thus depends on the long-term stability of UO2.
At the Rifle, CO, DOE field research site, field-scale in situ bioremediation studies using acetate as an exogenous electron donor have been carried out to determine the effectiveness of biostimulation for the bioreduction and attenuation of uranium. The aquifers at the Rifle field site exhibit substantial variations in DO ranging from <0.1 mg/L during fall and winter to ca. 1.5 mg/L during spring/summer. This variability confounds efforts to quantitatively model uranium behavior. While uraninite dissolution is expected to proceed under these conditions, uranium loss rates under naturally variable aquifer conditions over the long-term (multiple seasons) have not been determined until recently.
In this seminar, Dr Veeramani will present findings of a collaborative field scale experiment that assessed the (oxidative) dissolution of biogenic uraninite deployed in wells at the Rifle, CO, DOE research site over a 22-month period. This study makes use of a suite of analytical techniques ranging from synchrotron-based spectroscopy to electron microscopy and field-scale measurements. Dr Veeramani will discuss the role of DO and the importance of indigenous groundwater cations such as calcium in the dissolution of UO2 in situ.
Light refreshments will follow the seminar.
Dr. Harish Veeramani
Organisation: University of Glasgow
Biography: Dr. Harish Veeramani is a lecturer at the University of Glasgow’s School of Engineering. He received his PhD from the Swiss Federal Institute of Technology (EPFL) in Lausanne where he started his early work in microbe-metal-mineral interactions. He later diversified his research to study fundamental nanomineral reactivity in addition to uranium biogeochemistry after joining Virginia Tech, USA as a postdoctoral researcher. He pursued a second postdoctoral term at the University of Waterloo in Ontario, Canada where he researched the applications of non-traditional stable isotope fractionation for studying biogeochemical processes involving copper, nickel and zinc. His continued interdisciplinary work also included the study of microbial communities associated with mining environments, particularly a mine site in arctic Canada. He recently started his term in Glasgow (August 2015) where he intends to expand his expertise to study emerging water contaminants including micro-pollutants.
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