This report outlines the progress on Task 33 of the Department of Energy's Yucca Mountain Cooperative Agreement with the University and Community College System of Nevada (UCCSN). The task is titled "The Experimental Determination of a "Redox Scale" for Assigning an Oxidizing/Reducing Potential to Groundwater from Wells in the Nye County Early Warning Drilling Program: A Scale for Predicting the Solubility and Mobility of Elements Commonly Found in Nuclear Wastes". The purpose of the research was to determine the concentrations of the various electrochemical oxidation states or redox species of eleven elements in groundwater samples collected from the Nye County wells. The method of separation and quantification of the oxidation states depended on an ion chromatograph coupled to a highly sensitive inductively coupled plasma mass spectrometer. At the end of the task, methods had been developed for 10 of the 11 elements: antimony, arsenic, chromium, copper, manganese, molybdenum, selenium, tungsten, uranium and vanadium. A satisfactory method for determining the redox species for iron was not obtained. This report details the method development and presents Q'd data for arsenic and chromium. The oxidation/reduction potential of the groundwater samples in volts, or the Eh, was calculated from the arsenic redox species determinations and thermodynamic relationships. No correlation was observed between the calculated Eh and the percent of arsenic in its most oxidized state, the plus five state. Informational results are also presented which identify the redox species present for the other eight elements in the groundwater samples from Nye County. The major hurdle of the project, method development, was overcome. Future advances, such as the inclusion of the redox species of iron, cobalt, thallium and rhenium could be realized with a minimum investment of time. Likewise, examination of groundwater sample preservation techniques, which "lock in" the redox species present in the groundwater at the time of sampling, for the elements other than arsenic and chromium, for which very satisfactory techniques already exist, would also proceed rapidly. Although a "practical" redox scale was not developed, with the progress made on Task 33, there is little that stands in the path for achieving that goal.
Environmental Chemistry | Hydrology
Stetzenbach, K. J.,
Smiecinski, A. J.
Redox scale for assigning an oxidizing/reducing potential to groundwater: Method development and initial results.
Available at: http://digitalscholarship.unlv.edu/yucca_mtn_pubs/86