Actinide Sorption in Rainier Mesa Tunnel Waters from the Nevada Test Site

Abstract

The sorption behavior of americium (Am), plutonium (Pu), neptunium (Np), and uranium (U) in perched Rainier Mesa tunnel water was investigated. Both volcanic zeolitized tuff samples and groundwater samples were collected from Rainier Mesa, Nevada Test Site, NV for a series of batch sorption experiments. Sorption in groundwater with and without the presence of dissolved organic matter (DOM) was investigated.Am(III) and Pu(IV) are more soluble in groundwater that has high concentrations of DOM. The sorption K d for Am(III) and Pu(IV) on volcanic zeolitized tuff was up to two orders of magnitude lower in samples with high DOM (15 to 19 mg C/L) compared to samples with DOM removed (< 0.4 mg C/L) or samples with naturally low DOM (0.2 mg C/L). In contrast, Np(V) and U(VI) sorption to zeolitized tuff was much less affected by the presence of DOM. The Np(V) and U(VI) sorption K d s were low under all conditions. Importantly, the DOM was not found to significantly sorb to the zeolitized tuff during these experiment.The concentration of DOM in groundwater affects the transport behavior of actinides in the subsurface. The mobility of Am(III) and Pu(IV) is significantly higher in groundwater with elevated levels of DOM resulting in potentially enhanced transport. To accurately model the transport behavior of actinides in groundwater at Rainier Mesa, the low actinide K d values measured in groundwater with high DOM concentrations must be incorporated in predictive transport models.

Effect of Fulvic Acid Surface Coatings on Plutonium Sorption and Desorption Kinetics on Goethite

“…Natural organic matter (NOM), such as humic and fulvic acids, is known to affect Pu solution speciation, sorption behavior, ,, and mobility and may act as an important source or sink for mobile Pu in the environment. With respect to dissolved NOM , two primary mechanisms are expected to influence Pu sorption behavior.…”