The environmental fate of Pu at heavily contaminated sites, such as the Nevada National Security Site, USA and Mayak, Russia, will be controlled by reactions at mineral surfaces. Recent work has demonstrated both concentration-dependent Pu sorption and age-dependent desorption behavior in batch experiments. To further study these phenomena, we performed flow cell Pu(IV)-goethite desorption experiments at two different initial Pu(IV) concentrations (10-6 M and 10-9 M) and as a function of adsorption equilibration time. The concentrations were guided by previous sorption studies with goethite in which we saw evidence of surface precipitation of Pu at the higher concentration and monomeric sorption at the lower concentration. When Pu was adsorbed to goethite for 25 d prior to the desorption experiments, the fraction of Pu desorbed was much greater at 10-9 M compared to 10-6 M. Pu in the 10-9 M flow cell eluent passed through a 3K MWCO ultrafilter whereas that in the 10-6 M experiment did not, indicating that a difference in the nature of desorbed Pu could be responsible for the difference in desorption behavior. The Pu oxidation state in the 10-9 M flow cell eluent was predominantly Pu(V) despite the expectation that Pu will be present as Pu(IV) on the mineral surface, suggesting that oxidation of Pu(IV) to Pu(V) drives desorption. No clear change in desorption behavior was seen in the 10-9 M experiment between samples with an adsorption equilibration time of 25 d and 4 months, suggesting that Pu aging on the goethite surface may not necessarily lead to an increased stability of the adsorbed species. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Effect of concentration and time on Pu desorption from goethite

253rd National Meeting (2017)

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