Oxidative Alkaline Leaching of Americium from Simulated High‐Level Nuclear Waste Sludges

Abstract

Oxidative alkaline leaching has been proposed to pretreat the high‐level nuclear waste sludges to remove some of the problematic (e.g., Cr) and/or nonradioactive (e.g., Na, Al) constituents before vitrification. It is critical to understand the behavior of actinides, americium and plutonium in particular, in oxidative alkaline leaching. We have studied the leaching behavior of americium from four different sludge simulants (BiPO4, BiPO4 modified, Redox, PUREX) using potassium permanganate and potassium persulfate in alkaline solutions. Up to 60% of americium sorbed onto the simulants is leached from the sludges by alkaline persulfate and permanganate. The percentage of americium leached increases with [NaOH] (between 1.0 and 5.0 M). The initial rate of americium leaching by potassium persulfate increases in the order BiPO4 sludge<Redox sludge<PUREX sludge. The data are most consistent with oxidation of Am3+ in the sludge to either AmO2 + or AmO2 2+ in solution. Though neither of these species is expected to exhibit long‐term stability in solution, the potential for mobilization of americium from sludge samples would have to be accommodated in the design of any oxidative leaching process for real sludge samples. This work was supported by the Office of Science, Biological and Environmental Research, under U.S. Department of Energy Contract No. DE‐AC03‐76SF0098 at Lawrence Berkeley National Laboratory and Contract No. W‐31‐109‐ENG‐38 at Argonne National Laboratory.