Effect of 1-Hydroxyethane-1,1-diphosphonic Acid (HEDPA) on Partitioning of Np and Pu to Synthetic Boehmite

Abstract

The effect of 1-hydroxyethane-1,1-diphosphonic acid (HEDPA) on the sorption of Np(V) and Pu(V) to synthetic boehmite (γ-AlOOH) was examined as a function of time and pH (between 4 to 11). The sorption of both elements in boehmite suspensions (1 M NaCl, 600 mg L⁻¹ boehmite) increased with increasing pH. The sorption edges for neptunium and plutonium occurred at approximately pH 8.0 and 6.6, respectively. After steady state partitioning was reached, HEDPA was added to the neptunium-boehmite and plutonium-boehmite suspensions. Neptunium and plutonium partitioning appears to be primarily affected by the formation of soluble Np:HEDPA and Pu:HEDPA complexes, the dissolution of boehmite promoted by HEDPA, and the precipitation of Np:HEDPA and Pu:HEDPA colloids. The results are discussed in terms of applicability of HEDPA-promoted dissolution as a waste reduction method in the treatment of sludge phases contained within high-level nuclear waste storage tanks.

Keywords:

• 1-hydroxyethane-1,1-diphosphonic acid
• alumina
• boehmite
• HEDPA
• neptunium
• nuclear waste
• plutonium

ACKNOWLEDGEMENTS

This work was supported by the Director, Office of Science, Office of Basic Energy Sciences and Office of Biological and Environmental Research of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 at the Lawrence Berkeley National Laboratory. The authors also acknowledge the helpful comments provided during the review of this manuscript.

Notes

^a Error propagated from counting statistics.

^b Error represents standard deviation of 3 replicate measurements.