SREL Reprint #3280

 

 

 

Plutonium Immobilization and Remobilization by Soil Mineral and Organic Matter in the Far-Field of the Savannah River Site, U.S.

Chen Xu1, Matthew Athon1, Yi-Fang Ho1, Hyun-Shik Chang2, Saijin Zhang1, Daniel I. Kaplan3
Kathleen A. Schwehr1, Nicole DiDonato4, Patrick G. Hatcher4, and Peter H. Santschi1

1Department of Marine Sciences, Texas A&M University, Building 3029, Galveston, TX 77553, USA
2Savannah River Ecology Laboratory, University of Georgia, P.O. Drawer E, Aiken, SC 29802, USA
3Savannah River National Laboratory, Aiken, SC 29808, USA
4Department of Chemistry and Biochemistry, College of Sciences, Old Dominion University,
Norfolk, VA 23529, USA

Abstract: To study the effects of natural organic matter (NOM) on Pu sorption, Pu(IV) and (V) were amended at environmentally relevant concentrations (10-14 M) to two soils of contrasting particulate NOM concentrations collected from the F-Area of the Savannah River Site. More Pu(IV) than (V) was bound to soil colloidal organic matter (COM). A de-ashed humic acid (i.e., metals being removed) scavenged more
Pu(IV,V) into its colloidal fraction than the original HA incorporated into its colloidal fraction, and an inverse trend was thus observed for the particulate-fraction-bound Pu for these two types of HAs. However, the overall Pu binding capacity of HA (particulate + colloidal-Pu) decreased after de-ashing. The presence of NOM in the F-Area soil did not enhance Pu fixation to the organic-rich soil when compared to the organic-poor soil or the mineral phase from the same soil source, due to the formation of COM-bound Pu. Most importantly, Pu uptake by organic-rich soil decreased with increasing pH because more NOM in the colloidal size desorbed from the particulate fraction in the elevated pH systems, resulting in greater amounts of Pu associated with the COM fraction. This is in contrast to previous observations with low-NOM sediments or minerals, which showed increased Pu uptake with increasing pH levels. This demonstrates that despite Pu immobilization by NOM, COM can convert Pu into a more mobile form.

SREL Reprint #3280

Xu, C., M. Athon, Y. F. Ho, H. S. Chang, S. Zhang, D. I. Kaplan, K. A. Schwehr, N. DiDonato, P. G. Hatcher, and P. H. Santschi. 2014. Plutonium Immobilization and Remobilization by Soil Mineral and Organic Matter in the Far-Field of the Savannah River Site, U.S. Environmental Science and Technology 48(6): 3186-3195.

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