The reduction of Np(VI) and Pu(VI) by organic chelating agents.
The reduction of NpO{sup 2+} and PuO{sub 2}{sup 2+} by oxalate. citrate, and ethylenediaminetetraacetic acid (EDTA) was investigated in low ionic strength media and brines. This was done to help establish the stability of the An(VI) oxidation state in the presence of organic complexants. The stability of the An(VI) oxidation state depended on the pH and relative strength of the various oxidation state-specific complexes. At low ionic strength and pH 6, NpO{sub 2}O{sup 2+} was rapidly reduced to form NpO{sub 2}{sup +} organic complexes. At longer times, Np(IV) organic complexes were observed in the presence of citrate. PuO{sub 2}{sup 2+} was predominantly reduced to Pu{sup 4+}, resulting in the formation of organic complexes or polymeric/hydrolytic precipitates. The relative rates of reduction to the An(V) complex were EDTA > citrate > oxalate. Subsequent reduction to An(IV) complexes, however, occurred in the following order: citrate > EDTA > oxalate because of the stability of the An(V)-EDTA complex. The presence of organic complexants led to the rapid reduction of NpO{sub 2}{sup 2+} and PuO{sub 2}P{sup 2+} in G-seep brine at pHs 5 and 7. At pHs 8 and 10 in ERDA-6 brine, carbonate and hydrolytic complexes predominated and slowed down or prevented the reduction of An(VI) by the organics present.
- Research Organization:
- Argonne National Lab., IL (US)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- W-31-109-ENG-38
- OSTI ID:
- 7847
- Report Number(s):
- ANL/CMT/CP-92715; TRN: US0101825
- Resource Relation:
- Conference: 5th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products in the Geosphere, Sendai (JP), 10/26/1997--10/31/1997; Other Information: PBD: 19 Mar 1998
- Country of Publication:
- United States
- Language:
- English
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