REDUCTION OF Np ( V 1 ) AND Pu ( V 1 ) BY ORGANIC CHELATING AGENTS

Abstract The reduction of N p O P and P u O p by oxalate, citrate, and ethylenediaminetetraacetic acid OST1 (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, N p O F was rapidly reduced to form Np0: organic complexes. At longer times, Np(IV) organic complexes were observed in the presence of citrate. P u O p was predominantly reduced to Pu", resulting in the formation of organic complexes or polymerichydrolytic precipitates. The relative rates of reduction to the An(V) complex were EDTA> citrate > oxalate. Subsequent reduction to An(?X) 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 N p O F and P u O F 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.