Effect of Oxalate on the Recycle of Neptunium Filtrate Solution by Anion Exchange

Kyser, E

Savannah River Site (S.C.)

关键词: Catalytic Effects;    Neptunium;    Radioactive Waste Processing;    Oxalates;    Solubility;   

DOI  :  10.2172/890156
RP-ID  :  WSRC-TR-2004-00554
RP-ID  :  DE-AC09-96SR18500
RP-ID  :  890156

美国|英语

来源: UNT Digital Library

【 摘 要 】

A series of laboratory column runs has been performed that demonstrates the recovery of neptunium (Np) containing up to 0.05 M oxalate. Np losses were generally less than one percent to the raffinate for feed solutions that contained 2 to 10 g Np/L. Up to 16 percent Np losses were observed with lower Np feed concentrations, but those losses were attributed to the shortened residence times rather than the higher oxalate to Np ratios. Losses in the plant are expected to be significantly less due to the lower cross-section flowrate possible with existing plant pumps. Elimination of the permanganate treatment of filtrates appears to be reasonable since the amount of Np in those filtrates does not appear to be practical to recover. Combination of untreated filtrates with other actinide rich solutions is not advisable as precipitation problems are likely. If untreated filtrates are kept segregated from other actinide rich streams, the recovery of the remaining Np is probably still possible, but could be limited due to the excessively high oxalate to Np ratio. The persistence of hydrazine/hydrazoic acid in filtrate solutions dictates that the nitrite treatment be retained to eliminate those species from the filtrates prior to transfer to the canyon. Elimination of the permanganate treatment of precipitator flushes and recovery by anion exchange does not appear to be limited by the oxalate effect on anion exchange. Np from solutions with higher oxalate to Np molar ratios than expected in precipitator flushes was recovered with low to modest losses. Solubility problems appear to be unlikely when the moles of oxalate involved are less than the total number of moles of Np due to complexation effects. The presence of significant concentrations of iron (Fe) in the solutions will further decrease the probability of Np oxalate precipitation due the formation of Fe oxalate complexes. Np oxalate solubility data in 8 M HNO{sub 3} with from one to six times as much oxalate as Np have been obtained. These data supplement literature data in the high HNO{sub 3} low oxalate region, but provide additional data for solutions with relatively large amounts of Np present. Enhanced solubility of Np oxalate over that reported in the literature was observed.