Plutonium oxidation states

Only slightly less accurate ( 0.3—0.5%) and more versatile in scale are other titration techniques. Plutonium maybe oxidized in aqueous solution to PuO " 2 using AgO, and then reduced to Pu" " by a known excess of Fe", which is back-titrated with Ce" ". Pu" " may be titrated complexometricaHy with EDTA and a colorimetric indicator such as Arsenazo(I), even in the presence of a large excess of UO " 2- Solution spectrophotometry (Figs. 4 and 5) can be utilized if the plutonium oxidation state is known or controlled. The spectrophotometric method is very sensitive if a colored complex such as Arsenazo(III) is used. Analytically usehil absorption maxima and molar absorption coefficients ( s) are given in Table 10. Laser photoacoustic spectroscopy has been developed for both elemental analysis and speciation (oxidation state) at concentrations of lO " — 10 M (118). Chemical extraction can also be used to enhance this technique. 

Plutonium oxidation state Wavelength maximum, nm Molar ah sorptivities, L/(molcm) ... 

A second source of plutonium, dispersed more locally, is liquid effluent from fuel reprocessing facilities. One such is the fuel reprocessing plant at Windscale, Cumbria in the United Kingdom where liquid waste is released to the Irish Sea(6). Chemical analysis of this effluent shows that about one percent or less of the plutonium is in an oxidized form before it contacts the marine water(7). Approximately 95 percent of the plutonium rapidly adsorbs to particulate matter after discharge and deposits on the seabed while 5 percent is removed from the area as a soluble component ). Because this source provided concentrations that were readily detected, pioneering field research into plutonium oxidation states in the marine environment was conducted at this location. 

Colvin, C. A. Quantitative Determination of Plutonium Oxidation States in Variable Nitric Acid Solutions for Control Laboratories—Spectrophotometric, U.S. AEC Report RL-SA-33, General Electric Co., Richland, WA, 1965. 

In 1973, the United States Atomic Energy Commission (USAEC) conducted an intensive investigation into its research efforts relating to the development of nuclear power. The conclusion reached by the environmental team was that the environmental behaviour and long-term fate of the transuranium elements had not been addressed in an effective way. This conclusion prompted the USAEC to develop an investigative programme. Some important landmarks in the environmental research which led to the eventual separation and determination of the plutonium oxidation states in the aquatic environment were ... 

Table 13.3 Replicate determinations of plutonium oxidation-state species in filtered seawater using neodymium fluoride (100mgl-1) as co-precipitant...

Some results of plutonium oxidation-state analysis carried out on samples of Lake Trawsfynydd water which had been passed through different sizes of hollow-fibre cartridge are shown in Fig. 13.7 where it can be seen that over 90% of the plutonium which passed through the 3 k molecular weight nominal cut-off... 

Bondietti, E.A. and Reynolds, S.A. (1976) Field and laboratory observations on plutonium oxidation states. In Proceedings of an Actinide-Sediment Reactions Working Group Meeting, Seattle, Washington, BNWL2117, pp. 505-537. 

Schramke J. A., Rai D., Fulton R. W., and Choppin G. R. (1989) Determination of aqueous plutonium oxidation states by solvent extractions. J. Radioanalyt. Nuclear Chem. 130(2), 333-346. 

In order to effect a separation of uranium and plutonium it is necessary to adjust the plutonium oxidation state to (III), which is poorly extracted. Provided the uranium remains as U a partition is then possible with U remaining in the organic phase while Pu passes into the... 

The Al O column loaded with plutonium x as satisfactorily washed with an 0.1M HNO - 0.05M HF solution for the removal of the last traces of uranium and other elements not sorbed. The effluents contained less than 0.01% of plutonium. Washing the column with an 0.8M HNO - 0.05M HF solution resulted in 0.1% of plutonium activity in the effluent. This indicates that the column should be washed with more dilute nitric acid. The effectiviness of elution x ith FNO plus a reducing agent at room temperature and 50°C was confirmed m both cases. As Pu(IT0 is more sorbed onto alumina than the other plutonium oxidation states, it was reduced to Pu(III) to improve the elution. On the other hand HNO is the most convenient medium for further uses of nlutonium, so for that reason nitric acid (1-6M) was selected as elutrient. Pure 3M FNO at room temperature eluted 79% of plutonium. A 3V FN0 - 0,005M FeSO solution was chosen as eluting, agent and, the elution yield... 

Table 9.19 Relative amounts of plutonium oxidation states...

Among plutonium oxidation states from 4-3 to 4-6, the most stable forms are 4-3 and 4-4. Conversion between oxidation states is used for purification from other radionuclides. Plutonium is oxidized to the 4-4 state by hydrogen peroxide, permanganate, and nitrite, and reduced to the 4-3 state by bisulfite and ascorbic acid. A strongly acidic or complexing solution is needed to maintain the selected state and avoid hydrolysis with polymerization (Coleman 1965). 

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