Speciation plutonium

Fig. 6. Speciation diagram of plutonium as function of Eb and pH in aqueous solution at 25°C (a) carbonate-free (89) (b) 0.004 M total carbonate (90). Eb...

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. 

Prediction of the chemistry of plutonium in near-neutral aqueous media is highly dependent on understanding reactions that may be occurring in such media. One of the most important parameters is the stability and nature of complexes formed by plutonium in its four common oxidation states. Because Pu(III), Pu(IV), and Pu(VI) are readily hydrolysed, complexation reactions generally are studied in mildly to strongly acidic media. Data determined in acid media (and frequently at high concentrations of plutonium) then are used to predict the chemical speciation of plutonium at near-neutral pH and low concentrations of the metal ion. 

Several attempts to calculate plutonium solubility and speciation in environmental systems are given in the literature (e.g. 

In Figure 2 the solubility and speciation of plutonium have been calculated, using stability data for the hydroxy and carbonate complexes in Table III and standard potentials from Table IV, for the waters indicted in Figure 2. Here, the various carbonate concentrations would correspond to an open system in equilibrium with air (b) and closed systems with a total carbonate concentration of 30 mg/liter (c,e) and 485 mg/liter (d,f), respectively. The two redox potentials would roughly correspond to water in equilibrium wit air (a-d cf 50) and systems buffered by an Fe(III)(s)/Fe(II)(s)-equilibrium (e,f), respectively. Thus, the natural span of carbonate concentrations and redox conditions is illustrated. 

Eh-pH diagram for the speciation of plutonium in equilibrium with Pu02 in water (10). 

Speciation of plutonium leached from the glass cubes is shown in Figure 1. The first bar represents the total amount of insoluble plutonium and is the summation of suspended plutonium (the difference between the values for filtered and unfiltered waters) and sorbed plutonium—viz., the amount removed from the cubes by a 0.1 M perchloric acid wash, normalized to the volumes of leachant solutions so that it is comparable to the other values in the graphs. For simplicity, the insoluble fractions are combined in one bar, whereas the various oxidation states in the soluble fraction are represented by separate bars. It should be noted that the ordinate scale varies among the graphs. 

Clevelend, J.M. Rees, T.F. Nash, K.L. "Plutonium Speciation in Selected Basalt, Granite, Shale, and Tuff Ground Waters", in press. 

The chemistry of waste treatment processes and the development of new processes are fertile areas of research work. The speciation of plutonium in basic and laundry wastes is needed. For example, if soluble plutonium complexes in basic wastes can be destroyed, perhaps ultrafiltration could replace the flocculent-carrier precipitation process. The chemistry of plutonium(VII) and of ferrites—a candidate waste treatment process—needs to be explored.(23)... 

Bulman RA, Johnson TE, Ham GJ, et al. 1993. Speciation of plutonium in potato and the gastrointestinal transfer of plutonium and americium from potato. Sci Total Environ 129 267-289. 

Hirose and Sugimura [89] investigated the speciation of plutonium in seawater using adsorption of plutonium (IV)-xylenol orange and plutonium-arsenazo (III) complexes on the macroreticular synthetic resin XAD-2. Xylenol orange was selective for plutonium (IV) and arsenazo (III) for total plutonium. Plutonium levels were determined by a-ray spectrometry. 

Subsurface contamination by uranium wastes and contaminant speciation during transport from a wastewater pond (originating from a plutonium production plant) to groundwater were studied by Catalano et al. (2006). Land disposal of basic sodium aluminates and acidic U(VI)-Cn(ll) and their redistribution in the vadose zone resulted in development of a groundwater nraninm plume. The solid phase speciation of nraninm from the base of the pond, throngh the subsurface, to the... 

Conradson, S. D Abney, K. D. et al. 2004. Higher order speciation effects on plutonium L3 X-ray absorption near edge spectra. Inorganic Chemistry, 43, 116-131. 

Cleveland. J.M.. T.F. Rees, and K.L. Nash Plutonium Speciation in Water from Mono Lake, California, Science. 222. 1323-1325 (1983). 

Direct speciation of dissolved americium and plutonium is possible only for solutions with appreciable concentration ([Am(DI)] > 10-6 M and [Pu(VT)] s 10-5 M) using a spectrophotometer with cumulative data recording (21). Typical spectra measured for the Am3+ ion at pH = 6.5 are shown in Figure 5 for 1, 5, 10, and 40 times cumulation at 503 nm. With this method it is shown that only trivalent americium ions are present in both equilibrium solutions from Am02 and Am(0H)3>nH20 solids. For plutonium solutions, the spectrophotometric study indicates the presence of polymers as shown in Figure 4. 

Especially interesting in a discussion of radionuclide speciation is the behaviour of the transuranium elements neptunium, plutonium, americium and curium. These form part of the actinide series of elements which resemble the lanthanides in that electrons are progressively added to the 5f instead of the 4f orbital electron shell. The effective shielding of these 5f electrons is less than for the 4f electrons of the lanthanides and the differences in energy between adjacent shells is also smaller, with the result that the actinide elements tend to display more complex chemical properties than the lanthanides, especially in relation to their oxidation-reduction behaviour (Bagnall, 1972). The effect is especially noticeable in the case of uranium, neptunium and plutonium, the last of which has the unique feature that four oxidation states Pum, Pu, Puv and Pu are... 

In a review of available data relating to the physico-chemical speciation of plutonium in the Irish Sea and western Mediterranean, Mitchell et ai. (1995) concluded that a high percentage of the plutonium is present as Puv and not retained by a 1 kD filter, thus demonstrating that plutonium in the oxidised state is in true solution. The data also indicate that a significant proportion of plutonium in the reduced state is associated with colloids and that the size of the colloidal particles or aggregates involved (<10kD) is considerably smaller than those observed in non-saline waters. 

Aston, S.R. and Stanners, DA. (1981) Observations on the deposition, mobility and chemical associations of plutonium in intertidal sediments. In Techniques for Identifying Transuranic Speciation in Aquatic Environments. IAEA, Vienna, pp. 209-218. 

Mitchell, P.I., Battle, J., Vives I., Downes, A.B., Condren, O.M., Leon Vintro, L. and Sanchez Cabeza, J.A. (1995) Recent observations on the physico-chemical speciation of plutonium in the Irish Sea and the western Mediterranean. Appl. Radiat. Isot., 46(11), 1175-1190. 

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