Americium ions

Americium Ions in Solutions. Report A/Conf. 8/P/676. Proceedings, 1st Internat. Conference on the Peaceful Uses of Atomic Energy, Geneva 1955, Vol. 7, S. 363 ff. 

The americium ions which might be encountered in aqueous media are Am3+, AmOj and AmO +. In general, however, Am3+ is the ion normally encountered since very powerful oxidising agents are required to produce the higher oxidation states. 

The vast majority of electrochemical data on americium ions has heen obtained in aqueous solutions. Americium can exist in aqueous solutions in the oxidation states III, IV, V, and VI. The divalent state is difficult to attain in aqueous solutions because of the proximity of the standard potential of the Am(III)/Am(II) couple to the solvent/supporting electrolyte breakdown potential. Previous reviews have presented the formal and standard potentials for the various americium couples and these reviews should be consulted by the interested reader for more detailed discussion [133, 134]. Table 3 contains a summary of selected formal potentials Ef from these reviews in 1 M HCIO4 for convenience. AU values are calculated from various measurement techniques except for the Am(VI)/Am(V) couple (Am02 /Am02" "), which was determined directly. 

More recent experimental reports have focused on detailed electrochemical studies to characterize the different americium ions in solution in relation to their stability and molecular composition. The electrochemical behavior of americium in carbonate media has been studied by several different authors because of the tendency... 

Solubility of Americium Hydroxide. Solutions containing greater than 10-6 M americium were examined by spectrophotometry to verify whether or not polymers were present. The molar extinction coefficient measured for the 503 nm absorption band was found to remain constant at e = 390 5 for all investigated solutions at pH = 3 6. Spectra recorded up to 850 nm in this pH range show the typical absorption bands of the Am3+ ion, which are similar to those observed in a dilute HCIO4 solution, without broadening or displacement. The concentration of americium ions in equilibrium solutions, [Am]s, is, therefore, considered a composite of only monomer species ... 

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. 

Calculated concentrations of possible hydrolysis species as a function of the equilibrium pH are given in Figures 6 and 7 for americium ions and plutonium ions, respectively. In the americium solution, the predominant species at pH <7 are the Am3+ and Am(OH)2+ ions, whereas in the plutonium solution the Pu022+ ion is not the dominating species at near neutral media but polymers as postulated (Pu02)2(OH)22+ and(Pu02)3(0H)5+. 

Americium ions in the higher valency states (IV, V, VI, VII) are powerful oxidizing agents, and the known chemical processes for heterovalent actinide ion separations are not reliable because of the instability of Am ions in all valency states except (III). This paper deals with Am (VI) - Cm (III) separation in nitrate media. Three topics are examined in order to improve the performance of this process. 

Two new TSILs bearing 2-hydroxybenzylamine based on an imidazolium substructure and used for the extraction of americium ions have been repotted by Ouadi et al. [37] (Scheme 5.5-19). 

Serp, J., Chamelot, R, Fourcaudot, S. etai. (2006) Electrochemical behaviour of americium ions in LiCl-KCl eutectic melt. Electrochim. Acta, 51, 4024. 

Complexation and stability of americium ions in various media, including solids used for waste storage, are of increasing importance because of americium occurrence in nuclear process waste. Solutions to the problems of long-term, safe storage of americium must be found. To answer such questions, an increase in the study of americium chemistry is to be anticipated. 

Newton, T. W. (1975) The Kinetics of the Oxidation-Reduction Reactions of Uranium, Neptunium, Plutonium, and Americium Ions in Aqueous Solutions, ERDA Critical Review Series, TID-26506. 

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