Authors:Y. Takahashi, Y. Minai, T. Kimura, and T. Tominaga
Distribution of trace amount of Eu(III), or Am(III), in the aqueous/solid system containing humic acid and kaolinite, or montmorillonite,
was studied by batch experiments. Humic acid was also adsorbed on the clay minerals and its adsorption isotherm can be regarded
as a Langmuir type. It is shown that Eu(III), or Am(III), exists as humate complex either in the aqueous or on solid phase
in the system including kaolinite, or montmorillonite. These results suggest that the organic-inorganic complex like clay
minerals coated with humic substances is important as metal reservoir in the environment.
The results of curium chemiluminescence investigations are generalized and the results of search for americium chemiluminescence are described. Some chemiluminescence reactions of americium, where the initial and the final forms were Am(IV) or (VI) and Am(III), respectively, were discovered. The Am(III) ion was the emitter of chemiluminescence, problably, only in the reduction reaction of Am(IV) decatungstate by reductants such as N2H4, some of its derivatives, EDTA and DTPA. The yield of chemiluminescence was estimated as 10–9–10–10 quanta per reaction act. In other chemiluminescent reactions discovered, the emitter of chemiluminescence was probably the oxidation products of the reductant.
Authors:V. Vasilyev, E. Kalevich, V. Radchenko, E. Shimbarev, V. Egunov, A. Izmalkov, and V. Vasilyev
Thermal decomposition of oxalate and nitrate hydrates of transplutonium elements has been studied by differential thermal and X-ray analysis, under heating in helium and oxygen. The formation heats of anhydrous crystalline Am(III) and Cm(III) nitrates were estimated from DTA data. Data of the self-decomposition of244Cm(III) salts under the influence of inherent -radiation were obtained.
A generalized scheme of americium(III) hydrolysis is proposed for a wide range of pH (1–10) and concentrations (10–1–10–10M). The data on Am(III) hydrolysis are presented in the form of three-dimensional isothermal diagram. This approach to the study of hydrolysis can be used for investigation of hydrolytic behaviour of most polyvalent ions.
Authors:H. Suganuma, M. Nakamura, I. Satoh, and T. Omori
The stability constants, β1, of each monochloride complex of Am(III) have been determined in a mixed system of methanol and water at 1.0 mol·dm−3 ionic strength using a solvent extraction technique. The values of β1 of Am(III) decrease up to about 0.1 mole fraction of methanol (Xs) in the bulk solutions and then increase with increasingXs when 0.1<Xs≤0.4. The distance of Am3+−Cl− in the mixed system was estimated using a Born-type equation. From the estimated distance of Am3+−Cl− (dAm−Cl), it is concluded that AmCl2+ in the aqueous solution is present as a solvent-shared ion-pair. Further, based on the variation of dAm−Cl with increasingXs, the variations of β1 in the system are accounted for by the size-variation of the primary solvation sphere around Am(III) and by an effect due
to the presence of a slight covalency in the solvation of Am(III).
Radiation effects on the extraction of Am(III) with di (2-ethylhexyl) phosphoric acid (DEHPA) was studied by exposing DEHPA
to gamma rays under various conditions. Gamma irradiation of undiluted DEHPA causes an enhancement of extraction of Am(III)
due to the formation of mono (2-ethylhexyl) phosphoric acid (MEHPA) similarly to that of Nd(III). The presence of diluent
during irradiation brought about a slight difference from the results in the absence of a diluent. The marked change occurred
in Df when the organic solvent was exposed to γ-ray while being mixed with nitric acid solution. An initial slight increase
of Df for Am(III) and Nd(III) was followed by a subsequent decrease beyond an absorbed dose of approximately 200 Wh·1−1. This phenomenon was explained by the enhanced decomposition of DEHPA and the subsequent strong hydrolytic and radiolytic
decomposition of MEHPA to H3PO4 in the aqueous phase, and the complex forming nature of H3PO4 with Am(III) and Nd(III).
Systematic studies are carried out on the distribution of Pu(IV), Am(III) and Cm(III) from nitric acid media using solid (Dowex)
and liquid (TCMA) anion exchangers. The distribution of these elements from nitric acid-organic solvent mixtures is also investigated.
In view of the given results, convenient procedures for interseparation of the mentioned elements are recommended.
Authors:F. Rösch, T. Reimann, G. Buklanov, M. Milanov, V. Khalkin, and R. Dreyer
The electromigration behaviour of carrier-free241Am–Am(III) in inert electrolytes, =0.1 (C10
), T=298.1(1) K, was studied. On the basis of the overall ion mobilities of241Am–Am(III) on pH between pH 5.5 and 12.9, the stoichiometric hydrolysis constants p
=23.8(9), and pK1=6.9(2) were obtained. For K4 a limitation of pK4
14.4(3) was possible, because no formation of anionic hydrolysis products in solutions pH12.9 was registered. The individual ion mobility of the241Am–Am3+ decrease in the range pH 5.5–3 from +6.85(15) up to +5.50(15)·10–4 cm2·s–1·V–1. Dependences of this effect on overall ionic strength, inert electrolyte anion, and the temperature of the electrolytes were studied in acidic and neutral solutions.
Authors:T. Sakuragi, S. Sawa, S. Sato, T. Kozaki, T. Mitsugashira, M. Hara, and Y. Suzuki
Complexation of Am(III) with humic acid was studied at various pHs in 0.1M NaClO4. The stability constants of the Am(III)—humate complexes were determined by a cation-exchange method. The values of log
1 and log
2 increased slightly with increases of pH from 4 to 6 and were found to be 6.9 and 11.6, respectively, at a pH of 5. Markedly larger values than these were obtained by a solvent extraction method. This discrepancy was also revealed by summarizing data from several literature sources. It is very likely that this can be ascribed to decreases in either humic acid and/or the extractant from the extraction system due to humate interactions at the aqueous-organic interface.
Batchwise uptake of Am(III), Pm(III), Eu(III), U(VI) and Pu(IV) by dihexyl-N,N-diethylcarbamoylmethylphosphonate (CMP) adsorbed on chromosorb (CAC) at nitric acid concentrations between 0.01 to 6.0M has been studied. The difference between the uptake behavior of Pu(IV) as compared to other actinides and lanthanides is discussed. The Am(III) and U(VI) species taken up on CAC were found to be Am(NO3)3·3CMP and UO2(NO3)2·2CMP, respectively. The equilibrium constants for the formation of these species have been evaluated and compared with those of similar species formed in liquid-liquid extraction. Batchwise loading of Pm(III) on CAC from 3.0M HNO3 has also been studied.