No abstract available

[en] The solubilities of crystalline Am(OH)₃ and AmOHCO₃ were measured at 25⁰C in aqueous solutions of 0.1 M NaClO₄ by determination of the solution concentrations of Am. Prior to use in the measurements, the solid materials were characterized by their x-ray powder diffraction patterns. The solubility product quotients were calculated from the experimental data. The hydrolysis quotients of Am³⁺ were also estimated from the hydroxide solubility data. Using the thermodynamic data derived from these experiments and the recently reported formation constants for the Am³⁺ carbonate complexes, the solid phases and concentrations of solution species of americium in several aqueous carbonate systems were calculated using the computer code MINEQL. 20 references, 1 figure, 1 table

[en] Electron absorption spectra of Am₂(C₂O₄)₃xnH₂O (n = 0, 3,10), Am(OH)₃x4H₂O, AmOHCO₃x1.5H₂O and Am(OOCH)₃x0.2H₂O in the range of wave lengths 450-550 nm at room temperature were measured using the method of pressing in matrix from NaCl. The presence of intensive absorption bands in the spectra characteristic of f-f-transitions indicates noncentrally symmetric surrounding of americium atoms in the structures of the compounds. Americium(3) formate spectrum, in which absorption band splits into two components, possesses a significant peculiarity. It suggests the presence of crystallographically nonequivalent americium atoms in the structure of Am(OOCH)₃x0.2H₂O

No abstract available

No abstract available

[en] To elucidate the sorption behavior of americium(III) on bentonite, which is a mixture of montmorillonite clay, quartz and other minerals, simplified desorption experiments were applied to the solid phases collected after the sorption experiments. The sorption-desorption behavior was examined in the final pH range from 2 to 8. The desorption experiments revealed that most of the Am was sorbed on the montmorillonite moiety of the bentonite. The sorption of Am on montmorillonite was divided into two types: one was the 'exchangeable' sorption, in which the sorbed Am was desorbed with a 1 M KCl aqueous solution, and the rest was the 'unexchangeable' sorption. The exchangeable sorption was ion exchange of mostly Am³⁺. The unexchangeable sorption was the strong sorption of Am hydroxides. An accessory iron mineral, pyrite, might be involved in the Am sorption on bentonite at neutral pH. (author)

[en] Using the solubility method, the stability constants (β) and solubility products (SP) of americium(3) and plutonium(4) hydroxides are determined at 25 deg C, I = 3 ionic strength and in the pH 1.5-10 range. The SP and β values for Am(3) and Pu(4) are the follouring: 3.938x10^-28 and 3.675x10^-52, 4.072x10⁷ and 3.020x10¹² (β₁), 5.263x10¹⁴ and 1.900x10²⁴ (β₂), 4.416x10²¹ and 3,415x10³⁵ (β₃), 2.669x10⁴⁶ (β for P₄), respectively. The distribution of Am(3) and Pu(4) hydroxides according to complex forms in solutions with different pH values is considered. 3 figs.; 1 tab

[en] The solubilities of crystalline Nd(OH)₃ and Am(OH)₃ were measured at 25 +- 1⁰C in aqueous solutions of 0.1 M NaClO₄ under argon as a function of pH by determination of the solution concentrations of Nd and Am. Prior to use in the solubility measurements, the solid materials were characterized through their x-ray powder patterns. Analyses of the solubility data with the computer code MINEQL allowed estimates of the solubility product constants, K/sub s10/, and the second and third hydrolysis constants, K₁₂ and K₁₃, for Nd³⁺ and Am³⁺. Upper limits for the fourth hydrolysis constants were also estimated. For Nd, they are: log K/sub s10/ = 16.0 +- .2, log K₁₂ = -15.8 +- .5, log K₁₃ = -23.9 +- .2 and log K₁₄ < -34. For Am, they are: log K/sub s10/ = 15.9 +- .4, log K₁₂ = -16.0 +- .7, log K₁₃ = -24.3 +- .3 and log K₁₄ < -34.5. The crystalline Nd(OH)₃ was found to be a factor of 100 to 300 less soluble than predicted from previously reported thermodynamic data over much of the pH range of environmental interest. The measured solubility of crystalline Am(OH)₃ was also considerably less than predicted from the previously estimated solubility product constant, i.e., a factor of about 600. For Am, the solubility of the crystalline material was a factor of about 30 less than the amorphous material. The solubilities of crystalline Nd(OH)₃ and Am(OH)₃ as a function of pH were found to be very similar and Nd(OH)₃ should be a good analog compound for Am(OH)₃

[en] A generalized scheme of americium(III) hydrolysis is proposed for a wide range of pH (1-10) and concentrations (10^-1-10^-10 M). 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. (author) 17 refs.; 3 figs.; 2 tabs

[en] The electronic absorption spectra of Am₂(C₂O₄)₃·nH₂O (n = 0, 3, 10), Am(OH)₃·4H₂O, AmOHCO₃·1.5H₂O and Am(OOCH₃₎·0.2H₂O as pressed NaCl pellets are measured in the range 450-550 nm at room temperature. The presence of intense absorption bands characteristic of f-f-transitions is consistent with a noncentrosymmetric environment for the Am atoms in the structures. The position of the band maximum is practically independent of the ligand and shifts to long wavelength by ∼5 nm compared with that of hydrated Am³⁺. In the spectrum of Am(III)formate, the absorption band is split into two components (506 and 509 nm). This indicates the presence of crystallographically nonequivalent Am atoms in Am(OOCH₃)·0.2H₂O