Toshiaki Mitsugashira

Effects of humic acid on the sorption of Am(III) and Cm(III) on kaolinite

Sorption coefficients of Am(III) and Cm(III) on kaolinite were determined at pH from 3.5 to 10 and humic acid (HA) concentrations of 0 to 20 ppm at ionic strength of 0.1 M (NaClO4) at 298 K with N2 bubbling. The sorption ratio of HA on kaolinite was also measured under the same experimental conditions. The sorption coefficients of Am(III) and Cm(III) in the absence of HA increased with pH over the whole pH range. The presence of HA enhanced sorption coefficients at pH values up to around 5, above which the sorption coefficients were lowered by introducing HA. The effects of HA on sorption coefficients were interpreted by the use of a linear additive model, modified for metal-humate complex formation in the aqueous phase. The model was found to be in fairly good agreement with the experimental data.

Am(III) and Eu(III) uptake on hematite in the presence of humic acid

Summary The uptake of Am(III) and Eu(III) on hematite (1.0 g/L) in the presence of humic acid (HA; 4.7×10-5 M) was investigated at ionic strengths of 0.05 to 0.5 M (NaClO4) in the pH range of 4 to 10. The sorption behavior of Am(III) was similar to that of Eu(III). The Am(III) and Eu(III) exhibited 100% retention on the solid in the entire pH region studied at high ionic strength (0.5 M). As the ionic strength was decreased below 0.1 M, Am(III) and Eu(III) sorption which was complete at low pH values decreased stepwise with increasing pH from 5 to 7. In order to test the additivity and to understand the solid–water interface reactions for Am(III) sorption in ternary systems, binary interactions between Am(III), HA, and hematite were also examined under identical conditions. The additive results reproduced the stepwise decreases of sorption up to a pH of about 6 for lower ionic strengths, which can be ascribed to HA adsorption behavior. However, inconsistencies in additivity from experimental results were found in the pH regions above 7 at low ionic strengths and in the entire pH region at an ionic strength of 0.5 M. Some non-additive effects are discussed in this paper.

Thermodynamics of reductive extraction of actinides and lanthanides from molten chloride salt into liquid metal

For the development of a pyrochemical group-partitioning process of actinides and lanthanides, the equilibrium distributions of these elements were measured in some typical binary phase systems of molten salt and liquid metal. A LiCl-KCl mixture was selected as the salt phase, and Zn and Bi were examined as the metal phase. Generally speaking, actinides were more reducible and extractable from the salt phase into the metal phase than lanthanides, and the group partitioning of these elements was feasible in these systems. However, the separation factors which were the ratios in the distribution coefficient between actinides and lanthanides were found to be different in different systems due to different alloying energies. The thermodynamic quantities of actinides and lanthanides were evaluated from the equilibrium distributions and discussed in some detail.

Equilibrium distributions of actinides and lanthanides in molten chloride salt and liquid zinc binary phase system

As one of the basic investigations on the group partitioning of actinides and lanthanides by the pyrochemical reductive extraction system, their distribution behavior in a binary phase system of molten chloride and liquid zinc was studied at 873 and 1073 K. Generally speaking, actinides were a little more easily reduced and extracted from the salt phase into the metal phase than lanthanides. However, the separation factors which were the differences in the distribution coefficient between actinides and lanthanides were not so large even at the lower temperature at which those were larger and the group partitioning of these elements seemed less attractive in this system. The present results were much the same as those in the LiFBeF2/Zn system and the effect of the selection of the salt phase on the separation factors were hardly observed. For some details, the thermodynamic quantities of actinides and lanthanides in the system were calculated from the equilibrium distributions and discussed.

Group separation of trivalent actinides and lanthanides by tertiary pyridine-type anion-exchange resin embedded in silica beads

The separation of trivalent actinides and lanthanides was studied by using newly developed tertiary pyridine-type anion-exchange resin embedded in silica beads. Chromatographic elution experiments were carried out by using a packed column of the new resin and methanol-hydrochloric acid solution as an effluent. We confirmed that the actinides were eluted well from the elution bands of lanthanides. Actinides and lanthanides were eluted according to the reverse order of their atomic number.

Reductive extraction behaviour of actinide and lanthanide elements in molten salt and liquid metal binary phase systems

Abstract In support of the development of a pyrochemical group-partitioning process of actinides and lanthanides, the equilibrium distributions of these elements were measured in some binary phase systems of molten salt and liquid metal. An LiF—BeF2 mixture was selected as the salt phase and Bi, Sn, Cd and Zn were examined as the metal phase. In general, actinides were more easily reduced and extracted from the salt phase into the metal phase than were lanthanides. Group partitioning is thus feasible. In different partitioning systems a systematic difference in the separation factor between actinides and lanthanides was observed. The difference is attributable to the difference in alloying energies in the metal phase. The thermodynamic quantities of solute elements in the metal phase were evaluated from the present analysis. Some regularities were inferred from the analysis which are theoretically interesting and helpful to estimate unknown distribution coefficients.

Chromatographic Separation of Trivalent Actinides by Using Tertiary Pyridine Resin with Methanolic Nitric Acid Solutions

Chromatographic separation of trivalent actinides (Am, Cm and Cf) was performed by using a tertiary pyridine resin embedded in silica beads with methanolic nitric acid solutions. The trivalent actinides were eluted from the resin column in the reverse order of atomic numbers (Cf-Cm-Am). Higher concentration of methanol in the mixed solution accelerated both the adsorption of these elements on the resin and the separability for these elements. Americium was clearly separated from Cm and Cf by using a 1 cm-ø × 10 cm-height column with a 60vol% of methanol/40 vol% of concentrated nitric acid mixed solution at ambient temperature.

Development of a rapid source preparation method for high-resolution α-particle spectrometry

In order to prepare sources of short-lived actinides for alpha-particle spectrometry, a coprecipitation method with Sm hydroxide was developed. The preparation procedure can be completed within 5 min with a high chemical yield of over 90%. It was found that the uniformity of the produced sources was sufficient to provide a high resolution of better than 20 keV. Under this method, we successfully measured the alpha-particle spectrum of short-lived Cf isotopes produced in the (238)U((12)C, xn) reaction.

Effects of Calcium Ions on the Sorption of Am(III) and Eu(III) onto Kaolinite in the Presence of Humic Acid

The sorption of actinides onto minerals depending on groundwater chemistry plays an important role in the safety aspects of geological disposal of high-level waste. The effects of Ca(II) on the sorption of Am(III) and Eu(III) onto kaolinite in the presence of humic acid (HA) were examined in this study. Distribution coefficients (Kd) of Am(III) and Eu(III), and the fractional adsorption (fHA) of HA on kaolinite were determined by a batch method under initial Ca(II) concentrations of 0 to 1.0 × 10-3 M at a constant ionic strength of 0.1 M (NaClO4) and pH region from 3.5 to 10 in an N2 atmosphere at 298 K. The Kd increased with increasing Ca(II) concentrations in regions higher than 1.0 X10-4 M and in the range of pH 7 to 10. In this pH region, fHA was also enhanced by introducing Ca(II). Concentrations higher than 1.0 × 10-4 M Ca(II) can be regarded as a bridge between kaolinite and HA. It is very likely that the increase in the adsorbed HA on kaolinite, where the HA includes very stable Am(III) and Eu(M) humates, results in an increase in the Am(III) and Eu(IH) distribution coefficients.

Alpha-decay from the 3.5 eV isomer of 229Th

The alpha-decay of a low energy isomer of 229Th at about 3.5 eV was sought by producing it through the (g,n) reaction on a 230Th target. Thorium isotopes in the reaction products were isolated and purified by anion exchange chromatography in a concentrated nitric acid medium to remove lanthanides fission products. The thorium fraction was further purified by samarium fluoride coprecipitation and the precipitate was mounted as a source for a-spectroscopy. Decaying a-signals were observed in the energy region that was expected for 229mTh, i.e., between 4.83 and 5.08 MeV. The half-life of the decaying component was determined from repeated experiments to be 13.9±3 hours.