Yoshihiro Meguro

Modelling of the extraction of uranium with supercritical carbon dioxide

A model is presented for the analysis of the results of extraction of uranium in a flow system by supercritical fluid modified with tributylphosphate from a nitric acid matrix, in which the extraction is not limited by the solubility of the uranium species. The model used is that of diffusion out of a sphere into a medium in which the extracted uranium is infinitely dilute. Although not a completely accurate representation of the liquid-supercritical fluid system, the model is shown to be a reasonable representation and some conclusions discussed.

Applicability of a catalytic reduction method using a palladium–copper catalyst and hydrazine for the denitration of a highly concentrated nitrate salt solution

Denitration of a highly concentrated sodium nitrate (NaNO3) aqueous solution via a catalytic reduction method using a palladium–copper catalyst supported on carbon powder (Pd–Cu/C) and hydrazine (N2H4) was investigated. It was demonstrated that nitrate ion (NO3 −) in a 5 mol L−1 NaNO3 solution was completely reduced through an intermediate nitrite ion (NO2 −) to nitrogen compounds such as nitrogen, nitrous oxide, and ammonia. By comparing the reaction rates of NO3 − and NO2 − obtained using catalysts with various Pd–Cu compositions and different reductants (hydrogen (H2) or N2H4), it was determined that the catalyst with a molar ratio of Pd:Cu = 1:0.66 provides the maximum reaction rates for NO3 − and NO2 − using N2H4, and that not only the reactions of NO3 − and NO2 − but also that of N2H4 were affected by the Pd–Cu composition.

Swelling pressure and leaching behaviors of synthetic bituminized waste products with various salt contents under a constant-volume condition

ABSTRACT We investigated the swelling pressure of synthetic bituminized waste products (BWPs) and the amount of Na+ in the leachate from them under a constant-volume condition when the BWPs were in contact with water to understand influences of salt content on the surrounding environments after disposal of radioactive BWPs in a geological repository. The observation of the cross section of the synthetic BWP specimens revealed that micropores, which were formed after soluble salts leached out from the specimens, shrank and deformed near the surface of the specimens. The salt content in the synthetic BWP specimens depended on the amount of water taken up, indicating that an increase in the amount of water led to increases in the swelling pressure and the cumulative amount of Na+ in the leachate. It was found that the shrinkage and deformation of the micropores near the surface of the synthetic BWP specimens that arose under the constant-volume condition significantly influenced increases in the swelling pressure and cumulative amount of Na+ in the leachate.

Development of Separation Technique of Sodium Nitrate From Low-Level Radioactive Liquid Waste Using Electrodialysis With Selective Ion-Exchange Membranes

An advanced method, in which electrodialysis separation of sodium nitrate and decomposition of nitrate ion are combined, has been developed to remove nitrate ion from low-level radioactive liquid wastes including nitrate salts of high concentration. An engineering scale apparatus with two electrodialytic devices, in which the sodium and nitrate ions were separately removed by each device, was produced on the basis of the results of fundamental investigation previously reported, and the performance of the apparatus was tested. Both the ions were successfully removed at the same time, though these ions were separately transferred using two electrodialytic devices. And also effect of several experimental parameters such as current and temperature on current efficiency of both the ions of each device was investigated.Copyright

Elution Behavior of Heavy Metals From Cement Solidified Products of Incinerated Ash Waste

A method, in which incinerated ash is solidified with a cement material, has been developed to dispose radioactive incinerated ash waste. In order to bury the solidified product, it is required that elution of hazardous heavy metals included in the ash from the solidified products is inhibited. In this study, the elution behavior of the heavy metals from the synthetic solidified products, which included Pb(II), Cd(II), and Cr(VI) and were prepared using ordinary portland cement (OPC), blast furnace slag cement (BFS), or a cement material that showed low alkalinity (LA-Cement), was investigated. Several chemicals and materials were added as additive agents to prevent the elution of the heavy metals. When OPC was used, Cd elution was inhibited, but Pb and Cr were not enough even using the additive agent examined. FeSO4 and Na2 S additive agents worked effective to inhibit elution of Cr. When BFS was used, the elution of Pb, Cd and Cr was inhibited for the all products prepared. In the case of LA-Cement, the elution of Pb and Cd was inhibited for the all products, but only the product that was added FeSO4 showed good result of the elution of Cr.Copyright

Separation and Recovery of Sodium Nitrate From Low-Level Radioactive Liquid Waste by Electrodialysis

An advanced method, in which electrodialysis separation of sodium nitrate and decomposition of nitrate ion are combined, has been developed to remove nitrate ion from low-level radioactive liquid wastes including nitrate salts of high concentration. In the electrodialysis separation, the sodium nitrate was recovered as nitric acid and sodium hydroxide. When they are reused, it is necessary to reduce the quantity of impurities getting mixed with them from the waste fluid as much as possible. In this study, therefore, a cation exchange membrane with permselectivity for sodium ion and an anion exchange membrane with permselectivity for monovalent anion were employed. Using these membranes sodium and nitrate ions were effectively removed form a sodium nitrate solution of high concentration. And also it was confirmed that sodium ion was successfully separated from cesium and strontium ions and that nitrate ion was separated from sulfate and phosphate ions.Copyright

Phase Behavior and Reverse Micelle Formation in Supercritical CO2 With DTAB and F-Pentanol for Decontamination of Radioactive Wastes

To develop a metal separation method using supercritical CO2 (scCO2 ) solvent for the decontamination process of radioactive wastes, the reverse micelle formation in scCO2 was investigated. Dodecyltrimethylammonium bromide (DTAB) as a surfactant to form the reverse micelles and 2,2,3,3,4,4,5,5-octafluoro-1-pentanol (F-pentanol) as a modifier to increase the solubility of DTAB into scCO2 were used. The reverse micelles could be formed by using 0.02 mol/dm3 DTAB and 0.45 mol/dm3 F-pentanol. A water concentration dissolved in scCO2 was increased with an increase of pressure, and 0.42 mol/dm3 water, which was 3 times larger than that in the neat CO2 , could be dissolved in scCO2 at 38 MPa. Moreover, 0.1 mol/dm3 HNO3 could dissolve at the same pressure as water. On the other hand, it was found that the solubility of water at outside of reverse micelles increased with F-pentanol. The ratio of water and F-pentanol affected the phase behavior of water in scCO2 .Copyright