Shuichi Iso

Correlation between Extraction Equilibrium of Uranium(VI) and Density of CO2 Medium in a HNO3/Supercritical CO2−Tributyl Phosphate System

The extraction equilibrium of U(VI) between a nitric acid solution and a supercritical CO(2) phase containing tributyl phosphate (TBP) is formulated taking into account that (i) a distribution ratio of a metal extracted is a function of a distribution constant of each component involved in the extraction reaction, (ii) the distribution constant is defined as a ratio of solubilities of the component in both phases, and (iii) the solubility in the CO(2) phase is correlated with density of CO(2). A simple linear relationship between the distribution ratio, D(U), of U(VI) and density, ρ, of CO(2) is derived; log D(U) = a log ρ + A + B, in which a is a proportional constant implying the solvation characteristic of the solute in supercritical CO(2), A is a pressure-independent constant, and B is a variable determined by the distribution equilibrium of HNO(3). The equation derived was verified experimentally by the measurement of the distribution ratio of U(VI) and HNO(3) under various conditions of pressure and temperature. A novel concept of selective supercritical fluid extraction of metals by means of pressure-tuning or CO(2) density-tuning was proposed.

Pressure dependence of extraction behavior of plutonium(IV) and uranium(VI) from nitric acid solution to supercritical carbon dioxide containing tributylphosphate

Abstract Plutonium(IV) and uranium(VI) were extracted into supercritical CO2 fluid phase (SF-CO2) containing tributylphosphate (TBP) with equilibrium distribution ratios, D, e. g., DPu(IV) = 3.1 and DU(IV) = 2.0, for the extraction of 2 × 10−3 M Pu(IV) and U(VI) from 3 M HNO3 into SF-CO2 containing 0.3 M TBP at 60 °C and 15 MPa. A simple linear relation between D and density ϱ of CO2; long D = a log ϱ + b (a,b; constants), was observed, which was explained theoretically by the formulation of the extraction equilibrium taking into account the phase distribution behavior of extractant TBP and extracted species, i.e. Pu(IV)- and U(VI)-TBP complexes involved in the extraction reaction. The slopes a of the log D vs. log ϱ plots were −(1.6 ± 0.1) and −(2.7 ± 0.5) for the extraction of Pu(IV) and U(VI), respectively. The differences in D as well as the slope a between Pu(IV) and U(IV) make it possible to design the U and Pu separation method by which one can achieve an enhancement of the extraction efficiency and selectivity by tuning the operation pressure.

New Method for the Removal of Uranium from Solid Wastes with Supercritical CO2 Medium Containing HNO3-TBP Complex

This study aims at the development of a method for the decontamination of uranium from the solid wastes containing uranium oxides, UO 2 or U 3 O 8 , using supercritical CO 2 medium containing HNO 3 -TBP complex (TBP: tri-n-butylphosphate).

New Method for Synthesis of Strontium Titanate

A new method is presented for synthesizing strontium titanate. The reaction between strontium nitrate and meta-titanic acid or titanium dioxide (anatase or rutile) has been studied with use made of thermo-gravimetry and differential thermal analysis, and the compound produced was identified by X ray diffractometry. A mixture of strontium nitrate and meta-titanic acid is converted to strontium titanate at about 600°C by an apparently endothermic reaction. This process can be applied advantageously to the preparation of sources of radiation and heat that utilize radioactive strontium obtained from nuclear fission products.

Supercritical Carbon Dioxide Fluid Leaching (SFL) of Uranium from Solid Wastes Using HNO3-tributylphosphate (TBP) Complex as a Reactant

Supercritical carbon dioxide (CO2) leaching method (SFL), which is based on the efficient and selective dissolution of UO2 and U3O8 with supercritical CO2 containing HNO3-tributylphosphate (TBP) complex at 333 K and 15 - 20 MPa, has been developed for the removal and recovery of uranium from the solid waste contaminated by uranium oxides. The decontamination factor of UO2 or U3O8 of higher than 500 were attained by the recommended procedure, which was demonstrated using synthetic solid waste samples of a mixture of the uranium oxides and sea sand.