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In this study, simultaneous separation and recovery of Cs(I) and Sr(II) from nitric acid solution was investigated using a silica-based hybrid adsorbent. The adsorbent was prepared by successive impregnation and fixing of two supramolecular recognition agents namely, 1,3-[(2,4-diethylheptylethoxy)oxy]-2,4-crown-6-Calix[4]-arene(Calix[4]arene-R14) and 4',4' (5")-di(tert-butylcyclohexano)-18-crown-6, onto a silica-based polymer support(SiO2-P). Uptake properties, characterization, equilibrium kinetics, and dynamic adsorption properties of Cs(I) and Sr(II) were then assessed. Distribution coefficients (Kd) higher than 102 cm3/g for Cs(I) and Sr(II) were obtained using 3 M HNO3 at 298 K, and the Kd values decreased with increasing temperature. Adsorption kinetics and equilibrium studies fitted well with pseudo-second-order model and Redlich–Peterson isotherm model, respectively. The constant total organic carbon values in the aqueous phase were obtained after adding 10−3 ∼ 4 M HNO3. Results of the dyn...

The oxidation behavior of chromium and the corrosion behavior of austenitic stainless steel in boiling nitric acid solution containing highly concentrated nitrates were investigated using UV-visible spectroscopic measurements, Raman spectral measurements, immersion tests, and potentiodynamic polarization measurements. The oxidation rate measurement of chromium from Cr(III) to Cr(VI) was performed by 1 M boiling nitric acid solution containing each highly concentrated nitrates: Al(NO3)3, Nd(NO3)3, Ca(NO3)2, Mg(NO3)2, and NaNO3 as a simulant of uranium nitrate in uranium concentrator in reprocessing plants. As a result, the rate of chromium oxidation was different depending on the added nitrates even at the same nitric acid concentration. In addition, the oxidation rate of chromium was increased with increasing the calculated partial pressure of nitric acid in consideration of the hydration of cation of nitrates. Furthermore, the corrosion rate of type 310 stainless steel was accelerated by the solu...

We investigated the relationship between the corrosion of austenitic stainless steel (R-SUS304ULC) and the redox behavior of chromium in nitric acid solution under three conditions – boiling at atmospheric pressure, boiling at reduced pressure, and non-boiling – to evaluate the effects of the boiling phenomenon. In the Cr(III) oxidation rate measurement, about 20% of the Cr(III) was oxidized to Cr(VI) under atmospheric-pressure boiling at 384 K after 168 h. Under non-boiling conditions at 373 K, Cr(VI) was not observed. However, about 3% of Cr(III) oxidation was observed at 373 K with reduced-pressure boiling. Thermodynamic calculations showed that the abundance of Cr(VI) in boiling nitric acid was increased over that in non-boiling nitric acid, even at the same temperature. These results show that Cr(III) is more likely to oxidize under boiling conditions than non-boiling conditions. On the other hand, in the corrosion tests, we found that the apparent reduction rate of Cr(VI) as a result of corrosion of...

A crown ether loaded resin was prepared by successive impregnation and fixing the 4′,4′(5″)-di(tert-butylcyclohexano)-18-crown-6 (DtBuCH18C6) and its molecule modifier, 1-dodecanol, onto the porous silica/polymer composite support (SiO2-P particles). The characterization of DtBuCH18C6 loaded resin was examined by thermal gravimetry and differential thermal analysis and electron probe microanalysis. The adsorption behavior of Sr(II), Cs(I), Ru(III), Pd(II), La(III), Nd(III), Sm(III), Gd(III), Zr(IV), and Mo(VI) was investigated by the batch method. Furthermore, the column test for Sr (II) was performed. The batch experiments were carried out by varying the shaking times, HNO3 concentration, and initial concentration of metal ions. A relatively large K d value above 182 cm3/g for Sr(II) was obtained in the presence of 3 M HNO3. In contrast, the K d values of Cs(I), Ru(III), Pd(II), La(III), Nd(III), Sm(III), Gd(III), Zr(IV), and Mo(VI) were considerably lower than 10 cm3/g. The adsorption of Sr(II) was foun...

From a viewpoint of direct separation of trivalent minor actinides (MA: Am, Cm etc.) from fission products (FP) including rare earths (RE) in high level radioactive liquid waste, the authors have developed a simplified separation process using a single column packed with novel extraction adsorbents. Attention was paid to a new type of nitrogen-donor ligand, R-BTP (2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl)pyridine, R: alkyl group) as an extractant because it has higher extraction selectivity for Am(III) than RE(III). Since the R-BTP ligands show different properties such as adsorbability and stability when they have different alkyl groups, several R-BTP extraction adsorbents were prepared by impregnating the R-BTP ligands with different alkyl groups (isohexyl-, isoheptyl- and cyheptyl-BTP) into a porous silica/polymer composite support (SiO2-P particles). This work investigated: (1) fundamental properties of the synthesized R-BTP/SiO2-P adsorbents, (2) adsorption and desorption properties of Am and FP in nit...

Electrochemical studies on [UO2(DMF)5]2+, UO2(acac)2DMF, and UO2(salen)DMF (DMF=N, N-dimethylformamide, acac=acethylacetonate, and salen=N,N′-disalicylidene-ethylenediaminate) complexes in DMF containing tetrabutylammonium perchlorate as supporting electrolyte have been carried out by using cyclic voltammetry to compare the stabilities of the reduction products of U(Vi) complexes with unidentate or multidentate ligands. The [UO2(DMF)5]2+, UO2(acac)2DMF, and UO2(salen)DMF complexes were found to be quasi-reversibly reduced to U(V) species. The formal redox potentials (E°, vs. ferrocene/ferrocenium) for the U(Vi)/U(V) couple were determined to be -0.89 V for [UO2(DMF)5]2+, -1.47 V for UO2(acac)2DMF, and -1.67 V for UO2(salen)DMF. The U(V) species formed in the reduction of [UO2(DMF)5]2+ complex is not stable and further reduced to UO2, while those generated in the reduction of UO2(acac)2DMF and UO2(salen)DMF complexes can exist stably in DMF.

Electrochemical studies on [U(dmso)9]4+ and [UO2(dmso)5]2+ complexes in DMSO containing tetrabutylammonium perchlorate(TBAP) as supporting electrolyte have been carried out by using cyclic voltammetry(CV). A three electrode system was utilized, i.e., Pt working, Ag/Ag+ in TBAP/CH3CN reference, and Pt auxiliary electrodes. A ferrocene/ferrocenium (Fc/Fc+) couple was used as a reference redox system. Measurements of CV were carried out in the range of -0.025 to -2.025 V and -0.025 to -1.175 V for [U(dmso)9]4+ and [UO2(dmso)5]2+ complexes, respectively It was found that the [UO2(dmso)5]2+ complex is reduced quasi-reversibly to U(V) at around -1.0 V, and that the [U(dmso)9]4+ complex is reduced quasi-reversibly to U(III) at around -0.93 V and the resulting U(III) species is further reduced to U(0) irreversibly at around -1.7 V. The formal redox potentials(vs. Fc/Fc+) for U(VI)/U(V) and U(IV)/U(III) couples were determined to be -0.970 and -0.901 V, respectively Furthermore, in order to examine whether the [U(...

(2000). Electrochemical Study on Octakis(dimethyl sulfoxide)uranium(IV) Complex in Dimethyl Sulfoxide. Journal of Nuclear Science and Technology: Vol. 37, No. 11, pp. 999-1002.

The structural and kinetic studies of U(VI) complex with benzamidoxime (Hba) as ligand in CD3COCD3 have been studied by means of 1H and 13 C NMR. The Hba molecule was found to coordinate to UO2+ 2 in the form of anionic benzamidoximate (ba), and the number of ba coordinated to UO2+ 2 was determined to be 3 by analyzing the chemical shift of 13C NMR signal for Hba in the presence of UO2+ 2. The exchange rate constants (kex) of ba in [UO2(ba)3]- were determined by the NMR line-broadening method. The kinetic parameters were obtained as follows: kex (25°C)=1.3× 103 s-1, ΔH≠ =35.8±3.5kJ·mol-1, and ΔS≠=-65±13.7 J·K-1·mol-1. The UV-visible absorption spectra of solutions containing UO2+ 2 and Hba were also measured. The molar extinction coefficient of the complex was found to be extremely large compared with those of UO2(L)2+ 5 (L=unidentate oxygen donor ligands) complexes. This is due to the strong electron withdrawing of UO2+ 2 from Hba and suggests that an interaction between UO2+ 2 and Hba is very strong. Su...

The structure of uranyl nitrato complex with CMPO [n-Octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide] in solid state and in non-aqueous solvents without containing free CR/IPO has been studied by using IR spectrophotometer, 13C- and 31P-NMR. The carbonyl(vcO) and phosphoryl(vpO) stretching bands of coordinated CMPO were observed at lower wavenumber than the corresponding bands of free CMPO in both the states. The 13C and 31P peaks assigned to the carbonyl carbon and phosphoryl phosphine of coordinated CMPO was detected in the lower field than that of free CMPO. From these results, it was concluded that the uranyl nitrato complex with CMPO in both the states has the structure with two nitrate and one CMPO coordinated as bidentate in the equatorial plane of uranyl ion, i.e., UO2(NO3)2·CMPO. Furthermore, the electrochemical studies of UO2(NO3)2·CMPO complex in CH3CN have been carried out using cyclic and normal pulse voltammetric methods. It was found that the UO2(NO3)2·CMPO complex is reduced to ...

(1998). Preparation and Characterization of New Chelating Resin Containing n-Octyl(phenyl)-N, N-diisobutylcarbamoylmethylphosphine Oxide (CMPO) as a Functional Group. Journal of Nuclear Science and Technology: Vol. 35, No. 2, pp. 163-165.