Shoichi Tachimori

THE NOVEL EXTRACTANTS, DIGLYCOLAMIDES, FOR THE EXTRACTION OF LANTHANIDES AND ACTINIDES IN HNO3–n-DODECANE SYSTEM

The novel extractants, six diglycolamides synthesized in our laboratory, were investigated for actinide extraction from nitric acid into n-dodecane. The dependence of the distribution coefficients of Eu(III) and Am(III) on the length of alkyl chain in the extractants was examined. Among the diglycolamides studied, N,N,N′,N′-tetraoctyl-3-oxapentanediamide (TOOPDA) and N,N,N′,N′-tetradecyl-3-oxapentanediamide (TDOPDA) showed a sufficient solubility in n-dodecane, due to their appropriate lipophilicity modified by increasing the length of the alkyl chain attached to amidic N atoms. The distribution coefficients, D M, of actinides obtained by TOOPDA increased with an increase in HNO3 concentration. The number of diglycolamide molecules coordinated to the actinide ions was estimated to be three for Th(IV), U(VI), Pu(IV), and four for Am(III) and Cm(III) by slope analysis. The order of D M for the actinides at high nitric acid concentrations is An(III), An(IV) > An(VI) > An(V) and that for lanthanides, heavier > lighter. It is concluded that TOOPDA diluted in n-dodecane can extract both actinides and lanthanides completely from aqueous HNO3 solution.

EXTRACTION OF ACTINIDES(III), (IV), (V), (VI), AND LANTHANIDES(III) BY STRUCTURALLY TAILORED DIAMIDES

Eleven diamide extractants having the different backbones were synthesized and their extractability for lanthanides(III) and actinides(III), (IV), (V) and (VI) were measured and compared. The diamides investigated include (CH2) n ─(CONR1,R2)2, (n = 0, 1, 2, 3), O─((CH2) n′─CONR1,R2)2, S─((CH2) n″─CONR1,R2)2, and SS─((CH2)n′″─CONR1,R2)2, (n′, n″, n′″ = 1, 2). The diglycolamide introducing an ether oxygen into the main frame, O─(CH2─CONR1,R2)2, exhibited the highest extractability for An(III), (IV) and (VI), as compared with the other bidentate diamides. It is clear from the present results that the thiadiglycolamide, TDGA, which substitutes ether sulfur atom for oxygen in DGA molecule, also enhances the extraction of actinides. The lanthanide pattern, the distribution ratios versus the atomic number, by diglycolamide in HNO3-n-dodecane system exhibited a gradual increase of distribution ratio with increase in the atomic number, the opposite trend to that obtained by the other diamides.

MODIFICATION OF TODGA- n -DODECANE SOLVENT WITH A MONOAMIDE FOR HIGH LOADING OF LANTHANIDES(III) AND ACTINIDES(III)

ABSTRACT N,N,N  ′,N  ′-Tetraoctyl-3-oxapentanediamide (TODGA) in n-dodecane solvent was studied to clarify the characteristics of third phase formation in extraction of lanthanides(III) and to modify the solvent. The loading capacity of the solvent was found to be dependent not only on the aqueous acidity and the temperature but also on molecular size of alkane solvent and kinds of aqueous anions. The loading capacity of 0.1 M TODGA-n-dodecane was 0.008 M Nd(III) with an aqueous phase of 3 M HNO3. Addition of N,N,-dihexyloctanamide (DHOA) of more than 0.5 M to the solvent eliminated the third phase in the extraction of Nd(III). The modified solvent of 0.1 M or 0.2 M TODGA with 1 M DHOA exhibited a satisfactorily high metal loading and slightly lower extractability for Nd(III) and moderately higher extraction of HNO3 than neat TODGA.

Studies on hydrolysis and radiolysis of N, N, N', N'-tetraoctyl-3-oxapentane-1,5-diamide

Summary Hydrolytic and radiolytic stabilities of a promising extractant, N,N,N′,N′-tetraoctyl-3-oxapentane-1,5-diamide (TODGA), for actinides in high-level radioactive liquid waste from nuclear fuel reprocessing were investigated in air at room temperature. Hydrolysis by nitric acid was not observed, whereas radiolysis by gamma irradiation was notably observed. The radiolysis study showed that an amide-bond, an ether-bond, and a bond adjacent to the ether-bond tended to be broken by gamma irradiation, and dioctylamine and various N,N-dioctylmonoamides were identified as the main degradation products by GC/MS and NMR analyses. The G-value for degradation of neat TODGA was 8.5 ± 0.9, which value was higher than those for N,N′-dioctyl-N,N′-dimethyl-2-(3′-oxapentadecyl)-propane-1,3-diamide and N,N-dioctylhexanamide. It was obvious that n-dodecane, which was used for a diluent, had a sensitization effect on the radiolysis of these amidic extractants. In a TODGA–n-dodecane–HNO3 system, the coexisting nitric acid showed an insignificant effect on the radiolysis of TODGA.

STUDY ON THE EXTRACTION OF TRIVALENT LANTHANIDE IONS WITH N, N'-DIMETHYL-N, N'-DIPHENYL-MALONAMIDE AND -DIGLYCOLAMIDE

The extraction of trivalent lanthanide (Ln(III) ions with two diamides: (1) N,N′-dimethyl-N,N′-diphenyl-malonamide (MA) and (2) N,N′-dimethyl-N,N′-diphenyl-diglycolamide (DGA) from nitric acid solution was studied. Chemical bond properties of extracted complexes were investigated by UV-VIS and FT-IR spectroscopies. The chemical bond strength between Ln(III) ions and the ligands in extracted complexes was closely related with the magnitude of the distribution ratios of Ln(III) ions: the extracted complex having a stronger bond between Ln(III) ion and the ligand showed a higher magnitude of the distribution ratio of Ln(III) ion.

Extraction Studies of Lanthanide(III) Ions with N,N′‐Dimethyl‐N,N′‐diphenylpyridine‐2,6‐dicarboxyamide (DMDPhPDA) from Nitric Acid Solutions

Abstract The new diamide compound, N,N′‐dimethyl‐N,N′‐diphenylpyridine‐2,6‐dicarboxyamide (DMDPhPDA), was synthesized and the distribution ratios of lanthanides from 1 to 5 M nitric acid solutions into DMDPhPDA CHCl3 solution were determined. The extraction mechanism of lanthanide with DMDPhPDA was discussed based on the slope analysis of acid and ligand concentration dependencies and the variation of distribution ratio along the lanthanides series. The number of DMDPhPDA molecules in extracted complexes increase from 3 for lighter lanthanides to 4 for heavier lanthanides. From the previous EXAFS study of a complex similar in structure, Ln(III) would form an inner‐sphere complex with the two DMDPhPDA molecules and an outer‐sphere complex with the third and/or fourth DMDPhPDA molecules in addition to an inner‐sphere complex. Nitric acid concentration has more influence on the distribution ratio and the difference of distribution ratio among lanthanides than the ligand concentration.

Study of solvent extraction of lanthanide(III) with tetra(p-)tolylmethylene diphosphine dioxide (TTMDPDO) from a nitric acid solution

Distribution ratios (D,) of lanthanides with tetra(p-)tolylmethylene diphosphine dioxide (TTMDPDO) f rom nitric acid solutions were determined. D, values increased linearly in the extraction from 1 to 3 mol dm · nitric acid solutions, the maximum being about 3 mol d m 1 . After 3 mol dm 1 nitric acid, the distribution ratios decreased on an increase in nitric acid due to complexation of the extractant with nitric acid. The decrease patterns in the distribution ratio were (1) very sharp in light lanthanides ( L a ~ S m ) and (2) moderate in middle-to-heavy ones ( E u ~ L u ) . From the slope analysis of TTMDPDO dependencies, the number of TTMDPDO coordinating to the lanthanides in the extraction complexes were 3 or 4, light lanthanide preferentially complexed with 4 ligands and heavy ones with 3 ligands. The difference between light and heavy lanthanides in the extraction behavior, therefore, would be due to the type of complex which each lanthanide form. Distribution patterns for the lanthanides in the 1 mol d m 3 nitric acid solution showed a tendency to decrease according to the atomic number, having a tetrad pattern. The tetrad effect was observed more strongly in the light lanthanides rather than the heavy ones. Infrared studies on the phosphoryl group stretching indicated that the light lanthanides complexed with TTMDPDO much more weakly than the heavy ones. From these results, the bonds between the heavier lanthanides and TTMDPDO are more covalent than those of the lighter ones.

Extraction of Lanthanides with N,N′‐Dimethyl‐N,N′‐diphenyl‐malonamide and ‐3,6‐dioxaoctanediamide

Abstract The extraction properties of the trivalent lanthanides (Ln(III)) with the bidentate N,N′‐dimethyl‐N,N′‐diphenyl‐malonamide (MA) and the tetradentate N,N′‐dimethyl‐N,N′‐diphenyl‐3,6‐dioxaoctanediamide (DOODA) were investigated. These diamides formed by coupling two amide groups with methylene and/or ether groups are bidentate for the MA and tetradentate for the DOODA. By adding a previous data regarding the tridentate N,N′‐dimethyl‐N,N′‐diphenyl‐diglycolamide (DGA), these extraction results enabled us systematically study an effect of number of oxygen donor on its extraction behavior of Ln(III). The change in the distribution ratios (Ds) of Lu(III) with an increase in the HNO3 concentration is greater than that of La(III) in both the MA and DOODA systems. Therefore, the relationship between the D and atomic number, i.e., the lanthanide pattern, changes with the HNO3 concentration: the Ds decrease with an increasing atomic number at lower HNO3 concentrations. The Ds of the lighter Ln(III) are similar to the Ds of the heavier Ln(III) at higher HNO3 concentrations. The number of the extractant in the extracted species for La(III) and Lu(III) obtained from slope analysis at 4 M HNO3 in the MA system are about 3, while those in the DOODA system are quite different, i.e., 2 for La(III) and 1.5–3 for Lu(III). The comparison of the extractability of Ln(III) by MA, DOODA, and DGA shows that the magnitude of the Ds is in the sequence of MA < DOODA ≪ DGA. This suggests the introduction of one ether oxygen atom to the principal chain in the diamides leads to a good extractability for the Ln(III) from HNO3 solution.

Solvent extraction of alkaline earth metal ions by diglycolic amides from nitric acid solutions

Abstract N,N,N′,N′‐Tetraoctyl‐3‐oxapentane diamide (TODGA) and its homologues were shown to be usefully applied to the extraction of divalent alkaline earth metal: M(II) ions from aqueous solutions of high nitric acid concentration, specifically around 3 M. The stoichiometry of the extracted Sr(II)‐DGA species was found to depend mainly on the concentration of nitric acid and molecular structure of DGA. The degree of extraction of M(II) by TODGA decreases in the order of Ca(II) > Sr(II) > Ba(II).

Evaluation of the Altitude Variation of the Cosmic-ray Induced Environmental Neutrons in the Mt. Fuji Area

To assess the natural background neutron dose rate in Japan, a series of measurements of the cosmic-ray induced neutron energy spectra and the neutron dose rates were carried out in the Mt. Fuji area (altitude: 40-3,700m) by means of a Bonner multi-sphere neutron spectrometer (Bonner Spectrometer: BS) and a commercially available neutron rem-counter. The following results were obtained: 1. The neutron energy spectra at each altitude were almost the same in their shapes. 2. The total neutron fluence rate and the ambient dose equivalent H*(10) obtained by BS at sea level were estimated to be about 0.0075±0.00029cm−2.s−1 and 6.4+0.25nSv.h−1, respectively. 3. It was confirmed that the neutron fluence rate and the dose rate varied with the altitude according to an exponential law, ~ exp(αZ), where α=0.00071±0.00002m−1 for the fluence rate and α=0.00070±0.00001 m−1 for the dose rate, respectively. These α-values were smaller than those obtained at high geomagnetic latitudes in other studies.