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Developing the conventional separation method by which minor actinides (MA) such as Am and Cm are separated from lanthanides is important with respect to their recovery and isolation from high-level radioactive waste (HLW). Owing to the chemical behavior of trivalent lanthanide and actinide ions with similar ionic radii, realizing this separation is still challenging. All lanthanides, Am, and Cm can be extracted using diglycolamide (DGA) extractants, and relatively high An/Ln separation efficiencies have been obtained using diethylenetriamine-N,N’,N”-triacetic acid-N,N”-bis(diethylacetamide) (DTBA). Referring to our previous study, where a good separation and a MA recovery of approximately 95% with the co-existence of 5% Nd in the aqueous phase were observed. To improve these results as well as the separation conditions, under modified conditions by adding lactic acid to stabilize pH, the recovery rates observed were as follows: 97.1% for average Ln metals with the co-existence of 1.59% Am in the organic phase and 98.4% for Am with the co-existence of 2.95% Ln in the aqueous phase.

The extraction of lanthanide ion between an aqueous solution and a thermosensitive polymer gel, N-isopropylaciylamide (NIPA) gels copolymerized with 2-methaciyloyl-oxyethylacidphosphate (MR), was studied. This polymer gel shows a phase transition phenomena. The phase transition involves the structural change of the gel from swelling to shrinking with increasing temperature. The extraction equilibrium of lanthanide ions, La(III) and Sm(III), in an aqueous solution was measured batchwise. The distribution ratio, Kd, decreased with decreasing temperature. Lanthanide ions can be extracted at the shrinking state and then released by a conformational change of the polymer network during swelling. The temperature-dependence of Kd was more clear and sharper as the content of NIPA in the gel was increased. The difference of Kd between swelling and shrinking states tended to be larger as the content of crosslinker was decreased. The extraction mechanism of lanthanide ion, which was evaluated from the pH-de...

The extraction separation of Cd(II) and Zn(II) with an organodithiophosphorus extractant, bis(2,4,4‐trimethylpentyl)dithiophosphinic acid (Cyanex301), and a hexadentate ligand containing six nitrogen donors, N,N,N′,N′‐tetrakis(2‐pyridylmethyl)ethylenediamine (TPEN), was studied. When TPEN in amounts equimolar with divalent metal was added in the aqueous phase, most of TPEN molecules (>99%) were complexed with these divalent metals in the pH range above 2. Then, the extraction of Cd with Cyanex301 was little affected by the addition of TPEN, however, that of Zn was depressed remarkably and the extraction constant of Zn was reduced to less than 10−4 times that without TPEN. TPEN acts as a strong masking agent only for Zinc. The binary extraction tests of Cd and Zn were carried out under the conditions that the initial concentration of Cyanex301 was 0.0025 mol/L and TPEN in amounts equimolar with divalent metals was added in the aqueous phase. The separation factor of Cd was evaluated as 1000 at pH ...

The synergistic extraction with N,N,N′,N′‐tetrakis(2‐methylpyridyl)‐ethylenediamine (TPEN) and di(2‐ethylhexyl)phosphoric acid (D2EHPA) in 1‐octanol demonstrates good selectivity for Am(III) over Ln(III) in solutions containing macroscopic concentrations of the latter. The maximum apparent separation factor, which is defined as the ratio of the distribution ratio of Am(III) to that of Eu(III), is ca. 80 at the molar ratio of D2EHPA to TPEN, 2.0. This ratio corresponds to the result of the spectrophotometric titration, which indicates that TPEN and D2EHPA associate in 1‐octanol and two D2EHPA molecules coordinate to Eu(III)–TPEN complex, [Eu(TPEN)]3+. In the present study, association of D2EHPA and TPEN is one of the most important factors for the synergistic extraction and the complexation of TPEN and D2EHPA with Eu(III).

A poly-N-isopropylacrylamide (poly-NIPA) gel crosslinked with 2,6-di(3-vinylbenzyl-1,2,4-triazol-5-yl)pyridine (BTP) was prepared by the ultrasonic polymerization technique and the extraction of Cd(II) from an aqueous nitrate solution was tested. The BTP-NIPA gel showed phase transition phenomena, in which the gel was shrunken at temperature higher than the phase transition temperature (304 K) and swollen at less than 304 K. The extraction capacity of Cd(II) was affected by the phase transition phenomena and was decreased by the structural change of gel from the shrinking state to the swelling one. This is attributable to the configurational change of nitrogen donors in BTP, which occurs by the structural change of gel. When the extraction mechanism is assumed as the formation of a complex ion, Cd(BTP)2+ and its nitrate complex, Cd(BTP)(NO3)+ at both the shrinking and swelling states, the equilibrium constant for the complex formation of Cd(BTP)2+ at the shrinking state corresponds to about 2.5 times of t...

A mathematical model to predict the breakthrough curve of metal ion on an extraction chromatographic column was proposed. This model, which is the extension of that proposed in the previous paper (12), consists of the mass transfer equation of metal ion into a polymer gel impregnated with an extractant and the mass balance equation of chromatographic column. SDB (styrene-divinylbenzene copolymer) gels impregnated with CMP (dihexyl-N,N'-diethylcarbamoylmethylphosphonate), CMPO (octyl(phenyl)N,N'-diisobutylcarbamoylmethylphosphine oxide) and the equimolar mixture of CMP and CMPO were prepared. The column experiments for the extraction of Ce(III) from an aqueous solution containing nitrate ion were carried out. The predicted breakthrough curves of Ce(III) for the gels impregnated with CMP and the mixture of CMP and CMPO were in good agreement with the experimental ones. That for the gel impregnated with CMPO, however, overestimated the experimental data. This is due to adhesion among gel particles w...

A mathematical model to predict the extraction behavior of metal ion between a polymer gel and an aqueous solution was proposed. It consists of the Flory-Huggins formula for evaluating thermodynamically the physico-chemical properties of polymer gel, the modified Stokes-Einstein equation to evaluate the mass transfer rate of metal ion into polymer gel and the equation to evaluate the extraction equilibrium. The extraction of lanthanide elements, Nd(III), Sm(III) and Gd(III), from an aqueous solution containing nitrate ion was carried out by the use of SDB (styrene-divinylbenzene copolymer) gel swollen with a bidentate organophosphorus compound, CMP (dihexyl-N,N-diethylcarbamoylmethylphosphonate). The binary extraction and the effect of the crosslinking degree of SDB gel on the extraction rate were examined. These experimental results were in agreement with the predictions calculated by the proposed model. It was confirmed that the extraction behavior of lanthanide ions into- the SDB gel was predi...