Authors:Y. Takahashi, Y. Minai, T. Kimura, and T. Tominaga
Distribution of trace amount of Eu(III), or Am(III), in the aqueous/solid system containing humic acid and kaolinite, or montmorillonite,
was studied by batch experiments. Humic acid was also adsorbed on the clay minerals and its adsorption isotherm can be regarded
as a Langmuir type. It is shown that Eu(III), or Am(III), exists as humate complex either in the aqueous or on solid phase
in the system including kaolinite, or montmorillonite. These results suggest that the organic-inorganic complex like clay
minerals coated with humic substances is important as metal reservoir in the environment.
Solid-state Ln–C8H7O3 compounds, where Ln stands for Eu(III) and Gd(III) and C8H7O3 is 3-methoxybenzoate, have been synthesized. Simultaneous thermogravimetry and differential thermal analysis (TG-DTA), differential
scanning calorimetry (DSC), X-ray powder diffractometry, infrared spectroscopy, elemental analysis and complexometry were
used to characterize and to study the thermal behaviour of these compounds. The results led to information about the composition,
dehydration, thermal stability and decomposition of the isolated compounds.
Organic substances present in radioactive waste lower the sorption of metal ions at the high pH in cement matrices and, hence,
enhance their possible migration. The aim of this study was to develop a method to compare organic substances or their degradation
products with respect to what extent they affect metal sorption. Batch sorption studies were performed with cement or TiO2 as solid phase and Eu(III) as a model element for trivalent lanthanides and actinides at pH 12.5 (representative of a cement
waste matrix during the first approximately 100,000 years). Different kinds of ligands were studied in a broad concentration
range, e.g., organic acids, cement additives, cleaning agents and degradation products from ion-exchange resin.
The distribution of 137Cs, 152Eu, 238U, and 85Sr in a solid/aqueous system (poly(methyl acrylate)/phosphate/composite in contact with groundwater, was investigated using
γ-Spectrometry and flourometry. The results were compared with earlier results with mineral phosphate in the solid phase.
The effect of contact time, pH and the concentration of concurrent element were studied. The ability of the prepared polymer
composites to keep the studied radioisotopes in the solid phase is much higher than mineral phosphate. The used polymer composites
have been prepared consisting of natural phosphate powder and the monomer methyl acrylate using gamma irradiation. The yield
of polymerization was followed up with respect to the irradiation dose using thermogravimetric analyzer (TGA). A thermomechanical
analyzer (TMA) was used to locate the area of the glass transition temperatures (Tg) using the mode with alternative variable force; the mode with constant force was used to determine the Tg of the pure polymer and the polymer composite prepared at the same irradiation dose. The Tg of the pure poly(methyl acrylate) is 13 ± 3 °C, and the Tg of poly(methyl acrylate)/phosphate/composites is 8 ± 3 °C. The Tg were also determined using the DSC technique, and similar values were found.
The following extraction systems have been studied: (Ce3++Eu3+) (NO3)-(EDTA, DCTA, DTPA)/TBP in n-alkane and (Ce3++Eu3+)(NO3)/DEHPA in n-alkane at concentration ratios as follows: [Ce3+]=trace –1 mol·dm–3, [Eu3+]=trace –0.1 mol·dm–3. [TBP]=(0.183–1.83) mol·dm–3, [DEHPA]=(5·10–3–0.1) mol·dm–3, [(H, Na)NO3]=(0.1–6) mol·dm–3, [Eu3+]: [EDTA, DCTA, DTPA]=11–110. The initial concentration of Eu3+ in aqueous phase in the extraction system containing a mixture of Ce3+ and Eu3+ was trace, 1% and 10% compared with the Ce3+ concentration. The distribution of the elements between the phases was observed radiometrically using141Ce,152Eu and154Eu. The results are documented by the distribution ratios DCe, DEu and separation factor =DEu/DCe as functions of variable parameters of the systems.
Synergic extraction of trivalent Eu, Gd and Am from aqueous perchlorate medium has been studied using mixtures of thenoyltrifluoroacetone (HTTA) and 15-crown-5 or 18-crown-6 (CE) in chloroform at (25±1) °C. Slope analysis of the extraction results indicated a general formula of M(TTA)3·(CE)2 for the extracted species. The stability order took the sequence Eu(TTA)3·(CE)2>Am(TTA)3)·(CE)2>>Gd(TTA)3·(CE)2 with 15C5 and Am(TTA)3·(CE)2>Eu(TTA)3·(CE)2>Gd(TTA)3·(CE)2 with 18C6. The synergic factors, extracton constants and formation constants of the extracted species were determined and discussed in terms of the correspondence between cavity size of the crown ethers and ionic crystal radii.
The extraction behavior of Sm(III), Eu(III) and Dy(III) with 1-nitroso-2-naphthol (HA) and trioctylphosphine oxide (TOPO) in methyl isobutyl ketone (MIBK) from aqueous NaClO4 solutions in the pH range 4–9 at 0.1M ionic strength has been studied. The equilibrium concentrations of Sm and Dy were measured using their short-lived neutron activation products,155Sm and165mDy, respectively. In the case of Eu, the concentrations were assayed through the152,154Eu radiotracer. The distribution ratios of these elements were determined as a function of pH, 1-nitroso-2-naphthol and TOPO concentrations. The extractions of Sm, Eu and Dy were found to be quantitative with MIBK solutions in the pH range 5.9–7.5, 5.6–7.5 and 5.8–7.5, respectively. Quantitative extraction of Eu was also obtained between pH 5.8 and 8.8 with chloroform solutions. The results show that these lanthanides (Ln) are extracted as LnA3 chelates with 1-nitroso-2-naphthol alone, and in the presence of TOPO as LnA3(TOPO) and LnA3(TOPO)2 adducts. The extraction constants and the adduct formation constants of these complexes have been calculated.
Authors:W. Dembiński, Z. Janiszewski, and R. Fiedler
The151/153Eu isotope effects were investigated for the lignad exchange reaction between Eu(III) ions in the extraction system: [Eu(III),di(2-ethylhexyl)
phosphoric acid]org↔[Eu(III), H+A−(A−=Cl−,NO
)]aq. It was observed that the heavy isotope153Eu was preferentially fractionated into the organic phase. The following values of the unit separation gains, ε=ln(q), were
found: 7.3·10−5 for Cl−, 13.0·10−5 for NO
, and 9.4·10−5 for SO
. The direction of the effect was opposite, and its absolute value was about one order of magnitude lower, in respect to the
effect observed in the redox exchange, Eu(II)↔Eu(III), in a similar extraction system.
Temperature effect on the synergic extraction of Eu(III) by thenoyltrifluoroacetone (HTTA) in the presence of 2,2-bipyridyl(bipyr)
and 1,10-phenanthroline (phen) from sodium acetate buffer solution at pH 4.20 has been investigated. Extractions were carried
out at 15, 25, and 35°C. It was observed that the increasing temperature favours the extraction of Eu(III) by HTTA alone while
the reverse is true for synergic extractions. The extraction data indicate the formation of synergic adducts containing only
one molecule of the bidentate amine i.e. Eu(TTA)3. B where B=bipyr or phen. The synergic reaction is favoured by the enthalpy changes alone. Thermodynamic parameters suggest
a mechanism for the synergic extraction which involves complex formation with an increase or expansion of the coordination
number of the central metal atom. Larger synergic and enthalpy changes observed for phen as compared to bipyr are probably
due to the cis position of its N-atoms readily available for chelate ring formation.
Authors:Emanuel Makrlík, P. Vaňura, and P. Selucký
From extraction experiments and γ-activity measurements, the extraction constants corresponding to the general equilibrium Eu3+(aq) + 3A−(aq) + L(nb) ⇔ EuL3+(nb) + 3A−(nb) taking part in the two-phase water–nitrobenzene system (A− = CF3SO3−; L = p-tert-butylcalixarene, p-tert-butylcalixarene; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Further, the stability constants of the
EuL3+ complexes in nitrobenzene saturated with water were calculated for a temperature of 25 °C as log βnb(EuL3+) = 6.4 ± 0.1 (L = p-tert-butylcalixarene) and log βnb(EuL3+) = 11.3 ± 0.1 (L = p-tert-butylcalixarene).