Ionic liquid modified silica gel for the sorption of americium(III) and europium(III) from dilute nitric acid medium

The imidazolium bis(2-ethylhexyl) phosphate moiety was chemically attached on silica gel by chemical modification. The resulting product ([SG-Im]⁺ [DEHP]^?) was characterized by FT-IR spectroscopy, thermogravimetry and elemental analysis. The sorption behavior of Am(III) and Eu(III) on [SG-Im]⁺ [DEHP]^? was studied from dilute nitric acid medium for the separation of Am(III) and Eu(III) from aqueous waste. The effect of time, concentrations of nitric acid and europium in aqueous phase on the distribution coefficient (K _d) was studied. The study indicated the possibility of using modified silica for the separation of Eu(III) from Am(III) with high separation factors (>50 at 0.1 M HNO₃).     

Extraction of Am(III) by mixture of dihexyl N,N-diethylcarbamoylmethyl phosphonate and tributyl phosphate in benzene from nitric acid solutions

Extraction of Am(III) by dihexyl N,N-diethylcarbamoylmethyl phosphonate (CMP) in benzene from nitric acid solutions (pH 2.0 to 6.0M) has been studied. High extraction of Am(III) by CMP from 2–3M HNO₃ was observed. The species extracted was found to be Am(NO₃)₃·3CMP. The extraction was also done with mixtures of CMP+TBP and CMP+TOPO, where mixed species were extracted in the organic phase. The back-extraction experiments gave an efficient back-extraction of Am(III) by pH 2.0 (HNO₃) from the loaded CMP+TBP phase but a poor back-extraction from the loaded CMP+TOPO phase. The loading of Nd(III) by mixture of CMP and TBP was 50% of the CMP concentrations at a total Nd(III) concentration of 0.182M. The thermodynamic parameters of Am(III) extraction by a mixture of CMP and TBP were evaluated by temperature variation method, which suggests that the two-phase reaction is stabilized by enthalpy and opposed by entropy.     

Some parameters affecting the extraction chromatographic performance of TBP impregnated macroporous XAD-4 columns for Am(III)−Eu(III) separations

TBP impregnated macroporous styrene-divinylbenzene XAD-4 polymer was employed as the stationary phase in extraction chromatography of Eu(III) and Am(III). Parameters affecting the performance (HETP) of the chromatographic column were investigated. These include the effect of flow rate, TBP loading, aqueous nitrate concentration, and particle size. One striking result obtained is that the column performance improves as the TBP loading increases.     

Sorption behavior of Am(III) onto granite

Sorption behavior of Am(III) onto granite was investigated. The distribution coefficient (K _d ) of Am(III) onto granite was determined in the solution of which pH was ranged from 2.9 to 11.4 and ionic strength was set at 10⁻² and 10⁻¹. TheK _d values were found to increase with increasing pH and with decreasing ionic strength. The obtained data were successfully analyzed by applying an electrical double layer model. The optimum parameter values of the double layer electrostatics and adsorption reactions were obtained, and the selective adsorption behavior of Am(III) onto the granite was discussed.     

The interaction between trivalent 4f and 5f-block elements and thiocyanate ion

The formation constants of thiocyanate complexes of Eu(III) and Am(III) in trace concentrations were investigated in mixed solvent (CH₃OH+H₂O) solutions of different ionic strength. Furthermore, in paper electrophoresis, the moving velocities of the species of Eu(III) and Am(III) were investigated in 1.1M (H, Na)(SCN, ClO₄) mixed solvent (CH₃OH-H₂O) solutions. The results showed that the difference between the velocities of Eu(III) and Am(III) is explained by the difference of the mean charges calculated by the formation constants of thiocyanate complexes of Eu(III) and Am(III) in the solution.     

Uptake of actinides and lanthanides from nitric acid by dihexyl-N,N-diethylcarbamoylmethylphosphonate adsorbed on chromosorb

Batchwise uptake of Am(III), Pm(III), Eu(III), U(VI) and Pu(IV) by dihexyl-N,N-diethylcarbamoylmethylphosphonate (CMP) adsorbed on chromosorb (CAC) at nitric acid concentrations between 0.01 to 6.0M has been studied. The difference between the uptake behavior of Pu(IV) as compared to other actinides and lanthanides is discussed. The Am(III) and U(VI) species taken up on CAC were found to be Am(NO₃)₃·3CMP and UO₂(NO₃)₂·2CMP, respectively. The equilibrium constants for the formation of these species have been evaluated and compared with those of similar species formed in liquid-liquid extraction. Batchwise loading of Pm(III) on CAC from 3.0M HNO₃ has also been studied.     

Chromatographic separation of americium from europium using bis-2,6-(5,6,7,8-tetrahydro-5,9,9-trimethyl-5,8-methano-1,2,4-benzotriazin-3-yl) pyridine

The separation of americium(III) from europium(III) was achieved utilizing a bis-2,6-(5,6,7,8-tetrahydro-5,9,9-trimethyl-5,8-methano-1,2,4-benzotriazin-3-yl) pyridine (CA-BTP) chromatographic resin. The extraction chromatographic materials were prepared using various concentrations of CA-BTP. This new, hydrolytically stable extractant was impregnated on an inert polymeric support at 40% loading. The uptake of Am(III) and Eu(III) by this material from 0.1 to 4.0 M aqueous HNO₃ solutions was measured. The resulting dry weight distribution ratios, D _w , indicated a strong preference for Am(III) with little affinity for Eu(III). These results are similar to recently reported solvent extraction studies indicating a maximum uptake of Am(III) in the 0.5–1.0 M HNO₃ range. The resin preparation, performance, and characterization of the Am/Eu separation are reported herein.

     

Extraction separation of Am(III) and Eu(III) using divalent quadridentate Schiff bases-bis-salicylaldehyde ethylenediamine

For the selective extraction of Am(III) and Eu(III), quadridentate divalent phenolic Schiff bases-bis-salicylaldehyde ethylenediamine (H₂salen) was investigated as a kind of extractant. The influences of alkaline cation, inorganic anion, ionic strength, pH and the concentration of H₂salen on the distribution ratio of Am(III) and Eu(III) were investigated in detail. As a result, Am(III) and Eu(III) made anionic 1:1 complexes with the ligand (H₂salen) and could be extracted into nitrobenzene as ion-pairs with a suitable monovalent counter anion in the aqueous solution, the extracted species were possibly of the type Am(H₂salen) Eu(salen)Cl and Eu(H₂salen)Cl₃, respectively. The extractability of Eu(III) was significantly stronger than that of Am(III) and the maximum separation factor, SF_(Am/Eu), was 96 at pH 4.0. The results indicated that H₂salen had good selectivity for Am(III) and Eu(III).     

Density functional theory insight into Eu(III) and Am(III) complexes with two 2,6-dicarboxypyridine diamide-type ligands

Extraction complexes of Eu(III) and Am(III) with two 2,6-dicarboxypyridine diamide-type ligands L–A and L–B (Fig. 1) are studied by density functional theory (DFT). At both B3LYP/6-31G(d)/RECP and MP2/6-31G(d)/RECP levels of theory, the geometrical optimizations of the structures of the complexes can achieve the same accuracy and obtain the same geometrical configuration. At the B3LYP/6-311G(d,p)/RECP level of theory Eu³⁺ and Am³⁺ prefer to form [ML]³⁺ complexes under the solvation conditions, and the Am(III) complexes with L–A are more stable than the corresponding Eu(III) complexes. In the system with the ligand L–B, both [ML]³⁺ and [ML(NO₃)₃] species are very unstable.     

Adsorption and desorption of Am(III) on calcareous soil and its parent material

Summary The adsorption and desorption of Am(III) on a calcareous soil (sierozem) and its parent material (loess) were studied by batch technique. The molarities of the Am(III) aqueous solutions were less than 5 ^. 10^-9 mol/l. High adsorbability was found of Am(III) on the calcareous soil and its parent material. In order to decrease the adsorption and, hence, to investigate the adsorption characteristics properly, stable Eu³⁺ as hold back carrier and analogue was added to the aqueous solution. The relative contributions of CaCO₃, organic matter (OM) to the Am(III) adsorption on calcareous soil and its parent material were investigated. The adsorption and desorption isotherms of Am(III) on untreated soil and loess and the three kinds of treated soils and three kinds of treated loesses to remove CaCO₃, OM and both CaCO₃ and OM were determined, respectively. It was found that all isotherms were linear, the average distribution coefficients (K^-_d) for the untreated soil and for the untreated loess were almost equal, while there was an obvious difference between the values of the average distribution coefficients (K^-_d) for the treated soil and the treated loess to remove CaCO₃ or OM. The adsorption-desorption hysteresis on the untreated and treated soils and loesses actually occurred and there was an obvious difference between the hysteresis coefficients on both the corresponding treated soil and loess. It can be concluded that the adsorbability of Am(III) on calcareous soil is similar to that on its parent material, and that the contributions of CaCO₃ and OM to the Am(III) adsorption by the untreated soil are different from those by the untreated parent material.     

Kinetics and mechanism of distribution of Am(III) and Eu(III) between thenoyltrifluoroacetone-triphenylarsine oxide mixture in chloroform and aqueous nitrate medium

The kinetics of distribution of Am(III) and Eu(III) between thenoyltrifluoroacetone (HTTA) and triphenylarsine oxide (Ph₃AsO) mixture in chloroform and aqueous nitrate medium has been investigated using a stirred Lewis cell at ionic strength of 0.1M. The effect of the concentration of HTTA, Ph₃AsO, H⁺ and NO ₃ ^– on the rate of distribution of Am(III) and Eu(III) was studied. The results were interpreted by reaction mechanisms where the rate-determining steps are the parallel reactions of Am(OH)²⁺ or Eu(OH)²⁺ with one HTTA molecule and one Ph₃AsO molecule in the aqueous medium. The values at 25 °C of the rate constantk _HLL (HL=HTTA andL=Ph₃AsO) are 1.6±0.3·10⁶M^–2·s^–1 and 2.3±±0.3·10⁸M^–2·s^–1 for Am(III) and Eu(III), respectively.     

Use of Polyethylene Glycol (PEG) Based Aqueous Biphasic System (ABS) for the Extraction of Pu(IV), Pu(VI) and Am(III) with 18-Crown-6: A Thermodynamic Study

Extraction of Pu(IV), Pu(VI) and Am(III) using PEG-2000/ (NH₄)₂SO₄ (40% w/w of each) ABS with 18-crown-6 (18-C-6) as the extractant was studied at four fixed temperatures in the range 288 to 318 K. The distribution ratios follow the order: Pu(VI) > Pu(IV) > Am(III). The species extracted were identified to be [Pu·2(18-C-6)](SO₄)₂, [PuO₂·(18-C-6)]SO₄ and [Am·2(18-C-6)](SO₄)_1.5 for Pu(IV), Pu(VI) and Am(III), respectively. The equilibrium constants (K) evaluated for the extraction reactions follow the order, K _Pu(IV) > K _Pu(VI) > K _Am(III) as expected in accordance with the axial charge experienced by the incoming ligand (18-C-6). The thermodynamic parameters evaluated at 298 K showed the reaction to be stabilized by the decrease in enthalpy and counteracted by the decrease in entropy in all the three cases. The large decrease in the enthalpy observed in all the cases showed that there is direct bonding of crown ether to the central metal atom (i.e., the formation of inner sphere complex).     

Sorption of Am(III), U(VI) and Cs(I) on sodium potassium fluorophlogopite, an analogue of the fluorine mica mineral

The sorption of ²⁴¹Am, ²³³U and ¹³⁷Cs from nitric acid solutions on a synthesized sodium potassium fluoro-phlogopite (SPFP) gel, structurally close to the fluorine mica mineral, has been studied. The synthesized gel was characterized by energy dispersive spectrometry, X-ray powder diffraction pattern, FTIR and thermogravimetric analysis and has a composition of Na_0.5K_0.5Mg₃(Si₃AlO₁₀)F₂.6H₂O. Different parameters like contact time, acid concentration, amount of SPFP, metal ion concentrations, effect of competing cations, desorption of the nuclides from the loaded SPFP gel etc., were studied using batch technique. Also, the SPFP gel was loaded with Eu(III), U(VI) and Cs(I) and the amounts sorbed on the gel has been estimated by difference from the concentrations in the original solution and those remaining in the solution after loading. Na, K, Mg, Eu and U were estimated by ICP-AES and Cs by electrothermal atomization atomic absorption spectrometry. The exchange of Na, K and Mg with the loaded cations has been evaluated and discussed in the light of ion exchange and surface precipitate sorption mechanisms.     

Americium(III) Adsorption on Polyethylene from very Dilute Aqueous Solutions

The Am(III) adsorption from very dilute aqueous solutions on polyethylene was studied as a function of the pH value, the composition of dissolved salts and the presence or absence of adsorbent SiO₂. It was found that the Am(III) adsorption on polyethylene is decreased with increasing H⁺ concentration and dissolved salt concentrations and in the presence of SiO₂ as an adsorbent. The mechanisms of Am(III) adsorption on polyethylene were discussed. Based on the observations in this paper, extreme care is necessary to minimize and correct the Am(III) adsorption on the container walls in order to improve the accuracy of Am(III) distribution coefficient (K _d) between a solid and an aqueous solution.     

Use of organophosphorus extractants impregnated on silica gel for the extraction chromatographic separation of minor actinides from high level waste solutions

Silica-gel has been used as an inert support for the extraction chromatographic separation of actinides and lanthanides from HNO₃ and synthetic high level waste (HLW) solutions. Silica-gel was impregnated with tri-butyl phosphate (TBP), to yield STBP; 2-ethylhexyl phosphonic acid, mono 2-ethylhexyl ester (KSM-17, equivalent to PC-88A), SKSM; octyl(phenyl)-N,N-diisobutyl carbamoylmethylphosphine oxide (CMPO), SCMPO; and trialkylphosphine oxide (Cyanex-923), SCYN and sorption of Pu(IV), Am(III) and Eu(III) from HNO₃ solutions was studied batchwise. Several parameters, like time of equilibration, HNO₃ and Pu(IV) concentrations were varied. The uptake of Pu(IV) from 3.0M HNO₃ followed the order SCMPO>SCYN>SKSM>STBP. With increasing HNO₃ concentration, D _Pu increased up to 3.0M of HNO₃ for STBP, SKSM and SCMPO and then decreased. In the case of Am and Eu with SCMPO, the D values initially increased between 0.5 to 1.0M of HNO₃, remained constant up to 5.0M and then slightly decreased at 7.5M. Also, the effects of NaNO₃, Nd(III) and U(VI) concentrations on the uptake of Am(III) from HNO₃ solutions were evaluated. With increasing NaNO₃ concentration up to 3.0M, D _Am remained almost constant while it was observed that it decreases drastically by adding Nd(III) or U(VI). The uptake of Pu and Am from synthetic pressurized heavy water reactor high level waste (PHWR-HLW) in presence of high concentrations of uranium and after depleting the uranium content, and finally extraction chromatographic column separation of Pu and Am from U-depleted synthetic PHWR-HLW have been carried out. Using SCMPO, high sorption of Pu, Am and U was obtained from the U-depleted HLW solution. These metal ions were subsequently eluted using various reagents. The sorption results of the metal ions on silica-gel impregnated with several phosphorus based extractants have been compared. The uptake of Am, Pu and rare earths by SCMPO has been compared with those where CMPO was sorbed on Chromosorb-102, Amberchrom CG-71 and styrene divinylbenzene copolymer immobilized in porous silica particles.     

Studies on the separation treatment of high-level liquid waste by bisamide podand(I): Extraction and separation of An(III) from Ln(III)

A process for actinide(III) and lanthanum(III) extraction separation from high-level liquid waste (HLLW) was proposed, with N,N,N',N'-tetraoctyl diglycolamide (TODGA) as the extractant, tri-n?butyl phosphate (TBP) as the phase modifier and 2,6-bis[1-(propan-1-ol)-1,2,3-triazol-4-yl]pyridine (PyTri-Diol or PTD) as hydrophilic stripping agent. This ‘hot test’ was successfully carried out, achieving 99.92% removal of americium-241 (²⁴¹Am) with a separation factor SF_(Eu/Am) of 3.8 × 10³ in the actinide(III) product solution. The results show that bisamide podand extractants can effectively realize the extraction and separation of actinide(III) and lanthanum(III) from Chinese commercial HLLW and thus have a bright practical application potential for the treatment of commercial HLLW.     

Solvent Extraction of Uranium(VI), Plutonium(VI) and Americium(III) with HTTA/HPMBP Using Mono- and Bi-Functional Neutral Donors: Synergism and Thermodynamics

Synergistic extraction of hexavalent uranium and plutonium as well as trivalent americium was studied in HNO₃ with thenoyl, trifluoro-acetone (HTTA)/1-phenyl, 3-methyl, 4-benzoyl pyrazolone-5 (HPMBP) in combination with neutral donors viz, DPSO, TBP, TOPO (mono-functional) and DBDECMP, DHDECMP, CMPO (bi-functional) with wide basicity range using benzene as dileunt. A linear correlation was observed when the equilibrium constant log Ks for the organic phase synergistic reaction of both U(VI) and Pu(VI) with either of the chelating agents HTTA or HPMBP was plotted vs. the basicity (log Kh) of the donor (both mono- and bi-functional) indicating bi-functional donors also behave as mono-functional. This was supported by the thermodynamic data (G ⁰, H ⁰, S ⁰) obtained for these systems. The organic phase adduct formation reactions were identified for the above systems from the thermodynamic data. In the Am(III) HTTA system log K _s values of bi-functional donors were found to be very high and deviate from the linear plot (log K _s vs. log K _h ) obtained for mono-functional donors, indicating that they function as bi-functional for the Am(III)/HTTA system studied. This was supported by high +ve S ⁰ values obtained for this system.     

Distribution of Pu(VI) from nitric acid to tri-n-butyl phosphate saturated with uranium(VI)

Solvent extraction of plutonium(VI) from nitric acid (1 to 5M) into 20% and 30% TBP in dodecane saturated with uranium(VI) (0% to 80%) has been studied. For a particular nitric acid concentration, the distribution coefficient (K _d ) is found to decrease with the increase in saturation of organic phase with uranium(VI). At a fixed organic phase the saturationK _d increased with increase in nitric acid concentration, however, the magnitude of this increase inK _d decreased with the increase in saturation.     

Laser-induced fluorescence and infrared spectroscopic studies on the specific solvation of tris(1-(2-thienyl)-4,4,4-trifluoro-1,3-butanedionato)europium(III) in an ionic liquid

The extraction constant and the two-phase stability constant (K_D,Mβ₃) of tris(2-thenoyltrifluoroacetonato)europium(III) between 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C₄mim][Tf₂N]) as an ionic liquid and an aqueous phase were determined by considering the extraction equilibria including anionic tetrakis(2-thenoyltrifluoroacetonato)europate(III). Specific solute-solvent interactions between the neutral Eu(III) chelate and [C₄mim][Tf₂N] molecules were revealed from the relationships between the distribution constant of the enol form of 2-thenoyltrifluoroacetone (Htta) as a proton chelate and the distribution constant (K_D,M) of the neutral Eu(III) chelate because the [C₄mim][Tf₂N] system gave the high K_D,Mβ₃ value compared with those in conventional molecular solvents such as benzene and 1,2-dichloroethane. The coordination environment of Eu³⁺ in the neutral Eu(III) chelate in [C₄mim][Tf₂N] was investigated by time-resolved laser-induced fluorescence spectroscopy and infrared absorption spectroscopy. Both methods consistently indicated that not only the Eu(III) chelate extracted but also Eu(tta)₃(H₂O)₃ synthesized as a solid crystal were almost completely dehydrated in [C₄mim][Tf₂N] saturated with water. Consequently, the higher K_D,M or extractability of the neutral Eu(III) chelate in the [C₄mim][Tf₂N] system can be ascribed to the dehydration of the Eu(III) chelate, which is caused by the specific solvation with [C₄mim][Tf₂N] molecules.     

Interaction of americium(III) with humic acid over wide pH region

Summary In the wide pH range of 4 to 10, distribution ratios of Am(III)-humate species to free Am(III) ions (D_AmHA = [Am(III)HA]/[Am(III)]_free) were determined at 10 ppm (4.7 ^. 10^-5 eq/dm³) of humic acid and 0.1M NaClO₄ by a cation-exchange equilibrium method under N₂ atmosphere. The D_AmHA was insensitive to an increase in pH (logD_AmHA ≈ 2.6-2.8), which indicates the formation of mixed hydroxo-humate complexes. The present D_AmHA value is larger than the estimated value from available stability constants for ternary complexations by spectroscopic analysis (1.4-2.1) and is markedly smaller than that of Eu(III) obtained by the dialysis method (3.7-8.0) reported in the literatures. The D_AmHA obtained in the present study is widely applicable to estimate the actinide(III) and lanthanide(III) sorption on minerals in the presence of humic and fulvic acids.