Actinide uptake onto zeolite-L and SAPO-34

The characteristics of ion exchange of uranyl and americium, which are -emitting radioactive nuclides, were examined by batch and column methods. SAPO-34 showed good selectivity for uranyl ion at pH 2–3.5, and distribution coefficients of Am³⁺ and UO ₂ ²⁺ increased with equilibrium pH. -irradiation (2 MGy) did not show any significant effect on the uptake of both of actinide ions onto L and SAPO-34. Higher does of -irradiation (up to 10 MGy) created a change of equilibrium pH, and hence uptake, due to radiolysis of water and heat localization generated by -radiation and annealing processes.     

Extraction behaviors of Eu,Th, U and Am with diamides+thenoyltrifluoroacetone

N,N-dimethyl-N,N-dihexyl-3-oxapentanediamide, DMDHOPDA, N,N-dihexyl-3-thiopentanediamide, DHTPDA and N,N-dihexyl-3-oxapentanediamide, DHOPDA were synthesized and tested for the synergistic extraction of Eu³⁺, Th⁴⁺, UO ₂ ²⁺ , NpO ₂ ⁺ and Am³⁺ with thenoyltrifluoroacetone (HTTA). Although Eu³⁺, Th⁴⁺, UO ₂ ²⁺ and Am³⁺ were not extracted by DHTPDA or DHOPDA alone, they were extracted synergistically when combined with HTTA. Analysis of the dependency of extraction on pH and extractant concentration indicated that the dominant extracted species were Eu(TTA)₃(A), Th(TTA)₃(A)(X), UO₂(TTA)₂(A) and Am(TTA)₃(A) (where A is diamide, and X is chloroacetate or ClO ₄ ^– ).     

A new method of uranium preseparation and concentration for neutron activation analysis

This paper introduces a new type of extractant, sym-dibenzo-16-crown-5-oxyhydroxamic acid (HL). The extraction of UO ₂ ²⁺ , Na⁺, K⁺, Sr²⁺, Ba²⁺ and Br^– were studied with HL in chloroform. The results obtained show that UO ₂ ²⁺ can be quantitatively extracted at pH above 5, whereas the extractions of K⁺, Na⁺, Ba²⁺ and Br^– are negligible in the pH range of 2–7. The dependence of the distribution ratio of U(VI) on both the concentration of the HL and pH are linear, and they have the same slope of 2. This suggests that U(VI) appears to form a 12 complex with ligand.Uranium (VI) can be selectively separated and concentrated from interfering elements such Na, K, Sr and Br by solvent extraction with HL under specific conditions. The recovery of uranium is nearly 100% and the radionuclear purity of uranium is greater than 99.99%. Therefore, it has greatly improved the sensitivity and accuracy for the detection of trace uranium from seawater by neutron activation analysis.     

Comparative studies on the ion exchange behaviour of UO2(II), Ce(III) and Am(III) with Chelex-100 from thiocyanate media

The distribution of UO ₂ ²⁺ , Ce³⁺ and Am³⁺ between Chelex-100 and 0.2 and 5.0M ammonium thiocyanate solutions of different hydrogen ion concentrations has been investigated. The results obtained are compared with parallel experimental results using the anion exchanger Dowex-1×4 and the cation excharger Dowex-50×8. It is found that Chelex-100 can act as anion exchanger at pH<2 and as cation and chelate exchanger at higher pH. A main feature of the distribution results of UO ₂ ²⁺ , Am³⁺ and Ce³⁺ with Chelex-100 is the very high distribution coefficient for the three cations at pH higher than 3.5 from aqueous solutions containing 0.2 or 5.0M ammonium thiocyanate.     

Thermodynamic Modeling of Actinide Complexation with Acetate and Lactate at High Ionic Strength

The stability constants of NpO ₂ ⁺ , UO ₂ ²⁺ Am³⁺, and Th⁴⁺ with acetate and lactate anions has been measured in 0.3–5.0m NaCl media at 25°C by the solvent extraction technique. For the 1:1 complexation, the values of the stability constants increased in the order: NpO ₂ ⁺ < Am³⁺ < ₂ ²⁺ < Th⁴⁺, in accordance with the actinide charge density and reflecting the strongly ionic bonding of the complexes. The Pitzer ionic interaction parameters were calculated and used to estimate the thermodynamic stability constants at I = 0. Because our data were collected mainly in the high ionic strength region values of ⁽¹⁾ were estimated from values reported in the literature. For all stability constants the Pitzer model gives an excellent representation of the data using three interaction parameters ⁽⁰⁾, ⁽¹⁾, and COn leave from Institute of     

Extraction of certain actinide and lanthanide elements from different acid media by polyurethane foams loaded with di-(2-ethylhexyl)phosphoric acid (HDEHP)

The effect of added TBP on the extraction of uranium(VI) with a solution of di-(2-ethylhexyl)-phosphoric acid (HDEHP) in o-dichlorobenzene from nitric acid solutions has been investigated at varying concentrations of nitric acid, HDEHP, TBP and uranium(VI). The mechanism of the synergistic effect of TBP is discussed on the basis of the results and can be summarized in the following equation: UO _2(aq) ²⁺ +0.67(HX)_3(o)+2TBP_(o)UO₂X₂·2TBP_(o)+2H _(aq) ⁺ where HX denotes HDEHP and the HDEHP loaded on the foam is trimerized.     

Bacterial biosorption and retention of thorium and uranyl cations by Mycobacterium smegmatis

Biosorption of Th⁴⁺ and UO ₂ ²⁺ ions, both separately and in mixed equimolar ratio, was carried out using nitrate-buffered solutions of the cations at pH 1 in the presence of 5%w/w non-proliferative cell suspensions of Mycobacterium smegmatis. At equilibrium following a 3 h treatment, specific adsorption for 2 mM Th and U was, respectively, 102 and 115 mol g^–1 dry biomass for individual solutions and 102 and 42 mol g^–1 for the mixed 2/2 mM solution. Desorption studies of the cation-loaded biomass preparations in aqueous media and in soilbacterial suspensions within the pH range <1 to 11 showed that leaching of throium was generally less than 1% at pH 1–11 after 7 d, whereas uranium was leached to the extent of 2% at pH 1 and up to 10% under the same conditions in Th–U mixtures.     

Preparation and application of237U for the study of heterogeneous isotope exchange on an ion exchanger

The possibility of preparation of²³⁷U by the²³⁸U(, n)²³⁷U reaction, realized by irradiation of UO₃ on the microtron, has been verified. The relation between yields for (, n) and (, f) reaction was determined. The activated uranium was separated from fission products by extraction into diethyl ether.²³⁷U was used for the study of the kinetics of heterogeneous isotope exchange in the system aqueous solution of UO₂(NO₃)₂ — ion exchanger Wofatit CA-20 in UO ₂ ²⁺ form. The experimental results were evaluated by a model based on particle diffusion with simultaneous isotope exchange between two uranium forms in the ion exchanger.     

Autocatalysis by the nitroxyl radical in the cyclic mechanism of chain termination in polymer oxidation

The activation energy and rate constant of the reaction between the nitroxyl radical and N-alkoxyamine as a concerted abstraction–fragmentation reaction have been calculated using the intersecting parabolas model. This reaction proceeds fairly rapidly and leads to nitroxyl radical autoregeneration as a result of the following consecutive reactions:AmO^? + AmOR → AmOH + >C=O + Am^?, RO ₂ ^? + AmOH → ROOH + AmO^?, Am^?+ O₂ → Am ₂ ^? , and 2AmO ₂ ^? → 2AmO^? + O₂. Thus, the nitroxyl radical is an effective radical catalyst for its own regeneration from N-alkoxyamine. The rates of regeneration of the nitroxyl radical from its N-alkoxyamine under the action of alkyl, alkoxyl, peroxyl, nitroxyl, and hydroperoxyl radicals under conditions of polypropylene oxidation inhibited by the nitroxyl radical are compared. It is demonstrated that only peroxyl, hydroperoxyl, and nitroxyl radicals are involved in AmO^? regeneration from AmOR.     

Separation of uranium from thorium on cryptomelane-type hydrous manganese dioxide

The distribution of UO ₂ ²⁺ and Th⁴⁺ in nitric acid media on crypomelane-type hydrous manganese dioxide (CRYMO) has been investigated by batch equilibrations and column break-through techniques. The parameters studied involve the media composition and concentrations of HNO₃, NaNO₃, UO ₂ ²⁺ and Th⁴⁺. It is found that Th⁴⁺ is more strongly adsorbed on CRYMO than UO ₂ ²⁺ with sufficient differences for chromatographic separation from each other. Uranium was quantitatively eluted from a CRYMO column with 0.1M HNO₃. Th⁴⁺ has been recovered by using 1M HNO₃ as eluent.     

UO 2 2+ sorption on bentonite

The capacity of bentonite and purified bentonite to remove UO ₂ ²⁺ ions from aqueous solutions has been investigated. The UO ₂ ²⁺ uptake in these clays was determined for 0.2 and 0.002M uranyl nitrate solutions. It was found that under these conditions (0.2M) the maximum UO ₂ ²⁺ uptake was 1.010±0.070 meq UO ₂ ²⁺ /g of bentonite and 0.787±0.020 meq UO ₂ ²⁺ /g of purified bentonite. In purified bentonite UO ₂ ²⁺ sorption is irreversible up to 50 hours as no desorption was observed. Such is not the case in the natural bentonite. X-ray diffraction, thermal analyses, and transmission electron microscopy were used to characterize the solids. The uranium content was determined by neutron activation analysis.     

Energy of N-H-bond dissociation in phenothiazines and diphenylamines

Energies of the dissociation of N-H-bonds (D _N-H) in 3 phenothiazines, phenoxazine, phenoselenoazine, and 9 diphenylamines (AmH) are determined. The D _N-H values are calculated from kinetic data by means of intersecting parabolas. The rate constants of the following types of reaction are used in calculations: RO ₂ ^· + Am _i H, R^· + Am _i H, Am _i ^· + PhMe₂CH, and Am _i ^· + ROOH. As a rule, the results obtained for the reactions of different types are in good agreement with each other and with the results obtained using other methods.     

Separation of trivalent americium and europium by purified Cyanex 301 immobilized in macro porous polymer

The present work confirms the high separation ability of purified Cyanex 301 towards trivalent americium over europium in liquid-liquid extraction. Solvent 2-nitrophenyl octyl ether (NPOE) lowered the partitioning of Am³⁺ but remained the separation ability over europium. Solvent toluene and 3-octanone lowered the separation factor to 1000. It is feasible to separate Am³⁺ from Eu³⁺ by Cyanex 301 which was immobilized in the macro porous polymer (MPP). 3-Octanone is a suitable solvent for dissolving NH₄OH-saponified Cyanex 301 and MPP is a suitable solid supported material for column operation. A five-step column experiment demonstrated the feasibility to separate Am³⁺ from Eu³⁺ in column which was packed with Cyanex 301-impregnated MPP.     

Purification,Gene Cloning,and Characterization of a Novel Halohydrin Dehalogenase from Agromyces mediolanus ZJB120203

A novel halohydrin dehalogenase (HHDH), catalyzing the transformation of 1,3-dichloro-2-propanol (1,3-DCP) to epichlorohydrin (ECH), was purified from Agromyces mediolanus ZJB120203. The molecular mass of the enzyme was estimated to be 28 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). A 735-bp nucleotide fragment was obtained based on the N-terminal and internal amino acid sequences of the purified HHDH. The gene codes a protein sequence with 244 amino acid residues, and the protein sequence shows high similarity to Hhe A_AD2 (HHDH from Arthrobacter sp. AD2), defined as Hhe A_Am, which is the seventh reported HHDH. Expression of Hhe A_Am was carried out in Escherichia coli and purification was performed by nickel-affinity chromatography. The recombinant HheA_Am possessed an optimal pH of 8.5 and an optimal temperature of 50 °C and manifested a K _m of 4.58 mM and a V _max of 3.84 μmol/min^/mg. The activity of Hhe A_Am was not significantly affected by metal ions such as Zn²⁺, Ca²⁺, Cu²⁺, and EDTA, but was strongly inhibited by Hg²⁺ and Ag⁺. In particular, the Hhe A_Am exhibits an enantioselectivity for the conversion of prochiral 1,3-DCP to (S)-ECH. The applications of the Hhe A_Am as a catalyst for asymmetric synthesis are promising.     

Achieving highly selective CO2 adsorption on SAPO-35 zeolites by template-modulating the framework silicon content

Small-pore silicoaluminophosphate (SAPO) zeolites with 8-ring pore windows and appropriate acidities/polarities, for example, SAPO-34 (CHA) and SAPO-56 (AFX), have proven to be potential adsorbing materials for selective adsorption of CO₂. However, SAPO-35 zeolites (LEV framework topology) synthesized using conventional templates are less reported for highly selective CO₂ adsorption which might be due to inappropriate Si contents and acidities in the framework. In this work, by using N-methylpiperidine (NMP) as a template, SAPO-35 zeolites with various Si contents were synthesized under hydrothermal conditions, which allowed SAPO-35 zeolites with modulated acidities and polarities. The CO₂ adsorption and separation properties of SAPO-35_x (x: Si/(Si + P + Al) in molar ratio) were investigated, and a close relationship between the acidity, polarity and CO₂ adsorption and separation capacity was revealed. SAPO-35_0.14 with the strongest acidity showed the highest CO₂ uptake of 4.76 mmol g⁻¹ (273 K and 100 kPa), and appeared to be one of the best SAPO materials for CO₂ adsorption. Moreover, increased Brønsted acidity can significantly enhance the adsorption selectivity of CO₂ over N₂. At 298 K and 100 kPa, SAPO-35_0.14 showed the highest CO₂/N₂ selectivity of 49.9, exhibiting potential for industrial processes. Transient binary breakthrough experiments on SAPO-35_0.14 further proved the efficient separation performance and stable circulation. The results of this study prove that the framework Si content of SAPO-35 zeolites is essential for regulating their CO₂ adsorption performance. This work demonstrates that modulating the silicon content and acidity in SAPO zeolites via a suitable choice of template, as well as polarity, is of great significance for the rational synthesis of zeolites with superior CO₂ adsorption and separation abilities.

SAPO-35 zeolite with template-modulated framework Si content showed superior CO₂ affinity and separation of CO₂/N₂ mixtures.     

A quadridentate Schiff base as an extractant for thorium/IV/, uranium/VI/ and zirconium/IV/

Liquid-liquid extractions of zirconium/IV/, thorium/IV/ and uranium/VI/ with a tetradentate Schiff base, bis/salicylidene/ ethylenediamine /H₂Salen/ in benzene as the diluent have been studied. Comparison of such results with those in case of a bidentate Schiff base, N-salicylidene-p-toluidine /HSalTol/ shows that the extraction of UO ₂ ²⁺ is significantly improved if H₂Salen is used instead of HSalTol². A single extraction at pH 6.5 with H₂Salen removes uranium/VI/. Extraction of all the three metals becomes quantitative at pH 6.5. The extracted species, which have been derived from slope-analyses of extraction results, seem to be of the type [Zr₄/OH/₁₂ /HSalen/₂]Cl₂, [UO₂/OH/ /HSalen/] and [Th/OH/₃ /HSalen/].     

Effect of alkali ions (Na+, K+) on the solvent extraction of uranium(VI) with a di-carboxylated calix[4] arene

The solvent extraction of uranium(VI) with a di-carboxylated calix[4]arne (LH₂) in chloroform and 1,2-dichloroethane has been studied in the presence or absence of alkali ions (M=Na⁺,K⁺). For UO ₂ ²⁺ when studied alone, a 12 (metal: ligand) extracted species is evidenced, with a rather low associated extraction equilibrium constant. The efficiency of extraction increases drastically in the presence of alkali ions, due to the formation of heteronuclear complexes. In all cases, the extracted species are found to be both 122 and 112 (UO ₂ ²⁺ MLH₂) mixed complexes, except in chloroform with K⁺, where only the latter is formed. In the case of Na⁺, mass spectrometry spectra confirm the existence of both homo and heteronuclear complexes as determined in the extraction studies.     

Selective complexation of UO 2 2+ by the calix[6]arene6− anion: Structure and hydration studied by molecular dynamics simulations

Based on molecular dynamics simulations, we describe the structure and solvation pattern of thep-Me-calix[6]arene^6– anion in the free state, and complexed with UO ₂ ²⁺ in aqueous solution. UO ₂ ²⁺ is coordinated in its equatorial plane to five phenolate oxygens, and has no direct coordination with water molecules. The closest water molecules are strongly hydrogen bonded to the ligand. The complex of thep-Me-calix[5]arene^5– anion with UO ₂ ²⁺ displays similar binding and solvation features. For the purpose of comparison, a complex ofp-Me-calix[6]arene^6– with a spherical divalent cation, referred to as Cu²⁺ is simulated under the same conditions. In the most stable conformer, Cu²⁺ is coordinated to four phenolic oxygens in a square planar arrangement, and to one water molecule. An energy component analysis suggests that the high binding selectivity of the calixarene for uranyl relates to a large cation-guest interaction, and to a better hydration of the complex. In the UO ₂ ²⁺ complex the strong hydration of the negatively charged ligand is not significantly prevented by the complexed cation, unlike in the spherical cation complexes. It is stressed that entropic effects, which are not amenable to such calculations, play an important role in the binding selectivity of these calix[6] and calix[5]arenes for uranyl.     

Speciation of uranium in solids using time resolved photoluminescence technique

A comprehensive study regarding the speciation of uranium in five different solids, namely, YBO₃, Sr₂P₂O₇, SrB₄O₇, SrBPO₅ and SrZrO₃ is presented using time resolved photoluminescence spectroscopy. The ‘Sr’ based hosts are considered as potential phosphor materials where as the borate based matrices are known to have near tissue equivalent absorption coefficients making them potential candidates for dosimetric applications. It was observed that, in case of the pyrophosphate, borophosphate and yttrium borate matrices, uranium gets stabilized as uranyl ( \( {\text{UO}}_{2}^{2 + } \) ), whereas, in case of the tetraborate and zirconate matrices, it was the uranate species, \( {\text{UO}}_{6}^{6 - } \) that gets stabilized preferentially.