摘要:

Neutral 2-(N-hetarenyl)benzimidazoles (B) can extract Am(lll) with appreciable selectivity over Eu(lll), forming in the organic phase complexes of the type MA3nB (M = Am or Eu, A = anion of an acid HA and n = 1 - 3). The extractant properties of 2-(2-pyridyl)benzimidazole are improved by placing a methyl group into the 6-position, but little further improvement is achieved by the introduction of an another methyl group into the 5-position. Low extraction efficiency and deteriorated separation ability is exhibited by 2-(6-methyl-2-pyridyl)benzimidazoles. The efficiency of 6-methyl-2-(2-pyridyl)benzimidazole in the Am(lll)/Eu(lll) separation decreases in the anion sequence thiocyanate > nitrate ∼ perchlorate ∼ iodide > thenoate > 2-(2-pyridylazo)-1-naphtholate. Generally, the separation efficiency is suppressed by those factors which lower the average solvation number of the extracted complexes of Am(lll).

ISSN:0736-6299    

DOI:10.1080/07366299708934483

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The liquid/liquid extraction of Am(III) from nitric acid solutions with chloroform solutions of 2,6 bis[(diphenylphosphino)methyl] pyridine N,P,P′ trioxide (ENOPOPO) is examined. Americium(IU) is efficiently extracted from aqueous solutions at high nitric acid concentrations (DAM0>3000 at 6M HNO3) and can be totally back extracted from the organic phase at 0.01M HNO3. The ligand dependency data suggest that two ligand molecules are coordinated to the americium. Additional aspects of the extraction mechanism are described.

ISSN:0736-6299    

DOI:10.1080/07366299708934484

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The complexation and aggregation behavior of P,P′-di(2-elhylhexyl) ethanediphosphonic acid, H2DEH[EDP], a novel solvent extraction reagent for metal ions, was investigated. The aggregation of H2DEH[EDP] was studied in toluene at 25 °C by vapor pressure osmometry. H2DEH[EDP] was found to be hexameric in the concentration range 0.2 -0.005 m. Metal ions introduced into the organic phase were shown to have little effect on the aggregation of the extractant. The infrared spectra of metal containing solutions of the extractant and that of the ligand itself suggest that H2DEH[EDP] exists in toluene as a cyclic hexamer similar to an inverted micelle with a large hydrophilic cavity. Ca(II), Ba(II), Eu(m), Fe(UJ), Th(IV) and U(VI) salts of H2DEH[EDP] were also investigated. The infrared spectra of these compounds reveal that the asymmetric, VASYM(POO−), and symmetric, VASYM (POO−), phosphorus-oxygen stretching modes of the ligand are sensitive to the metal ion present. The shift of both VASYM (POO−) and VASYM (POO−) to lower frequencies relative to their values in the sodium salt indicates symmetrical coordination of the phosphonate groups through chelate and/or bridging interactions. The difference (A v) between the two frequencies, i.e. [ VASYM POO′) - VASYM (POO−)], becomes smaller as the ionic potential of the metal ion increases.

ISSN:0736-6299    

DOI:10.1080/07366299708934485

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

As part of an ongoing investigation of the properties of dialkyl substituted diphosphonic acids as solvent extraction reagents for metal cations, we have studied the extraction of alkaline earth cations, Fe(III) and representative actinides (Am(III), U(VI) and Th(IV)) at tracer concentration levels by o-xylene solutions of P,P′-di(2-ethylhexyl) ethanediphosphonic acid, H2DEH[EDP]. The extractant and acid dependencies of these metal ions were determined by measuring their distribution ratio as a function of the concentrations of H2DEH[EDP] and aqueous nitric acid. From an analysis of the extractant dependencies, a micellar extraction process has been proposed for the alkaline earth cations, Am(III), and, under some conditions, for U(VI). The hydrated metal cations are transferred into the hydrophilic internal cavity of the hexameric extractant aggregate with simultaneous release of H+ions to compensate for the cation charge. With Fe(DI), variable slopes were measured for the extractant dependencies, the values being strongly dependent upon the acidity of the aqueous phase. The slope of the extractant dependency has a value of about two if the metal ion is extracted from highly acidic solutions. This value becomes progressively lower as the aqueous acidity is reduced, approaching zero at pH 1. This phenomenon has been attributed to the formation of metal complexes having different stoichiometrics and ligand protonation through strong interaction of the metal with the phosphonate groups of the ligand.

ISSN:0736-6299    

DOI:10.1080/07366299708934486

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

New organoarsenic ligands were investigated as potential separating agents for trivalent lanthanide ions. Organofluoro-substituents were employed to increase the acidity of arsinic and arsinic acids to enable these to complex metal ions in the lower pH region. Potentiometric studies were carried out in order to determine the acid constants of these derivatives with subsequent determination of the lanthanide-ligand stability constants in aqueous and ethanolic media.

ISSN:0736-6299    

DOI:10.1080/07366299708934487

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A physicochemical expression of the separation factor derived from the Mikulin-Sergievskii-Dannus' model is proposed to predict the medium effect on the separation of lanthanide nitrates by liquid-liquid extraction from nitrate media, using tri-n-butyphosphate (TBP) as extractant. The factors exerting an influence on the separation factor have been highlighted and discussed more deeply in this paper, mainly the water activity functions and the extraction equilibrium constant ratio of lanthanide nitrates. It has been shown that the water activity is a central variable to be controlled, particularly in concentrated aqueous solution. The present work is partly a review of the effects of aqueous media on the lanthanide separations and partly an analytical approach based on the physicochemical properties of aqueous solutions. Results of qualitative and quantitative predictions of changes in the separation factor with the aqueous solution composition are discussed. The proposed model provides a coherent explanation to the great number of experimental observations.

ISSN:0736-6299    

DOI:10.1080/07366299708934488

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Several techniques, such as the Lewis cell and highly stirred tanks, operate in turbulent conditions for the study of liquid-liquid extraction kinetics. However, since the hydrodynamics in these cells are poorly known, phenomenological models, such as the two-film or the penetration model, have been used to describe the contribution arising from transport. In the present paper, a non-phenomenological description, based on the boundary layer theory, is proposed for extraction kinetics coupled to controlled turbulent rotating disk hydrodynamics. In principle, such flows can be obtained with the use of a rotating diffusion cell or a rotating stabilized cell (R.SC). However, up to now, these techniques have not been used in a turbulent regime. In this work, experiments have been performed with the RSC, in which the aqueous phase was stabilized with a gel and a turbulent flow was created in the organic phase. Two systems have been studied: acetic acid at the HCl-water/isopropylmyristate interface, and Cobalt(II) ion at the water (pH 3)/HDEHP interface. For the first system, experimental results have been obtained, that are consistent with a relationship valid for a flat disk. Experiments conducted with the same gels, for Cobalt(II), lead to a contrasting behaviour. The results may be described with the use of an interfacial kinetic rate which increases with the degree of turbulence.

ISSN:0736-6299    

DOI:10.1080/07366299708934489

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The extraction of lincomycin with long-chain alcohols as solvent was studied. The experimental results indicated that the power of n-alkyl alcohols for the extraction of lincomycin depends mainly on the molarity of alcohols in solvent used. For alcohols with short carbon chain, the steric hindrance of alkyl groups in alcohols with different structure has only little influence on the extraction of lincomycin. The chemistry of extraction of lincomycin with alcohols as solvent was discussed.

ISSN:0736-6299    

DOI:10.1080/07366299708934490

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Spherically granulated titanium phosphate of formula TiO1.25(OH)(0.47(H2PO4)0.77(HPO4)0.13-2.3H2O (THP) was synthesized by a gel method. The material was characterized by chemical analysis, X-ray diffraction, TGA and31P MAS NMR spectroscopy methods. Ion exchange of alkali, alkaline earth and some other di- and trivalent metal cations by THP was studied in both batch and column conditions. It was found that THP is a weak acid cation exchanger with a maximum ion exchange capacity of 4.7 meq/g. It exhibits a high affinity for heavy metal cations (Pb2+Cr3+, Ba2+, Cs+). Exchange of micro amounts of some polyvalent cations was studied on salt forms (Na, K) of THP. It was shown that the conversion of the exchanger into the salt form enhances significantly its ion exchange performance for transition and heavy metal cations. THP converted into Na+or K−ion

ISSN:0736-6299    

DOI:10.1080/07366299708934491

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Various crystalline forms of manganese oxides were synthesized by redox reaction between alkali metal permanganates and manganese sulphate. The structure of samples precipitated from0 KMnO4, RbMnO4and NH4MnO4were similar to those reported for α-crystalline form of MnO2and exhibited a high selectivity for the cations whose ionic radii are included in the range 135-155 pm i.e. K+, NH4+. Rb+, Ba2+and Ra2+. The samples precipitated from NaMnO4were more similar to the γ-form of MnO2and exhibit much lower affinity for the Ra2+cations. High selective α-type MnO2samples can also be obtained in strong acidic solutions. The obtained α-MnO2samples can be used for the determination of226,228Ra in natural water at a very low level of radioactivity.

ISSN:0736-6299    

DOI:10.1080/07366299708934492

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor