Search Results

You are looking at 11 - 20 of 22 items for

  • Author or Editor: R. Kopunec x
  • Refine by Access: All Content x
Clear All Modify Search

Carrier-mediated transport of rare earth elements through liquid membranes

III. Transport of Sc, Y, Ce, Eu, Gd, Tm, Yb through supported liquid membrane containing DEHPA

Journal of Radioanalytical and Nuclear Chemistry
Authors: R. Kopunec and Thang Ngo Manh

Abstract  

Transport of tervalent REEs–Sc, Y, Ce, Eu, Gd, Tm, Yb—from nitrate medium through flat-sheet SLM containing DEHPA in n-dodecane, supported on a nucleoporous filter, has been studied. Influences of both aqueous phase acidities, concentrations of metal and carrier were investigated. Transport courses of the metals in question had been obtained and their premeation coefficients or initial fluxes were evaluated. Separation of some binary mixtures Ce–Tm, Ce–Yb, Ce–Sc was experimentally achieved.

Restricted access

Carrier-mediated transport of rare earth elements through liquid membranes

IV. Transport of Sc, Y, Ce, Eu, Gd, Tm, Yb through a supported liquid membrane containing TBP

Journal of Radioanalytical and Nuclear Chemistry
Authors: R. Kopunec and Th. Ngo Manh

Abstract  

Transport of tervalent REEs — Sc, Y, Ce, Eu, Gd, Tm, Yb — from nitrate medium through a liquid membrane containing TBP in n-dodecane, impregnated on a flat-sheet nucleoporous support, has been studied as a function of time and initial metal concentration, salting-out agent concentration and pH of the feed phase. Influences of various complexing agents dissolved in the strip phase was investigated, too. Adding a suitable amount of EDTA into the feed phase, separation of binary mixtures of REEs was experimentally achieved.

Restricted access

Abstract  

The first works in this field were realized approximately 25 years ago, when BLOCK et al. reported1,2 their studies about carrier-mediated transport (also called pertraction or membrane extraction) of uranium through plasticized membranes with neutral esters derived from phosphoric acid. At this time, the methodical principles of selective pertraction of ionic compounds through so-called bulk liquid membranes containing carriers were known.3 However, these membranes, similarly as plasticized membranes, have not achieved a broader use. This is probably because bulk liquid membranes are from a technical point of view fairly distant from the idea of a typical membrane system, and plasticized membranes (sometimes also called gel membranes) present great resistance. By the end of the 1960's and at the beginning of the 1970's, LI4–7 and CUSSLER8 worked out the principles for two widely used pertraction techniques, called pertraction through emulsion liquid and supported liquid membranes (ELM and SLM). These two techniques not only have greatest significance in laboratory practice, but they also are interesting for technological aims because of the attainable large phase boundaries, e. g. 103–104 m2/m3. Many ways to arrange membrane systems are described in papers.9,10 Recently, the significance of carrier-mediated transport through liquid membranes has grown to have (since 1980) separate section at the International Solvent Extraction Conference.This paper does not deal with mathematical models and the mechanism of pertraction in general, but it gives an overview of results obtained in publications referring to pertraction of two related element groups — actinoids and rare earth elements — using various membrane types.

Restricted access

Abstract  

The preparation of technetium-99m-humic complex without presence of any metal reductant was studied. For the preparation of Tc-HA complex by ligand substitution hexakis(thiourea-S)technetium(III) complex was used as a precursor. Ligand exchanging reaction was studied with two different humate/thiourea concentration ratios. After mixing of [99mTc(tu)6]3+ complex with natrium humate under a nitrogen atmosphere a formation of technetium humate wasobserved. The determination of reaction products was performed by combination of gel and paper chromatography. Reaction yields are dependent on humate/thiourea concentration ratio and reaction time. Tc-HA complex was obtained with the highest yield of 62%. Reaction mixture also contains a technetium dioxide as a side product of exchanging reaction and other technetium species, which are also discussed. Oxidation state of technetium in prepared Tc-HA complex is apparently unchanged.

Restricted access

Abstract  

Standard Gibbs energies of transfer of cesium ion from water to nitrobenzene and nitrobenzene-carbon tetrachloride mixture have been evaluated from electrochemical measurements. From the results the conclusion can be drawn that with increasing dielectric permitivity of organic mixed solvents the value of the Gibbs transfer energy of Cs+ ion decreases.

Restricted access

Abstract  

Solvent extraction of pertechnetate anions from aqueous solutions of some mineral acids (HCl, HNO3, HClO4, H2SO4), (NaCl, NaNO3, NaClO4, K2CrO4, NaCO3), NaOH and NH4OH by tetraphenylphosphonium chloride in chloroform and nitrobenzene was studied. The results are presented in the form of the dependencies of extraction characteristics of TcO 4 (distribution ratio, percentage of extraction) on the (C6H5)4PCl, H+ and competitive anion concentrations. The solvent extraction of sub-and super-stoichiometric ratio of TcO 4 : (C6H5)4P+ was performed. The extraction constant values of ion pairs TcO 4 −Cl, TcO 4 −NO 3 , TcO 4 −ClO 4 and of individual anions TcO 4 , Cl, NO 3 , ClO 4 were calculated.

Restricted access

Abstract  

Selected extraction systems of TcO 4 –(H,Na)A–H2O/R(TcO4,A)–CHCl3, C6H5NO2 type, where A=Cl, NO 3 , ClO 4 , R=(C6H5)4As+, were studied. The solvent extraction of sub- and super-stoichiometric ratio of TcR was performed. The solubility of (C6H5)4AsTcO4 in water, chloroform and nitrobenzene were determined too. The results of the extractions are presented in the form of TcO 4 distribution dependencies on the phase composition and the extraction constants of individual TcO 4 , Cl, NO 3 , ClO 4 anions and TcO 4 -Cl, TcO 4 –NO 3 , TcO 4 –ClO 4 ion pairs.

Restricted access

Abstract  

The technetium sorption behaviour in different samples of soils was studied under aerobic conditions. Tc(VII) was reduced to Tc(IV) by Sn2+ ions. About 99% of reduced technetium is absorbed by the soils under investigation. Sorption of TcO4 was studied in short-term (1-hour) and long-term (1-month) experiments. Sorption of TcO4 in presence of sodium humate (Aldrich) was generally lower than from pure water (from 99% to 12%) and depends on the depth of origin of the ground. Immobilisation of TcO4 after sorption on superficial sample of soils was studied by paper chromatography. Oxidation of Tc(IV) in presence of NO3 and NO2 (concentration range 10–1–10–5 mol·dm–3) ions was studied as a function of time and concentration of NO3 and NO2 ions. The content of Tc(IV) in NO3 and NO2 solutions decreases with time (46 hours) relatively slowly.

Restricted access

Abstract  

The specific phenomena accompanying the daughter nuclide formation by radioactive β-decay of complex parent compounds cause certain deviations from a thermodynamic distribution of daughter elements in separation procedures (e.g. in radionuclidic generators) and they are shown to complicate or, less probably, simplify their separation. A simple kinetic model has been proposed to explain such processes as the distribution of some daughter nuclides of fission products by solvent extraction with chelating compounds (systems of99Mo−99mTc and144Ce−144Pr with oxines).

Restricted access

Abstract  

Membrane extraction is treated as an analogue of solvent extraction in three-phase distribution systems. Its advantages and drawbacks are discussed with respect to separation and preconcentration of radionuclides, fission products of uranium and uranium itself.

Restricted access