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.
The results of a comparative study of pertechnetate reduction by thiourea in mineral acid (HCl, HNO3, HClO4, H2SO4) media using spectrophotometric, solvent extraction and ion-exchange chromatographic methods are presented. Changes of spectral characteristics of redox systems and distribution characteristics of reduced technetium (cationic) forms on extraction with bis(1,2-dicarbollide)cobaltic acid and on ion exchange on Dowex 50WX8 were established as a function of time and either aqueous or organic phase composition. Thiourea was tested as a reagent for reduction back-extraction of technetium from organic phases containing the amines Aliquat 336 and trilaurylmethylammonium as convenient extraction reagents for pertechnetate.
Transport of trivalent rare earth elements-REE (Sc, Y, Ce, Eu, Gd, Tm, Yb) from nitrate medium through SLM containing TOPO in n-dodecane, supported on a nucleoporous filter, into a strip solution with EDTA, has been studied. Permeability coefficients of metal transport decreased with increasing of their atomic number except for Ce and Tm. At higher concentration of TOPO in the membrane, metal transport was faster, but the differences among the transport rates of the investigated elements decreased. A good separation of Ce from its binary mixtures with other investigated REE was achieved using DTPA as masking agent, added the feed solution.
Transport of yttrium(III) from nitrate medium through liquid membrane containing tri-n-octyl-phosphine oxide (TOPO) in n-dodecane, supported on a nucleoporous filter, into a strip solution with ethylenediaminetetraacetic acid (EDTA) has been studied. The kinetic dependences of transport were obtained and compared with a model, resulting in calculation of permeability coeffients and initial fluxes of yttrium. The influence of salting-out agent, initial metal and nitric acid concentrations in the feed, and of concentration of carrier in membrane are discussed.
The complexation of technetium with humic acid is usually done by a reduction of pertechnetate by Sn2+ ions. A Tc-HA complex can be scavenged in a Sn-HA complex, if tin is present as reductant. The main aim of the study was a preparation of the Tc-HA complex without impurities of Sn ions or other metal reductant, which was performed by a ligand exchange with hexakis(thiourea-S)technetium(III) under nitrogen atmosphere at pH 5.5. The [Tc(tu)6]3+ complex was prepared from TcO4- in acidic solution with thiourea as a reductant. Presence of the Tc-HA complex and other technetium species was determined by gel chromatography, paper chromatography and dialysis. Yield of Tc-HA complex was about 80% and reaction mixture contains about 20% of technetium dioxide, which is a side product of ligand-exchange.
The membrane extraction of Y, Ce, Eu, Tm and their binary mixtures Ce–Y, Ce–Eu, Ce–Tm with supported liquid membranes containing TBP and HDEHP as carriers in decanedodecane hydrocarbon solvent, has been studied. Upon extraction with TBP aqueous nitrate solutions of rare earth elements (REE) were used as feed phase. In some cases they also contained EDTA or DCTA. In most cases, the receiving phase was an aqueous solution of EDTA. Extraction with HDEHP was performed from nitrate and chloride solutions and the receiving phase was the corresponding dilute acid. Pertraction of an element through a membrane was studied as a function of time and of initial composition of phases. The results are presented in the following forms: flux of metal through membrane, coefficients of permeability, separation factors and effective diffusion coefficients.
The extraction of pertechnetate in form of ionogene associates with triphenyltin and trioctyltin cations into chloroform,
benzene, toluene and nitrobenzene was studied. As aqucous phases solutions of99mTcO
in deionized water and in diluted solutions of NaCl, HCl, NaNO3, HNO3 NaClO4, HClO4 and NaOH were used. Concerning the organic phases, at the use of triphenyltin chloride the extractibility of pertechnetate
increases in the sequence: toluene «chloroform, benzene nitrobenzene and approximately in the sequence: NaOH<NaCl, HCl<NaNO3<H2O<NaClO4 concerning aqueous phases. For trioctyltin chloride in chloroform the extractibility of TcO
increases approximately in the sequence of aqueous phases: NaOH<HCl, NaNO3, NaClO4, NaCl«H2O and in nitobenzene in the sequence NaOH<NaClO4<HCl<NaNO3, NaCl«H2O. The extractibility for trioctyltin chloride is in general slightly lower as compared with triphenyltin chloride. The results
of the extraction are presented in the form of graphical plots of technetium distribution ratio (DTe′ logDTc) or extraction yield (ETc, %) against concentration of the investigated component in aqueous or organic phase. In some of the systems of the systems
studied practically quantitative extraction of pertechnetate into organic phase has been achieved.
Conductivity of tetraphenylarsonium chloride (Ph4AsCl), tetraphenylphosphonium chloride (Ph4PCI), tetraphenylarsonium pertechnetate (Ph4AsTcO4), tetraphenylphosphonium pertechnetate (Ph4PTcO4), triphenyltin chloride (Ph3SnCl) and trioctyltin chloride (Oct3SnCl) solutions in nitrobenzene and chloroform was studied. On the basis of determined molar conductivity A values at different
concentrations of the electrolyte in solution, values of dissociation degree of the electrolyte α, molar conductivity at infinite
dilution A0 and dissociation costant Ki for compounds of type Ph4(As or P) (Cl or TcO4) were calculated. It was shown that for some of the investigated systems the Kohlrausch's empirical relation applies. In
chloroform solutions a parabolic dependence of molar conductivity on electrolyte concentration was observed which testifies
that a formation of ion triplets at higher electrolyte concentration can occur.
Uranium is extracted by a water-in-oil emulsion consisted from 0.01M 8-hydroxyquinoline /HOx/ in cyclohexane and aqueous solution or Arsenazo III and glycine. Analyzed solution is adjusted to 0.02M 1,2-diaminocyclohexane-N,N,N,N-tetraacetic acid /DCTA/ and pH 7.5±0.1. Preconcentration factor of about 400 can be achieved and when the uranium concentration in the outer solution is above 5 g.dm–3 /5 ppb/ its spectrophotometric determination in the inner solution of the double emulsion system is possible. Thorium practically does not interfere at the ratio Th:U=20:1.
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.