Kinetic study of uranium transport via a bulk liquid membrane containing Alamine 336 as a carrier

Journal of Radioanalytical and Nuclear Chemistry - A kinetic study of the uranium transport from the sulfate medium through the bulk liquid membrane was conducted by Alamine 336 as a carrier. The...     

Transport of carbonate ions through supported liquid membrane by using Alamine 336 and trioctylphosphine oxide as carriers

Abstract

Transport studies were carried out for carbonate ions through supported liquid membrane (SLMs) by using Alamine 336 and trioctylphosphine oxide (TOPO) as carriers. Experimental variables were investigated, such as concentration of carbonate ion (10^?5 to 4×10^?2 M), carriers (10^?5 to 10^?1 M), and alkali (0.01–0.5); and stirring speed (50–150 rpm) of bulk solutions. The use of combined carriers Alamine 336 and TOPO shows a synergic transport of carbonate ions. The stability of the SLM system in relation to the transport of carbonate ions has been studied. The enrichment of carbonate ions (10^?6 to 4×10^?2 M) from the dilute solution was explored. The different combinations of amines with TOPO show synergic permeability of the carbonate ions through SLM system.     

Carrier-mediated transport of yttrium(III) through a supported liquid membrane containing TOPO in n-dodecane

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.     

Carrier facilitated transport of thorium from HCl medium using Cyanex 923 in n-dodecane containing supported liquid membrane

Present studies deal with supported liquid membrane (SLM) technique for the separation of thorium from hydrochloric acid (HCl) medium using Cyanex 923 as a carrier. Effects of feed acidity, strippant, and membrane pore size and membrane thickness on the transport of thorium have been studied in detail. The optimized parameters were applied for separation of thorium from a radioanalytical waste. Stability of the membrane and membrane support was investigated. Transport of thorium increased from 78.3 to about 93.7 % with increase in acidity from 0.5 to 2 M using 0.3 M Cyanex 923 in n-dodecane as carrier and 2 M ammonium carbonate as stripping phase. The transport of thorium decreased above 2 M HCl. An attempt was made to model the physicochemical transport of thorium in SLM and understand the mechanism of thorium transport.     

Studies on extraction of chromium (VI) from acidic solutions containing various metal ions by emulsion liquid membrane using Alamine 336 as extractant

The extraction of chromium (VI) ions from acidic solutions containing various metal ions by emulsion liquid membrane (ELM) was studied. Liquid membrane consists of a diluent, a surfactant, and an extractant. 0.5 M ammonium carbonate solution was used as stripping solution. Effects of acid concentration in feed solution, type and concentration of stripping solution, mixing speed, surfactant concentration, phase ratio and the influence of membrane characteristics were studied and optimum conditions were determined. Under the optimum conditions, extraction of chromium (VI) was tested and it was possible to selectively extract 99% of chromium from the acidic feed solution. This study also examined the effect of extractant concentration and acid type in the feed solution on the extraction of Cr (VI) ions and almost all of Cr (VI) from the acidic feed solution containing 500 mg/L from each of Co (II), Ni (II), Cd (II), Zn (II), and Cu (II) ions, and 100–500 mg/L Cr (VI) was extracted within 5–10 min.     

Facilitated transport of saccharides through a supported liquid membrane containing a neutral lipophilic resorcinarene carrier

The facilitated transport of several types of saccharidess has been studied across a supported liquid membrane containing a resorcinarene carrier. The rate-determining step is believed to be the migration of a carrier-saccharide-water ternary complex in the organic solvent. The transport kinetics obey a saturation law, that allows the calculation of the stability constants of the various complexes. The stability constants are related to the saccharide structures: important factors are chain length, configuration and substitution of key hydroxyl groups.     

Selective permeation of plutonium(IV) through supported liquid membrane containing 2-ethylhexyl 2-ethylhexyl phosphonic acid as ion carrier

The selective transport of plutonium across supported liquid membrane using an indigenously synthesized 2-ethylhexyl 2-ethylhexyl phosphonic acid (KSM-17, equivalent to PC 88A) dissolved in dodecane as carrier has been investigated in this work. Laminar type polypropylene hydrophobic microporous membranes were used as solid supports. Transport experiments were carried out to evaluate the effect of varied hydrodynamic and chemical compositions of the system, i.e., stirring speed, carrier concentration, anionic composition (e.g. SO²⁻₄, NO⁻₃, PO³⁻₄, ClO⁻₄, Cl⁻) and acidity of source phase (SP) solution. Transport rates of plutonium from SP solutions of different anionic composition followed the order: ClO⁻₄>NO⁻₃>Cl⁻>SO²⁻₄>PO³⁻₄. Selective permeability of plutonium was observed in the presence of several cationic impurities such as Al, B, Be, Ca, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Si, Zn, Ce, Dy, Eu, Gd and Sm. Using this technique, separation of plutonium from laboratory analytical waste was accomplished with an average flux 8.94×10⁻⁶ mol m⁻² s⁻¹ and with an enrichment factor greater than 2. The product solution obtained from this process was in oxalate medium with negligible contamination from other cationic and anionic impurities. From this solution, plutonium was precipitated as Pu-oxalate for further processing. Reusability of the membrane support was found to be satisfactory.     

Dysprosium pertraction through facilitated supported liquid membrane using D2EHPA as carrier

The pertraction of dysprosium (Dy) through a supported liquid membrane (SLM) system consisting of PTFE (polytetrafluoroethylene) support, D2EHPA (di-2-ethylhexyl phosphoric acid) dissolved in kerosene as membrane solution, and HNO₃ solution as stripping solution, was studied. The experiments were designed by the Taguchi method in order to investigate the effects of initial Dy concentration, feed phase pH, different stripping solution concentration, and D2EHPA concentration in the membrane phase on Dy pertraction. Optimal experimental conditions for Dy pertraction were obtained using an analysis of variance (ANOVA) (feed concentration: 130 mg L^?1, D2EHPA concentration: 0.90 M, feed phase pH: 5, stripping phase concentration: 2 M). In addition, the stability of the carrier in terms of its leaching from the membrane support was studied over a period of 6 days and was found to be satisfactory over that time.     

Uranium(VI) transport through tri-n-butylphosphate kerosene oil liquid membrane supported in polypropylene film

Gamma-rays emitted from the surfaces of atmosphere-free extraterrestrial bodies such as asteroids, planets, or moons, can be measured to determine their chemical surface composition. Gamma-rays are emitted from naturally radioactive elements and, in their majority, are induced by the interaction of the energetic galactic cosmic particle radiation. Neutrons of the secondary hadron cascade contribute considerably to the gamma-ray line surface fluxes via nonelastic scattering and neutron-capture reactions. In principle, planetary gamma-ray spectroscopy resembles laboratory applications of prompt activation techniques. However, the evaluation of an orbital gamma-ray spectrum of other bodies than the Moon is difficult, as comparisons to so-called ground truth values, which functioned as standards, are not possible. Future planetary exploration missions will require the evaluation of recorded gamma-ray spectra without such standards. Therefore, in an attempt to overcome some of these difficulties, prompt gamma-ray spectra of planetary constituents were measured in a set of laboratory experiments with neutron-generator and cyclotron produced neutrons of energies up to 78 MeV. The significance of neutron-capture and nonelastic scattering gamma-ray lines for the characterization of major elements were established, and the application of the results to planetary gamma-ray spectroscopy of asteroids is discussed.     

Extraction and transport of chromium(VI) through a bulk liquid membrane containing triphenylphosphine

The solvent extraction of chromium(VI) in chloroform, dichloromethane, dichloroethane and its transport through a chloroformic bulk liquid membrane from sulphuric acid solutions with the neutral extractant triphenylphosphine (TPP) were studied. It was highlighted that the TPP extractant is an interesting complexing and efficient carrier for transport of chromium(VI) as [(HTPP)HCr2O7] complex from a 2M sulphuric acid solutions. It has a high ability to concentrate the chromium(VI) in the receiving phase according to the Donnan equilibrium. The co-extraction and the co-transport of sulphuric acid is very low and has no effect on the transport efficiency. The transport rate depends mainly on the initial concentration of the extractant.     

Modelling of mass transfer in facilitated supported liquid membrane transport of copper(II) using MOC-55 TD in Iberfluid

The transport of copper(II) through a supported liquid membrane using MOC-55 TD (oxime derivative), dissolved in Iberfluid, as a carrier has been studied. A physico-chemical model is derived to describe the transport mechanism which consists of: diffusion process through the feed aqueous diffusion layer, fast interfacial chemical reaction and diffusion through the membrane. The experimental data can be explained by mathematical equations describing the rate of transport. The mass transfer coefficient was calculated from the described model as 2.8×10⁻³ cm s⁻¹, the thickness of the aqueous boundary layer as 2.6×10⁻³ cm⁻¹ and the membrane diffusion coefficient of the copper-containing species as 1.2×10⁻⁸ cm² s⁻¹.     

Kinetics of europium(III) transport through a liquid membrane containing HEH(EHP) in kerosene

Coupled transport of Eu(III) ions through a bulk liquid membrane containing mono(2-ethylhexyl)2-ethylhexyl phosphonate [HEH(EHP)] in kerosene has been examined. The influences of the carrier concentration, the HCl concentration in the stripping solution, the pH in the feed solution and the temperature were investigated. The transport of the Eu(III) ions is coupled by counter-transport of protons. The kinetics of the Eu(III) transport could be analyzed in the formalism of two consecutive irreversible first order reactions. The pseudo-first order apparent rate constants of the interfacial transport of the Eu(III) species are determined, varying temperature. The activation energy values are 14.0±1.0 and 54.0±3.4 kJ mol⁻¹ for extraction and stripping, respectively.     

Facilitated transport of Am(III) through a flat-sheet supported liquid membrane (FSSLM) containing tetra(2-ethyl hexyl) diglycolamide (TEHDGA) as carrier

Facilitated transport of Am(III) in nitric acid medium using tetra(2-ethyl hexyl) diglycolamide (TEHDGA) in n-dodecane as carrier was studied. It was aimed at finding out the physico-chemical model for the transport of Am(III) using TEHDGA/n-dodecane as carrier under various experimental parameters like feed acidity, carrier concentration, varying strippant, varying membrane pore size, etc. The feed acidity and carrier concentrations were varied from 1 M to 6 M HNO₃ and 0.1 M to 0.3 M TEHDGA/n-dodecane, respectively. The transport of Am(III) increased with increase in feed acidity and carrier concentration reaching maximum at 3 M HNO₃ and 0.2 M TEHDGA/n-dodecane, respectively. Several stripping agents were tested and 0.1 M HNO₃ was found to be the most suitable stripping agent for this system. Almost quantitative transport of Am(III) was observed at about 180 min with feed acidity of 3 M HNO₃, 0.1 M HNO₃ as strippant and 0.2 M TEHDGA/n-dodecane as carrier. The pore size of the membrane support was varied from 0.20 μm to 5 μm and the permeation coefficient increased with increase in pore size up to 0.45 μm (2.43 × 10⁻³ cm/s), and then decreased with further increase in pore size. The plot between permeation coefficient vs. (membrane thickness)⁻¹ was linear which showed that the Am(III) transport was membrane diffusion limited. The membrane diffusion coefficient calculated from the graph was found to be 1.27 × 10⁻⁶ cm²/s and its theoretical value was 1.22 × 10⁻⁶ cm²/s. The stability of the carrier against leaching out of the membrane support as well as the integrity of membrane support was studied over a period of 30 days and was found to be satisfactory within the studied time period.     

Transient behaviour of facilitated transport through liquid membranes

During the transient period of facilitated transport of a permeant across a thin liquid film, the ratio of the concentrations of the carrier at the two ends of the film as a function of time has a shape which is sensitive to the values of the physicochemical parameters. In certain systems involving ionic carriers, the above concentration ratio can be related to a conveniently measurable electrical potential difference, ΔV, across a pair of electrodes attached to the two faces of the liquid film. Bdzil et al. measured ΔV vs. time for NO FeCl₂FeCl₃—formamide system and observed that it goes through a maximum (ΔV_max), before reaching the asymptotic value corresponding to the steady state, ΔV_s.In the present paper, we solve numerically the species conservation equations, which describe the transients of the facilitated transport in the film, when the reversible reaction occurring in the film is of the form: A↑ + B = P (where A is the permeant and B and P are the carrier and permeant—carrier complex, respectively). The analysis takes into account: (i) the electrical effects which arise when B and P are ions of different diffusion coefficients and (ii) the effect of a second electrolyte added to the film to provide the cations which participate in an electrode reaction with the carrier ions. On this basis, an explanation is provided for the overshoot observed experimentally by Bdzil et al. in the ΔV vs. time curve. Such a maximum is exhibited by systems for which the time scales of diffusion and backward reaction in the film are of comparable magnitude. (Of course, for viable facilitation, the characteristic times of the forward and backward reactions should also be comparable.)The profile of ΔVvs. time is very sensitive to the values of the kinetic constants as well as the diffusion coefficients of the species A, B, and P. Therefore, measurements of ΔV vs. time (or equivalently the ratio of concentrations of the carrier on the two sides of the film as a function of time) can provide a more accurate method of determining the above parameters than those based on flux measurements.     

Enzyme-facilitated enantioselective transport of (S)-ibuprofen through a supported liquid membrane based on ionic liquids

Coupling lipase reactions with a supported liquid membrane (SLM) based on ionic liquids showed facilitative and selective permeation of (S)-ibuprofen through the SLM, indicating successful optical resolution of a racemic mixture using the enzyme-facilitative SLM.     

New mixed heteropolytungstates containing Ge(IV) or Sn(IV)

New mixed heteropolyanions with formulae XZW₁₁O₃₉(OH)^m?[X = Si, Ge, B, As(V), Ga, Co(II), Zn; Z = Ge(IV), Sn(IV)] and X₂′ZW₁₇O₆₁(OH)^7?[X′= As(V), P(V);Z = Ge(IV), Sn(IV)] were prepared. Crystal systems of the potassium salts were determined. The stability range of the anions is given in terms of the pH. The acids corresponding to the salts were obtained and their neutralization studied. Spectroscopic and polarographic reduction studies are reported.     

Selective facilitated transport of benzene across supported and flowing liquid membranes containing silver nitrate as a carrier

Separation of benzene from cyclohexane was performed using two types of liquid membranes, i.e., a supported liquid membrane and a flowing liquid membrane. Silver nitrate was used as the carrier of benzene. The permeation rate of benzene increased with increasing carrier concentration, and the separation factor, which is defined as the ratio of permeability of benzene to that of cyclohexane, was about 630 when the supported liquid membrane prepared by immobilizing 4 mol/L aqueous silver nitrate solution in cellulose filter paper was used. Compared with the supported liquid membrane, the flowing liquid membrane, where a liquid membrane solution was forced to flow in a thin compartment between two microporous membranes, showed one order of magnitude higher permeation rate at high flow rate of the membrane solution. The flowing liquid membrane was very stable and no noticeable decrease in both the flux and the selectivity was observed during 11 days operation. The mechanisms of the facilitated transport of benzene through both types of liquid membrane were proposed. The permeation rate and the selectivity were quantitatively simulated by the proposed model.     

Selective transport of zirconium (IV) and niobium (V) from hydrochloric media through a bulk liquid membrane

The selective transport of zirconium/niobium from hydrochloric medium has been investigated through a bulk liquid membrane (BLM) using tri-n-butyl-phosphate (TBP), tri-n-octylamine and dibenzo-18-crown-6 (DBC-6) as the extractants (carriers). The Optimization studies have been carried out by scrutinizing the effect of variables such as the hydrochloric acid concentration in the feed solution, membrane type and hydrochloric acid concentration in the strip solution using the Taguchi approach. The Quantitative transport of zirconium/niobium has been observed by 30% (v/v) TBP in 1200 min from the feed composed of a 9.0 M hydrochloric acid solution of Zr(IV), Nb(V) and lanthanide cations, while the transport of other cations, which have been presented along with Zr/Nb are less than 3% during the same time. Moreover, the possible mechanism of Zr(IV)/Nb(V) ion transport through the BLM has also been discussed and the results show a consecutive, irreversible second-order reaction at the interfaces. Transfer kinetics studies show that niobium transfer process exhibits slightly faster kinetics than zirconium.     

Study of the transport of silver across a supported liquid membrane containing sulphide podand

The transport of silver through a supported liquid membrane saturated with a polydentate neutral ionophore 1,12-di-thienyl-2,5,8,11-tetrathiadodecane in m-chlorotoluene has been studied. Thiosulphate was used as the stripping solution. The influence of the feed solution composition, the type of a microporous polypropylene Celgard support, the ratio of feed/receiving solution volume, and the initial Ag concentration on the rate of transport of silver was examined. Transport of Ag is selective towards Cu(II), Pb and Zn, but these cations affected the rate of the Ag flux.     

Factors influencing the transport of tryptophan hydrochloride through supported liquid membranes containing macrocyclic carriers

Commercially available PTFE membranes were used as a support for liquid membranes in amino acid transport. Using tryptophan as a model amino acid, the influence of the type of organic liquid, kind of macrocyclic carrier and counter-ion on transport efficiency was examined. These studies show the strong influence of the kind of the counter-ion co-transported with amino acid cation, and the type of macrocyclic carrier used on the transport efficiency. The transport efficiency depends also on the pH of the source phase and on the nature of the organic liquid used as a membrane solvent. Liquid membranes supported on commercial porous-PTFE-membranes with hydrophobic solvents are stable for more than two months, while those with more hydrophilic solvents, for more than 30 days. The use of dodecylbenzenesulfonic acid as a counter-ion results in the highest flux of tryptophan, but in this case, the stability of membranes appeared to be five times lower.