Nitrate ion transport across TBP-kerosene oil supported liquid membranes coupled with uranyl ions

The role of nitrate ions in uranyl ions transport across TBP-kerosene oil supported liquid membranes (SLM) at varied concentrations of HNO₃ and NaNO₃ has been studied. It has been found that nitrate ions move faster compared to uranyl ions at the uranium feed solution concentrations studied. The nitrate to uranyl ions flux ratio vary from 355 to 2636 under different chemical conditions. At low uranium concentration the nitrate ions transport as HNO₃ · TBP, in addition to as UO₂(NO₃)₂ · 2TBP type complex species. The flux of nitrate ions is of the order of 12.10 · 10^–3 mol · m^–2 · s^–1 compared to that of uranium ions (4.56 · 10^–6 mol · m^–2 · s^–1). The permeability coefficient of the membrane for nitrate ions varies with chemical composition of the feed solution and is in the order of 2.5 · 10^–10 m^–2 · s^–1. The data is useful to estimate the nitrate ions required to move a given amount of uranyl ions across such an SLM and in simple solvent extraction.     

Transport of99mTc across TBP-kerosene oil supported liquid membranes

Transport of^99mTc across tri-n-butylphosphate (TBP) kerosene oil supported liquid membranes (SLM) has been studied under various conditions. Presence of dichromate ions helps avoid activity scavenging effects. Concentration increase of TBP, the complexing carrier used in the present study has a positive effect on flux (J) and permeability (P) of these ions, as up to 2.87M there is an increase in J and P values. HCl concentration in the feed solution increases J and P with their maximum values at 2.5–3.0M HCl in the feed. Above this concentration there is a decrease in flux and permeability of^99mTc(VII) ions. The given ions are stripped with LiCl or NaCl solutions but more with NaOH. The optimum conditions of transport of the given ions are 2.5M HCl concentration in the feed, 2.87M TBP concentration in the membrane and 1M NaOH concentration in the strip solution. Equations have been developed to indicate the relation between flux, J, viscosity, of TBP in organic membrane phase, temperature, T, [H⁺], in the aqueous feed solutions and Tc ion concentration in the feed solution. Based on P, the values determined from liquid membrane experiments, the quantitative flux values of Tc(VII) ions were also determined as a function of TBP concentration in the membranes, and HCl and Tc concentration in the feed solution using the given equations. This experimental technique provides quantitative results from trace level activity transfer experiments.     

Nitric acid transport across TBP—Kerosene oil supported liquid membranes

HNO₃ transport across tri-n-butyl phosphate kerosene oil supported liquid membrane with or without uranyl ion transport has been studied. Parameters studied are the effect of TBP in the membrane, nitric acid in the feed solution and nitrate ion concentration in the feed solution. The flux of protons for 1 to 10 mol·dm^–3 HNO₃ solution is in the range of (0–25)·10^–4 mol·m^–2·s^–1 and for the TBP concentration range of 0.359 to 3.59 mol·dm^–3, the flux determined is (8.9 to 22)·10^–4 mol·m^–2·s^–1. From the experimental data and using theoretical equations the complex under transport through the membrane appears to be 2TBP·HNO₃ both in the presence and absence of uranyl ions. The diffusion coefficient for H⁺ ions through the membrane as a function of TBP concentration varies from (53 to 6)·10^–12 m²·s^–1, based on experimental flux and permeability data. The values of this coefficient supposing 2TBP·HNO₃ as diffusing species, based on viscosity data and theoretical estimation varies from (82.50 to 3.30)·10^–12 m²·s^–1. The value of distribution coefficient varies in the reverse direction from 0.06 to 1.46 at the same TBP concentration.     

Transport of U(VI) ions in high concentrations across coupled transport TBP-kerosene oil supported liquid membranes

Work so far has been done with low uranium concentrations in the feed solution in supported liquid coupled transport systems of metal ion separations. In the present work the uranium concentration range is 0.1–28.5%. The flux values have been found to increase with increasing uranium concentration. This indicates reduced overall supporting device area. Thicker membranes serve the purpose better than the thinner ones due to their longer membrane life.     

Transport of titanium(IV) ions across di-2-ethylhexylphosphoric acid-CCl4 supported liquid membranes

Transport study for Ti(IV) ions using di-2-ethylhexylphosphoric acid (D2EHPA) (carrier)-CCl₄ (diluent) liquid supported membrane in microporous polypropylene hydrophobic film has been performed. The parameters studied are effects of carrier, H₂SO₄, stripping agent (NH₄F) concentrations and temperature variation on flux and permeability coefficients of the metal ion. The optimum concentrations of transport found are 2.04 mol·dm^–3 D2EHPA, 1.0 mol·dm^–3 H₂SO₄ in the feed and 1 mol·dm^–3 NH₄F as stripping agent. The maximum flux and permeability coefficient determined are 1.32·10^–5 mol·m^–2·s^–1 and 8.02·10^–12 mol·m^–2·s^–1, respectively. The transport of this metal ion is increased with increase in temperature. The mechanism of transport appears to be based on coupled counter ion transport phenomenon.     

Technetium-99m extraction and transport across tri-n-octylamine-xylene based supported liquid membranes

The nuclear properties of^99mTc radionuclide are ideal for organ imaging. Study of the technetium transport across supported liquid membranes has been performed to get data for its separation from other elements. Tri-n-octylamine diluted in xylene was used to constitute the liquid membranes, supported in polypropylene microporous films. Stripping on the product solution side was performed with dilute NaOH solutions. The effect of sulphuric acid, nitric acid and hydrochloric acid in the feed on transport of^99mTc as TcO ₄ ^– ions has been studied. The permeability of the given ions determined from kinetic activity data has been found to be in the order of PH₂SO₄>PHCl>PHNO₃. The flux values have been calculated based on this permeability data. The increase in carrier concentration has shown an increase in flux and permeability values to a given optimum concentration. The increase in temperature has been found to reduce the transport of Tc ions. The optimum conditions for transport of^99mTc for the given acid concentration have been determined. Mechanism of Tc ion transport has also been provided based on chemical reactions involved at the membrane interfaces and uptake of Tc ions by the membrane. MoO ₄ ^2– ions do not permeate through membrane under optimum conditions of transport for TcO ₄ ^2– ions from H₂SO₄ solution.     

Transport of strontium cation through hollow fiber supported liquid membranes

Transport of strontium through supported hollow fiber dichlorobenzene liquid membranes has been studied. The possible mechanism of strontium transport with 18-crown-6 ether as a carrier and picrate as co-counter-ion as well as the construction of a pertraction device with on-line radiometric detection of strontium using⁸⁵Sr tracer is described. Preliminary results of strontium pertraction in a recycling and one-pass mode with different concentrations of crown are shown.     

Extraction of Pd(II) ions using tri-n-octylamine xylene base supported liquid membranes

Membranes, based on tri-n-octylamine (TOA) xylene liquid, supported in hydrophobic microporous films have been used to study the transport of Pd(II) ions, after extraction into the membrane. Various parameters, such as the effect of hydrochloric acid concentration in the feed solution, TOA concentration in the membrane phase, effect of stripping agent like nitric acid concentration, and temperature on the flux of Pd(II) ions across the liquid membranes have been investigated. The optimum conditions of transport for these metal ions determined are, TOA concentration, 1.25 mol·dm^–3, HCl concentration in the feed solution, 5 mol·dm^–3, and concentration of nitric acid used as a stripping, agent 5 mol·dm^–3. The maximum values of the flux and permeability determined under the optimum condition are 23·10^–6 mol·m^–2·s^–1 and 2.40·10³ m²·s^–1 at 25°C. The results obtained have been used to elucidate the mechanism of palladium transport.     

Extraction of strontium ions with emulsion liquid membrane technique

The aims of this study are to form a liquid membrane suitable for the extraction of strontium ions from aqueous solutions and to determine the factors influencing the stability of the membrane, the extraction efficiency and the rate of transport. The suggested membrane is composed of kerosene, Span 80 and D2EHPA. It has been observed that the extraction efficiency and the rate of transport increase with increasing ratio of emulsion to outer phase volume, stirring rate and D2EHPA concentration and decreasing pH of the inner phase. As the strontium ion concentration in the outer phase increases, the transport rate increases but the separation efficiency decreases. The maximum separation efficiency achieved in the experiments was 92%.     

Simultaneous diffusion of ions and ion pairs across liquid membranes

The flux of tetrabutylammonium nitrate (Bu₄ NNO₃) across a liquid membrane of n-heptyl cyanide varies with the salt concentrations in dilute solution, but with the concentration squared in more concentrated solution. The results are consistent with a mechanism which includes parallel diffusion of ions and ion pairs. This type of behavior, which will be common in homogeneous membranes of low dielectric constant, is a form of facilitated diffusion in which the salt acts as its own carrier.     

Extraction of Uranium(VI) using D2EHPA/TOPO based supported liquid membrane

This work concerns the extraction of U(VI) using supported liquid membrane (SLM) by di-(2-ethylhexyl) phosphoric acid (D2EHPA) and tri-n-octyl phosphine oxide (TOPO) with polyvinylidene difluoride (PVDF) as a membrane support. The influence of ionic strength (S), stirring rate (V) and extraction time (t) were studied. The effect of membrane thickness on the permeability and extraction yield of uranium was investigated. A comparative study was carried out using a 2³ full factorial design between SLMs with one membrane and two membranes, and to achieve the best conditions of recovery procedure, obtaining the mutual interaction among variables and optimizing these variables. The recovery of U(VI) is almost quantitative, and the supported liquid membrane with two membranes in series is effective.     

Microextraction across supported liquid membranes forced by pH gradients and electrical fields

The present work has for the first time compared extraction of basic analytes across a supported liquid membrane (SLM) based on (1) passive diffusion in a pH gradient sustained over the SLM and (2) electrokinetic migration in an electrical field sustained over the SLM. For the passive diffusion experiments, performed as liquid-phase microextraction (LPME), five basic drugs were extracted under strong agitation from alkaline samples (10mM NaOH), through 2-nitrophenyl octylether immobilized in the pores of a porous hollow fibre of polypropylene (SLM), and into 25 microl of 10mM HCl as the acceptor solution. The experiments based on electrokinetic migration, performed as electro membrane isolation (EMI), were conducted under strong agitation from acidic samples (10mM HCl), through the same SLM as in LPME, and into 25 microl of 10mM HCl as the acceptor solution. Whereas LPME relied on diffusion and to some extent also convection as the principal mechanisms of mass transfer, mass transfer in EMI also included a strong contribution from electrokinetic migration. Thus, extraction kinetics was improved by a factor between 6 and 17 utilizing EMI instead of LPME. This major difference in terms of speed was especially pronounced from small sample volumes (150 microl), and suggest that EMI may be a very interesting future concept for miniaturized sample preparation. In addition to improved extraction kinetics, extraction rates were strongly compound dependent in EMI, opening the possibility to control the extraction selectivity by the extraction time.     

Uranyi ion transport through tri-n-octylamine-xylene based supported liquid membranes

Tri-n-octylamine (TOA) dissolved in xylene has been used as carrier, constituting liquid membrane supported in Celgard 2400 polypropylene microporous film for the transport of uranyl ions against their concentration gradient from aqueous acid solutions to an alkaline aqueous phase. Effect of sttrring rate, nitric acid concentration and TOA concentration in the organic membrane phase, on the flux of uranyl ions through the membrane has been studied. Viscosity and density data have been obtained to estimate diffusion coefficients and hence the permeability coefficients to compare the same with experimental values, using distribution coefficient data, measured from solvent extraction experiments and available in the literature. Analysis of the flux data has been performed to study the stoichiometry of the chemical reaction involved in complex formation reaction. The results have been compared with simple liquid-liquid extraction data.     

Permeation of metal ions through a series of two complementary supported liquid membranes

The permeation of Am³⁺ and Eu³⁺. through two composite supported liquid membranes, SLM, consisting of a series of two complementary SLMs, separated by an aqueous solution, has been studied. The first liquid membrane was a neutral membrane, i.e., a solution of a bifunctional neutral organophosphorous extractant in decalin. The second liquid membrane was an acidic membrane, i.e., a solution of bis(2-ethylhexyl)phosphoric acid in n-dodecane or of dinonylnaphthalene sulphonie acid in decalin. The solid support was a microporous polypropylene film. The composite SLM system had the sequence “Solution A — SLM(A) -Solution B — SLM(B) — Solution A”, where aqueous solution A promotes extraction of th the metal cations into SLM(A) and their stripping from SLM(B), and aqueous solution B promotes stripping of metal cations from SLM(A) and their extraction into SLM(B). SLM(A) and SLM(B) are a neutral or an acidic S/aVis or vice versa. The study has demonstrated that the single-stage character of SLM separations of metal ions in solution can be in principle overcome by repeating the composite SLM arrangement a number of times. The equations describing the concentration variations in the aqueous solutions which are adjacent to the acidic and neutral SLMs are also reported. They allow one to predict quantitatively the degree of enrichment of each aqueous solution as function of time and the degree of separation among different cations achievable with the composite SLM system. The overall permeability of the composite SLM system to a given cation is shown to be a function of the single-membrane permeability coefficients as well as of the volumes of the aqueous solutions and the SLM area.     

Multistage separation of metal ions with a series of composite supported liquid membranes

The possibility of performing multistage separations of metal cations, present at low concentrations in aqueous solutions, using a series of composite supported liquid membranes (SLM), interposed between compartments containing identical aqueous electrolyte solutions, is discussed. The multistage separation of Eu³⁺. from Am³⁺ and of Sm³⁺ from Nd³⁺ and Ce³⁺ is theoretically analyzed. A single separation stage, using a thin, three-layer asymmetrical composite SLM, which allows differential permeation of Eu³⁺. and Am³⁺, is described and experimentally studied. The composite SLM consists of a 1 mm thick aqueous slab sandwiched between acidic and neutral supported liquid membranes. The results demonstrate that the permeation of each cation through the thin composite SLM can be described by a single permeation parameter which is equal to the permeability coefficient through the first acidic supported liquid membrane of the composite layer.     

SO2 gas separation using supported ionic liquid membranes

Measurements of permeability of sulfur dioxide (SO2) in five imidazolium-based ionic liquids supported on the polyethersulfone microfiltration membranes at temperatures from 25 to 45 degrees C and atmospheric pressure indicate that under the same conditions, the SO2 selectivity of separations using supported ionic liquid membranes are 9-19 times that of CO2.     

Fundamental studies on the electrokinetic transfer of net cationic peptides across supported liquid membranes

By the application of an electrical potential difference (25 V), 37 different peptides were extracted from 500 μL aqueous sample (10 mM formic acid, positive electrode), through a supported liquid membrane (SLM) impregnated in the walls of a porous hollow fiber, and into 25 μL aqueous acceptor solution (100 mM formic acid, negative electrode) present inside the lumen of the fiber. Most of the peptides were obtained by tryptic digestion of cytochrome c and bovine serum albumin, which yielded complex samples for extraction. Three different SLMs were utilized to correlate the peptides extractability with the highly variable physical-chemical properties of the peptides. The first SLM (pure eugenol) provided an electromembrane extraction system for hydrophobic and intermediate peptides (hydrophilicity values below 0.2), where the extraction of peptides into the SLM was mainly based on solvent interactions. The second SLM (1-octanol/di-isobutylketone/di-(2-ethylhexyl) phosphate) extracted both hydrophobic and hydrophilic peptides (hydrophilicity values in the range from -2 to+1) successfully, and the transfer of peptides was principally based on ionic interactions with di-(2-ethylhexyl) phosphate. The third SLM (1-octanol/15-crown-5 ether) was selective for hydrophobic peptides (negative hydrophilicity values), and complexation of the peptides with the crown ether was important for the migration of peptides into the acceptor solution.     

The effect of component partitioning on potassium picrate transport across multicomponent supported liquid membranes

Supported liquid membrane experiments were performed with systematically varied liquid membrane compositions including dicyclohexyl-18-crown-6 ether as the carrier and various ratios of methylene chloride and a 35 carbon aliphatic oil. The partitioning of the crown ether species toward the membrane phase increased markedly with methylene chloride addition to the aliphatic oil. p]The unanticipated unsteady state transport of potassium picrate across the liquidfilled microporous membranes resulted from evaporation of methylene chloride from the aqueous reservoirs and subsequent depletion from the membrane phase. The depletion of methylene chloride from the liquid membrane caused progressively reduced partitioning of the carrier and carrier complexes to the membrane relative to the contiguous aqueous phases. The reduction in carrier concentration in the membrane phase resulted in progressively decreased concentration gradients of the carrier complex. The rate of potassium picrate transport decreased during the course of the experiments even though the upstream potassium concentration was insignificantly decreased and the downstream concentration of potassium picrate remained small compared with the upstream concentration. p]These experimental results focus attention upon the important practical problem of non-infinite partitioning of carrier and key solvent components between the membrane phase and the contiguous aqueous phases. Subtle changes in the carrier distribution coefficient markedly compromise process efficacy since the volume ratio of the aqueous and membrane phases is enormous.     

Extraction of rare earth elements with organophosphorus extractants as carriers in supported liquid membranes

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.