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.     

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.     

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.     

A simplified model for the coupled transport of metal ions through hollow-fiber supported liquid membranes

This paper describes a simplified model for the carrier-facilitated transport of metal ions through hollow-fiber supported liquid membranes, HFSLM. The model leads to approximate and simple equations describing the concentration variations expected when an aqueous feed solution is flowing through the lumens of a HFSLM module. The equations incorporate simple and independently measurable parameters and apply to two situations: (a) a once-through mode, i.e., the feed solution passes only once through the module, and (b) a recycling mode, i.e., the feed solution is continuously recirculated through the module. The equations have been tested by measuring the transport of Cu²⁺ ions through microporous polypropylene hollow fibers containing a 0.3 F solution of bis(2-ethylhexyl)phosphoric acid in n-dodecane. HFSLM modules containing a variable number of fibers, fibers of different lengths and operated at different linear flow velocities have been used.     

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 stripping study of strontium ions across D2EHPA-TBP-kerosene oil based supported liquid membranes

A Sr ion transport study across D2EHPA-TBP kerosene oil based liquid membranes supported on microporous polypropylene film has been performed. The parameters studied were the effect of di(2-ethylhexyl)phosphoric acid (D2EHPA) and TBP concentration variation in the membrane liquid, HNO₃ concentration variation in the stripping phase and citric acid concentration variation in the feed solution. The optimum conditions of transport are 0.3 mol/dm³ D2EHPA, 0.1 mol/dm³ TBP, 0.01 mol/dm³ citric acid in feed and 2 mol/dm³ HNO₃ in the stripping phase. The mechanism of transport observed is counter-ion coupled transport. The coupling ions are protons. The maximum flux for Sr ion transport observed is 5.33·10^–5 mol·m^–2·s^–1 and maximum permeability under optimum conditions observed is 8.08·10^–11 m^–2·s^–1.     

Coupled transport of Ag(I) ions through triethanolamine–cyclohexanone-based supported liquid membranes

Facilitated transport of silver(I) ions in acidic medium, across a supported liquid membrane (SLM) by using triethanolamine (TEA) as carrier, dissolved in cyclohexanone, has been investigated. The parameters studied are HNO₃ concentration variation in the feed, pH of the feed solution, carrier concentration in the membrane phase, silver(I) ions concentration in the feed phase and KCN concentration in the stripping phase. Increase in H⁺ concentration by increasing HNO₃ concentration from 0.5 to 1 M results into an increase in silver ions flux but a decrease in flux has been found beyond 1 M HNO₃ concentration in the feed, providing a maximum flux of 3.21 × 10⁻⁷ mol/m² s at 1 M HNO₃. Increase in TEA concentration inside the membrane enhances flux with its maximum value at 2.25 M TEA. Further increase in the concentration of TEA leads to a decreased rate of transport due to the increase in viscosity of membrane liquid. The optimum conditions for Ag(I) ions transport are 1 M HNO₃ (feed), 2.25 M TEA (membrane) and 1.5 M KCN in the stripping phase. It has been observed that Ag(I) flux across the membrane tends to increase with increase in Ag(I) ions concentration in the feed phase. Applying the studied conditions to silver plating waste solutions, Ag ions have been removed up to 99% in a time interval of 5 h.     

Transport across liquid membranes containing vitamin A (retinol acetate)

The role of the surface activity of vitamin A has been studied in the light of the liquid membrane hypothesis of drug action. Transport of relevant amino acids such as serine, threonine, arginine, and histidine and various ions such as calcium, sodium, and potassium in the presence of liquid membranes generated by vitamin A has been studied. The data on the modifications in the permeability of relevant amino acids and ions indicate that the liquid membranes generated by vitamin A may also play a significant role in its physiological action.     

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.     

Direct determination of U(VI) in TBP-kerosene extracts using first derivative ultraviolet spectroscopy

Summary The extractive first order derivative spectrophotometry is a selective method for the separation and determination of U(VI) using tri-n-butyl phosphate (TBP), which combines the roles of solvent and complexing agent. The complex is formed by extracting U(VI) from an aqueous 6M sodium nitrate solution at initial pH 3.0 into a 25% solution of TBP in kerosene. This extraction also separates U(VI) from many diverse ions that interfere. After extraction, the determination of uranium shows good accuracy and precision with relative standard deviation of 1.5% (n = 5) at 20 ppm using zero-order spectrum at l_max = 250 nm. Calibration curve was also found to obey Beer's law in the range of 10-100 ppm with 3.33 ppm detection limit. However, these accuracy and precision have been improved to give relative standard deviation of 0.7% (n = 5) at 20 ppm with a lower detection limit of 2.24 ppm using the first-derivative spectrum at l = 263 nm comparing to the normal one.     

Analytical utility of coupled transport across a supported liquid membrane Selective preconcentration of zinc

A liquid membrane comprising 5-10% bis(2,4,4-trimethylpentyl)phosphinic acid in dodecane that is supported between an aqueous sample at pH 4.7-6.0 and a 0.1M HCl receiver results in uphill transport of Zn(II) from the sample into the receiver. With 2 ml of receiver, a 5 cm(2) membrane and 60 min dialysis time, Zn(II) is preconcentrated by a factor of ca. 13 when the initial concentration in the sample is in the range 1.5 x 10(-7)-1.5 x 10(-4)M. The enrichment factor is directly proportional to time up to 30 min since the transport rate of Zn(II) across the membrane is constant over this period. At longer times the flux is slowed as the system begins to approach equilibrium. The presence of other metals such as Cu(II), Co(II), Ni(II), Cd(II), Pb(II) and Fe(II) does not change the enrichment factor for Zn(II), even when the interferent is at a concentration high enough for the rate of transport (nmole/min) of the interferent and Zn(II) to be about the same. The flux of Zn(II) was about 40 times that of Cu(II) and 100 times that of Co(II) when their concentrations in the sample were equal. The other metal ions examined are not significantly transported.     

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 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.     

Transport of U(VI) from sulphuric acid medium across supported liquid membrane (SLM) containing di-(2-ethylhexyl) phosphoric acid (D2EHPA)/n-dodecane as a carrier

This paper reports on the supported liquid membrane (SLM) based transport studies of U(VI) from sulphate medium using di-(2-ethylhexyl) phosphoric acid/n-dodecane as carrier. Polytetrafluoroethylene membrane was used as solid support and H₂SO₄ as receiver phase. The effects of various parameters such as receiver phase concentration, feed acidity, carrier concentration, U(VI) concentration, membrane thickness and membrane pore size on U(VI) transport had been investigated. With increase in H₂SO₄ concentrations and pH of feed solution there is an increase in U(VI) transport across the SLM. Similarly with increase in membrane thickness the U(VI) transport decrease whereas in case of pore size variation reverse results are obtained. The membrane thickness variation results showed that the U(VI) transport across the SLM is entirely diffusion controlled and the diffusion coefficient the D _(o) was calculated as 1.36 × 10^?7 cm² s^?1. Based on optimized condition, a scheme had been tested for selective recovery of U(VI) from ore leach solution containing a large number of other metal ions.     

Kinetic analysis of coupled transport of thiocyanate ions through liquid membranes at different temperatures

Non-steady-state kinetics of coupled transport of thiocyanate ions through liquid membrane (trichloromethane), containing hexadecyl trimethyl ammonium chloride as a carrier, was examined at different temperatures. The kinetics of thiocyanate transport could be analyzed in the formalism of two, consecutive, irreversible first order reactions. The influence of temperature on the kinetic parameters (k_1d, k_2m, R_m^max, t_max, J_d^max, J_a^max) have been also investigated. The membrane entrance rate, k_1d, and the membrane exit rates, k_2m and k_2a, increase with temperature. For maximum membrane entrance and exit fluxes, J_d^max and J_a^max, the activation energies were found from the slopes of the two linear relationships: 7:75 and 8.30 kcal/mol, respectively. The values of the found activation energy indicate that the process is controlled by species difussion.     

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.     

Transport study of V(V), Zn(II) and Be(II) using supported liquid membranes

V(V), Zn(II) and Be(II) have been studied to test oxine and tri-n-butylphosphate (TBP) as carriers for transport through supported liquid membranes in polypropylene film. All the three types of ions can be passed through such membranes using oxine in case of V(V) and TBP in case of Zn(II) and Be(II). Maximum flux of metal ions has been observed from 0.01M H₂SO₄ for V(V) (3.22·10^–6 mol·m^–2·s^–1) and 2M HCl containing 3M CaCl₂ for Zn(II) solution (1.4·10^–6 mol·m^–2·s^–1). Low flux was observed in case of Be(II) since the membrane was affected by sulphocyanide group and did not remain hydrophobic. Mechanism of transport for these metal ions have been proposed separately. Distribution coefficient data for V(V) have also been evaluated to determine theoretical values of the permeability coefficient, and compared with experimental values.     

Selective transport of copper(II) ions across a liquid membrane mediated by Piroxicam

Piroxicam was found to be a highly selective carrier for uphill transport of Cu²⁺ ions through a chloroform liquid membrane. The transport occurs via a counterflow of protons from the receiving phase to the source phase. The effects of several parameters on the transport of Cu²⁺ ions, such as the carrier concentration, pH of the source phase, composition of the receiving phase, and duration are described. A high transport efficiency (98±2%) was provided by the carrier for Cu²⁺ ions in a receiving phase of 0.01 mol l⁻¹ sulfuric acid after 4 h. Different metal ion transport experiments showed that Cu²⁺ ions were selectively transported over other ions, such as Co²⁺, Ni²⁺, Cd²⁺, Pb²⁺, Zn²⁺, UO₂²⁺ and ZrO₂²⁺. In the presence of fluoride ions (used as a suitable masking agent in the source phase), the interfering effects of UO₂²⁺ and ZrO₂²⁺ ions were eliminated. The applicability of the method was tested on a real sample, and the results obtained show that it is potentially useful for solvent extraction of copper.