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 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.     

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.     

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 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.     

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.     

Extraction of metal ions with a primary amine

This paper describes some experimental results obtained at the extraction of sulfate solutions of U(VI), Mo(VI), V(V), Ce(IV), Zr(IV), Fe(III), Al(III) with a benzene solution of Primene JMT. The aqueous solutions consist of metal sulfates (or other metal salts) in the presence of sulfuric acid with a concentration range of 0–2.1 mol·dm^–3, the concentration of amine in the organic phase being 0.1–0.3 mol·dm^–3. The presence of various species of metal ions in the aqueous phase is considered and the equilibrium concentration of substances extracted in the organic phase is determined. On the basis of the results of chemical analysis (concentration of metals and sulfate ions) the composition of the prevailing complexes in the organic phase is proposed.     

Separation of 99mTc from 99Mo by Using TOPO — Kerosene Supported Liquid Membrane

Transport of ^99mTcO₄ ^– ions across TOPO-kerosene based supported liquid membrane was investigated at different concentrations of phosphoric acid as a feed solution and different concentrations of TOPO in the membrane, where 0.9% NaCl aqueous solution was used as a stripping solution. The flux of TcO₄ ^– ions across this liquid membrane varied with the concentration of both H₃PO₄ and TOPO. The best permeability coefficient was obtained at concentrations, [H₃PO₄] = 3 mole·l^–1 and [TOPO] = 0.5 mole·l^–1 (P = 2.08·10^–9 m²·s^–1). The results were utilized for the separation of ^99mTc from ⁹⁹Mo, where a selective and effective separation was obtained since no ⁹⁹Mo transport across this liquid membrane was noticed while a high rate of ^99mTc transport took place.     

Precipitation separation of strontium and calcium from acidic solutions using crown ether and tungstosilicic acid

Strontium forms a compound of composition (SrL)₂A·nH₂O with low solubility (5.0·10^–6 mol Sr·dm^–3) in the presence of 18-crown-6 (L) and tungstosilicic acid (H₄A) in acid media, as has been found by radiometric precipitation titration. Formation of the compound with limited solubility was used for separation of strontium and calcium from 1 mol·dm^–3 HCl. It is possible to separate strontium in the range from trace to 6 mmol·dm^–3 in the presence of calcium with its concentration up to 0.2 mol ·dm^–3 and the recovery determined was 95% of Sr and 5% Ca or 90% of Sr and 4% Ca, respectively. The ratio of Sr/Ca depends on the stability constants ratio of metal-L (⊃_SR/⊃_ca) in the case of gradual addition of L. Potassium up to the concentration of 0.05 mol·dm^–3 does not influence recovery of strontium.     

Electron irradiation studies on ammonium molybdophosphate

Ammonium molybdophosphate (AMP) was irradiated with electrons up to a dose of 1 MGy. X-ray diffraction patterns and FT-IR of irradiated and control AMP samples were recorded. Uptake of¹³⁷Cs from nitric acid in the range of 0.2 to 10 mol·dm^–3 was estimated by a batch equilibration technique. AMP undergoes perceptible changes in its physico-chemical characteristics on irradiation with electrons. Uptake of¹³⁷Cs from nitric acid by irradiated AMP was nearly the same as the control AMP in the nitric acid concentration range of 6 to 10 mol·dm^–3 and relatively higher in the range of 0.2 to 6 mol·dm^–3. The results are discussed in terms of available information on the physicochemical properties of 12-heteropoly acids and their salts.     

Simultaneous reactive extraction separation of amino acids from water with D2EHPA in hollow fiber contactors

Reactive extraction separation of binary amino acids from water using a microporous hollow fiber has been studied, in which the acidic extractant di(2-ethylhexyl)phosphoric acid (D2EHPA) was selected as an active carrier dissolved in kerosene. l-Phenylalanine (Phe) was extracted from an aqueous solution through the shell side of module to the organic phase through the lumen of fiber in the extraction module, in which l-Phe was then back-extracted to stripping phase in stripping module. Experiments were conducted as a function of the initial feed concentration of equimolar Phe and l-aspartic acid (l-Asp) (5 mol/m³), feed pH (3–5), the carrier concentration (0.1–0.5 mol/dm³), and stripping acidity (0.1–2 mol/dm³). The effect of process variables on the separation factor of Phe/Asp and the possible transport resistances including aqueous-layer diffusion, membrane diffusion, organic-layer, and interfacial chemical reaction were quantitatively studied and discussed. The high separation factor (β) of Phe/Asp was obtained to be 18.5 at feed pH 5 and 2 mol/dm³ of strip solution (HCl). The extraction and stripping processes appear to rely on pH dependence of the distribution coefficient of amino acids in reactive extraction system. The separation factor (β) was enhanced in hollow fiber membrane (HFM) process compared with conventional solvent process, which was a result of the counter transport of hydrogen ions.     

Pulse radiolysis of Triton X-100 aqueous solution

Pulse radiolysis of deaerated aqueous solutions of 4·10^–5–2.4·10^–3 mol dm^–3 Triton X-100 gives rise to a transient species originating from the reactions of OH radicals and H atoms. The rate constants of these reactions were found to be 8.8·10⁹ mol^–1·dm³·s^–1 and 1.25·10⁹ mol^–1·dm³·s^–1, respectively, for Triton X-100 concentrations below CMC. The corresponding transient species were found to decay according to second order kinetics. The mechanism of the reactions involved including concentration effects is discussed.     

Separation and Removal of Metal Ionic Species by Polymer Inclusion Membranes

Competitive alkali metal cation transport across polymer inclusion membranes (PIMs) containing sym-(alkyl)dibenzo-16-crown-5-oxyacetic acid carriers provides excellent selectivity for Na⁺ transport with the total fluxes being strongly influenced by the length of the alkyl chain that is attached geminal to the functional side arm in the lariat ether. Removal of chromium(VI) anions by PIMs from acidic aqueous phases was also investigated. Using tri-n-octylamine (TOA) as the ion carrier, Cr(VI) was removed by a PIM to decrease the source phase metal concentration from 1.0 to 0.010 ppm after 30 hours of transport. Competitive transport of Cr(VI) and Cr(III) ions from acidic source phases through PIMs and supported liquid membranes (SLMs) containing TOA and tri-n-octylphosphine oxide (TOPO) as carriers was evaluated and a very high Cr(VI)/Cr(III) separation ratio of 4800 was achieved with a PIM containing TOA. Competitive transport of Zn(II), Cd(II), and Cr(VI) from acidic aqueous solutions through PIMs containing TOA was investigated. The selectivity order for metal ion transport was: HCrO₄ ^–>CdCl₄ ^2–+CdCl₃ ^–>ZnCl₄ ^2–+ ZnCl₃ ^–. Non-contact atomic force microscopy was used to obtain images of the pores in cellulose triacetate membranes containing a plasticizer.     

Separation of cerium and europium by extraction with tributyl phosphate and di(2-ethylhexyl)phosphoric acid in n-alkane from nitrate solutions

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 D_Ce, D_Eu and separation factor =D_Eu/D_Ce as functions of variable parameters of the systems.     

Formation and decay of phenoxyl radicals: Variation with pH and pulse dose

Phenoxyl type radicals were produced from tyrosine methyl ester (TME) using azide (N ₃ ^. ) radicals. The rate constant of formation increased from 2·10⁸ dm³·mol^–1·s^–1 at pH 7 to 4·10⁹ dm³·mol^–1·s^–1 at pH 11, whereas that of the decay, 2k=(6±1)·10⁸ dm³·mol^–1·s^–1, remained constant. The maximum yield of the radicals varied with pH and pulse dose consistently with the kinetic scheme, which involved a competition of the oxidation of TME by azide radicals with the natural decay of N ₃ ^. .     

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.     

Sorption of europium on zirconium oxide from aqueous solutions

Sorption of europium on zirconium oxide has been studies as a function of shaking time, concentration and nature of electrolyte. The effect of initial europium concentration and the amount of adsorbent has been investigated in the range from 6.6·10^–10 to 6.6·10^–8 mol·dm^–3 and between 10 to 200 mg of the oxide. Maximum sorption (>99.8%) from pH 10 buffer and low sorption (<3%) was observed from 0.01 mol·dm^–3 nitric or perchloric acid solution. Citrate, sulfate, EDTA and carbonate reduced the sorption significantly. Under optimal conditions Ag(I), Cs(I), Tc(VII), Sb(V), Cu(II), Nd(III), Fe(III), and especially Nd and Fe showed low distribution coefficients. The data followed both Dubinin-Radushkevich and Langmuir-type isotherms. The mean free energy, of sorption was evaluated to be 10.1 kJ mol^–1 and the sorption capacity was found to be 22.2 mmol g^–1, using the Dubinin-Radushkevich isotherm.     

One electron oxidation of Ni(II)-iminodiacetate by carbonate radical

Reactions of carbonate radical (CO₃ ^–), generated by photolysis or by radiolysis of a carbonate solution with nickel(II)-iminodiacetate (Ni(II)IDA) were studied at pH 10.5 and ionic strength (I)==0.2 mol·dm^–3. The stable product arising from the ligand degradation in the complex is mainly glyxalic acid. Time-resolved spectroscopy and transient kinetics were studied using flash photolysis. From the kinetic data it was suggested that the carbonate radical initially reacts with Ni(III)IDA with a rate constant (2.4±0.4)·10⁶ dm³·mol^–1·s^–1 to form a Ni(II)IDA species which, however, undergoes a first-order transformation (k=2.7·10²·s^–1) to give a radical intermediate of the type Ni(II)RNHCHCO ₂ ^– ) which rapidly forms an adduct containing a Ni–C bond. This adduct decays very slowly to give rise to glyoxalic acid. From a consideration of equilibrium between Ni(II)IDA and Ni(III)IDA, the one electron reduction potential for the Ni(III)IDA/Ni(II)IDA couple was determined to be 1.467 V.     

The aggregation ofn-dodecanephosphonic acid in water

Several techniques were employed to study the aggregation ofn-Dodecanephosphonic Acid (DPA) in water. At 22°C, the solubillity of DPA increases, probably due to the formation of small premicellar aggregates. The CMC is (5.4±2.4) ×10^–4 mol·dm^–3 and the solubility reaches the CMC value at 26°C. At 30°C and at a concentration of about 9×10^–3 mol·dm^–3, a lamellar mesophase appears. Both micelles and liquid crystal lamellae are almost uncharged. Their polar heads have strong hydrogen bonds between them. The ionization of DPA molecules in micelles and mesophase structures is strongly reduced in comparison with monomerically dissolved molecules.     

Reversed-phase partition chromatographic separation of minor actinides with bis(2-ethylhexyl) sulfoxide from acidic nitrate PUREX waste solutions

The uptake behavior of U(VI), Pu(IV), Am(III) and a few long-lived fission products from nitric acid media by bis(2-ethylhexyl) sulfoxide (BESO) adsorbed on Chromosorb has been studied U(VI), Pu(IV) and Zr(IV) are taken up appreciably as compared to trivalent actinides/lanthanides including some coexisting fission product contaminants which are weakly sorbed on the column. Chromosorb could be loaded with (1.12±0.03) g of BESO per g of the support. Maximum sorption is observed around 4–5 mol·dm^–3 HNO₃ for both U(VI) and Pu(IV), which are sorbed as their disolvates. The elution of (U(VI) and Pu(IV) from the metal loaded sorbent has also been optimized. Desorption of U(VI) is easily accomplished with dilute nitric acid (ca. 0.01 mol·dm^–3)while Pu(IV) is reductively stripped with 0.1 mol·dm^–3 NH₂OH·HCl. Effective sequential separation of U(VI), Pu(IV) and Am(III) from their several admixtures could be readily achieved from real medium and low level active acidic process raffinates.