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.     

Supported liquid membrane extraction of W(VI) ions using tri-n-octylamine as carrier

Study of the extraction of W(VI) ions using supported liquid membrane has been carried out. The carrier used for this metal ion transport, is tri-n-octylamine (TOA) dissolved in xylene. The liquid was supported in microporous polypropylene film. The parameters studied are effect of carrier concentration in the membrane, acid concentrations in the feed solution, concentration of stripping agent on transport of W(VI) ions and of temperature on the transport properties of these supported liquid membranes. The optimum conditions of transport for these metal ions determined are, TOA concentration, 0.66 mol·dm^–3 (TOA); HF concentration in the feed solution, 0.01 mol·dm^–3 and concentration of NaOH used as stripping agent 2.5 mol·dm^–3. The maximum flux and permeability determined under optimum conditions are 3.06·10^–5 mol·m^–2·s^–1 and 8.44·10^–11 mol· ·m²·s^–1 at 25±2°C and 4.21·10^–5 mol·m^–2·s^–1 and 11.55·10^–11 mol·m²·s^–1 at 65°C, respectively. The diffusion coefficients for the metal ion carrier complex in the membrane have also been determined. Under the optimum conditions the value for the metal ion carrier complex is 0.14·10^–11 mol·m²·s^–1. Mechanism of transport and the complex formed in the presence of HF have also been discussed. The transport process involves two carrier amine molecules and two protons.     

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.     

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 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.     

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.     

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.     

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.     

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.     

Radiolytic reduction of merocyanine 540 in methanol solution

Radiolytic reduction of merocyanine 540 (MC) in acidic (0.02 mol · dm^–3 in H₂SO₄) and neutral methanol solution was studied by pulse radiolysis. The spectra centered around 400 and 700 nm of the MC reduced transients recorded in acidic methanol and in neutral solution were found to be quite similar but they disappeared with different rates suggesting that different radicals (MCH· and MC·^–) were responsible for these spectra. The rate constant of ·CH₂OH reaction with MC was found to be 7·10⁸ mol^–1·dm³·s^–1.     

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.     

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.     

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 ^. .     

On the characteristics and mechanism of the radiation-induced chain reaction between sulfur dioxide and molecular oxygen in acid solutions

Characteristics of the -induced chain reaction between sulfur dioxide and molecular oxygen in perchloric and sulfuric acid media in the presence of Ce(III) ions have been studied. The concentration effects of dissolved oxygen (0.2·10^–3–9.4·10^–3 mol/dm³, sulfur dioxide (0.3·10^–1–2.0·10^–1 mol/dm³ and Ce(III) (0.2·10^–3–4.8·10^–3 mol/dm³) and dose rate (0.26·10¹⁹–1.0·10¹⁹ eV/dm³·s) on the radiation — chemical yield of oxygen consumption G(–O₂) and accumulation of sulfate G(HSO ₄ ^– ), have been investigated. The reaction proceeds with G(–O₂) reaching 10²–10³ molecule/100eV in a catalytic regime. The reaction rate in perchloric acid medium is 3–4 times lower than that in the sulfuric acid medium and depends on the SO₂, O₂ and Ce(III) concentrations, the reaction order varying from 1.0 to 0 and/or in the reverse direction. The mechanism of the process involves chain propagation with 3 stages and 3 intermediates: SO₃H, HSO₅ and Ce(IV). The catalytic effect is caused by the interaction of HSO₄ with Ce(IV) ions followed by their reduction when interacting with SO₂, yielding SO₃H radicals. Chain termination may be due to one or two of the three intermediates or due to all three particles, the kinetics depending on this. Kinetic equations describing the experimental data have been obtained.     

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.     

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.     

Anion-exchange of the chemical species of tracer concentrations of polonium(IV) in chloride solutions

An anion-exchange method is used for determining the average anionic charge of polonium species in chloride solutions. This method is based on measurements of the distribution ratio of polonium at a constant internal chloride ion concentration of the anion-exchanger phase. In 1.0 mol·dm^–1 (H, Na)CL solution in a vicinity of –log[H⁺]=1.0, tracer concentrations of polonium(IV) is found to exist in both chemical forms of [PoCl₄(OH) ₂ ^2– ] and [PoCl₃(OH) ₂ ^– ].     

Pulse radiolysis investigations on the reactions of primary radiolytic species of water with atropine

On pulse radiolysis of N₂O saturated aqueous solutions of atropine, an optical absorption band (_max at 320 nm,e=2.81·10³ dm³·mol^–1·cm^–1) was observed, which is assigned to the product of reaction of OH radicals with the solute. This absorption decayed following second order kinetics with a rate constant of 4.5·10⁸ dm³·mol^–1·s^–1. The rate constant for the reaction of OH radicals with atropine as estimated by following the build-up kinetics is 2.7·10⁹ dm³·mol^–1·s^–1. The H atoms also reacted with this compound to produce a transient absorption band behaving similarly to the one observed in the case of reaction with OH radicals. The transient species formed in both cases is assigned to a radical derived by H atom abstraction by H/OH radicals from the parent compound. This radical was unreactive towards 2-mercaptoethanol. e _aq ^– was found to react with atropine forming a transient band with _max at 310 nm (=3.55·10³ dm³·mol^–1). Its decay was also second order with a rate constant of 1.64·10⁹ dm³·mol^–1·s^–1. The bimolecular rate constant for the reaction of e _aq ^– with atropine as estimated from the decay of e _aq ^– absorption at 720 nm is 3.9·10⁹ dm³·mol^–1·s^–1. Specific one-electron oxidizing and reducing agents (such as Cl ₂ ^– , Tl²⁺, SO ₄ ^– and (CH₃)₂COH, CO ₂ ^– , respectively) failed to oxidize or reduce this compound in aqoues solutions. The radical anion of atropine formed by its reaction with e _aq ^– was found to reduce thionine and methyl viologen with bimolecular rate constant of 3.8·10⁹ and 3.2·10⁹ dm³·mol^–1·s^–1, respectively.     

Der Einfluß großer Salzkonzentrationen auf die Oxydationsreaktion von Fe(phen) 3 2+ mit Ce(IV) in Schwefelsäure

The influence of NaClO₄, NaCl and Na₂SO₄ on the oxidation of Fe(phen) ₃ ²⁺ by Ce(IV) was investigated by means of the stopped-flow method. At the concentrations range of NaClO₄ and NaCl 0.1–1.0M the rate constant values decrease from 1.03·10⁵ to 0.56·10⁵M^–1s^–1 and from 1.08·10⁵ to 0.81·10⁵M^–1s^–1 respectively.In varying concentrations of Na₂SO₄ solutions (0.05–0.35M) the rate constant values decrease from 1.05·10⁵M^–1s^–1 to 0.45·10⁵M^–1s^–1.Taking into account the negative salt effect the mechanism of the reaction progress is proposed.

     

Determination of trace concentration of boron in ADU by the nuclear track technique

A method for the determination of boron concentration in extracted (NH₄)₂ U₂O₇·H₂O (ADU) has been used. One ml of the aqueous solution is irradiated with thermal neutrons from a 10 Ci Am/Be neutron source with a flux of 0.2·10⁵ n·cm^–2·s^–1 and thermal column in the IRT-5000 with a flux of about 10⁷ n·cm^–2·s^–1. The alpha-activity due to the reaction¹⁰B(n, )⁷Li is recorded by a CR-39 alpha track detector. After the exposure, the alpha tracks are made visible in an optical microscope at magnification of 800X by etching the detector in 6N NaOH, and the track density is determined using calibration curves of known concentrations of boron. The boron concentration of the extracted ADU was found to be 5 ppm.