Multitracer study on permeation of rare earth elements through a supported liquid membrane

Separation by means of supported liquid membranes is a useful method for the preparation and preconcentration of radioactive nuclides. The permeation of rare earth elements through a bis(2-ethylhexyl) hydrogen phosphate-decalin membrane supported on a microporous polytetrafluoroethylene sheet was studied using a multitracer containing radioactive nuclides of Sc, Zr, Nb, Hf, Ce, Pm, Gd, Yb, and Lu. Permeation rates of these elements from feed solutions of various acidity to receiving solutions of 0.5 mol·dm⁻³ HCl were determined simultaneously. The feed solution at pH 1.4 gave the highest permeation rate for Ce, Pm, and Gd, amounting to about 95% of permeation for Ce and Pm, 80% for Gd, and 10% for Yb in 21 h. Scandium, Zr, Nb, Hf, and Lu were not transported at all from the feed solution. Permeation rates of Yb and Lu from the feed solution at pH 1.4 to receiving solutions of 0.75, 1.0, 2.3, and 4.0 mol·dm⁻³ HCl increased with the concentration. The results obtained indicate that the light rare earth elements can be separated from the heavy ones by this method.     

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.     

Separation and concentration of cobalt from ammoniacal solutions containing cobalt and nickel by emulsion liquid membranes using 5,7-dibromo-8-hydroxyquinoline (DBHQ)

The separation and concentration of cobalt from ammoniacal solutions containing nickel and cobalt by an emulsion liquid membranes (ELMs) using 5,7-dibromo-8-hydroxyquinoline as extractant has been presented. Membrane solution consists of a diluent (kerosene), a surfactant (Span 80), a modifier (tributylphosphate), and an extractant (DBHQ). Very dilute sulphuric solution containing EDTA as complexing agent, buffered at pH 5.0, has been used as a stripping solution. pH of ammoniacal feed solution containing cobalt and nickel was adjusted to 9.0 with hydrochloric acid. The important variables governing the permeation of cobalt have been studied. These variables are membrane composition, pH of the feed solution, cobalt and nickel concentrations of the feed solution, mixing speed, surfactant concentration, extractant concentration, EDTA concentration and pH of the stripping solution, and phase ratio. After the optimum conditions had been determined, it was possible to selectively extract 99.0% of cobalt from ammoniacal feed solution containing Co²⁺ and Ni²⁺ ions. The separation factors of cobalt with respect to nickel, based on initial feed concentration, have experimentally found to be of as high as 247.5 for about equimolar Co–Ni feed solutions.     

Solvent extraction of neodymium,europium and thulium by di-(2-ethylhexyl)phosphoric acid

The extraction of Na³⁺, Eu³⁺ and Tm³⁺ by di-(2-ethylhexyl)phosphoric acid, HDEHP has been studied from various aqueous acidic solutions. The extraction of these elements is inversely proportional to the third power of the hydrogen ion concentration. Antagonistic effects were observed when the extraction was studied by mixtures of HDEHP and tributyl phosphate, TBP, or trioctylphosphine oxide, TOPO. The presence of water-miscible alcohols and acetone generally increases the extraction of these three elements from HCl solutions. Reaction mechanisms have been suggested and discussed in the light of the data obtained.     

Theoretical study on concentration polarization in gas separation membrane processes

A mathematical model was established successfully to analyze the gas separation concentration polarization which becomes an important problem due to the rapid development of membranes, especially the increase of permeation rate. The influences of membrane performance and operation parameters on concentration polarization were studied in terms of permeation fluxes of the more and the less permeable gases and separation factor. Sample calculations were presented for the two typical gas separation applications, hydrogen recovery and air separation, with shell side feed in hollow fiber module. The permeation rate was found to be a dominating factor in affecting concentration polarization, while the influences of separation factor to be significant initially and to level off gradually. Increasing feed gas velocity leads to a decrease in the concentration polarization. Operation pressures' effect is limited and the composition of feed gas shows no effect. The range in which concentration polarization is significant has been identified by studying the combined effects of the permeation rate, separation factor and feed gas velocity. Concentration polarization is important for process analysis and design when the permeation rate of the more permeable gas is larger than 1×10⁻⁴ cm³ (STP) cm⁻² s⁻¹ cmHg⁻¹ (100 GPU).     

Mass-transfer in hollow-fiber modules for extraction and back-extraction of copper(II) with LIX64N carriers

The extraction of Cu²⁺ ions from sulfate solutions across a hollow-fiber membrane containing LIX64N carriers dissolved in kerosene has been studied, in which Cu(II) was then back-extracted to a stripping-phase containing HCl. Experiments were conducted as a function of the initial feed concentration of Cu²⁺ (1–10 mol/m³), feed pH (2–6), the carrier concentration (0.1–0.4 mol/dm³), and stripping acidity (0.4–4 mol/dm³). A mass-transfer model was developed to predict the extent of Cu²⁺ extraction from aqueous feed in hollow-fiber contactors. The calculated time profiles of Cu²⁺ concentrations were in reasonable agreement with the experimental data (average standard deviation 9% in both extraction and back-extraction modules). The rate-controlling step(s) of such dispersion-free extraction processes were identified. It was shown that the extraction was governed by combined interfacial reaction and aqueous diffusion under the ranges studied, whereas the back-extraction was limited by combined membrane diffusion and aqueous diffusion.     

239+240Pu and137Cs distributions in seawater from the Yamato Basin and the Tsushima Basin in the Japan Sea

Comparative studies between column and batch liquid emulsion membrane techniques based on HDEHP/HCl system were carried out to develop a system for isolation of²³⁴Th from natural uranium. For column investigations a spray column was constructed and used with two different modes. In the first mode the feed solution was circulated through the membrane while in the second mode the membrane phase was circulated through the feed solution. The results showed that, kinetically, the equilibrium for thorium separation using batch technique is faster than the continous column system. Quantitative permeation of thorium was achieved within one minute of mixing whereby the permeation of uranium reached equilibrium after 3 minutes with a permeation percentage less than 6%. A procedure was developed to separate²³⁴Th from natural uranium with high radiochemical purity of more than 98%.     

Extraction chromatographic separation of iron from complex liquid samples and the determination of <Superscript>55</Superscript>Fe

Summary Iron separation is described from liquid samples with a high concentration of ions that enables simple determination of ⁵⁵Fe. One of the described methods consists of iron precipitation from a large volume seawater by sodium hydroxide and/or ammonium carbonate and separation from other elements (Ca, Sr, Cu, Mg, etc.) on a TRU column with 4M HCl or 8M HNO₃. In the other procedure iron is separated directly from a mixture of seawater samples and HCl on a TRU column. In both methods, the iron recovery is almost 100%. After separation, ⁵⁵Fe is determined by counting with a liquid scintillation counter. The binding of Fe and Zn on TEVA, U/TEVA and TRU resins from seawater solutions of HCl and HNO₃depends on the type of the resin, concentration of acid and other ions. Iron and zinc can be separated from seawater on a U/TEVA column with 2M HCl.     

Spectrophotometric Determination of Zirconium in Monazite Sand

A sensitive spectrophotometric method was developed for the determination of zirconium in monazite sand. The zirconium ion was previously separated from the other interfering elements by a 0.5 M thenoyltrifluoroacetone (TTA)-xylene extraction, then determined with Arsenazo III in 9 M HCl medium. Zirconium reacted with Arsenazo III to form an emeraled green coloured complex having maximum absorbance at 665 nm in 9 M HCl medium. The color was stable for at least 2 hours. Effects of time, HCl concentration, gelatine and various ions have been studied. The system confirms the Beer's law over the concentration range investigated. Optimum condition range for measurement in 1.0 cm quartz cell is 0.1–0.5 μg/ml of zirconium. The molar absorptivity is 1.51×10⁵ liter mole^?1 cm^?1. The metal-ligand ratio of 1:4 was confirmed by Job's Continuous Variation method and the conditional stability constant of Zirconium-Arsenazo III Complex in 4 M HCl and 9 M HCl were also determined by this method.     

Americium(III) sorption from multicomponent solutions by macrocyclic polyester-based sorbents

Americium sorption by crown-ether-impregnated polymeric sorbents from nitric acid solutions and multicomponent nitrate solutions that model process solutions was studied. Sorption of ballast elements by the unimpregnated Porolas-T support was studied. The sorption coefficients K _d of these elements on Porolas-T do not exceed 0.01. Sorption of the same elements by crown-ether-impregnated sorbents was also studied. Dicyclohexano-18-crown-6 (DCH18C6) and its alkyl derivatives were used. Sorption coefficients were determined for all ballast elements. At the final stage of the study, ²⁴¹Am sorption coefficients of from multi-component solutions were determined. The data obtained signify the utility of crown-ether-impregnated sorbents for recovering ²⁴¹Am from multicomponent technological solutions.     

Copper and Nickel Removal from Aqueous Solutions Using New Chelating Poly[Acrylamide/N‐vinyl pyrrolidone/3‐(2‐hydroxyethyl carbamoyl)acrylic acid] Hydrogels

New poly[Acrylamide/N‐vinyl pyrrolidone/3‐(2‐hydroxyethyl carbamoyl)acrylic acid], poly [AAm/NVP/HECA], chelating hydrogels with different composition of HECA monomer have been prepared via free radical solution polymerization using N,N‐methylene bisacrylamide as a crosslinker. The hydrogels obtained were loaded with metal ions and characterized by FT‐IR spectroscopy, Scanning Electron Microscope (SEM) and Thermogravimatric analysis (TGA). The removal of Cu²⁺ and Ni²⁺ from aqueous solutions by the hydrogel was examined by a batch equilibrium method. The influence of treatment time, pH, initial concentration of the metal ions and HECA content in the feed compositions on the amount of adsorbed metal ions was studied. Swelling of the hydrogel was also carried out in distilled water and metal ion solutions. The removal of the metal ions followed the following order: Ni²⁺>Cu²⁺. The amount of metal ions removed increased with increasing HECA content in the feed composition, treatment time, pH of the medium and initial concentration of metal ions. The desorption of metal ions were carried out using 1 N HCl and 0.5 N H₂SO₄. The poly[AAm/NVP/HECA] hydrogels could be used many times without significantly decreasing their adsorption capacity.     

Transport of Tb3+in Dispersion Supported Liquid Membrane System with Carrier P507

The Tb³⁺ transport in dispersion supported liquid membrane (DSLM) consisting of polyvinylidene fluoride membrane (PVDF) as the liquid membrane support and dispersion solution including HCl solution as the stripping solution and 2‐ethyl hexyl phosphonic acid‐mono‐2‐ethyl hexyl ester (P507) dissolved in kerosene as the membrane solution, has been studied. The effects of pH value, initial concentration of Tb³⁺ and different ionic strength in the feed phase, volume ratio of membrane solution and stripping solution, concentration of HCl solution, concentration of carrier, different stripping agents in the dispersion phase on transport of Tb³⁺ has also been investigated, respectively. As a result, the optimum transport conditon of Tb³⁺ was that concentration of HCl solution was 4.0 mol/L, concentration of P507 was 0.10 mol/L, and volume ratio of membrane solution and stripping solution was 1.0 in the dispersion phase, and pH value was 5.2 in the feed phase. Ionic strength had no obvious effect on transport of Tb³⁺. Under the optimum condition studied, when initial concentration of Tb³⁺ was 1.0×10^?4 mol/L, the transport rate of Tb³⁺ was up to 95.2% during the transport time of 95 min. The kinetic equation was developed in terms of the law of mass diffusion and the theory of interface chemistry. The results were in good agreement with the literature data.     

Extraction of Iridium(IV) by 1-(2-(2,4-Dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl-methyl)-1H-1,2,4-triazole from Hydrochloric Solutions

Extraction of iridium(IV) by 1-(2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl-methyl)-¹H-1,2,4-triazole from hydrochloric solutions was studied. Optimal extraction parameters were determined. The mechanism of iridium(IV) extraction in this system is ion exchange (3.0 mol/L HCl and τ_cont = 5 min). Electronic, ¹H NMR, ¹³C NMR, and IR spectroscopy and elemental analysis were used to determine the composition of the extracted compound.     

Mechanistic interpretation of solute permeation through a fully aromatic polyamide reverse osmosis membrane

The objective of this study was to assess the contribution of various mass transfer steps (concentration polarization, partitioning, and diffusive and convective transport) toward overall permeation of major solute sodium chloride (NaCl), and trace component nitrobenzene across the fully aromatic polyamide FT-30^® membrane. Experiments were performed with a closed-loop flat-leaf reverse osmosis apparatus. Feed solutions tested contained 2000, 4000 or 6000 mg/l NaCl, and 10 mg/l nitrobenzene at pH 6 and 25°C. Solute rejection ranged from 95 to 99.2% for NaCl and from 20 to 60% for nitrobenzene. The overall permeation of both NaCl and nitrobenzene appeared to be primarily by partitioning at water/membrane interfaces and diffusion across the membrane phase. Convection accounting for less than 25 and 0.4% of the overall NaCl and nitrobenzene permeation, respectively, appeared to be the result of a small leakage of feed solution through membrane imperfections estimated at 0.14% of the overall product water flux. Solute permeation was affected by concentration polarization taking place primarily within a fouling film of corrosion products. Concentration polarization levels corresponded to solute concentrations next to the feed water/membrane interface ranging from 5 to 70% (NaCl), and from 8 to 140% (nitrobenzene) higher than bulk feed concentrations.     

Spectrophotometric determination of titanium(IV) as a mixed thiocyanate—monooctyl-α-anilinobenzylphosphonate complex

Extraction of titanium(IV) thiocyanate complexes by monooctyl-α-anilinobenzylphosphonate (MOABP) dissolved in chloroform has been investigated as a function of hydrochloric and sulfuric acid concentration. Chloroform solutions follow Beer's law and are stable for at least 24 h. A sensitive and reproducible spectrophotometric determination of titanium is possible. Two complexes were identified; the first formed at acid concentrations less than 1 M, has the ratio Ti:SCN:MOABP 1:1:2 and the second, formed at higher acidity, has the ratio Ti:SCN:MOABP 1:2:2. The method is based on the extraction of titanium thiocyanate with MOABP from either 0.5 M H2SO4, and measurement of the absorbance at 336 nm (? = 11 000 l mol^-1 cm^-1 ), or from 6.5 M HCl, and measurement of the absorbance at 420 nm (? = 22 000 l mol^-1 cm^-1). The polymerization of thiocyanate has been studied; isoperthiocyanic acid has been identified as the polymerization product. Although both procedures give reproducible results, extraction from 6.5 M HCl is more sensitive, fewer elements interfere, and the precipitation of isoperthiocyanic acid is avoided.     

Analysis of Th, U, Pu, and Am in radioactive metal waste using extraction chromatography

In order to analyze actinide elements in radioactive metal waste, the dissolution and chemical separation conditions were optimized. The surfaces of a type 304 stainless steel plate and of pipe waste sampled from the prototype advanced thermal reactor (Fugen) were dissolved in mixed acid solution (HNO₃:HCl:H₂O = 1:1:4). The resulting solution was evaporated to dryness and dissolved with 2 mol/dm³ of HNO₃ to prepare sample solutions. In order to analyze trivalent actinide elements in the sample solution containing a large amount of Fe(III) (>0.1 g) using TRU resin, the effect of Fe(III) concentration on the recovery of Am(III) and reduction effect of Fe(III) to Fe(II) with ascorbic acid were studied. On the basis of results of this study, chemical separation scheme was constructed and Pu and Am in the sample solutions were separated. Thorium and U in the sample solutions were separated with UTEVA resin. High recoveries for all experimented elements were obtained from the analysis of spiked sample solutions, the effectiveness of the method was confirmed.     

Sorption of mercury on chemically synthesized polyaniline

Summary Sorption of inorganic mercury (Hg²⁺) and methyl mercury, on chemically synthesized polyaniline, in 0.1-10N HCl solutions has been studied. Hg²⁺ is strongly sorbed at low acidities and the extent of sorption decreases with increase in acidity. The sorption of methyl mercury is very low in the HCl concentration range studied. Sorption of Hg²⁺ on polyaniline in 0.1-10N LiCl and H₂SO₄ solutions has also been studied. The analysis of the data indicates that the sorption of Hg²⁺ depends on the degree of protonation of polyaniline and the nature of mercury(II) chloride complexes in solution. X-ray photoelectron spectroscopy analysis (XPS) of polyaniline sorbed with mercury show that mercury is bound as Hg²⁺. Sorbed mercury is quantitatively eluted from polyaniline with 0.5N HNO₃. Polyaniline can be used for separation and pre-concentration of inorganic mercury from aqueous samples.     

The acidity functionsH 0 s of HCl solutions in EtOH with low water content

The acidity functionsH ₀ ^s of HCl solutions in EtOH-H₂O solvents containing 1.09, 3.0, and 5.0% water have been measured at 25 and 40 °C by the indicator method. The concentration of HCl changes from 10^–2 to 36m. Nitroanilines, for which a protonation mechanism is realized in the studied systems, were used as indicators.For each solvent,H ₀ ^s is temperature independent atm _HCl < 4, and acidity atm _HCl > 4 mol L^–1 increases more rapidly at 25 °C than at 40 °C. The acidity functions of aqueous and water-ethanol solutions of HCl were compared, and the concentrations of proton solvates of different compositions and their relative protonating ability were evaluated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1722–1725, October, 1994.This work was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-18356).     

Sorption of elements from mineral acid solutions by alkylated dibenzocrown ethers

Sorption of various elements by alkylated dibenzocrown ethers (CE) from HCl and HNO₃ solutions was studied. The distribution coefficients of elements depend on the size of the macrocyclic ring of CE and the type and concentration of the acid. Di-tert-butyldibenzo-24-crown-8 possesses optimal properties upon sorption of Au, Ga, Fe, Mo, Sb, Sn, and Re from 5 M HCl. In these cases, the elements are selectively sorbed from mixtures of complex composition, which can be used to develop methods of recovery and separation of elements.     

Anodic dissolution of osmium in acid media

The anodic dissolution of Os in acidic solutions was studied under potentiostatic conditions. The results show high dissolution rates that increase markedly at rising potential. The presence of chloride ions and to a greater extent the increase in acidity of the solutions inhibit the anodic corrosion process. The nature of the dissolution products did depend on the solution pH and the concentration of the complexing anion. Thus, in HClO₄ acid and in chloride solutions at low concentration or acidity, Os goes into solution as OsO₄; in concentrated HCl solution, tetraoxide and chloro-osmyl anions are formed. No OsCl₆^2? complex was detected in solution even at high HCl concentration.