Liquid–liquid extraction of cadmium(II) by Cyanex 923 and its application to a solid‐supported liquid membrane system

The extraction of cadmium(II) by Cyanex 923 (a mixture of alkylphosphine oxides) in Solvesso 100 from hydrochloric acid solution has been investigated. The extraction reaction is exothermic. The numerical analysis of metal distribution data suggests the formation of CdCl₂.2L, HCdCl₃.2L and H₂CdCl₄.2L (L = ligand) in the organic phase. The results obtained for cadmium(II) distribution have been implemented in a solid‐supported liquid membrane system. The influences of feed phase stirring speed (400–1400 min^?1), membrane composition (carrier concentration: 0.06–1 mol dm^?3) and metal concentration (0.01–0.08 g dm^?3) on cadmium transport have been investigated. Copyright © 2005 Society of Chemical Industry     

Solvent extraction of uranium from acidic sulfate media by Alamine® 336: computer simulation and optimization of the flow‐sheets

BACKGROUND: A series of nine conventional and non‐conventional flow‐sheets have been considered for the recovery of uranium from acidic sulfate solution by liquid–liquid extraction with 0.146 mol L^?1 Alamine^® 336 in kerosene modified with 5% w/w 1‐tridecanol and stripping with a 199 g L^?1 Na₂CO₃ solution. The reference flow‐sheet was a classical counter‐current configuration with four mixers–settlers in the extraction stage and three mixers–settlers in the stripping stage. The others flow‐sheets possessing a total of eight mixers–settlers are unusual combined solvent extraction flow‐sheets with one or two independent extraction stripping loops and with one or two feed inlets. RESULTS: The configuration of the flow‐sheets strongly influences the extraction performance of the process depending on the working conditions (feed, stripping and solvent flow rates). The presence of two independent extraction–stripping loops may allow the delay of the saturation phenomenon encountered in the conventional flow‐sheet and thus, to operate at higher feed flow rates without loss of performance, as far as the residual fraction in the raffinate and the concentration factor in the stripping solution are concerned. Furthermore, the presence of a modification in the non‐conventional flow‐sheets with two independent extraction–stripping loops and two feed inlets leads to interesting configurations for uranium recovery from less concentrated solutions, such as heap leach solutions. CONCLUSION: The use of non‐conventional flow‐sheets is interesting as it allows the process of uranium (VI) recovery by liquid–liquid extraction to be improved. Copyright © 2009 Society of Chemical Industry     

Liquid Emulsion Membrane (LEM) Process for Vanadium (IV) Enrichment: Process Intensification

Abstract

A liquid emulsion membrane (LEM) system for vanadium (IV) transport has been designed using di‐2‐ethylhexyl phosphoric acid (D2EHPA), dissolved in n‐dodecane as carrier. The selection of extractant, D2EHPA, was made on the basis of conventional liquid‐liquid extraction studies. The work has been undertaken by first carrying out liquid‐liquid extraction studies for vanadium (IV) to get stoichiometric constant (n), and equilibrium constant (K_ex), which are important for process design.

Transport experiments were carried out at low vanadium (IV) concentration (ppm level). The studies on liquid emulsion membrane included i) the influence of process parameters i.e. feed phase pH, speed of agitation, treat ratio, residence time and ii) emulsion preparation study i.e., organic solvent, extractant concentration, surfactant concentration, internal strip phase concentration. When the strip phase concentration was 2 mol/dm³ (H₂SO₄) and feed phase pH 3 better extraction of vanadium was obtained. Higher V_m/V₁ gave higher extraction of vanadium (IV). A simplified, design engineer friendly model was developed.     

Valeric acid extraction with tri‐n‐butyl phosphate impregnated in a macroporous resin: II. Studies in fixed bed columns

Extraction and back‐extraction of valeric acid in a fixed bed packed with Amberlite XAD‐4 resin impregnated with tri‐n‐butyl phosphate were experimentally studied at 25 °C. The effects of the feed flow rate, acid concentration in the feed solution and extractant concentration in the impregnated resin on the breakthrough curves, were investigated. The bed saturation capacity was larger under the conditions of higher extractant concentration in the resin phase and higher acid concentration in the feed solution. A dynamic model that considers intraparticle diffusion and external liquid film diffusion as limiting steps in mass transfer rates was successfully applied. The intraparticle effective diffusivities (10^?9 dm² s^?1) were from one to three orders of magnitude lower than the diffusivities in the external liquid film (10^?8–10^?6 dm² s^?1). A fast and complete back‐extraction of valeric acid from the saturated bed was carried out with sodium hydroxide solutions. The operational life of the impregnated resin was also studied. Copyright © 2005 Society of Chemical Industry     

Separation of Carrier Free 90Y from 90Sr by Hollow Fiber Supported Liquid Membrane Containing Bis(2-ethylhexyl) Phosphonic Acid

The present article gives a comparative account of the efficiency of carrier-free ⁹⁰Y separation from ⁹⁰Sr by solvent extraction, flat sheet-supported liquid membrane (FSSLM) and hollow fiber-supported liquid membrane (HFSLM) methods using bis(2-ethylhexyl) phosphonic acid (PC88A) as the carrier extractant. The major focus of this work has been to develop the HFSLM method for the separation of Y(III) on a relatively large scale. The feed and receiver phase conditions were optimized by carrying out batch solvent-extraction studies. The extraction of Sr(II) by PC88A was negligible in the acidity range of 0.01–3 M HNO₃, whereas the extraction of Y(III) was significantly large at lower acidity (≤0.1 M HNO₃) with a separation factor (SF = D_Y/D_Sr) of 8.5 × 10⁴. HFSLM studies suggested selective and efficient transport of Y(III) into 3 M HNO₃ from a feed solution containing a mixture of Y(III) and Sr(II) at 0.1 M HNO₃. On the other hand, transport of Sr(II) was negligible in the receiver phase. The purity of the separated ⁹⁰Y was ascertained by paper chromatography and by half-life measurement. The radiation stability of the carrier was excellent as studied up to 1000 KGy dose.     

Selective enantioseparation of levocetirizine via a hollow fiber supported liquid membrane and mass transfer prediction

The enantioselective separation of levocetirizine via a hollow fiber supported liquid membrane was examined. O,O′-dibenzoyl-(2R,3R)-tartaric acid ((?)-DBTA) diluted in 1-decanol was used as a chiral selector extractant. The influence of concentrations of feed and stripping phases, and extractant concentration in the membrane phase, was also investigated. A mathematical model focusing on the extraction side of the liquid membrane system was presented to predict the concentration of levocetirizine at different times. The extraction and recovery of levocetirizine from feed phase were 75.00% and 72.00%, respectively. The mass transfer coefficients at aqueous feed boundary layer (k _f ) and the organic liquid membrane phase (k _m ) were calculated as 2.41×10² and 1.89×10² cm/s, respectively. The validity of the developed model was evaluated through a comparison with experimental data, and good agreement was obtained.     

Equilibrium and kinetic studies on the extraction of gadolinium(III) from nitrate medium by di‐2‐ethylhexylphosphoric acid in kerosene using a single drop technique

The liquid–liquid extraction of Gd(III) from aqueous nitrate medium was studied using di‐2‐ethylhexylphosphoric acid (HDEHP) in kerosene. On the basis of the slope analysis data, the composition of the extracted species was found to be [Gd A₃(HA)] with the extraction equilibrium constant (K_ex) = (1.48 ± 0.042) × 10^?12 mol dm^?3. The results of the effect of temperature on the value of the equilibrium extraction constant indicated the endothermic character of the extraction system. The kinetics of the forward extraction of Gd³⁺ from nitrate medium by HDEHP in kerosene was investigated using the single drop column technique. The rate of flux (mass transfer per unit area) was found to be proportional to [Gd(III)], [H₂A₂]_(o), [NO₃^?], and [H⁺]^?1 in the liquid drop organic phase. The forward extraction rate constant, k_f, was 2.24 × 10^?3 m s^?1 using the equation: Copyright © 2005 Society of Chemical Industry     

Solid–liquid extraction of terbium from phosphoric acid solutions using solvent‐impregnated resin containing TOPS 99

BACKGROUND: In this work, the solid‐liquid extraction of terbium from phosphoric acid solutions using solvent‐impregnated resin containing TOPS 99, an equivalent of di‐2‐ethylhexyl phosphoric acid, has been investigated. The parameters studied include equilibration time, acid concentration, amount of resin, metal concentration, kinetics, temperature, loading, elution, regeneration and recycling. RESULTS: FT‐IR results confirm the physical interaction of the extractant with the resin. The extraction of terbium with TOPS 99 impregnated Amberlite XAD 4 resin was acid dependent and transfer of metal follows a cation exchange mechanism. The loading capacity of TOPS 99‐impregnated resin for terbium was calculated to be 23.8 mg g^?1 resin. Controlling mechanism of the adsorption was found to be a chemical reaction following pseudo‐second‐order kinetics. The endothermic nature of extraction was confirmed by temperature studies. Among the various eluants studied, H₂SO₄ was the best. Regeneration and recycling of the resin indicated the resin can be used for continuous cycles. CONCLUSIONS: Terbium was successfully extracted from phosphoric acid using TOPS 99 extractant impregnated into Amberlite XAD4 with a maximum loading of 23.8 mg g^?1 resin and fully recovered with 1 mol L^?1sulfuric acid. The resin was subjected to seven cycles of extraction and elution without any loss of performance. Further studies showed that terbium could be separated from lutetium. Copyright © 2010 Society of Chemical Industry     

Cobalt removal from waste‐water by means of supported liquid membranes

BACKGROUND: Supported liquid membranes (SLM) are an alternative technique to remove and recover metals from diluted process solutions and waste‐water. In the present work, the removal of Co(II) from a synthetic CoSO₄ solution containing initial amounts of cobalt(II) in the range 100–200 ppm (0.1–0.2 g dm^?3) has been studied on a pilot scale. By performing batch equilibrium experiments, the optimal settings, i.e. the composition of the organic phase, the pH of the feed, the type and concentration of the stripping agent were determined. RESULTS: It is shown that the equilibrium characteristics of a synergistic extractant mixture containing di‐2‐ethyl‐hexylphosphoric acid (D2EHPA) and 5‐dodecylsalicylaldoxime (LIX 860‐I) are superior to D2EHPA. Both hydrochloric acid and sulfuric acid have been evaluated as stripping solutions in liquid–liquid extraction tests and as the receiving phase in a SLM configuration. Although equilibrium tests showed no difference in stripping characteristics between both chemicals, it was observed that in a SLM configuration the stability of the system when hydrochloric acid is used is poor. With a commercially available SLM module (Liqui‐Cel Extra‐Flow 4 × 28) having a surface area of 19 m², a steady Co(II) flux of 0.140 gm^?2h^?1 has been obtained at influent concentrations of cobalt between 100 and 200 ppm with 3 mol dm^?3 sulfuric acid as stripping phase. CONCLUSIONS: The results obtained show that a supported liquid membrane containing a synergistic mixture of LIX 860‐I and D2EHPA gives the possibility of recovering cobalt from dilute solutions. Copyright © 2008 Society of Chemical Industry     

Separation of As(III) and As(V) by hollow fiber supported liquid membrane based on the mass transfer theory

Separation of As(III) and As(V) ions from sulphate media by hollow fiber supported liquid membrane has been examined. Cyanex 923 was diluted in toluene and used as an extractant. Water was used as a stripping solution. The extractability of As(V) was higher than As(III). When the concentration of sulphuric acid in feed solution and Cyanex 923 in liquid membrane increased, more arsenic ions were extracted into liquid membrane and recovered into the stripping solution. The mathematical model was focused on the extraction side of the liquid membrane system. The mass transfer coefficients of the aqueous phase (k _i ) and organic phase (k _m ) are 7.15×10⁻³ and 3.45×10⁻² cm/s for As(III), and 1.07×10⁻² and 1.79×10⁻² cm/s for As(V). Therefore, the rate-controlling step for As(III) and As(V) in liquid membrane process is the mass transfer in the aqueous film between the feed solution and liquid membrane. The calculated mass transfer coefficients agree with the experimental results.     

Equilibrium and Kinetics of the Extraction of Propionic Acid Using Tri‐n‐Octylphosphineoxide

Organophosphorous compounds have been widely used in inorganic analysis for the extraction and separation of inorganic acids or metal species. Since these compounds can form hydrogen bonds to proton donors, they can also be used for the extraction of acidic organic compounds. Therefore, the reactive extraction of propionic acid using tri‐n‐octylphosphine oxide (TOPO) in hexane was studied. Equilibrium and kinetics experiments were performed. The extraction of propionic acid using n‐heptane, light liquid paraffin, heavy liquid paraffin and hexane was studied and hexane was found to be most suitable diluent. The equilibrium complexation constant for the propionic acid‐TOPO complex was determined to be 0.702 m³/kmol. The extraction was found to be first order in propionic acid and first order in TOPO with the overall rate constant as 46.91 (m³/kmol)²/s.     

Selective Transport of Bismuth Ions through Supported Liquid Membrane

A new supported liquid membrane (SLM) system was prepared for the selective transport of bismuth ions from the aqueous feed into the aqueous permeate phase. The support of the SLM was a thin porous polypropylene or polyvinylidene fluoride membrane impregnated with diisooctyldithiophosphinic acid (Cyanex 301) as mobile carrier in 4‐chloroacetophenon as organic solvent. Cyanex 301 acts as a highly selective carrier for the uphill transport of bismuth ions through the SLM. In the presence of HNO₃ as a metal ion acceptor in the strip solution, the transport of bismuth ions into the strip side reached 70 % of the initial feed concentration after 3.5 hours. The selectivity and efficiency of bismuth transport from aqueous solutions containing different mixtures of cations were investigated. In the presence of P₂O₇^2– ions as suitable masking agent in the feed solution, the interfering effects of other cations were completely eliminated. The selective transport of bismuth through SLM is superior to liquid‐liquid extraction or through bulk liquid membranes. This is due to the high efficiency. The SLM reduces the solvent requirements, combines extraction and stripping operations in a single process and allows the use of highly selective extractants. The system may be applied to samples containing very low bismuth concentrations.     

Coupled transport of Tl3+ through triethanolamine–xylene–polypropylene supported liquid membranes

This study has been carried out for the uphill transport of Tl³⁺ across triethanolamine (TEA)–xylene based supported liquid membrane. The mechanism of transport of Tl³⁺ has been found to be based on the association of Tl³⁺ with six chloride ions to form anions, which associate with three protonated triethanolamine molecular cations (HOH₄C₂)₃N⁺H at the feed side of the membrane face and form a complex. The complex is extracted into the liquid membrane organic phase, from where it diffuses towards the stripping side of membrane due to the concentration gradient and is dissociated due to alkaline conditions present in the stripping phase. It is also confirmed that proton addition to triethanolamine takes place at the N site and not at the –OH sites. 5.26 mol/dm³ of TEA in xylene in membrane phase, 1.0 mol/dm³ of HCl in feed and 1.0 mol/dm³ of NaOH in stripping phase have been found to be the optimum concentrations for the extraction of Tl³⁺. The method developed for transport of Tl³⁺ has been successfully applied to remove Tl³⁺ from coal ash acid leach liquors along with nickel, chromium and zinc ions.     

Modeling of facilitated transport of Cr(III) using (RNH3+HSO4−) ionic liquid and pseudo-emulsion hollow fiber strip dispersion (PEHFSD) technology

The permeation of chromium (III) using PEHFSD technology and the ionic liquid (RNH₃⁺HSO₄^?), formed by reaction of the primary amine PRIMENE JMT and sulphuric acid, dissolved in n-decane as mobile carrier has been investigated. The alkaline feed solution containing Cr(III) was passed through the tube side, and pseudo-emulsions of the ionic liquid + n-decane + n-decanol and sulphuric acid were passed through the shell side in counter-current mode and using a single hollow fiber module for extraction and stripping. In this advanced membrane technology, the aqueous acidic strip solution is dispersed in the organic membrane solution in a tank with an impeller stirrer to form a strip dispersion. The pseudo-emulsion phase is circulated from the tank to the membrane module to provide a constant supply of the organic solution to the membrane micropores. Factors affecting chromium permeability, such as hydrodynamic conditions, carrier concentration in the organic phase, metal and NaOH concentrations in the feed phase, have been analyzed. A model is reported describing the transport mechanism, whereas the experimental data are quantitatively explained by mathematical equations describing the rate of transport. Different rate-controlling processes take place as long as the metal transport occurs.     

Propriétés photocatalytiques de Ta2O5/SiO2

The photocatalytic properties of deposited tantalum oxide (Ta₂O₅) on silica, in the reaction of photocatalytic oxidation of cyclohexane by oxygen, have been studied. The properties of this catalyst were compared with those of the previously studied system V₂O₅/SiO₂, and it was concluded that the mobilities of V⁺⁵ and Ta⁺⁵ ions on the surface of silica under radiation arc verymuch different. This study was completed by an analysis of the diffuse reflectance spectra and a thermogravimetric analysis of the used catalysts. The conclusion was that the site active in the photocatalytic reaction, is hydrated during the oxidation of cyclohexane.     

Coupled Transport of Zr(IV) through Tri-n-butylphosphate-Xylene-Based Supported Liquid Membranes

Abstract

The transport of Zr(IV) through tri-n-butylphosphate-xylene-based liquid membranes, supported in a polypropylene hydrophobic microporous film, has been studied. The concentration of HNO₃ in the feed solution and tri-n-butylphosphate (TBP) carrier in the membrane were varied, and the flux and permeability coefficients were determined. The optimum conditions found for maximum flux were determined to be 10 mol/dm³ HNO₃ and 2.93 mol/dm³ TBP with a flux value of 12.9 × 10^?6 mol · m^?2 · s^?1. The solvent extraction study revealed that 1.25 to 3.5 protons are involved in zirconium transport, and that two molecules of TBP are involved in the complex formation. The value of protons involved varies with acid concentration. The zirconium ion transport is coupled with nitrate ions transport.     

Transport of Thorium(IV) Across a Supported Liquid Membrane Containing N,N,N′,N′-Tetraoctyl-3-oxapentanediamide (TODGA) as the Extractant

The transport behavior of Th⁴⁺ was investigated from a feed containing 3.0 M HNO₃ into a receiver phase containing 0.1 M oxalic acid across a PTFE flat sheet supported liquid membrane (SLM) which contained TODGA (N,N,N′,N′-Tetraoctyl-3-oxapentanediamide) in n-dodecane as the extractant. Effects of the nature of the strippant, extractant concentration, Th concentration in the feed, and feed acidity on the transport rates were investigated. The transport behavior apparently depended on the rate of extraction of the metal ion at the feed-membrane interface and was not diffusion controlled. Influence of Th concentration on flux was also investigated. Transport mechanism was elucidated and the diffusion coefficient was calculated to be 2.13 × 10^?7 cm²/s. Solvent extraction studies at varying feed acidity and TODGA concentration were also carried out.     

Modeling of Phosphoric Acid Purification by Liquid‐Liquid Extraction

Phosphoric acid is an important industrial chemical. It is mainly produced by the wet process which consists of an attack of the phosphate rock by sulphuric acid leading to a complex solution containing a large number of impurities such as metal ions like Fe³⁺, Al³⁺, Mg²⁺, Cd²⁺ etc., which can effectively be recovered by solvent extraction process. In this present work a model of the liquid‐liquid extraction process is presented. It is mainly based on thermodynamics, where two different routes have been tested for the modeling of the complexation process. The method has been tested using a model system with Al³⁺ as the contaminant, dodecyl naphthalene sulphonic acid (HDDNSA) as the complexing agent and kerosene as the diluent. The study has also investigated the influence of various parameters such as the pH of the aqueous phase and the initial concentration of the phosphoric acid.     

Solvent extraction studies of Sm(III) from nitrate medium and separation factors of rare earth elements with mixtures of sec‐octylphenoxyacetic acid and 1,10‐phenthroline

BACKGROUND: Liquid–liquid extraction is widely used for the separation of rare earths, among which synergistic extraction has attracted more and more attention. Numerous types of synergistic extraction systems have been applied to rare earths with high extraction efficiency and selectivities. In the present study, mixtures of sec‐octylphenoxyacetic acid (CA12, H₂A₂) and 1,10‐phenanthroline (phen, B) have been used for the extraction of rare earths from nitrate medium. The stoichiometry of samarium(III) extraction has been studied using the methods of slope analysis and constant molar ratio. The possibility of using synergistic extraction effects to separate rare earths has also been studied. RESULTS: Mixtures of CA12 and phen display synergistic effects in the extraction of rare earth elements giving maximum enhancement coefficients of 5.5 (La); 13.7 (Nd); 15.9 (Sm); 24.5 (Tb); 45.4 (Yb) and 12.3 (Y). Samarium(III) is extracted as SmHA₄B₃ with mixtures of CA12 and phen instead of SmHA₄ when extracted with CA12 alone. The calculated logarithm of the equilibrium constant is 6.0 and the thermodynamic functions, ΔH, ΔG, and ΔS, have been calculated as 4.3 kJ mol^?1, ? 33.7 kJ mol^?1 and 129.7 J mol^?1 K^?1, respectively. CONCLUSION: Mixtures of CA12 and phen exhibit synergistic effects on rare earth elements. Graphical and numerical methods have been successfully used to determine their stoichiometries. The different synergistic effects may provide the possibility of separating yttrium from heavy lanthanoids at an appropriate ratio of CA12 and phen. Copyright © 2010 Society of Chemical Industry     

Extraction of Rare Earth Metals Using Liquid Surfactant Membranes Prepared by a Synthesized Surfactant

Abstract

Three surfactants, l-glutamic acid dioleyl ester ribitol (nonionic, 2C ₁₈Δ⁹ GE), l-glutamic acid dioleyl ester quaternary ammonium chloride (cationic, 2C ₁₈Δ⁹ GEC ₂ QA), and dioleyl dimethyl quaternary ammonium chloride (cationic, 2C ₁₈Δ⁹ QA) were synthesized for potential use in liquid membrane operations. These surfactants have strongly hydrophobic, twin oleyl chains as the hydrophobic moiety. Using the synthesized surfactants, extraction of rare earth metals was carried out by liquid surfactant membranes in a stirred tank. The extraction behavior of 12 kinds of rare earth metals was systematically studied with 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester (commercial name: PC-88A) as a carrier. Different surfactants having an identical hydrophobic moiety can have significantly different behaviors in rare earth extractions by liquid surfactant membranes, where extraction efficiency appears to be governed by the nature of the interfacial microenvironment between oil and water. An interfacial reaction model which takes into account the adsorption of a surfactant at the interface has been proposed to evaluate the permeation rate of rare earth metals by liquid surfactant membranes. It was found that a cationic surfactant strongly enhances the extraction rate of rare earth metals compared with the conventional surfactant, Span 80. The cationic surfactant 2C ₁₈Δ⁹ GEC ₂ QA appears to be one of the best surfactants currently available for rare earth extraction by liquid surfactant membranes.