Selective and Efficient Liquid Membrane Transport of Thallium (III) Ion by Potassium‐dicyclohexyl‐18‐crown‐6 as Specific Carrier

Abstract

Potassium‐dicyclohexyl‐18‐crown‐6 was used as a selective and efficient carrier for the uphill transport of thallium (III) ion as [TlCl₄]^? complex ion through a chloroform bulk liquid membrane. By using oxalate anion as a metal ion acceptor in the receiving phase, the amount of thallium (III) transported across the liquid membrane after 120 min was 96±2%. The selectivity and efficiencies of thallium transport from aqueous solutions containing Cu²⁺, Zn²⁺, Ni²⁺, Cd²⁺, Pb²⁺, Co³⁺, Mn²⁺ _, Cr³⁺, Mg²⁺, Ca²⁺, K⁺, Na⁺, and Fe³⁺ ions were investigated. In the presence of Na₃PO₄ (0.01 M) at pH=3 as a suitable precipitation agent in the source phase, the interfering effect of Pb²⁺ ion were diminished drastically.     

Recovery of Plutonium(IV) from Aqueous Solutions Using Emulsion Liquid Membrane Containing 2‐Ethylhexyl Phosphonic Acid Mono‐2‐Ethylhexyl Ester as Ion Transporter

Abstract

An emulsion liquid membranes (ELMs) containing 2‐ethylhexyl phosphonic acid mono‐2‐ethylhexyl ester (H₂A₂) was tested for the extraction of plutonium(IV) from aqueous nitrate solutions of different compositions. Span 80 was used as the surface‐active agent and a mixture of 0.05 mol dm^?3 HNO₃+0.3 mol dm^?3 H₂C₂O₄ was used as the internal phase. Influence of some important experimental parameters such as exterior phase nitric acid concentration, ionic impurities in the exterior phase, concentration of H₂A₂ in ELM phase, and organic solvents on the ELM permeation process were systematically studied. The maximum efficiency of Pu extraction among group of experiments was 98% with permeability coefficient=0.508 min^?1, and the corresponding concentration factor of Pu in the receiving phase was ca. 10. The stability of the emulsions was tested in the presence of different organic solvents and at different concentrations of Span 80 in LM phase. The extractions of Pu by ELM from actual and simulated waste solutions as well as in presence of some added ionic impurities were investigated. Rate of Pu extraction by ELM was studied at different treatment ratios and under repeat extractions by the same emulsion. The repeat extraction experiments showed that a concentration factor of more than 80 for Pu could be achieved.     

Selective Separation of Toluene from n‐Heptane via Emulsion Liquid Membranes Containing Substituted Cyclodextrins as Carrier

Abstract

The selective separation of toluene from n‐heptane is investigated using unsubstituted α‐cyclodextrin (αCD), β‐cyclodextrin (βCD) and also with two substituted CDs as a carrier in oil/water/oil‐type emulsion liquid membranes. The separation factor for toluene to n‐heptane is evaluated from the extraction of an equimolar mixture of toluene and n‐heptane. βCD shows the highest selectivity followed by αCD, hydroxypropyl‐αCD and hydroxypropyl‐βCD. The separation performances, represented by the permeation rate and separation factor, are analyzed systematically by varying the operating parameters: contact time, concentration of carriers, volume fraction of the membrane phase, and the relative amount of solvent. In this paper the effects of carriers and interfacial tension on dispersed phase drop size, internal droplets size, and size distribution are also systematically investigated.     

Kinetics of Rare Earth Leaching from a Mangnese‐Removed Weathered Rare‐Earth Mud in Hydrochloric Acid Solutions

Abstract

The kinetics of leaching rare earth from a manganese‐removed weathered rare earth mud (MRW‐RE mud) in hydrochloric acid solutions was investigated in this study as a function of temperature, particle size, and HCl concentration. It was found that the leaching process can be described by a shrinking‐core model, with the apparent activation energy about 10.17 kJ/M. When the concentration of hydrochloric acid was below 4M, the RE leaching rate was controlled by the diffusion of reactants and leaching products through a porous ore. However, when HCl concentration was higher than 4 M, the leaching process was limited by both chemical reaction and reagent diffusion. Based on the experimental results, an empirical equation relating the rate constant of rare earth leaching to the particle size and leaching temperature was established for the purpose of process deign.     

Carrier Facilitated Transport of Europium(III) Across Supported Liquid Membranes Containing N,N,N′,N′-tetra-2-ethylhexyl-3-oxapentane-diamide (T2EHDGA) as the Extractant

Studies on the solvent extraction and pertraction behavior of europium(III) was carried out from acidic feed solutions using N,N,N′,N′-tetra-2-ethylhexyl-3-oxapentane-diamide (T2EHDGA) in n-dodecane as the solvent. The nature of the extracted species from the solvent extraction studies conformed to Eu(NO₃)₃ · 3T2EHDGA which is in variance with the analogous Eu(III) – TODGA (linear homolog of T2EHDGA) extraction system. The transport behavior of Eu(III) was investigated from a feed containing 3.0 M HNO₃ into a receiver phase containing 0.01 M HNO₃ across a PTFE flat sheet supported liquid membrane (SLM) containing 0.2 M T2EHDGA in n-dodecane as the carrier solvent and 30% iso-decanol as the phase modifier. Effects of feed acidity, carrier extractant concentration, membrane pore size, and Eu concentration in the feed on the transport rates of Eu(III) were also investigated. Membrane diffusion coefficient (D _o) for the pertracted species was calculated using the Wilke-Chang equation as 4.25 × 10^?6 cm² · s^?1. The influence of Eu concentration on the flux was also investigated. The role of temperature on the transport rates was investigated and the thermodynamic parameters were calculated.     

Highly Selective Extraction and Transport through a Bulk Liquid Membrane of L-Cysteine Using [K • DC18C6]+ Complexes

It is shown that dicyclohexyl-18-crown-6 (DC18C6) dissolved in chloroform can extract efficiently and selectively the anionic form of L-cysteine from aqueous solutions containing potassium ions. This ability depends on the aqueous phase pH and type of the salt used in this phase. Under optimized conditions L-cysteine can be quantitatively extracted into the organic phase. In such conditions there was no detectable extraction of amino acids tryptophan, tyrosine, leucine, methionine, arginine, asparagine, aspartic acid, glycine, serine, and threonine. The transport of L-cysteine from potassium chloride/potassium hydroxide solution across a bulk liquid membrane containing DC18C6 dissolved in chloroform has been investigated. The parameters influencing the transport efficiency such as the pH of the feed phase, the kind and concentration of the receiving phase, carrier concentration, the kind of organic diluents, and time were examined and optimized. An efficient stripping at the membrane/stripping phase interface was found using hydrochloric acid as strippant. Selectivity of the proposed system was evaluated by performing a series of competitive transport experiments on the binary mixtures containing L-cysteine with the competitor amino acids noted earlier. This investigation exhibits excellent transport selectivity of the process towards L-cysteine with respect to the examined amino acids.     

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.     

Studies on Permeation of Nd (III) through Supported Liquid Membrane Using DNPPA + TOPO as Carrier

The transport behavior of Nd (III) through a supported liquid membrane (SLM) containing PTFE as support with organophosphorus extractant dinonyl phenyl phosphoric acid (DNPPA) carrier has been studied. The effect of neutral donors such as TOPO (tri-n-octyl phosphine oxide) TBP (tri-n-butyl phosphate), TEHP (tris 2-ethylhexyl phosphate) and Cyanex 923 (a mixture of four trialkyl phosphine oxides) in combination with DNPPA on transport of Nd (III) from HCl across SLM has been examined and the following trend was observed: TOPO > Cyanex 923 > TBP > TEHP. The effect of experimental variables such as feed acidity (0.5 to 5 M HCl), neodymium metal ion concentration (6.94 × 10^?4 to 6.94 × 10^?3 M), DNPPA concentration (0.2 to 0.6 M), stripping reagents in the receiving phase on Nd (III) transport across SLM were investigated. The percentage transport of Nd (III) was 97% after 6 hr run with 0.6 MDNPPA + 0.13 MTOPO as carrier. The permeability of Nd (III) decreased with increase in HCl and Nd (III) concentration in the feed solution. The transport of Nd (III) decreased with increase in membrane thickness as well as with decrease in pore size. Under optimized conditions transport behavior of other rare earths was also investigated independently, the trend observed was: La > Pr ≥ Nd > Sm > Eu > Gd > Tb > Dy > Ho > Er > Tm > Lu ≥ Y.     

Multivariate Analysis of Selected Metal Ion Transport through a Hollow‐Fiber Supported Liquid Membrane Device used for Passive Sampling Monitoring

A hollow fiber supported liquid membrane module using one single fiber impregnated with a mixture of 1,10‐dibenzyl‐1,10‐diaza‐18‐crown‐6 and bis(2‐ethylhexyl)phosphate dissolved in hexylbenzene was used for passive sampling of ppb levels of Pb(II), Cu(II), Zn(II), Mn(II), Ni(II), and Cd(II) in water. The target ions were simultaneously transported and preconcentrated into a citric acid acceptor solution within the lumen of the hollow fiber with enrichment factors between 5 and 4000 times. A multivariate analysis of several physical and chemical parameters that affect transport was performed. Under conditions of constant concentration profiles a more robust performance of the device was observed.     

Transport of Cr(VI) from HCl Media Using (PJMTH+Cl−) Ionic Liquid as Carrier by Advanced Membrane Extraction Processing

The transport of Cr(VI) from acidic media through pseudo-emulsion based membrane strip dispersion (PEMSD) containing the ionic liquid (PJMTH⁺Cl^?) as carrier in the form of a pseudo-emulsion with sodium hydroxide has been investigated. The ionic liquid was generated in situ by reaction of the primary amine Primene JMT and HCl. The transport of Cr(VI) is evaluated as a function of various experimental variables: stirring speed in the feed phase, concentration of Cr(VI) and HCl in the feed phase, carrier concentration, and organic diluents in pseudo-emulsion, and NaOH concentration in pseudo-emulsion as strippant. In PEMSD, pseudo-emulsion is an emulsion that is formed temporarily between the organic and the stripping solutions. Both solutions are separated when the stirring device is stopped. The value of the overall permeation coefficient obtained under standard experimental conditions was 3.1 × 10^?3 cm s^?1, whereas the transport process is controlled by diffusion of chromium species in the stagnant film of the feed phase. The performance of the system against other carriers (amines, quaternary phosphonium salt and quaternary ammonium salt) was also evaluated.     

Highly Selective and Efficient Membrane Transport of Copper as Cu(SCN)2− 4 Ion Using K+-Dicyclohexyl-18-crown-6 as Carrier

Abstract

Potassium-Dicyclohexyl-18-Crown-6 Complex Was Used As A Highly Efficient Carrier For The Uphill Transport Of Copper As Cu(SCN)^2? ₄ Complex Ion Through A Chloroform Bulk Liquid Membrane. By Using Histidine As A Metal Ion Acceptor In The Receiving Phase At The Optimum Ph Of 7.4, The Amount Of Copper Transported Across The Liquid Membrane After 2 Hours Was 90.2 ± 1.0%. The Selectivity And Efficiency Of Copper Transport From Aqueous Solutions Containing Equimolar Mixtures Of Ag⁺, Cd²⁺, Zn²⁺, Ni²⁺, Fe²⁺, Co²⁺, Pb²⁺, Mn²⁺, Fe³⁺, Bi³⁺, And Cr³⁺ Ions Were Investigated. In The Presence Of Pyrophosphate As A Suitable Masking Agent In The Source Phase, The Interfering Effects Of Co²⁺, Zn²⁺, Pb²⁺, And Cd²⁺ Ions Were Completely Eliminated.     

Liquid‐Liquid Extraction of Tetravalent Hafnium from Acidic Chloride Solutions using Bis(2,4,4‐trimethylpentyl) Dithiophosphinic Acid (Cyanex 301)

Abstract

Liquid‐liquid extraction studies of tetravalent hafnium from acidic chloride solutions have been carried out with bis(2,4,4‐trimethylpentyl) dithiophosphinic acid (Cyanex 301) as an extractant diluted in kerosene. Increase of acid concentration decreases the percentage extraction of metal. Plot of log D vs. log [HCl] gave a straight line with a negative slope of 2±0.1 indicating the exchange of two moles of hydrogen ions for every mole of Hf(IV) extractacted into the organic phase. Extraction of Hf(IV) increases with increase of extractant concentration. The plot of log D vs. log [HA] is linear with slope 2±0.1, indicating the association of two moles of extractant with the extracted metal species. The addition of sodium salts enhanced the percentage extraction of metal, and followed the order NaSCN>Na₂SO₄> NaNO₃>NaCl. Stripping of metal from the loaded organic (LO) with HCl and H₂SO₄ indicated sulphuric acid as the best stripping agent. Increase of temperature increases the percentage extraction of metal indicating the process is endothermic. Regeneration and recycling capacity of Cyanex 301, extraction behavior of associated elements such as Zr(IV), Ti(IV), Al(III), Fe(III), and IR spectra of the Hf(IV)‐Cyanex 301 complex was studied.     

A Striking Effect of Ionic‐Liquid Anions in the Extraction of Sr2+ and Cs+ by Dicyclohexano‐18‐Crown‐6

Abstract

The nature of the ionic‐liquid (IL) anion has been found to have a remarkable effect on the solvent extraction of Sr²⁺ and Cs⁺ by dicyclohexano‐18‐crown‐6 dissolved in ionic liquids. In particular, the extraction efficiency increases with the hydrophobicity of the IL anion as reflected by the solubility in water of ILs having a common cation. Since a cation‐exchange mechanism is operating in these systems, the influence of the IL anion is in large part attributable to an expected Le Chatelier effect in which a greater aqueous concentration of IL cation, obtained when using an IL anion of lower hydrophobicity, opposes cation exchange. This dependence is opposite to that found for IL cations, indicating a significant advantage of using ILs with hydrophobic anions for cation extraction. Furthermore, the extraction selectivity for Sr²⁺ over Na⁺, K⁺, and Cs⁺ can be significantly improved through the use of hydrophobic anions for the ILs containing 1‐ethyl‐3‐methylimidazolium or 1‐butyl‐3‐methylimidazolium cations.     

Separation of Zinc Ions from an Acidic Mine Drainage using a Stirred Transfer Cell–Type Emulsion Liquid Membrane Contactor

Abstract

This is a report on the separation and recovery of zinc ions from an acidic mine drainage using a stirred transfer cell‐type emulsion liquid membrane contactor. Di(2‐ethylhexyl) phosphoric acid was used as a highly selective carrier for the transport of zinc ions through the emulsified liquid membrane. A study was made of the effect on the extraction extent and initial extraction rate of the following variables: pH and initial metal concentration of the feed phase, carrier content in the organic solution, a stripping agent concentration in the receiving phase, and stirring speed in the transfer cell. The content of sulfuric acid as a stripping agent did not show in the studied range any significant influence on metal permeation through the SLM, although a minimum hydrogen ion concentration of 100 g/L is suggested in the internal aqueous solution to ensure an acidity gradient between both aqueous phases to promote the permeation of metal ions toward the strip liquor. Results show that using a pH of 4.0 in the feed acid solution, a concentration of 3% w/w_o of phosphoric carrier in the organic phase and a H₂SO₄ content of 100 g/L in the strip liquor, the extent and rate of extraction through the liquid membrane can be highly favored, pointing to the potential of this method for extracting heavy metals from many kinds of dilute aqueous solutions.     

Transport of AgBr2−, PdBr4 2−, and AuBr4- in an Emulsion Membrane System Using K+-Dicyclohexano-18-crown-6 as Carrier

Abstract

Silver, palladium, and gold have been transported through a 1.5 M KBr/toluene/0.025 M MgS₂O₃ (or Mg(NO₂)₃) emulsion membrane system as AgBr₂ ^?, PdBr₄ ^2? and AuBr₄, respectively, using K⁺-dicyclohexano-18-crown-6(DCl8C6) as carrier. The transport studies are carried out in AgBr₂ ^?, PdBr₄ ^2?, and AuBr₄ ^? single solutions and in AgBr^2?/PdBr₄ ^2?, AgBr^2?/AuBr₄ ^?, and PdBr₄ ^2?/AuBr₄ ^? binary solutions. The presence of DC18C6 in the toluene membrane is found to greatly enhance ion transport. When MgS₂O₃ is in the receiving phase, AuBr_{4 -} is found to transport well even without DC18C6 in the membrane. The transport of AgBr₂ ^?, PdBr₄ ^2?, and AuBr₄ ^? is greater for those systems containing MgS₂O₃ in the receiving phase than for those with Mg(NO₃)². In binary studies with MgS₂O₃ in the receiving phase, PdBr₄ ^2? is transported selectively over AgBr₂ ^? and AuBr₄ ^? is transported selectively over either PdBr₄ ^2? or AgBr₂ ^?.     

Extraction Studies of Lanthanide(III) Ions with N,N′‐Dimethyl‐N,N′‐diphenylpyridine‐2,6‐dicarboxyamide (DMDPhPDA) from Nitric Acid Solutions

Abstract

The new diamide compound, N,N′‐dimethyl‐N,N′‐diphenylpyridine‐2,6‐dicarboxyamide (DMDPhPDA), was synthesized and the distribution ratios of lanthanides from 1 to 5 M nitric acid solutions into DMDPhPDA CHCl₃ solution were determined. The extraction mechanism of lanthanide with DMDPhPDA was discussed based on the slope analysis of acid and ligand concentration dependencies and the variation of distribution ratio along the lanthanides series. The number of DMDPhPDA molecules in extracted complexes increase from 3 for lighter lanthanides to 4 for heavier lanthanides. From the previous EXAFS study of a complex similar in structure, Ln(III) would form an inner‐sphere complex with the two DMDPhPDA molecules and an outer‐sphere complex with the third and/or fourth DMDPhPDA molecules in addition to an inner‐sphere complex. Nitric acid concentration has more influence on the distribution ratio and the difference of distribution ratio among lanthanides than the ligand concentration.     

Extraction of Palladium(II) from Nitric Acid Solutions with 1‐Benzoyl‐3‐[6‐(3‐benzoyl‐thioureido)‐hexyl]‐thiourea

The extraction of palladium (II) from HNO₃ solutions with 1‐Benzoyl‐3‐[6‐(3‐benzoyl‐thioureido)‐hexyl]‐thiourea (Ia) and several monodentate thiourea derivatives in 1,2‐dichloroethane has been studied. The effect of HNO₃ concentration in the aqueous phase and that of the extractant in the organic phase on the Pd(II) extraction is considered. The stoichiometry of the extracted complexes has been determined. The increasing number of thioamide groups in the molecule of Ia increases its extraction efficiency towards Pd(II). The potentialities of a polymeric resin impregnated with compound Ia for selective extraction of Pd(II) from nitric acid solutions are demonstrated.     

Adsorption Behavior of Sr(II) and some Typical Co‐existent Metals Contained in High Level Liquid Waste onto a Modified Macroporous Silica‐Based Polymeric DtBuCH18C6 Composite

To significantly reduce the bleeding of 4,4′,(5′)‐di(tert‐butylcyclohexano)‐18‐crown‐ 6 (DtBuCH18C6), an improved novel macroporous silica‐based polymeric composite (DtBuCH18C6+TBP)/SiO₂‐P was synthesized. It was performed by impregnating and immobilizing DtBuCH18C6 into the pores of the SiO₂‐P particles via the molecular modification of DtBuCH18C6 with a tri‐n‐butyl phosphate (TBP) through hydrogen bonding. The adsorption of a few typical simulated fission and non‐fission products Pd(II), La(III), Na(I), K(I), Sr(II), Ba(II), Ru(III), Cs(I), Mo(VI), and Y(III) onto (DtBuCH18C6+TBP)/SiO₂‐P was investigated at 323 K. It was done by examining the effect of contact time and the HNO₃ concentration in a range of 0.1–5.0 M. Sr(II), one of the main heat emitting nuclides, showed optimum adsorption onto (DtBuCH18C6+TBP)/SiO₂‐P in 2.0 HNO₃, while others showed very weak or almost no adsorption except a portion of Ba(II). The leaching of TBP and DtBuCH18C6 from (DtBuCH18C6+TBP)/SiO₂‐P was evaluated. The average content of DtBuCH18C6, 298.7 ppm, leached from (DtBuCH18C6+TBP)/SiO₂‐P in 2.0 M HNO₃ at 323 K was obviously lower than that of 797.3 ppm leached from DtBuCH18C6/SiO₂‐P at 298 K. The significant reduction of DtBuCH18C6 leaching from its macroporous silica‐based polymeric adsorbent was achieved. It is useful for the recycle operation of the silica‐based DtBuCH18C6 impregnated polymeric composite in chromatographic partitioning of Sr(II) from high level liquid waste (HLLW).     

Acid Strength of H3PW x Mo12−x O40 and H6P2W x Mo18−x O62 Heteropolyacid Catalysts as a Probe of Acid Catalysis for 2-Propanol Conversion Reaction

Acid strength of H₃PW _x Mo_12?x O₄₀ (x = 0, 3, 6, 9, and 12) Keggin heteropolyacid (HPA) and H₆P₂W _x Mo_18?x O₆₂ (x = 0, 3, 9, 15, and 18) Wells-Dawson HPA catalysts was determined by NH₃-TPD measurements. Desorption peak temperature (acid strength) of H₃PW _x Mo_12?x O₄₀ and H₆P₂W _x Mo_18?x O₆₂ catalysts showed the same trend with respect to tungsten substitution, and increased with increasing tungsten substitution in both families of HPA catalysts. In order to correlate the acid strength with the acid catalysis of HPAs, vapor-phase 2-propanol conversion reaction was carried out as a model reaction. Yield for propylene (a product formed by acid catalysis of HPA) increased with increasing tungsten substitution and with increasing desorption peak temperature (acid strength) across both HPA families, regardless of the identity of HPA catalyst (without HPA structural sensitivity). The acid strength of H₃PW _x Mo_12?x O₄₀ and H₆P₂W _x Mo_18?x O₆₂ catalysts could be utilized as a probe of acid catalysis for 2-propanol conversion reaction.