Mass Transfer and Immobilized Organic Phase Instability Studies for Cobalt(II)–Nickel(II) Separation by PEHFSD

Pseudo-emulsion-based hollow-fiber strip dispersion (PEHFSD) technique was examined as an alternative to solvent extraction for simultaneous separation and concentration of cobalt(II)–nickel(II) mixture using Cyanex-272 as the extractant. Experiments were carried out by continuous recirculation of the feed and pseudo-emulsion phases through a hollow-fiber module. The separation factor increased rapidly after 60 min of operation. The maximum value after 120 min of operation was ～128 (pH = 6.5) for the operating conditions studied. The mass transfer resistance from the extraction reaction appeared to be dominant. The results of mathematical modeling of the mass transfer process indicated that higher separation factor and extraction rate can be achieved using PEHFSD in comparison to solvent extraction. Mixing of the stripping and the feed solution was observed at high dispersed phase volume fraction in the pseudo-emulsion and low flow rate of this phase. The maximum value of backtransport flux from the stripping phase due to mixing was estimated to be approximately two orders lower than the initial extraction rates.     

Extraction of Uranium(VI) and Plutonium(IV) with Tetra-Alkylcarbamides

ABSTRACT

The use of tetra-alkylcarbamides as novel extractants for the separation of uranium(VI) and plutonium(IV) by solvent extraction from spent nuclear fuels is investigated in this study. Batch extraction experiments show that tetra-alkylcarbamides strongly extract U(VI) with high distribution ratios. Plutonium(IV) can be co-extracted with U(VI) at high nitric acid concentration, while high U(VI)/Pu(IV) selectivities can be reached at lower acidity. Loading capacity experiments with high uranium concentrations show that alkyl chains longer than butyl are necessary to avoid third phase formation. Nevertheless, the viscosity of uranium-loaded solvents gets too high with alkyl chains longer than pentyl. Overall, this study shows that with TPU extractant (with four pentyl chains), an efficient co-extraction of uranium and plutonium can be reached (D_U,Pu > 1) for a concentration of nitric acid higher than 4 mol?L^?1, while the partition between uranium(VI) and plutonium(IV) could be operated even at 2 mol?L^?1 nitric acid without redox chemistry.     

New liquid membrane technology for simultaneous extraction and stripping of copper(II) from wastewater

In this paper, a new liquid membrane technique, hollow fiber renewal liquid membrane (HFRLM), is presented, which is based on the surface renewal theory, and integrates the advantages of fiber membrane extraction, liquid film permeation and other liquid membrane processes. The results from the system of CuSO₄+D2EHPA in kerosene+HCl show that the HFRLM process is very stable. The liquid membrane is renewed constantly during the process, the direct contact of organic droplets and aqueous phase provides large mass transfer area. These effects can significantly reduce the mass transfer resistance in the lumen side. Then the mixture of feed phase and organic phase flowing through the lumen side gives a higher mass transfer rate than that of stripping phase and organic phase, because the aqueous layer diffusion of feed phase is the rate-controlling step. The overall mass transfer coefficient increases with increasing flow rates and D2EHPA concentration in the organic phase, and with decreasing initial copper concentration in the feed phase. The overall mass transfer coefficient also increases with increasing pH in the feed phase, and reaches a maximum value at pH of 4.44, then decreases. Also, there is a favorable w/o volume ratio of 20:1 to 30:1 for this process. Compared with hollow fiber supported liquid membrane and hollow fiber membrane extraction processes, HFRLM process has a high mass transfer rate. Mathematical model for the HFRLM process based on the surface renewal theory is developed. The calculated results are in good agreement with experimental results under the conditions studied.     

Extraction of U(VI), Th(IV), and Lanthanides(III) from Nitric Acid Solutions with CMPO-Functionalized Ionic Liquid in Molecular Diluents

The extraction of microquantities of U(VI), Th(IV), and lanthanides(III) from nitric acid solutions with CMPO-functionalized ionic liquid 1-[3[[(diphenylphosphinyl)acetyl]amino]propyl]-3-tetradecyl-1H-imidazol-3-ium hexafluorophosphate, CMPO-FIL(I) in molecular organic diluents has been studied. The effect of HNO₃ concentration in the aqueous phase and that of extractant concentration in the organic phase on the extraction of metal ions is considered. The stoichiometry of the extracted complexes was determined. CMPO-FIL(I) demonstrates greater extraction ability towards Ln(III) than its neutral CMPO analog, diphenylphosphorylacetic acid N-nonylamide. This inner synergistic effect increases with a decreasing organic diluent polarity. The partition of CMPO-FIL(I) between the equilibrium organic and aqueous phases is the dominant factor governing the extractability of Ln(III) ions in the extraction system.     

Uranium Permeation Studies from Nitric Acid Medium across Supported Liquid Membrane Impregnated with PC88A and its Mixtures with Neutral Oxodonors in n-paraffin as Carriers

The permeation of U(VI) from nitric acid medium using supported liquid membrane (SLM) technique has been studied employing varying compositions of feed (uranium concentration and acidity), carrier, and receiving phase. Microporous polytetrafluoroethylene (PTFE) membranes were used as a solid support and 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC88A) either alone or as a mixture of neutral donors like tri-n-butyl phosphate (TBP), tris(2-ethylhexyl) phosphate (TEHP), and tri-n-octyl phosphine oxide (TOPO) dissolved in n-parrafin as the carrier. Oxalic acid/Na₂CO₃ solutions were used as the receiving phase. The permeability coefficient (P) of U(VI) decreased with increased nitric acid concentration up to 3 M HNO₃ and thereafter increased up to 5 M HNO₃. Uranium permeation was also investigated from its binary mixtures with other metal ions such as Zr(IV), Th(IV), and Y(III) at 2 M HNO₃ employing 0.1 M PC88A/n-paraffin as the carrier, and 0.5 M oxalic acid as the receiver phase. The presence of neutral donors in the carrier solution enhanced the permeation of U(VI) across the SLM in the following order: TEHP ～ TBP > TOPO using 0.1 M oxalic acid as receiver phase. There was significant enhancement in uranium transport for feed acidity ≤2 M HNO₃ employing 1 M Na₂CO₃ as the receiver phase. These studies suggested that 0.1 M PC88A and 0.5 M oxalic acid as carrier and receiver phases appear suitable for selective and faster transport of uranium from the uranyl nitrate raffinate (UNR) waste solutions.     

Vanadium Extraction using Pseudo-Emulsion Based Hollow-Fiber with Strip Dispersion Technique

The present work investigated the removal rates of vanadium (V) from aqueous solution using PEHFSD technology. A pseudo-emulsion was prepared by dispersing hydrochloric acid (stripping) solution into an organic phase constituted of kerosene, Aliquat 336(carrier), and 1-decanol. Within 60 min, typical results with continuous recycling of both the feed and the pseudo-emulsion employing carrier concentration of 0.025 M and feed pH 5 showed that extraction was nearly 99% whereas maximum recovery in the HCl solution achieved was over 85%. Mathematical analysis suggested that the removal rates are controlled by mass transfer resistance from extraction and stripping reactions.     

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.     

Performance of hollow fiber supported liquid membrane on the extraction of mercury(II) ions

The extraction and recovery or stripping of mercury ions from chloride media using microporous hydrophobic hollow fiber supported liquid membranes (HFSLM) has been studied. Tri-n-octylamine (TOA) dissolved in kerosene was used as an extractant. Sodium hydroxide was used as a stripping solution. The transport system was studied as a function of several variables: the concentration of hydrochloric acid in the feed solution, the concentration of TOA in the liquid membrane, the concentration of sodium hydroxide in the stripping solution, the concentration of mercury ions in the feed solution and the flow rates of both feed and stripping solutions. The results indicated that the maximum percentages of the extraction and recovery of mercury ions of 100% and 97% were achieved at the concentration of hydrochloric acid in the feed solution of 0.1 mol/l, the concentration of TOA at 3% v/v, the concentration of sodium hydroxide at 0.5 mol/l and the flow rates of the feed and stripping solutions of 100 ml/min. However, the concentration of mercury ions from 1–100 ppm in the feed solution had no effect on the percentages of extraction and recovery of mercury ions. Thus, these results have identified that the hollow fiber supported liquid membrane process has high efficiency on both the extraction and recovery of mercury (II) ions. Moreover, the mass transfer coefficients of the aqueous phase (k _i ) and membrane or organic phase (k _m ) were calculated. The mass transfer coefficients of the aqueous phase and organic phase are 0.42 and 1.67 cm/s, respectively. The mass transfer coefficient of the organic phase is higher than that of the aqueous phase. Therefore, the mass transfer controlling step is the diffusion of the mercury ions through the film layer between the feed solution and the liquid membrane.     

EXTRACTION OF PLUTONIUM (III) BY TBP IN PRESENCE OF URANIUM

ABSTRACT

The distribution ratio (D) values for the extraction of plutonium (III) from nitric acid medium into 30% TBP in n-dodecane saturated with uranium(VI) (0% to 80%) were determined. For a fixed saturation of TBP with uranium, the D values for Pu(III) were found to increase with increase in nitric acid concentration (1M to 5M). At a fixed nitric acid concentration, the D values were found to decrease with increase in loading of TBP with uranium. The D values for the extraction of Pu(III) using 20% TBP in n-dodecane and 30% TBP in n-paraffin at 80% uranium saturation were also determined The distribution data was least squares analysed against concentration of HNO₃ as well as percentage saturation of TBP with uranium and the coefficients obtained are reported. For all these extraction systems, D values for U(VI) were also determined.     

Transport of Au(CN)2 − by Mixtures of Amine Primene JMT and Phosphine Oxide Cyanex 923 Using the Pseudo-Emulsion Based Hollow-Fiber Strip Dispersion Technology

The transport of Au(CN)₂ ^? between alkaline aqueous solutions and organic phases consisting of a mixture of the amine Primene JMT and the phosphine oxide Cyanex 923 in xylene was studied using the pseudo-emulsion based hollow-fiber strip dispersion (PEHFSD) technology. The feed phase was passed through the lumen side, and the pseudo-emulsions of the extractant mixtures and NaOH were passed through the shell side in a countercurrent mode using a single hollow-fiber contactor for extraction and stripping. In this membrane technology, the strippant (NaOH solution) is dispersed in the organic (Primene JMT + Cyanex 923 in xylene) membrane solution in a tank with an impeller stirrer adequate to form strip dispersion. The pseudo-emulsion phase is circulated from the reservoir tank to the membrane contactor to provide a constant supply of the organic solution to the membrane fibers. Furthermore, this technology allows a direct contact between the organic and strip solutions, providing a greater area for stripping and facilitating the metal recovery from the strip solution once both phases are separated. Various hydrodynamic and chemical parameters, such as flow of feed phase, extractant mixtures and gold concentrations, organic diluents, variation in feed pH, and the selectivity of the system with respect to the transport of different metal-cyano complexes, were investigated. Aqueous and membrane mass transfer coefficients were estimated for the present system.     

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.     

Comparative Evaluation of Tri-n-butyl Phosphate (TBP) and Tris(2-ethylhexyl) Phosphate (TEHP) for the Recovery of Uranium from Monazite Leach Solution

Separation of U(VI) from Th(IV) and rare earth elements (REEs) present in monazite leach solution (nitric acid medium) has been studied using tris(2-ethylhexyl) phosphate (TEHP) and tri-n-butyl phosphate (TBP) dissolved in n-paraffin as solvents under varying experimental conditions such as nitric acid, extractant and metal ion concentrations etc. There is an increase in distribution ratio of U(VI) (D _U ) with increase in aqueous phase acidity up to 5 M HNO₃ beyond which a decrease is observed. Typically for 1 × 10^?3 M U(VI), the D_U values increase from 8 (0.5 M HNO₃) to 80 (5 M HNO₃) for 1.1 M TEHP, and from 2 (0.5 M HNO₃) to 43 (5 M HNO₃) for 1.1 M TBP in n-paraffin. The separation factors of U(VI) (β: D_U/D_M) over metal ions (M) such as Th(IV) and Y(III) (chosen as a representative of heavy REEs) are better for TEHP than TBP at all nitric acid concentrations. Batch solvent extraction data have been used to construct the McCabe-Thiele diagrams for the recovery of U(VI) employing TEHP as the extractant. A process flow sheet has been proposed with 0.2 M TEHP in n-paraffin as solvent for the recovery of U(VI) from simulated monazite leach solution in HNO₃ medium.     

Studies on permeation of uranium (VI) from phosphoric acid medium through supported liquid membrane comprising a binary mixture of PC88A and Cyanex 923 in n-dodecane as carrier

Present studies deal with the application of supported liquid membrane (SLM) technique for the separation of uranium (VI) from phosphoric acid medium using a binary mixture of 2-ethyl hexyl phosphoric acid-mono-2-ethyl hexyl ester (PC88A) and neutral donor which is a mixture of four tri-alkyl phosphine oxide better known as Cyanex 923 in n-dodecane as a carrier and (NH₄)₂CO₃ as a receiving phase. Various parameters like feed acidity, nature of strippant, carrier concentration, membrane pore size, membrane thickness etc. which affect the transport of U(VI) have been studied in detail. Experiments have also been carried out to see the transport behaviour of different fission products from a diluted High Level Waste (HLW) solution. Stability of the membrane against the leaching of the extractant and stability of the membrane support have also been investigated. We have tried to model the physicochemical transport of U(VI) in SLM as well as establishing the mechanism (Diffusion controlled) of transport. More than 95% uranium (VI) is recovered in 360 min using a binary mixture of 0.60 M PC88A and 0.15 M Cyanex 923 in n-dodecane as carrier and 0.5 M (NH₄)₂CO₃ as stripping phase from the 0.5 M H₃PO₄ feed. Lower concentration of H₃PO₄ (0.5 M) and optimum carrier concentration (0.60 M PC88A + 0.15 M Cyanex 923) in the mole ratio of 4:1 is found to be the most suitable condition for maximum transport of uranium (VI). The optimum conditions obtained from this study was also applied to recover uranium from analytical waste in phosphoric acid medium generated in the laboratory.     

Rhodamine-B modified silica for uranium(VI) extraction from aqueous waste samples

Silica modified with rhodamine-B has been synthesized, characterized and used for solid phase extraction (SPE) of uranium(VI) (U(VI)) from aqueous waste solutions. Adsorption efficiency was influenced by various parameters, which have been investigated such as solution pH, shaking time, initial concentration, adsorbent dose and possible competing ions. The study showed that uranium adsorption was found to be quantitative at pH 5. The adsorption percentage of U(VI) was found to be 94% at the optimum conditions. Desorption conditions were also examined. About 99% of uranium loaded on modified silica was desorbed by 6% of HCl. The method was applicable for removal of uranium from natural samples.     

Copper removal from acidic wastewaters using 2-hydroxy-5-nonylbenzaldehyde oxime as ionophore in pseudo-emulsion membrane with strip dispersion (PEMSD) technology

Results on Cu(II) extraction from acidic media through pseudo-emulsion based membrane strip dispersion (PEMSD) containing Acorga M5640/Iberfluid as organic phase in the form of a pseudo-emulsion with H₂SO₄ were presented. The transport of Cu(II) is investigated as a function of several experimental variables: hydrodynamic conditions, feed solution pH, Acorga M5640 (salicylaldoxime derivative) concentration in the organic solution, and initial metal concentration in feed phase. In this membrane technology, pseudo-emulsion is an emulsion that is formed temporarily between organic and stripping solutions, both solutions are completely separated when mixing is stopped. The value of the overall mass transfer coefficient obtained under standard experimental conditions was 5.5 × 10^?3 cm/s, being the recovery of copper in the stripping solution around 80–85%. The influence of the membrane support, the selectivity of Acorga M5640/Inerfluid based PEMSD towards different metals (Fe(III), Ni(II), Co(II), Zn(II), Cr(III)) an the performance of the system Cu/Acorga M5640/Ibefluid against other commercially available salicylaldoximes (LIX 860, Acorga PT5050) were also examined.     

PURIFICATION OF THORIUM FROM URANIUM-233 PROCESS RESIDUE

ABSTRACT

Thorium-229 can be used to produce ²¹³Bi. Researchers in phase I human trials are investigating the use of antibodies labeled with ²¹³Bi for selectively destroying leukemia cells. Other types of cancer may potentially be treated using similar approaches. Crude ²²⁹Th was liberated from Rachig rings by sonication in 7.5 M HNO₃ followed by filtration. Contaminants, included significant levels of uranium, a number of other metals, and radiolytic by-products of di-(2-butyl) phosphoric acid extractant (which was used in the original separation of ²³³U from thorium). Thorium was selectively retained on Reillex HPQ anion-exchange resin from 7.5 M HNO₃ at 65°C, where U(VI), Ac(III), Fe(III), Al(III); Ra(II), and Pb(II) were eluted. Thorium and uranium isotherms on Reillex HPQ are reported. The thorium was then easily eluted from the bed with 0.1 M HNO₃. To overcome mass transfer limitations of the resin, the separation was conducted at 65°C. The resin stood up well to use over several campaigns. Other researchers have reported that HPQ has excellent radiological and chemical stability. The eluted thorium was further purified by hydroxide precipitation from the organic contaminants. This process yielded 65 mCi of ²²⁹Th.

     

Influence of lactic acid on the solvent extraction separation of Sm(III) and Co(II) from chloride medium using DEHPA

ABSTRACT

A novel process for the separation of Sm (III) and Co (II) from chloride medium using lactic acid in the aqueous feed employing Di-2-ethylhexyl phosphoric acid (DEHPA) in petrofin as organic phase solvent has been developed. Complete separation has been accomplished with 1 M HLac and 0.1 M DEHPA in the pH range 1–3 and using 2.2 M HLac at pH 3 with 0.2 M DEHPA. Sm (III) could be entirely stripped off the loaded organic solvent by means of 1.2 M HCl and HNO₃. The extraction process is heat releasing for Sm (III) and heat absorbing for Co (II).     

Efficient hollow fiber supported liquid membrane system for the removal and preconcentration of Cr(VI) at trace levels

A hollow fiber supported liquid membrane (HFSLM) system for the removal and preconcentration of Cr(VI) has been developed and characterized using Aliquat 336 as carrier. The influence of the chemical composition on the efficiency of the membrane system has been investigated, such as the organic solvent and the stripping composition. Among the stripping reagents tested, a solution of 0.5 M HNO₃ was found to be the most effective to strip Cr(VI) from the loaded organic phase. Moreover, physical parameters such as the stability of the membrane and the operation mode of the module were also evaluated. The results demonstrated the effectiveness of the HFSLM system during 8 non-stop days’ operation. This membrane-based separation system has effectively been used to remove Cr(VI) from different aqueous samples, such as industrial waters and spiked natural waters at μg L⁻¹ levels. Moreover, the system has allowed both the separation and enrichment of the metal and, thus, facilitating the detection of chromate contained in aqueous samples and reducing the volume of polluted water to be treated.     

EVALUATION OF DI(2-ETHYLHEXYL)ISOBUTYRAMIDE (D2EHIBA) AS A PROCESS EXTRACTANT FOR THE RECOVERY OF 233U FROM IRRADIATED Th

ABSTRACT

Extraction behaviour of U(VI) and Th(IV) has been studied employing 0.5?M D2EHIBA (di(2-ethylhexyl)isobutyramide) in n-dodecane as a function of nitric acid concentration. An improved separation of U from Th could be achieved in the presence of fluoride ion. Use of 1?M Al(NO₃)₃ in 2?M HNO₃ has been suggested as the scrubbing solution. Various physico-chemical properties like density, viscosity, interfacial tension (IFT) and limiting organic concentration (LOC) of Th/U have been measured to evaluate the use of D2EHIBA as a process solvent. Degradation behaviour (acid hydrolysis as well as gamma radiolysis) of D2EHIBA under process conditions has been investigated using potentiometry as well as distribution studies.     

Studies on the Recovery of Uranium from Phosphoric Acid Medium by D2EHPA/n-Dodecane Supported Liquid Membrane

Abstract

Present studies deal with the application of supported liquid membrane (SLM) technique for the separation of uranium (VI) from phosphoric acid medium using Di-2 ethyl hexyl phosphoric acid (D2EHPA)/n-dodecane as a carrier and ammonium carbonate as a receiving phase. The studies involve the investigation of process controlling parameters like feed acidity of phosphoric acid, carrier concentration, stripping agents, and the effect of thickness and the pore size of the membrane. The transport of uranium decreases with increase in the concentration of phosphoric acid in feed solution whereas it increases with increase in carrier concentration in supported liquid membrane. More than 90% uranium (VI) is recovered in 360 minutes using 0.5 M D2EHPA/dodecane as carrier and 0.5 M ammonium carbonate as stripping phase from the 0.001 M H₃PO₄ feed. Lower concentration of phosphoric acid and higher carrier concentration is found to be the most suitable condition for maximum transport of uranium (VI) from its lean sources like commercial phosphoric acid and analytical wastes generated from the analysis of uranium by Volumetric (Davis-Gray) method.