Liquid-liquid Extraction System Research Articles

Study on the Complex Equilibria of Molybdenum(VI) with 3,5-Dinitrocatechol and Ditetrazolium Salt.

The complex formed between an anionic chelate of Mo(VI)-3,5-dinitrocatechol (3,5-DNC) with the cation of 3,3'-(3,3'-dimethoxy-4,4'-biphenylene)bis(2,5-diphenyl-2H-tetrazolium chloride) (Blue Tetrazolium Chloride, BTC) in the liquid-liquid extraction system Mo(VI)-3,5-DNC-BTC-H2O-CHCl3 was studied. The optimum conditions for the complex formation and extraction of the ion-associated complex were established by spectrophotometry. The molar ratio of the reagents was determined by independent methods. The validity of Beer's law was checked and some analytical characteristics were calculated. The association process in aqueous phase and the extraction equilibria were investigated and quantitatively characterized. The following key constants of the processes were calculated: association constant, distribution constant, extraction constant and recovery factor. Based on this, a reaction scheme, a general formula and a structure of the complex were suggested.

Thermodynamic representation of ionic liquids phase equilibrium with the Wilson-NRF model

Ionic liquids (ILs) with their limitless combinations of cations and anions can offer an optimal solvent for a specific purpose especially separation processes such as liquid-liquid extraction (LLE). The present work inquired phase behavior of 32-types ILs with various cations (including imidazolium, pyridinium, piperidinium, morpholinium, pyrrolidinium and phosphonium-based) and various anions (including Cl, FeCl4, BF4, B(CN)4, PF6, NTf2, FAP and alkylsulfates) in LLE systems. Calculation of LLE for 38 binary (220 Tie-Line) and 52 ternary (545 Tie-Line) systems were carried out using Wilson-Non-Random-Factor (Wilson-NRF) model. All the data were in the temperature range of 298.15–408.15K. Therefore, in order to obtain an temperature-independent interaction parameters, the adjustable parameter assumed to be as a function of T as: λij=aij+bij/T. All the interaction parameters either for binary or ternary systems were directly regressed from the experimental data using an optimization program based on two objective functions. All the results were expressed by root mean square deviation (rmsd) between the calculated and experimental compositions (the solubility data from the literature). The applied model had very good satisfactory results for ternary and binary systems with rmsd values of 8.78 and 4.08 respectively. Besides, the effect of cation-type, anion-type and the other organic compound on the model behavior was illustrated. Finally, the results represented that Wilson-NRF model could be satisfying model for evaluation of thermodynamic behavior of various LLE containing ILs.

Acid-switched Eu(III) coordination inside reverse aggregates: Insights into a synergistic liquid-liquid extraction system

Determining the structure of complex solutions bearing metal ions is challenging, but crucial for developing important technologies such as liquid-liquid extraction for metal refining and separation purposes. Herein, the structure of an organic Eu(III) solution consisting a binary mixture of lipophilic ligands di-2-ethylhexyl phosphoric acid (HDEHP) and tetraoctyl diglycolamide (TODGA) in dodecane is studied using synchrotron small angle X-ray scattering (SAXS) and X-ray absorption fine structure spectroscopy (EXAFS). This system is of technological importance in f-element separation for nuclear fuel cycle applications, where extraction is controlled by varying nitric acid concentration. Extraction is promoted at low and high concentration, but is retarded at intermediate concentration, leading to a U-shaped function; the structural origins of which we investigate. At the nanoscale, the solution is apparently comprised of reverse micelles with polar cores of approximately 1nm in size, and these remain virtually unchanged as acid concentration is varied. Inside the polar cores, the coordination environment of Eu(III) switches from a 9-coordinate [Eu(TODGA)3]3+ motif at high acid, to a 6-coordinate HDEHP-dominated complex resembling Eu(HDEHP·DEHP)3 at low acid. The results show that extraction is controlled within the coordination sphere, where it is promoted under conditions that favor coordination of either one of the two organic ligands, but is retarded under conditions that encourage mixed complexes. Our results link solution structure with ion transport properties in a technologically-important liquid-liquid ion extraction system.

Development of a Liquid‐liquid Extraction System for Rhodium(III) by 2‐octylaminopyridine from Weak Malonate Media

AbstractWe have developed the extraction method of rhodium(III) from malonate media with 2‐octylaminopyridine (2‐OAP) in xylene at pH 8.0. The quantitative extraction of rhodium(III) with extractant was found by screening of different physicochemical parameters like malonate concentration, extractant concentration, pH, diluents, effect of temperature, aq: org phase ratio, loading capacity of 2‐OAP. The optimum condition was malonate=0.025 M, pH=8.0, 2‐OAP=0.05 M in xylene. The complete stripping of rhodium(III) from the loaded organic phase was carried out with 2 M HCl. Log‐log plot was investigated to determine the stoichiometry of the extracted species and it was found to be 1 : 2 : 1 (metal : acid :extractant). The versatility of the proposed method was checked for extraction and separation of rhodium(III) from binary, ternary mixture of associated metal ions as well as platinum group metals and from the synthetic solution of rhodium minerals and alloys.

Comparative Molecular Dynamics Study on Tri-n-butyl Phosphate in Organic and Aqueous Environments and Its Relevance to Nuclear Extraction Processes.

A refined model for tri-n-butyl phosphate (TBP), which uses a new set of partial charges generated from our ab initio density functional theory calculations, has been proposed in this study. Molecular dynamics simulations are conducted to determine the thermodynamic properties, transport properties, and the microscopic structures of liquid TBP, TBP/water mixtures, and TBP/n-alkane mixtures. These results are compared with those obtained from four other TBP models, previously described in the literature. We conclude that our refined TBP model appears to be the only TBP model from this set that, with reasonable accuracy, can simultaneously predict the properties of TBP in bulk TBP, in organic diluents, and in aqueous solution. The other models only work well for two of the three systems mentioned above. This new TBP model is thus appropriate for the simulation of liquid-liquid extraction systems in the nuclear extraction process, where one needs to simultaneously model TBP in both aqueous and organic phases. It is also promising for the investigation of the microscopic structure of the organic phase in these processes and for the characterization of third-phase formation, where TBP again interacts simultaneously with both polar and nonpolar molecules. Because the proposed TBP model uses OPLS-2005 Lennard-Jones parameters, it may be used with confidence to model mixtures of TBP with other species whose parameters are given by the OPLS-2005 force field.

Liquid-liquid extraction of lithium using lipophilic dibenzo-14-crown-4 ether carboxylic acid in hydrophobic room temperature ionic liquid

A green liquid-liquid extraction (LLE) system was developed for the recovery of lithium (Li+) from sodium and potassium ions, which are typically present at high concentrations in seawater. Dibenzo-14-crown-4ether (DB14C4) was functionalized with a long lipophilic alkyl C18 chain and a pendent proton ionizable carboxylic acid group to obtain a lithium (Li+) carrier system (DB14C4-C18-COOH) with high Li+ extraction performance and good stability in the room temperature ionic liquid diluent, CYPHOSIL 109. The Li+ extraction efficiency of DB14C4-C18-COOH/CYPHOSIL 109 can be enhanced by increasing the solution pH and DB14C4-C18-COOH concentration. Further examination of extraction results reveal 1:1 coordination between DB14C4-C18-COOH and Li+ which was also supported by density functional theory calculations. At room temperature, the developed LLE system effectively extracted dilute Li+ from Na+ (selectivity αLi+/Na+=1954) and K+ (αLi+/K+=138). Kinetic and thermodynamic parameters were evaluated for optimum Li+ extraction conditions. Sequestered Li+ can be easily recovered from the LLE system using dilute hydrochloric acid. Results from recycling tests showed stable Li+ extraction performance hence it can be used for long term application. Overall results indicate the potential application of DB14C4-C18-COOH/CYPHOSIL 109 as a treatment step to recover Li+ from brine or seawater.

Complex Formation in a Liquid-Liquid Extraction System Containing Co(II), 4-(2-Thiazolylazo)resorcinol and Monotetrazolium Salt.

The ion-associated complex formed between anionic chelate of Co(II)-4-(2-Thiazolylazo)resorcinol (TAR) with the monotetrazolium cation of 2-(4-Iodophenyl)-3-(4-nitrophenyl)-5-phenyl-2H-tetrazolium chloride (INT) in the liquid-liquid extraction system Co(II)-TAR-INT-H(2)O-CHCl(3) was studied by the spectrophotometric method. The optimum extraction conditions of Co(II) were found. The extraction equilibria were studied. The equilibrium constants, the recovery factor and some analytical characteristics were calculated. The validity of Beer's law was checked. The molar ratio of the components in the ternary ion-associated complex Co(II)-TAR-INT was determined. The general formula of the complex was suggested. The effect of various foreign ions and reagents on the process of complex formation in the liquid-liquid extraction system was studied.

Flow Dynamic Behavior of Fish Oil/Silver Nitrate Solution in Mini-Channel, Effect of Alkane Addition on Flow Pattern and Interfacial Tension

The mini-fluidic contacting system is developed as process intensification platform as an attractive alternative for existing liquid-liquid extraction system for separation of Omega 3 PUFA from using Aqueous 50% Wt. Silver nitrate solution. To improve the performance of extraction in mini-fluidics, it is necessary to study the flow-dynamic behavior of fish oil silver nitrate system in the channel. Moreover, different flow patterns influence mass transfer and mixing which indirectly influence the separation efficiency of omega 3 PUFA from fish oil. Therefore, Different flow patterns were studied at Y-junction that connected to mini-channel and classified over a range of organic phase and aqueous flow rate. The flow is stratified at the “Y” Junction after phase inversion and also due to the reduction of interfacial tension between fish oil and silver nitrate solution. The addition of alkane’s solvents into the fish oil ethyl ester is attempted to change the flow pattern of fish oil silver nitrate system by elevation of interfacial tension. The formation mechanism of slug and stratified flow was studied by a competition between the gravity, inertia, viscous forces and the interfacial tension forces. The flow patterns maps is presented in terms of Ca, Re and We and identified the three regions namely gravity force dominant region, transition region and interfacial force dominant region. The flow patterns observed in real Fish Oil/AgNO3 system was significantly different than previously reported for a synthetic DHA/AgNO3 system. The addition of organic solvent into the fish oil ethyl ester increase the interfacial tension between fish oil and silver nitrate system, however, the increase was not sufficient to produce slug flow. This would suggest that practical processing of fish oils with AgNO3 would require the handling of stratified flow within the processing units.

Selective Recovery of Au(III) from Binary Metal Solution Using Aliquat-336-Impregnated Alginate Capsule

Aliquat-336-impregnated alginate capsule (Aliquat-336-AC) was fabricated using a facile method. Ionic liquid Aliquat-336 was used as a model extractant owing to its good extraction performance toward precious metals (PMs). Aliquat-336-AC was prepared by dropping the mixture solution (Aliquat-336 + Tween 80 + CaCl2) into the alginate solution. CaCl2was used to form Ca-alginate shell, leading to Aliquat-336-AC. Two types of binary metal solutions, Au (III)/Pt (IV) and Au (III)/Pd (II) were used to evaluate metal sorption capacity of Aliquat-336-AC. The maximum Au (III) uptake in Au (III)/Pt (IV) and Au (III)/Pd (II) systems were 61.38 and 82.97 mg/g, respectively. Whereas, the uptakes of Pt (IV) and Pd (II) were almost closed to zero, indicating excellent Au (III) selectivity of Aliquat-336-AC. A comparative study was carried out between liquid/liquid extraction (LLE) using Aliquat-336 and solid/liquid adsorption (SLA) using Aliquat-336-AC for Au (III) selective recovery from Au (III)/Pt (IV) and Au (III)/Pd (II) solutions. The data of selectivity coefficients (αsel) showed that the values of αAu/Ptand αAu/Pdwere 10253.34 and 5817.61 in the SLA system, respectively. These values were much higher than 2033.38 of αAu/Ptand 1879.80 of αAu/Pdin the LLE system. Therefore, Aliquat-336-AC can be used as a selective adsorbent for Au (III).

Study on the complex formation of anionic chelates of Co(II)–4-(2-thiazolylazo)resorcinol with ditetrazolium cations

The ion-associated complexes formed between anionic chelates of Co(II)–4-(2-thiazoly-lazo)resorcinol (TAR) and cations of ditetrazolium salts (DTS)—Nitro Blue Tetrazolium Chloride (NBT), Blue Tetrazolium chloride (BTC) and Neotetrazolium chloride (NTC)—in the liquid-liquid extraction system Co(II)–TAR–DTS–H2O–CHCl3 were studied. The optimum conditions for the formation and the solvent extraction of the ternary ion-associated complexes Co–TAR–DTS were found. The molar ratio of the components in the associates was determined by independent methods. Based on this, a reaction scheme and a general formula of the complexes were suggested. The extraction equilibria were investigated quantitatively. The following key constants were calculated: association constant, distribution constant, extraction constant and recovery factor. The validity of Beer’s law was checked and some analytical characteristics were calculated. Based on the obtained results and the lower price of the ditetrazolium salt BTC compared with NBT, the ion-associated complex of Co–TAR–BTC can be successfully used for determining of cobalt in alloys, biological, medical and pharmaceutical formulations.

The Effect of Nanoparticles on Liquid Holdups in a Randomly Packed Liquid-Liquid Extraction Column

In the present study, the dispersed phase holdup was measured in a randomly packed column filled with stainless steel Raschig ring packings using water-toluene chemical system. Based on holdup data, the results were analyzed with the aim of determining the influence of dispersed phase flow rate and drop diameter in the presence and absence of silica nanoparticles with particle sizes of 10, 30, and 80 nm and concentrations of 0.01, 0.05, and 0.1 vol%. The results indicate that liquid holdups increase with increase in dispersed phase flow rate. The presence of the nanoparticles influence in both static and dynamic holdups. The experimental results showed that increasing nanoparticle content in dispersed phase increases the dynamic holdup while static holdup decreases. However, by increasing the size of nanoparticles the dynamic and static holdup also follow a similar trend. Finally a successful correlation is proposed for total liquid holdup, which yielded an average error of 6% and shows a good agreement between predicted and experimental results. This is for the first time that a correlation is proposed to estimate total liquid holdup as a function of nanoparticle size and concentration in liquid-liquid extraction systems.

Application of affinity aqueous two-phase systems for the fractionation of CD133(+) stem cells from human umbilical cord blood.

In a further attempt to establish a novel stem cell primary recovery strategy, the use of aqueous two-phase systems (ATPS) complemented with the use of antibodies (known as immunoaffinity ATPS) is explored in this work. This type of liquid-liquid extraction systems exploits antigen-antibody affinity and represents a novel and selective approach for the purification of stem cells. The proposed bioengineering strategies include the implementation of traditional [polyethylene glycol (PEG), dextran (DEX) and ficoll] and novel (Ucon) immunoaffinity ATPS to prove the viability of cluster of differentiation 133 (CD133(+) ) stem cells from human umbilical cord blood. Furthermore, the addition of the antibody is implemented to identify conditions under which contaminants and stem cells of interest concentrate in opposite phases. The objective of this work is to establish the initial basis for the development of a novel and scalable purification bioprocess for the selective recovery of CD133(+) stem cells employing immunoaffinity ATPS. The reported methodology allows a partitioning of 62% CD133(+) stem cells to the top phase of the ficoll 400,000-DEX 70,000 immunoaffinity ATPS. In PEG 8,000-DEX 500,000 and Ucon-DEX 75,000 systems, no difference was observed when compared with the conventional ATPS (without antibody addition), as the CD133 antibody does not have preference for the desired clean top phase. In all experiments, cell viability was at least 98% after ATPS recovery. This research highlights the challenges that must be addressed to allow the potential establishment of a separation process using immunoaffinity ATPS for the recovery and purification of stem cells.

Digital liquid-scintillation counting and effective pulse-shape discrimination with artificial neural networks

Abstract A typical problem in low-level liquid scintillation (LS) counting is the identification of α particles in the presence of a high background of β and γ particles. Especially the occurrence of β-β and β-γ pile-ups may prevent the unambiguous identification of an α signal by commonly used analog electronics. In this case, pulse-shape discrimination (PSD) and pile-up rejection (PUR) units show an insufficient performance. This problem was also observed in own earlier experiments on the chemical behaviour of transactinide elements using the liquid-liquid extraction system SISAK in combination with LS counting. α-particle signals from the decay of the transactinides could not be unambiguously assigned. However, the availability of instruments for the digital recording of LS pulses changes the situation and provides possibilities for new approaches in the treatment of LS pulse shapes. In a SISAK experiment performed at PSI, Villigen, a fast transient recorder, a PC card with oscilloscope characteristics and a sampling rate of 1 giga samples s−1 (1 ns per point), was used for the first time to record LS signals. It turned out, that the recorded signals were predominantly α, β-β and β-γ pile up, and fission events. This paper describes the subsequent development and use of artificial neural networks (ANN) based on the method of “back-propagation of errors” to automatically distinguish between different pulse shapes. Such networks can “learn” pulse shapes and classify hitherto unknown pulses correctly after a learning period. The results show that ANN in combination with fast digital recording of pulse shapes can be a powerful tool in LS spectrometry even at high background count rates.

Liquid–liquid extraction of Li+ using mixed ion carrier system at room temperature ionic liquid

An environmentally benign technique for the separation and recovery of lithium (Li+) from aqueous streams, containing mixed metal ions was developed via liquid–liquid extraction (LLE). Hydrophobic room temperature ionic liquids (RTIL) were tested as the main extracting solvents. To increase the metal extraction, a proton-ionizable agent bis(2-ethylhexyl) phosphoric acid (DEHPA) was added into the RTIL. To enhance the metal uptake selectivity, three Li+-selective neutral ion carriers such as 6-hydroxy-dibenzo-14-crown-4, dibenzo-14-crown-4, and tri-n-octyl-phosphine (TOPO) were also used and tested as extractant additives. Among the tested RTILs, phosphonium-based CYPHOS IL 109 was the most stable extractant as it exhibited the lowest loss when contacted with water. Addition of proton-ionizable agent DEHPA in CYPHOS IL 109 afforded a high extraction of multivalent cations with negligible recovery of monovalent metals. On the other hand, the addition of neutral ion carrier TOPO in DEHPA/CYPHOS IL 109 extractant resulted in a selective Li+ uptake which was maximized when the pH of the aqueous solution was maintained at 13, with TOPO/DEHPA molar ratio = 8. The overall process could be a two-stage LLE system wherein the unwanted multivalent cations are initially removed using DEHPA/CYPHOS IL 109 followed by the selective extraction of Li+, using TOPO/DEHPA/CYPHOS IL 109 system.

Radiolysis of Tributyl Phosphate by Particles of High Linear Energy Transfer

Tributyl Phosphate (TBP), used in chemical separation processes for used nuclear fuel, is susceptible to radiolysis causing losses in process performance. We have studied its degradation by exposing dry 1M TBP/n-dodecane solutions to gamma radiation from a cesium-137 source and in a mix of low and high linear energy transfer (LET) radiation by irradiating samples in the UC Irvine TRIGA® reactor and utilizing the 10B(n,α)7Li reaction. In a 1 M solution of TBP in n-dodecane the degradation of TBP (G−TBP) was found to be 0.36 and 0.14 μmol/J for low and high LET radiation, respectively. The formation of dibutyl phosphoric acid, DBP, (G+DBP) in this solution was found to be 0.18 and 0.047 μmol/J for low and high LET radiation, respectively. In samples exposed to low LET as well as a mix of low and high LET a variety of TBP degradation products containing phosphorus were observed indicating that other degradation products than DBP and the monobutyl diacid (MBP) were formed. Our results for both low and high LET radiation compare well with previous studies on these systems indicating that high LET degrades TBP to a lesser extent than gamma radiation. Available data for high LET is not as abundant as for low LET making such comparisons challenging. Nevertheless, our method yields a value for G+DBP that agrees well with previous alpha radiolysis studies indicating that our method shows promise for studying high LET radiolysis in liquid-liquid extraction systems.

Thermodynamic Modeling of Multi-Staged Extraction Systems for Chiral Separations through Coupled Analysis of Species Equilibria and Mass Transfer

A flexible and comprehensive model for predicting and optimizing separations of racemates of amino acids and other chiral metabolites in liquid-liquid multi-staged extraction systems is presented. Enantiomer partition coefficients are computed along the extraction path using multiple chemical equilibria theory and measured equilibrium formation constants for every complex formed in the two phases. The large number of speciation reactions typically occurring in ligand-exchange extraction systems requires the development of a robust numerical algorithm, and we present a method to rapidly and accurately solve the large nonlinear set of governing equations. Model performance is assessed through comparison to data for continuous extraction of various racemates within a series of hollow-fiber membrane modules. For each extraction, a chiral-ligand exchange selector molecule is solubilized in the organic phase flowing countercurrent to the aqueous phase into which the racemate is loaded. Enantiomer eluent profiles predicted at different conditions are in very good agreement with experiment. Through its predictive power, the model provides a useful in silico platform for optimizing these complex separations, and model results demonstrating this capability are presented.

Calculation of Solubility of Oxyquinolinates

The solubilities (s, mol/L) of different oxyquinolinates (oxinates, MeL2) are calculated using the formulae obtained according to elementary algebra, with the use of Excel spreadsheets. The calculations are involved with solution of algebraic equation of the third degree, obtained on the basis of concentration balances. The root of this equation, , is then inserted into the charge balance, and resolved according to zeroing procedure. In principle, the calculations are related to aqueous media. Nonetheless, the extension on liquid-liquid extraction systems is also proposed.

Methyl Violet Removal from Synthetic Wastewater by Liquid-Liquid Extraction using Vegetable Oils as Solvent

A laboratory study on methyl violet removal from aqueous solutions by liquid-liquid extraction system has been carried out, using crude palm oil and soy bean oil as solvent. The concentration of methyl violet has been studied in the range of 100 mg/L to 200 mg/L. The efficiency of dye extraction increased when two extractant di-2-ethylhexyl phosphoric acid and tributhyl phosphate were used as carrier. Under optimized conditions, 82% to 89% dye removal in 5 minutes rapid mix followed by 60 minutes slow mixing was achieved. The aqueous to organic phase volume ratio (A/O) was fixed at 1, pH varied from 1-6 and extraction study was carried out at (TBP): 200mM and (D2EHPA): 75mM.

Modeling of Liquid-Liquid Extraction (LLE) Equilibria Using Gibbs Energy Minimization (GEM) for the System TBP–HNO3–UO2–H2O–Diluent

Liquid-liquid extraction (LLE) is a widely used separation method for an extensive range of metals including actinides. The Gibbs energy minimization (GEM) method is used to compute the complex chemical equilibria for the LLE system HNO3–H2O–UO2(NO3)2–TBP plus diluent at 25°C. The nonelectrolyte phase is treated as an ideal mixture defined by eight tri-n-butyl phosphate (TBP) complexes plus the inert diluent. The Pitzer method is used to capture nonidealities in the concentrated electrolyte phase. The generated extraction isotherms are in very good agreement with reported experimental data for various TBP loadings and electrolyte concentrations demonstrating the adequacy of this approach to analyze complex multiphase multicomponent systems. The model is robust and yet flexible allowing for expansion to other LLE systems and coupling with computational tools for parameter analysis and optimization.

Experimental Measurements of Drop Size Distributions in 30 mm Diameter Annular Centrifugal Contactor with 30% TBP-Nitric Acid Biphasic System

For design and development of liquid-liquid extraction systems, it is essential to have an accurate estimation of hydrodynamic and mass transfer characteristics of the employed contactor. In the present study, experimental evaluations consisted primarily of determining the maximum solution throughput that could be processed without cross-phase contamination at a given rotor speed, O/A flow ratio, and organic-aqueous solution pair in a 30 mm bowl diameter centrifugal contactor. In addition, analysis included experimental drop size determinations as well as holdup determination. The experimental drop size distributions are expected to be helpful for modeling work.