Di(2-ethylhexyl)phosphoric Acid Concentration Research Articles

Mechanistic analysis of solvent extraction of heavy metals in membrane contactors

The extraction of Zn 2+ and Cu 2+ in a hollow fiber membrane module with a kerosene solution of di(2-ethylhexyl)phosphoric acid (D2EHPA) was studied. Experiments were performed at different aqueous metal concentrations (0.78–15.7 mol/m 3), pH2–6, and organic D2EHPA concentrations (25–100 mol/m 3). A mass transfer model was presented that considers aqueous layer diffusion, membrane diffusion, and organic layer diffusion. The calculated time profiles of aqueous metal concentrations agreed reasonably with the measured data (standard deviation, 9%) based on a good knowledge of the chemistry of extraction reactions and the transport properties of the relevant geometry. By comparing the relative resistance of each diffusion step, the extraction of Zn 2+ was predominantly governed by aqueous layer diffusion; however, the diffusion in aqueous layer, membrane, and organic layer all played a certain role for the extraction of Cu 2+. The changes of rate-controlling step(s) with time during the experiments were also evaluated.

Separation of heavy metals in seawater by liquid membranes: preconcentration of copper

A bulk liquid membrane system has been used to preconcentrate and separate the copper ions present in a seawater sample prior to its analysis by flame atomic absorption spectroscopy. The liquid membrane comprised an organic solution containing di-(2-ethylhexyl) phosphoric acid (DEHPA) in kerosene. The preconcentration system was optimized by studying the influence of the acidity of the sample and the receiving solution, the DEHPA concentration in the organic membrane, and the stirring rate. Under optimum conditions, the preconcentration yield for real samples was 87.0%. The average relative error of the determination was 3.6%, while relative standard deviation averaged 7.8%. The reliability of the new method was confirmed by analyzing several real samples of seawater, analyzed previously by a well-established technique.

Statistical study of factors affecting the co-extraction of uranium and iron in the second cycle of extraction with DEHPA/TOPO in kerosene

The co-extraction of uranium and iron with di-(2-ethylhexyl) phosphoric acid (DEHPA)/tri- n-octyl phosphine oxide (TOPO) in kerosene from loaded phosphoric acid in the second extraction cycle is influenced by the factors uranium, iron, DEHPA concentration, P 2O 5% and organic-to-acid ratio (O/A). From a general regression equation, two mathematical models have been generated representing the effect of these five factors on the selectivity and yield: the interaction between factors has been ascertained. Analysis and interpretation of the results enabled us to determine the best experimental operating conditions of the second extraction cycle to obtain a least contaminated loaded solvent and to improve the quality of the yellow cake.

Removal of silver and copper ions from acidic thiourea solutions with a supported liquid membrane containing D2EHPA as carrier

Abstract Facilitated counter-transport of silver and copper ions, both in acidic thiourea medium, across a supported liquid membrane (SLM) by using di(2-ethylhexyl)phosphoric acid (D2EHPA) as carrier, dissolved in chloroform, has been investigated. The fundamental parameters influencing the transport of silver and copper ions have been determined. They are: thiourea concentration in the feed phase, pH of the strip solution, D2EHPA concentration in the membrane phase, silver and copper concentrations in the feed phase, pH of feed solution, temperature of the system, membrane support characteristics and the type of acid. Thiourea can form, with both ions, successive complexes, which are less mobile than the free metal cation. In fact, the mass transport flux of silver and copper ions decreases when the concentration of thiourea in the feed phase increases. The obtained results show that Ag(I) and Cu(II) species predominate at very low thiourea concentration (10−5–10−4 M) and they are substituted by complexes M(Tu)n+ (M=Ag, Cu with n=1–4 and Tu refers to thiourea) with increasing thiourea concentration. Transport fluxes of silver and copper ions from feed solutions of different anionic composition, in absence and presence of thiourea, followed the order: NO3−>Cl−>SO42−>PO43−. This means that preferentially nitric acid should be used in preparing leaching solutions of polymetallic ores that are then used as feed in the SLM system. It was possible to take advantage of the different fundamental parameters for the separation of Ag(I) and Cu(II) in presence of thiourea, indeed working in the optimal conditions, the selectivity of the transport (JAg(I)/JCu(II)) increased from 1.29 to 1.96 with increasing thiourea concentration from 0 to 0.1 M.

Modeling of nondispersive extraction of binary Zn(II) and Cu(II) with D2EHPA in hollow fiber devices

The extraction of Zn 2+ and Cu 2+ from binary solutions in a microporous hollow fiber with di(2-ethylhexyl)phosphoric acid (D2EHPA) in kerosene was examined. Experiments were performed at different metal concentrations (3.13–15.7 mol/m 3), metal concentration ratios (0.25–4), pH (3–5), and D2EHPA concentrations (50–200 mol/m 3). A mass transfer model was presented that considers diffusion in the aqueous layer, membrane, and organic layer. On the basis of the knowledge of extraction chemistry and transport properties of the relevant geometry, the validity of the model was checked from time changes of aqueous metal concentrations in the single systems (standard deviation, 9%). For binary systems, comparisons of the experimental data and the calculated results which directly taking the model parameters obtained in the single systems revealed that a synergistic effect on Zn 2+ extraction occurred at the latter stage of the processes.

Kinetic study of l-isoleucine transport through a liquid membrane containing di(2-ethylhexyl) phosphoric acid in kerosene

A kinetic study of l-isoleucine transport through a liquid membrane containing di(2-ethylhexyl) phosphoric acid (D2EHPA) in kerosene is presented. The influences of pH in the aqueous feed solution, D2EHPA concentration in the organic phase, the stripping solution composition and H 2SO 4 concentration in the stripping solution were investigated, and the effects of stirring speed and temperature on the transport of l-isoleucine through a bulk liquid membrane (BLM) were studied. The kinetics of l-isoleucine transport could be analyzed in the formalism of a reversible pseudo-first-order reaction followed by an irreversible pseudo-first-order reaction. The pseudo-first-order apparent rate constants of the interfacial transport of l-isoleucine species are determined for the liquid membrane, at various temperatures. The apparent activation energy values are 21.3±1.9, 57.6±5.1 and 31.8±2.7 kJ mol −1 for the extraction reaction, extraction back reaction and stripping reaction, respectively.

EFFECT OF ADDED COMPLEXING AGENTS ON EXTRACTION OF Cu(II) FROM SULFATE SOLUTIONS BY DI(2-ETHYLHEXYL)PHOSPHORIC ACID

The efficiencies of Cu(II) extraction from 0.5 mol/dm3 (Na,H)SO4 solutions by di(2-ethylhexyl)phosphoric acid (D2EHPA) in kerosene were measured in the presence of complexing agents EDTA, nitrilotriacetic acid (NTA), and citric acid. All experiments were performed in solution at pH 1.8–4.1; Cu(II) concentration of 0.005, 0.01, and 0.02 mol/dm3; the concentration of complexing agent to Cu(II) as 0, 0.1, 0.2, 0.5; and a D2EHPA concentration of 0.01–0.5 mol/dm3. The extraction efficiency of Cu(II) decreased with the addition of EDTA and NTA, but not with citric acid. The presence of complexing agents resulted in a change of reaction stoichiometry of Cu(II) and D2EHPA, likely due to the mutual interaction of Cu(II)-D2EHPA complexes and the complexing agents. The coextraction of citric acid into the organic phase could explain the increase in extraction efficiency with increasing citric acid concentration.

Selective transport of lanthanides through supported liquid membranes containing non-selective extractant, di-(2-ethylhexyl)phosphoric acid, as a carrier

Permeation of lanthanides (Ln) between aqueous nitrate solutions of different acidity through supported kerosene membrane containing di-(2-ethylhexyl)phosphoric acid (DEHPA) as a carrier has been studied. Mass transfer of Ln cations has been determined in terms of permeability coefficients ( P) by on-line FIA measurement of metal concentrations in strip solution. Acidity of feed solution ranged from pH 1.2 to 4.2 (ionic strength 0.1 mol l −1 (HNO 3, NaNO 3)) while that of strip solution was kept constant at 0.1 mol l −1 HNO 3. Carrier concentration has been changed in the range from 10 to 10 3 mmol l −1. Both, the P versus feed pH plots measured at low and at high DEHPA concentrations as well as P versus DEHPA concentration plots exhibited maxima. Permeability coefficients were decreasing when advancing in the lanthanide series and significant differences in behaviour of individual lanthanides has been observed. The conditions of separation of light and heavy lanthanides and mutual separation of light lanthanides have been suggested. Based on these and previous results, composition of transported species, presence of maxima on measured curves, and formation of gel-like substance in feed solution and on membrane-feed solution interface are discussed.

Mechanism of rate enhancement in the extraction of Zn(II) by di(2-ethylhexyl)phosphoric acid in the presence of sodium lauryl sulphate micelles

The effect of a sodium lauryl sulphate (NaLS) micellar phase on the rate of Zn(II) extraction from a sulphate medium by a 0.01 M solution of di(2-ethyl-hexyl)phosphoric acid (DEHPA) in dodecane was investigated in a constant area stirred cell. The concentration of NaLS was varied between 5.1×10 −5 and 7.7×10 −3 M. Below the critical micellar concentration (CMC) the presence of the surfactant decreased the extraction flux, whereas substantial flux enhancements were observed above the CMC reaching an enhancement ratio of 10 at a concentration of 4.6×10 −3 M. Solubilization of DEHPA in the Zn-free micellar aqueous phase at different concentrations of NaLS was investigated using Fourier transform infra-red spectroscopy. Solubility increased with NaLS concentration, reaching a maximum at the highest NaLS used, rendering a calculated concentration of DEHPA in the aqueous phase of 0.8×10 −3 M. As DEHPA is practically insoluble in water it was concluded that DEHPA molecules were incorporated in the micellar interface, thus producing a substantial enlargement of the reaction site for the interfacial Zn complexation reaction, together with a reaction rate enhancement due to micellar catalysis. It is proposed that the main mechanism of flux enhancement is the additional production of Zn complex at the micellar interface, coupled with a high rate of complex transfer to the organic phase due to micellar interaction with the system interface. The effect of the negative electrical charge at both the interface and the micellar interface is also discussed.

Facilitated transport of lead(II) and cadmium(II) through novel activated composite membranes containing di-(2-ethyl-hexyl)phosphoric acid as carrier

This paper describes an approach to the chemical characterisation of the facilitated transport of lead(II) and cadmium(II) by an activated composite membrane (ACM) containing immobilised di-(2-ethyl-hexyl)phosphoric acid (DEHPA). Such membranes were prepared, by interfacial polymerisation and characterised physically and chemically. The ACMs were used to experimentally determine their transport behaviour for Pb(II) and Cd(II). So, the influence of some chemical parameters (i.e. DEHPA concentration on the ACM, the feed solution composition, the concentration of nitric acid in the stripping solution, and the ionic strength of the feed and stripping aqueous solutions) was assayed for each metal ion. A correlation of the chemical behaviour of those ACM systems with the physical characterisation of those membranes, prior to and after their use, is reported. The optimum chemical conditions for Pb(II) and Cd(II) transport enhance the lifetime of the ACMs, giving higher DEHPA immobilisation on the polymeric phase of the composite membrane.

Distribution Behavior of L-Tryptophane by Extraction with Di(2-ethylhexyl) Phosphoric Acid

To demonstrate that the proton-transfer reaction occurs in the extraction of α-amino acid and to explain the complicated phenomenon present in the extraction of L-tryptophane, a series of extraction equilibrium experiment for L-tryptophane with di(2-ethylhexyl) phosphoric acid (D2EHPA) dissolved in n-octane (System A) and a mixture of n-octane and n-octanol (System B) using L-tryptophane (L-Trp) as a model amino acid were carried out. The effects of L-tryptophane (L-Trp) concentration, D2EHPA concentration, n-octanol concentration, and pH on the extraction distribution ratio are discussed in detail. In System A, in the 1.0 < pH < 3.5 range, distribution ratio D increases with an increase of pH, but changes slightly in the 3.5 < pH < 5.0 range. The data indicate the formation of both (1:1) and (1:2) L-tryptophane–D2EHPA (dimeric) complexes, and the complexes tend to cluster together, away from the low-polarity bulk solvent. The infrared spectrogram of the organic-phase-loaded solute illustrates that the pH condition has little effect on the structure of complex. In System B, both the (1:1) and (1:2) L-tryptophane-D2EHPA (dimeric) complex form, but they do not cluster together because of the diluent that improves the polarity of the bulk solvent. The proton-transfer reaction is again demonstrated in the extraction of α-amino acid with D2EHPA. Expressions of the equilibrium distribution are proposed.

Non-dispersive extraction separation of metals using hydrophilic microporous and cation exchange membranes

Non-dispersive extraction of Zn(II) and Cu(II) from single and binary solutions across a flat-sheet membrane to an organic solution containing di(2-ethylhexyl)phosphoric acid (D2EHPA) was studied. Hydrophilic microporous and cation exchange membranes were used. Experiments were performed as a function of the pH (2–6), metal concentration (0.31–3.13 mol/m 3), and D2EHPA concentration (50–500 mol/m 3). It was shown that the presence of one metal retarded the transport of the other. Compared to the hydrophilic microporous membrane, the cation exchange membrane gave a low extraction rate of both metals in either single or binary systems, but gave a higher selectivity of Zn(II) over Cu(II) in binary systems at high D2EHPA concentrations.

Distribution Behavior of L-Phenylalanine by Extraction with Di(2-Ethylhexyl) Phosphoric Acid

In the separation processes of amino acids, zwitterionic species are prevented from being exchanged because of the spatial proximity of two opposite charges on the molecule. There would be a high chemicals cost due to the need to change the solution pH. It is therefore desirable to develop a novel recovery technology for amino acids in the middle pH range. A series of extraction equilibrium experiments for L-phenylalanine (L-phe) with di(2-ethylhexyl) phosphoric acid (D2EHPA) dissolved in n-octane was carried out. The effects of L-phe concentration, D2EHPA concentration, and pH on the distribution ratio were discussed in detail. The infrared spectrogram of the organic-phase-loaded solute illustrated that the pH condition had little effect on the structure of the complex. There are proton-transfer and ion-exchange reactions in the extraction. One L-phe molecule is extracted by forming a complex with two dimeric D2EHPA molecules. An expression of the equilibrium distribution was proposed.

Competitive sorption of metal ions from binary sulfate solutions with solvent-impregnated resins

Equilibrium and kinetics for the sorption of Cu(II) and Zn(II) from binary sulfate media with macroporous resins containing di(2-ethylhexyl)phosphoric acid (D2EHPA) were studied and compared with those obtained in the single systems. Experiments were performed as a function of aqueous pH, the concentration ratio of metal ions in the aqueous phase, and the concentration of D2EHPA in the resin phase. The rate of sorption was determined using initial rate: technique by the Elovich equation. It was shown that the sorption equilibrium of one metal was hardly affected by the presence of the other. However, the sorption rate obtained in the binary systems was always less than that in the single systems. The separation factors based on equilibrium and kinetic aspects were obtained. Finally, the competitive effect in rates was discussed in terms of sorption mechanism.

Distribution Behavior of Amino Acid by Extraction with Di(2-ethylhexyl) Phosphoric Acid

The distribution equilibrium of l-tryptophan (l-Trp) by extraction with di(2-ethylhexyl) phosphoric acid (D2EHPA) dissolved in n-hexane was studied. The effects of L-Trp and D2EHPA concentrations, pH, and ionic strength, particularly of L-Trp loading in the organic phase, on extraction equilibrium were examined in detail. When the amino acid loading ratio (the molar concentration ratio of the equilibrium amino acid in the organic phase to the initial dimeric D2EHPA) was less than 3 × 10−3, one L-Trp molecule was extracted by forming a complex with four monomeric D2EHPA molecules, and the extraction equilibrium constant (K e) was determined to be 0.045 dm3/mol. Above this loading ratio the equilibrium formula did not hold, and the apparent equilibrium constant (K a) increased significantly with increasing loading ratio. The phenomenon was explained by taking into account two parallel reactions in which fewer D2EHPA molecules, two and one respectively, were needed to extract one l-Trp molecule.

Peptide separation by pH-zone-refining countercurrent chromatography

Peptides without protecting groups have been successfully separated by pH-zone-refining countercurrent chromatography (CCC) using an ion-pair reagent, di-(2-ethylhexyl)phosphoric acid (DEHPA), as a modifier in the statinary phase. Preliminary studies indicated that two parameters, i.e., the DEHPA concentration in the stationary phase and hydrophobicity of the solvent system should be adjusted according to the hydrophobicity of the analytes. Hydrophobic and hydrophilic groups of dipeptides were each separated under optimized conditions. The method was successfully applied to gram-quantity separations of bacitracin complex and bovine insulin.

Column separation of divalent metals from sulfate solutions using impregnated resins containing di(2-ethylhexyl)phosphoric acid

Column separation of divalent zinc and copper ions from binary aqueous sulfate solutions using di(2ethylhexyl)phosphoric acid (D2EHPA)-impregnated macroporous resins was systematically studied at 298 K. The breakthrough curves for binary metal sorption were measured as a function of resin type, feed flow rate, feed metal concentration ratio and aqueous pH, and D2EHPA concentration in the resin phase. It was shown that an overshoot behavior in the breakthrough curve for copper, the metal having a lower affinity with the impregnated resins, was observed near the breakpoint for other metal, zinc. The dependence of the degree of separation of zinc to copper on experimental parameters was quantitatively discussed.

Kinetics of Mn(II) Transport from Aqueous Sulfate Solution through a Supported Liquid Membrane Containing Di(2-ethylhexyl) Phosphoric Acid in Kerosene

Abstract The permeation rate of Co2+ from its aqueous sulfate solution through a solid supported liquid membrane containing di(2-ethylhexyl) phosphoric acid (D2EHPA) in kerosene as mobile carrier has been studied as a function of hydrodynamic conditions, concentrations of Co2+ (0.17−4.25 mol/m3) and H+ (pH 3.5−6.0) in the feed solution, carrier concentration (20–400 mol/m3) in the membrane, and temperature. It has been observed that Co2+ flux across the membrane tends to reach a plateau region at a higher concentration of Co(II) or a lower concentration of H+ due to carrier saturation within the membrane, leading to a diffusion-controlled process. It is also observed that Co2+ flux is about second order with respect to dimerized carrier at a lower D2EHPA concentration (≶150 mol/m3) and exhibits a lower order (0.6–1.0) at a higher concentration of D2EHPA. Necessary kinetic parameters have been derived from the model equations based on the combination of aqueous film diffusion, interfacial chemical reaction...

Extraction kinetics of zinc from aqueous perchlorate solution by D2EHPA dissolved in Isopar-H

The rate of extraction of zinc(II) from aqueous perchlorate solutions at 1 M ionic strength by di(2-ethylhexyl) phosphoric acid (DEHPA) in Isopar-H (ESSO chemicals) was studied. The study was performed using a modified Lewis cell at 25°C. The experimental hydrodynamic conditions were chosen so that the contribution from diffusion on the measured rate of reaction was minimized. The rate of zinc extraction was measured at different chemical composition by varying zinc, hydrogen ion and DEHPA concentrations. The data were analysed in terms of pseudo-first order constants and a reaction mechanism was developed where a zinc-DEHPA complex is formed at the interface. The results of this kinetic model are in agreement with the equilibrium study reported previously for the same system.

Transport of zinc through a supported liquid membrane using di(2-ethylhexyl) phosphoric acid as a mobile carrier

The rate and mechanism of zinc transport through a supported liquid membrane containing di(2-ethylhexyl)phosphoric acid (D2EHPA) as a mobile carrier has been studied. An equation describing the permeation rate has been derived, taking into account aqueous film diffusion, interfacial chemical reaction, and membrane diffusion as simultaneous controlling factors. The permeation rate of zinc was found to be mainly controlled by diffusion in the membrane in the majority of cases, but controlled by diffusion in the membrane and aqueous film when a higher concentration of total D2EHPA in the membrane solution and lower concentrations of zinc and hydrogen ions in the feed solution were employed simultaneously. The mass transfer coefficient in the aqueous film and the diffusivity of the zinc-D2EHPA complex in the bulk membrane solution were measured employing a permeation cell. The observed rates agree well with the mechanism proposed in this study.