Organic Phase Concentration Research Articles

Thermodynamics of the Extraction of Lead, Copper, Cadmium, Cobalt, and Nickel with Mono‐2‐ethylhexyl Phosphoric Acid

The extraction of Pb2+, Cu2+, Cd2+, Co2+, and Ni2+ from aqueous nitric acid medium by mono‐2‐ethylhexyl phosphoric acid (H2MEHP) dissolved in o‐xylene and aggregation of the extractant was studied in the temperature range 25–60°C. The extractions were investigated as a function of aqueous nitric acid concentration and extractant organic phase concentration. The extractant aggregation and extraction stoichiometries for the metal ions did not change with temperature. The thermodynamics of the extraction process was studied by measuring extraction coefficients in this temperature range. The slopes of the extractant dependencies are unity and acid dependencies have values equal to negative values of the formal charge on the metal ions; except for Pb2+ where extraction is favored by both enthalpy and entropy, extraction of the other metal ions is strongly opposed by entropy.

Efficient synthesis of optically active organosilyl alcohol via asymmetric reduction of acyl silane with immobilized yeast

Synthesis of optically active organosilyl alcohol via asymmetric reduction of prochiral acyl silane with immobilized Saccharomyces cerevisiae type II (a mutant from S. cerevisiae by UV irradiation treatment, named UV SC II) cells compared to free UV SC II cells was studied. It has been found that higher yield and enantiomeric excess (e.e.) of the product could be achieved with immobilized UV SC II cells. To further enhance the product yield and the product e.e., an aqueous/organic biphasic system was used as the reaction medium. The influence of various factors, such as shake speed, organic solvent, volume ratio of water phase to organic phase, buffer pH of water phase, reaction temperature and substrate concentration, was systematically studied and the reaction conditions were optimized with respect to the initial reaction rate, the product yield and the product e.e. All the above-mentioned factors had effect on the reaction to some extent. n-Hexane was found to be the best organic solvent. The optimum shake speed, volume ratio of water phase to organic phase, buffer pH, reaction temperature and substrate concentration were 150 rpm, 1/2, 8.0, 30 °C and 42 mM, respectively, under which the product yield and the product e.e. were as high as 97.4 and 95.4%.

Partitioning of crude oil polycyclic aromatic hydrocarbons in aquatic systems.

This paper investigates the hypothesis that observed polycyclic aromatic hydrocarbon (PAH) concentrations in an aqueous system are equal to the sum of the organic phase and soluble phase molar concentrations. While the organic phase concentrations are proportional to the PAH mole fraction in the oil, the soluble phase molar concentrations are estimated using Raoult's law. A batch laboratory mixing vessel with a scalable mixing energy was loaded initially at various oil layer thicknesses (0.4-3.2 mm) which correspond to oil surface loadings (40-310 mg/cm2). The vessel was agitated at constant mean shear rates (Gm = 5, 20 s(-1)). Total petroleum hydrocarbon (TPH) samples were taken periodically to estimate the entrainment rate as a function of initial oil layer thickness. TPH concentrations were measured in-situ using a laser scattering instrument (LISST-100) and ex-situ using gravimetric analysis. At a steady-state TPH concentration (>72 h), additional samples were analyzed for PAH concentration using GC/MS analysis. TPH concentrations increased over time according to a first-order kinetic model. Generally, the first-order rate constant and steady-state concentration both increased with increased oil loading and with increased Gm. In addition, measured PAH concentrations correlated well (r2 > 0.96) with those predicted by a partitioning model. These results are useful for assessing the effects of mixing and oil loading conditions on crude oil entrainment and PAH partitioning.

A solution to stripping problems caused by organophilic anion impurities in crown-ether-based solvent extraction systems: a case study of cesium removal from radioactive wastes

A problem related to stripping efficiency has been identified in the use of crown ether derivatives to extract alkali metal salts, and a simple solution is proposed. Focusing on the specific case of cesium extraction from simulants of alkaline nuclear waste by a calix-crown ether, calix[4]arene-bis( tert-octylbenzo-crown-6) (BOBCalixC6), it has been shown that low concentrations of a common surfactant, dodecylsulfonate, seriously impairs stripping. This surfactant has been identified as a trace component in laboratory simulants and was subsequently studied in experiments in which it was added in controlled amounts. Computer modeling of stripping behavior is consistent with the formation of a 1:1:1 organic-phase complex of the calix-crown with cesium and its nitrate counterion. In the presence of an organophilic surfactant anion, cesium ion can only effectively be stripped from the solvent until its organic-phase concentration becomes equivalent to that of the surfactant anion. Cleanup of nuclear waste requires a high decontamination factor for 137Cs, and insufficient stripping therefore leads to process failure. This difficulty raises a generic issue for use of crown ethers for waste decontamination or for other hydrometallurgical applications. However, remediation is possible by simply adding an alkylamine to the solvent. The alkylamine in its ammonium form acts as a counterion of the organophilic anion, suppressing the deleterious effects of the organophilic anion and allowing the cesium cation to be stripped efficiently. Trioctylamine (TOA) at a concentration of only 1 mM was found effective at restoring stripping performance while not affecting extraction. Ultimately, this solvent amendment enabled the development of a robust solvent for the Caustic-Side Solvent Extraction (CSSX) process and its successful demonstration on actual nuclear waste.

Extraction of vanadium(V) from sulfate solutions by ACORGA M5640

AbstractACORGA M5640 (hydroxy‐oxime derivative) has been applied as an extraction reagent for vanadium(V) from sulfate media. The extraction system was studied as a function of contact time, temperature, aqueous pH, diluent of the organic phase, and metal and extractant concentrations. The extraction reaction is endothermic and it is dependent on the organic diluent, aqueous pH and extractant concentration. The data have been analysed numerically to determine the stoichiometry of extracted species and their equilibrium constants. It was found that vanadium was extracted into the organic phase by a complex mechanism which involves the formation of two species (VO2R and VO2R. HR, where R represents the extractant). Vanadium stripping by acidic and ammonium hydroxide solutions was also studied. Copyright © 2003 Society of Chemical Industry

Distribution of major and trace elements in La Luna Formation, Southwestern Venezuelan Basin

The La Luna Formation (Maraca section), Maracaibo Basin, was studied by means of V and Ni analysis of the bitumen, total organic carbon (TOC), total sulfur (St), major elements (Si, Al, Fe, Mg, Mn, Ca, Ti, Na, K, P), trace elements (V, Ni, Co, Cr, Cu, and Zn), and electron microprobe analysis (EPMA) of the whole rock, and St, major elements (Si, Al, Fe, Mg, Mn, Ca, Ti, Na, K, P), trace elements (V, Ni, Co, Cr, Cu, Zn, Mo, Ba, U, Th) and rare earth elements (La, Ce, Nd, Sn, Eu, Th, Yb, Lu) of the carbonate-free fraction. The results are discussed based on the organic and inorganic association of trace elements and their use as paleoenvironmental indicators of sedimentation. An association between V and organic matter is suggested by means of correlation between V and Ni vs. TOC, the use of EPMA (whole rock) and V and Ni concentrations (carbonate-free fraction), whereas Ni is found in the organic matter and the sulfide phase. Fe is present as massive and framboidal pyrite, whereas Zn precipitates into a separate phase (sphalerite), and Ni, Cu and, in some cases, Zn, can be found as sulfides associated with pyrite. Concentrations of V and Ni (bitumen), TOC, St, V, Ni, Cr, Cu and Zn (whole rock), U, Th, Mo (carbonate-free fraction) are indicative of changes in the dysoxic sedimentation conditions in the chert layers (TOC, St, V, Ni, Cu and low Zn and V/Cr <4) to euxinic anoxic conditions in the argillaceous limestone (TOC, St, V, Ni, Cu and high Zn and V/Cr >4). In the sequence corresponding to the argillaceous limestone, variations in the concentrations of TOC, St, V, Ni, Zn, Cu and Cr (whole rock) can be observed, also suggesting variable sedimentation conditions. The following is proposed: (i) sedimentation intervals under euxinic conditions associated with high contribution and/or preservation of organic matter, allowing a high concentration level of V and Ni in the organic phase and the accumulation of Cu, Zn and Ni (in a smaller proportion) in the sulfide phase; (ii) sedimentation intervals under anoxic conditions and in the presence of relatively lower H2S, which allowed lower concentrations of V and Ni in the organic phase and higher concentrations of Cu, Zn, and Ni in the sulfide phase. Rare earth elements (REE) concentrations exhibit a marked increase in Ce, Nd, Sm, Eu, Y and Lu for the QM-3 interval, relative to Post-Archean Average Shale (PAAS). REE enrichment in shales has been related to the presence of phosphate minerals such as monazite or apatite. However, these minerals were not detected through XRD or EPMA in the whole rock or in the carbonate-free fraction. The association of REE with organic matter is suggested due to the absence of phosphate minerals, although assessment of these elements require further analysis.

Interfacial Mass Transfer in Nitroxide-Mediated Miniemulsion Polymerization

Nitroxide-mediated polymerization (NMP) represents a viable way to produce polymers with predictable molecular weights (MWs) and well-defined architectures. Such polymers have potential application in the fabrication of commercially valuable block copolymers, drug delivery systems, nanotechnology, adhesives, surfactants, and polymer compatibilizers. The distinguishing feature of NMP is the use of a nitroxide, such as 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO), to reversibly deactivate active polymer radicals to give a dormant alkoxyamine molecule (see Scheme 1). In Scheme 1, ka is the alkoxyamine dissociation rate coefficient, and kd is the radical deactivation rate coefficient. At 125 8C, the equilibrium coefficient for the reversible deactivation of polystyrene radicals by TEMPO has been measured to be Keq1⁄4 ka/kd1⁄4 2.1 10 11 M. Thus, the chemical equilibrium of the radical deactivation reaction favors the formation of the dormant alkoxyamine. As a result, the concentration of active polymer radicals in NMP systems is lower than in conventional free-radical polymerization systems, which reduces the likelihood Full Paper: A mathematical model has been developed to describe the interfacial mass transfer of TEMPO in a nitroxide-mediated miniemulsion polymerization (NMMP) system in the absence of chemical reactions. The model is used to examine how the diffusivity of TEMPO in the aqueous and organic droplet phases, the average droplet diameter and the nitroxide partition coefficient influences the time required for the nitroxide to reach phase equilibrium under non-steady state conditions. Our model predicts that phase equilibrium is achieved quickly (< 1 10 4 s) in NMMP systems under typical polymerization conditions and even at high monomer conversions when there is significant resistance to molecular diffusion. The characteristic time for reversible radical deactivation by TEMPO was found to be more than ten times greater than the predicted equilibration times, indicating that phase equilibrium will be achieved before TEMPO has an opportunity to react with active polymer radicals. However, significantly longer equilibration times are predicted, when average droplet diameters are as large as those typically found in emulsion and suspension polymerization systems, indicating that the aqueous and organic phase concentrations of nitroxide may not always be at phase equilibrium during polymerization in these systems. Influence of droplet phase TEMPO diffusivity, DTEMPO,drop, on the predicted organic phase concentration of TEMPO. Macromol. Theory Simul. 2002, 11, 953–960 953

Effect of ph on the extraction characteristics of succinic acid and the stability of colloidal liquid aphrons

Predispersed solvent extraction (PDSE) by colloidal liquid aphrons (CLAs) was used for the extraction of succinic acid from aqueous solution. The loading values for succinic acid in PDSE by CLAs increased with increasing pH values in aqueous phase. This was due to increasing of the concentration of the undissociated succinic acid. The extractability of PDSE was higher than that of conventional contacting type extraction because of the interaction between factant and acid molecule. The stability of CLAs increased with increasing of the pH values in aqueous phase and decreasing of trioctylamine (TOA) concentration in organic phase. However, the structure of CLAs was stable at all the pH range except very low pH condition.

Extractive spectrophotometric and inductively coupled plasma atomic emission spectrophotometric determination of titanium by using dibenzo-18-crown-6

Dibenzo-18-crown-6 (DB18C6) is used for the liquid–liquid extraction, and recovery of titanium from paints, pigment, paper and pulp industries. The extraction mechanism of titanium(IV) from pH 4 medium with DB18C6 in dichloromethane was investigated. The DB18C6 concentration in organic phase, the concentration of titanium, the effect of pH and interference ions such as Mo 6+, V 5+, Nb 5+, Ta 5+, Zr 4+, Fe 3+, etc. in the aqueous phase and the temperature on the distribution coefficient for the Ti(IV) have been examined. The titanium was determined by spectrophotometric and inductively coupled plasma atomic emission spectroscopic (ICP-AES) method. Titanium forms a colourless complex with DB18C6 at pH 4.0 which is extracted with dichloromethane having molar absorptivity 1.53×10 4 l mol −1 cm −1 at 285 nm. It obeys Beer's law in the range of 0.16–3.84 ppm of titanium. The colour was developed with thiocyanate which has molar absorptivity 1.50×10 3 l mol −1 cm −1 at 425 nm. The extract is directly inserted in the plasma for ICP-AES measurement, which enhance the sensitivity several folds and the limits for estimation are 0.5–30 ng ml −1. The overall formation (log β 2K'e) and extraction ( K ex) constants calculated are 18.61±0.02 and 1.03±0.03×10 −10, respectively. The transportation of titanium has been discussed. The titanium is preconcentrated and determined in standard and environmental samples.

Extraction of rare earth metals with a multistage mixer-settler extraction column

Extraction behavior of rare earth metals within a mixer–settler extraction column has been analyzed with the stage efficiency calculated from mass transfer coefficients and interfacial area. The mass transfer coefficient within the dispersed drops is determined from a rigid sphere model by taking into account the residence time distribution of drops, and the coefficient around the drops is calculated by Ranz–Marshall's correlation with the terminal settling velocity of a rigid sphere. The interfacial area of dispersed drops is calculated by the use of correlations for the drop diameter and the holdup of dispersed phase in the mixer–settler extraction column. The calculated results for the separation of samarium and gadolinium with a five-stage mixer–settler extraction column are compared with the experimental results at various agitation speeds and flow ratios between two phases. The extraction behavior in the multistage column is explained by a model based on the hydrodynamics and the mass transfer within the mixer. Effects of the pH value in aqueous phase, the extractant concentration in organic phase and the number of stages on the extraction behavior in the mixer–settler column are also shown.

Modelling multiple chemical equilbria in chiral partition systems

Ligand-exchange chiral extraction (LEXCEX) is an emerging technology for large-scale continuous resolution of enantiomers of amino acids and a wide range of chiral therapeutics and drug precursors. LEXCEX is based on the ability of a chiral ligand (Li), solubilized in the non-aqueous phase of a water/alcohol two-phase system through complexation with a transition metal ion (i.e., Cu), to preferentially extract one enantiomer (En) into the organic phase through formation of a ternary Li : Cu : En electroneutral complex. Here we show that the efficiency of the extraction depends, often strongly, on a number of process variables, including the selectivity of the ligand, the solubility of the enantiomers and complexes containing them in the organic phase, pH and transition-metal ion (Cu) concentration. Phase-equilibria in LEXCEX systems is governed by the complex chemical equilibria in both the aqueous and organic phases. To better understand this extraction process, we develop a model for ligand-exchange chiral extraction which couples a complete description of chemical equilibria in each phase with the overall phase equilibria of the system. The model requires the complete set of protonation constants and binary and ternary formation constants for each species present in either the aqueous or organic phase. When coupled with phase equilibrium constraints, the model quantitatively predicts extraction performance as a function of key operating parameters, thereby providing a simple computational approach to process optimization. Measured equilibrium formation constants for ternary complexes containing the N-decyl- l-hydropxy-proline ligand are found to depend strongly on solvent environment, with complex stabilities in general decreasing when the complex is transferred from water to n-octanol. The role of solvent in ternary complex stability is explored through a series of molecular mechanics simulations.

SOLVENT EXTRACTION OF TRIVALENT LANTHANIDES AND YTTRIUM FROM NITRATE MEDIA BY DIALKYL SULPHOXIDES

The solvent extraction of the trivalent rare-earth metals (the lanthanides and yttrium, Ln3+) from nitrate media by xylene solutions of some dialkyl sulphoxides (R2SO, where R=alkyl) was studied. The salting-out effect of added metal nitrate (5.00 M) increases in the order: NH4NO3>NaNO3>LiNO3. Extraction is independent of pH in the range from 2 up to at least 4, but decreases gradually below pH 2 due to the competing extraction of nitric acid. Vapour-pressure osmometry data indicate that the dialkyl sulphoxides are not appreciably self-associated under the conditions studied (0.10 to 0.60M in xylene or toluene solutions at 30°C), which permits the use of organic-phase concentration terms (in place of activities) in the slope-analysis studies. The distribution ratios for the extraction of yttrium, gadolinium and lutetium show a third-order dependence on the concentration of the sulphoxide in the organic phase, with a slightly higher dependence (3.3) for lanthanum. In addition, the mole ratio of nitrate to metal in the loaded organic phase is close to 3, which suggests that the stoichiometry of the extracted complexes is Ln(NO3)3(R2SO)3. Increasing the steric bulk of the substituent alkyl groups (R) in the sulphoxides causes a marked decrease in metal extraction, and a reasonable correlation exists between the extraction of a given metal and the sum of the steric parameters of the alkyl groups in each of the sulphoxides used. In traversing the lanthanide series, the extraction increases in the interval La to Sm, and decreases thereafter to the end of the series. The behaviour of yttrium most closely resembles that of thulium or ytterbium.

Extraction of glyphosate by a supported liquid membrane technique

The possible application of the supported liquid membrane (SLM) technique for the extraction of glyphosate is presented. For the extraction of this compound the SLM system has been applied with utilisation of Aliquat 336 as a cationic carrier incorporated into the membrane phase. The extraction efficiency of glyphosate [ N-(phosphonomethyl)glycine] is dependent on the donor phase pH, carrier concentration in the organic phase and NaCl concentration in the acceptor phase. The optimal extraction conditions are: donor phase pH>11, acceptor phase of 2 M NaCl solution and the organic phase composed of 20% (w/w) Aliquot 336 solution in di-hexyl ether. Counter-coupled transport of chloride anions from the acceptor phase to the donor phase is a driving force of the mass transfer in this system.

Extraction Kinetics of Uranium(VI) with di(2-ethylhexyl) Phosphoric Acid Using a Hollow Fiber Membrane Extractor

The kinetics of solvent extraction of U(VI) with di(2-ethylhexyl) phosphoric acid (HDEHP) using a microporous hydrophobic hollow fiber membrane extractor has been investigated. The effects of U(VI) and hydrogen ion concentrations in aqueous phase, HDEHP concentration in organic phase, flow velocities of aqueous and organic phase and temperature on extraction rate of U(VI) were examined. The experimental results suggest that the extraction rate of U(VI) is controlled by diffusion.

Roles of Extractant Concentration and Flow Rate of Organic Phase in Countercurrent Multistage Metal Solvent Extraction-Stripping Process for Metal Ions.

The effects of the extractant concentration, CHAo, and the flow rate of the organic phase, S, on the metal recovery in a steady-state countercurrent multi-stage metal solvent extraction-stripping process (ESP) using cation-exchange reagents have been assessed by computer simulation. The results show that, with increasing CHAo or S, (i) the recovery fraction monotonically increases when the number of stages in the extraction or stripping section (N or N′, respectively) is unity and (ii) the recovery fraction first increases, then reaches a maximum, and thereafter very slowly decreases when N and N′ are larger than unity. The optimum combination of CHAo and S will be determined by using the equi-recovery-fraction and equi-operating-cost curves. In order to obtain in-depth understanding of the simulation results, steady-state local linearization (SLL) analysis which theoretically considers the infinitesimal variations in the metal concentrations in each stage caused by the infinitesimal variation in the operational parameters has been done. As a result, it is proved that the balance between the quantities ψ (CHAo) of the extraction and stripping sections determines the trend of the recovery fraction with CHAo, where ψ (CHAo) is the partial derivative of the metal molarity in the organic phase at the outlet of the extraction or stripping section with respect to CHAo: At the maximum recovery fraction, these values are equal to each other. Similar results are obtained also in the effect of S. Furthermore, it is proved that, with increasing CHAo or S, (i) the maximum of the recovery fraction never appears when N or N′ is unity and (ii) the decrease in the recovery fraction after reaching the maximum is much slower than the increase before reaching the maximum when N and N′ are larger than unity.

Study of kinetics of forward extraction of Fe(III) from chloride medium by di-2-ethylhexylphosphoric acid in kerosene using the single drop technique

The kinetics of the title system have been investigated as functions of Fe 3+, H + and Cl − concentrations in aqueous phase, D2EHPA (di-2-ethylhexylphosphoric acid, H 2A 2) concentration in organic phase and temperature using the single rising drop technique. The reaction order wrt [Fe 3+] is always unity. The logarithm of flux vs. −log[HCl] plots pass through a minimum at 0.5 M HCl with a limiting slope of −2.4 in the high concentration region (hcr) of HCl and +1 in the low concentration region (lcr) of HCl. This effect is due to the combined effect of H + and Cl −. At lcr of Cl −, the rate is inversely proportional to [H +], whereas at hcr of Cl − the rate is directly proportional to [H +]. The exponent of the [Cl −] term in the rate equation is found to vary within 0–1.2 on varying [H +] from lower to higher values. When the aqueous acidity is kept low, the rate is directly proportional to [D2EHPA] and at higher acidities of aqueous phase, the rate is independent of its concentration. A rate equation involving the extractions of Fe 3+, FeCl 2+, FeCl 2 + and FeCl 3 has been derived empirically to describe the system. The treatment of the temperature dependence data on rate gives the activation energies ( E a) of 76, 63, 15 and 10 kJ/mol for the extraction of species Fe 3+, FeCl 2+, FeCl 2 + and FeCl 3 respectively. Similarly, the enthalpy (Δ H ±) and entropy (Δ S ±) of activation have been calculated to be 76 kJ/mol and −130 J/K mol, 55 kJ/mol and −140 J/K mol, 20 kJ/mol and −392 J/K mol, and 6 kJ/mol and −280 J/K mol, respectively, for the four species. The mechanisms of extraction particularly of the rate-determining steps have been suggested.

Investigation on process parameters involved in preparation of poly- dl-lactide-poly(ethylene glycol) microspheres containing Leptospira Interrogans antigens

Block copolymer, poly- dl-lactide-poly(ethylene glycol) (PELA) with 11.5% of poly(ethylene glycol) (PEG) content was prepared by bulk ring-opening polymerization using stannous chloride as initiator. PELA microspheres with entrapped Leptospira Interrogans antigens, outer membrane protein (OMP) were elaborated by solvent extraction method based on the formation of multiple w/o/w emulsion, and the resulting microspheres were characterized with respect to particle size, OMP entrapment and morphology characteristics. The purpose of the present study is to perform the optimization of preparative parameters for OMP-loaded PELA micropsheres to control particle size and improve the OMP encapsulation efficiency. Of all the parameters investigated, the polymer concentration of organic phase and the external aqueous phase volume play major roles on particle size, while the organic phase volume, internal aqueous phase volume and the addition of surfactant into the internal aqueous phase display considerable effects on OMP loading efficiency. A small volume of internal aqueous phase and intermediate volumes of organic phase and external aqueous phase were favorable to achieve micropsheres with a size of 1–2 μm and high antigen encapsulation efficiency (70–80%). In vitro OMP release profiles from PELA microspheres consist of a small burst release followed by a gradual release phase. The OMP release rate shows some relations with the porous and water-swollen inner structure of the microspheres matrix. The presence of surfactant in microspheres accelerates OMP release, but the OMP entrapment within microspheres shows limited effects on the release profile.

Relationship between Retention Characteristics and Physicochemical Parameters of Solutes on a Porous Graphitized Carbon Column Studied by Canonical Correlation Analysis

ABSTRACT The retention of 44 barbituric acid derivatives was determined on a porous graphitized carbon column using water-tetrahydrofuran mixtures as eluents. Good linear relationships were found between the logk values and the organic mobile phase concentration in the eluent. The slope and intercept values of the relationship were correlated with the physicochemical parameters of the barbituric acid derivatives by means of canonical correlation analysis. The results indicate that the electronic parameters exerted the highest impact on the retention with the effect of hydrophobicity being negligible. The data indicates that the retention mechanism of a porous graphitized carbon column considerably deviates from that of traditional reversed-phase column although the eluent systems are identical.

Solvent extraction of Fe 3+ from chloride solution by D2EHPA in kerosene

The solvent extraction of Fe 3+ from chloride solution by di-2-ethylhexylphosphoric acid (D2EHPA, H 2A 2) dissolved in kerosene has been investigated over a wide range of aqueous acidity as a function of phase contact time, Fe 3+, HCl, H + and Cl − concentrations in aqueous phase, D2EHPA concentration in organic phase and temperature. The dependencies of the distribution coefficient on the concentrations of Fe 3+, H +, Cl − and D2EHPA vary with the extraction conditions used which indicates that the composition of Fe 3+ species in both the aqueous and the organic phases vary with the HCl or Cl − concentration in the aqueous phase. The experimental results are best fitted by the following equation: D=K 1x 0 [ H 2A 2 ] 3 ( O) [ H +] 3 +K 2x 1 [ H 2A 2 ] 2 ( O) [ H +] 2 +K 3x 2 [ H 2A 2 ] 1.5 ( O) [ H +] +K 4x 3[ H 2A 2 ] 1.5[ HCl] where, x 0, x 1, x 2 and x 3 are the fractions of Fe 3+, FeCl 2+, FeCl 2 + and FeCl 3 present in the aqueous phase at the particular HCl/Cl − concentration used; the values of K 1, K 2, K 3 and K 4 are found to be 1.315, 15, 12 and 320, respectively. The treatment of the temperature dependence data gives the apparent enthalpy changes (Δ H) of 125, 104, 20.8 and 33.3 kJ/mol for the extraction of the species Fe 3+, FeCl 2+, FeCl 2 + and FeCl 3, respectively. The loading of D2EHPA in the organic phase by Fe 3+ has also been investigated and the structures of the maximum loaded extracted species obtained at 0.05 and 1.0 M aqueous HCl concentrations have been demonstrated to be [FeCl(H 2O)A 2] and [FeCl 2·A·(HA) 2·(HA·HCl) 2], respectively.

Solvent extraction of tetravalent titanium from chloride solution by di-2-ethylhexyl phosphoric acid in kerosene

The solvent extraction of Ti 4+ from chloride solution by di-2-ethylhexyl phosphoric acid (D2EHPA, H 2A 2) dissolved in kerosene has been investigated over a wide range of aqueous acidity as a function of phase contact time, Ti 4+, H + and Cl − concentrations in aqueous phase, D2EHPA concentration in organic phase and temperature. The equilibrium is reached within 2 h. The distribution coefficient is found to be independent of Ti 4+ concentration at least up to 1 g/l Ti 4+ in the aqueous phase. The pH and log extractant concentration dependences are approximately −2 and 2, respectively. The extraction is independent of Cl − concentration. These results suggest that extraction occurs via the following reaction: TiO 2++2H 2A 2(O)⇌[TiO(HA 2) 2] (O)+2H +. The temperature dependence data give Δ H values of 30 kJ/mol in the higher temperature region (>30°C) and 78 kJ/mol in the lower temperature region (∼15°C) under investigation. The equilibrium constant, K ex at lower loading is 1×10 3.95 with a standard deviation of log K ex of 0.023. The loading capacity of D2EHPA for Ti 4+ is 7.31 g Ti(IV)/100 g D2EHPA. The loading study suggests that a variation of the extraction equilibrium reaction occurs during the course of loading. At high loading Ti 4+ is extracted by the reaction: TiO 2++H 2A 2(0)⇌[TiOA 2] (0)+2H +. The structure of the solid complex prepared from the high loaded organic phase has been established by determining the Ti/P ratio and using infrared spectroscopy.