Search

The extraction of aluminium from dilute phosphoric acid with di-2-ethylhexyl phosphoric acid (DEHPA) was optimized using response surface methodology. The optimization was based on the experimental three-level central composite face-centred design (CCF) and was conducted on real-life samples. The three variables included were pH, extractant concentration and aqueous to organic phase ratio (AO). Under the optimized conditions (pH 2.5, 0.6 M DEHPA and AO ratio 1:2), extraction efficiency of 99% for aluminium in four extraction stages is achieved. The purified phosphoric acid solution can then be utilized by the fertilizing industry. Stripping tests for organic phase loaded with aluminium were conducted with sulphuric acid. Extremely high stripping efficiency was obtained with 0.9 M sulphuric acid resulting in the recovery rate of 88% in one stage. After stripping, the aluminium sulphate solution can be reused as a precipitation agent for phosphorus in the wastewater treatment process.

Dissolution of uranium oxide was carried out using a solution of HD2EHP in C8mim·NTf2, which was apparently facilitated by the in situ generation of water during the complex formation reaction. The dissolved complex in the ionic liquid phase led to splitting of the latter into a light phase and a heavy phase where the former contained predominantly the UO2(HL2)2 complex (HL = HD2EHP), while the latter contained the ionic liquid as supported by FTIR and UV-Visible spectral analyses. The complexation of the uranyl ion was suggested to take place in the equatorial plane where two dimeric units of the H-bonded HD2EHP molecules took part in complexation. An increase in temperature facilitated the dissolution rate with an activation energy of 31.0 ± 2.8 kJ/mol. The cyclic voltammetry studies indicated potential chances of recovery of the dissolved uranium by electrodeposition at the cathode. The proposed dimeric structure of HD2EHP in the complexation with U(VI) was supported by DFT studies also.

The extraction of copper (II) ions using di (2-ethylhexyl) phosphoric acid – based liquid membranes during a galvanostatic electrodialysis-electrolysis process was studied. Effects of the current density, copper (II) and hydrochloric acid concentration in the feed solution, carrier and admixture concentration in the liquid membrane, type of acid in the catholyte were studied, and the optimal conditions were determined. A practically complete removal of copper (II) from the feed solution containing 0.01 M CuCl2 was achieved during 3.0 −4.0 h of electrodialysis. A possibility of effective transfer and electrodeposition of copper (II) from dilute solutions of sulfuric, hydrochloric, perchloric, nitric and acetic acids was shown. Adherent copper coatings with a fine-grained structure were obtained from dilute sulfuric acid solutions. A maximum stripping degree into the catholyte of 88 % and an electrodeposition degree of 73 % were achieved in the studied system.

The solvent extraction behavior of cobalt and lithium from mixed sulfate solution using di(2-ethylhexyl)phosphoric acid (D2EHPA)/kerosene as extractant system has been investigated. The effect of different process parameters such as pH of feed solution, extractant concentration, cobalt and lithium ion concentrations in the feed solution have been studied. Extraction equilibrium constants have been calculated and found to be log Kex Co = –2.01 and log Kex Li = –2.42. The highest separation factor of 292 was achieved using 1.59 M D2EHPA at pH 1.85 from mixed sulfate solution. 93.9% of cobalt and 11.4% lithium was co-extracted from 0.01 M cobalt and lithium sulfate solution. Extraction of cobalt-lithium by D2EHPA is affected by cation exchange mechanism, cobalt is extracted as [Co(HA2)2] and [CoA2] depending on the metal concentration in the feed solution while the lithium is extracted as [Li(A2H)]. Quantitative extraction of cobalt was achieved in two-stage counter-current batch extraction (with McCabe–Thiele plot) using 0.477 M D2EHPA at an O : A phase ratio of 1. The data obtained from loaded organic and raffinate indicate a composition which reveals nearly complete extraction of cobalt and rejection of lithium resulting significant separation of these elements from mixed sulfate solution.

We report on the separation and recovery of scandium(III) from sulfate solutions using solvent extraction and a membrane transport system utilizing newly synthesized amic acid extractants. Scandium(III) was quantitatively extracted with 50 mmol dm–3N-[N,N-di(2-ethylhexyl)aminocarbonylmethyl]glycine (D2EHAG) or N-[N,N-di(2-ethylhexyl)aminocarbonylmethyl]phenylalanine (D2EHAF) in n-dodecane at pH 2 and easily stripped using a 0.5 mol dm–3 sulfuric acid solution. The extraction mechanisms of scandium(III) extraction with D2EHAG and D2EHAF were examined, and it was established that scandium(III) formed a 1:3 complex with both extractants (HR), that is, Sc(SO4)2–aq + 1.5(HR)2org ⇄ Sc(SO4)R(HR)2org + H+aq + SO42–aq. The equilibrium constants of extraction were evaluated to be 4.87 and 9.99 (mol dm–3)0.5 for D2EHAG and D2EHAF, respectively. D2EHAG and D2EHAF preferentially extracted scandium(III) with a high selectivity compared to common transition metal ions under high acidic conditions (0 < pH ≤ 3). In addition, scandium(III) was quantitatively transported from a feed solution into a 0.5 mol dm–3 sulfuric acid receiving solution through a polymer inclusion membrane (PIM) containing D2EHAF as a carrier. Scandium(III) was completely separated thermodynamically from nickel(II), aluminum(III), cobalt(II), manganese(II), chromium(III), calcium(II), and magnesium(II), and partially separated from iron(III) kinetically using a PIM containing D2EHAF as a carrier. The initial flux value for scandium(III) (J0,Sc = 1.9 × 10–7 mol m–2 s–1) was two times higher than that of iron(III) (J0,Fe = 9.3 × 10–8 mol m–2 s–1).

The effect of local vibration in an interfacial layer of a heterogeneous liquid system on the wettability of the material of interfacial formations based on a d- or f-metal di-(2-ethylhexyl)phosphate salt adhered to glass has been studied. It has been demonstrated that, in the field of mechanical vibrations, one can obtain a hydrophobic material with a desired wetting angle value. It has been established that the influence of mechanical vibrations is caused by changes in the hydrodynamic situation in the transition region and is a result of complex interplay mainly between hydrodynamic and coagulation processes in the interfacial layer of the di-(2-ethylhexyl)phosphoric acid–solvent/aqueous solution of a d- or f-metal salt system. The wettability of the material of interfacial formations adhered to glass turns out to depend on the parameters of the force field (vibration frequency and amplitude), the design features of the experimental setup, and the composition of the system.

The main objective of this work was to develop a nanomaterial able to selectively extract and recover indium (In) from obsolete cell phone LCD screens. For this, Nylon 6 nanofibers were produced and modified with di-(2-ethylhexyl)phosphoric acid (DEHPA) for application in the solid-phase extraction of In. The best extraction conditions for concentration of In were 30% DEHPA, pH 0.5, 7.5 min contact time, and S:L ratio of 1:300. In this step, an In extraction efficiency of around 74% was obtained. In stripping steps, an efficiency of 92% was achieved using 1.5 M HCl, S:L ratio of 1:20, and 5 min contact time. Under the best extraction and stripping conditions, it was possible to obtain up to 6-fold concentration of In, compared to the initial concentration. In addition, the nanofibers were evaluated in terms of their stability and capacity for reuse, which showed that there was no significant loss of DEHPA and that the extraction efficiency remained almost constant. The findings demonstrated the possibility of using the Nylon 6/DEHPA nanofibers in a highly efficient extraction/stripping procedure for the selective recovery of In and Sn, with reduced environmental impacts.

Objective and Background: Synergistic extraction was introduced to replace single extraction due to enhanced extraction efficiency of heavy metal. Methodology: In order to improve extraction efficiency, di-(2-ethylhexyl) phosphoric acid (D2EHPA) was mixed with isodecanol to provide a synergistic effect together with leaching solution which is thiourea. From the single extraction system, the optimum temperature is found at 30°C producing the highest yield of %E of 91.30%. The single extraction also happened better with the presence of Fe(III) solution and thiourea as the %E is at 91.23%. Results and Conclusion: It was found that the synergistic D2EHPA-isodecanol extraction is successful as it yields higher %E than the single D2EHPA extraction.

A new process of extraction of zinc(II) ions with the use of liquid membranes under the conditions of galvanostatic electrodialysis with metal electrodeposition in the catholyte is presented. Liquid membranes represent solutions of di(2-ethylhexyl)phosphoric acid with addition of tri-n-octylamine in 1,2-dichloroethane. The effect of the electrodialysis current density and the composition of aqueous solutions and organic membranes on the rates of extraction, transmembrane transfer of metal ions, and electrodeposition of metal is studied. Fine-crystalline cathodic deposits of zinc are obtained from solutions of hydrochloric, sulfuric, perchloric, and acetic acids. It is shown that in the process under study, the virtually complete (>99.9%) extraction of zinc(II) ions by liquid membranes from their original solution containing 0.01 M ZnSO4 is achieved after 1–2.5 h of electrodialysis. The maximum degree of metal re-extraction is 98% and the degree of electrodeposition is 78%. It is shown that the shape of chronopotentiograms can serve as a criterion of completeness of zinc(II) extraction from the original solution.

The saponification process of di(2-ethylhexyl)phosphoric acid extractant (D2EHPA) was investigated by the isothermal titration calorimetry (ITC), attenuated total reflection infrared (ATR-IR), and small-angle X-ray scattering (SAXS) spectroscopies. The effects of the temperature, types of saponifier, and diluent on the saponification process of D2EHPA were disclosed by ITC method. The saponification reaction is an exothermic process, but the contribution of temperature on the maximum saponification degree of D2EHPA is slight. The theoretical maximum saponification degree of D2EHPA is about 40%. Moreover, the maximum effective saponification degree of D2EHPA is the same at the condition of different saponifiers because the two systems release the same amount of heat. The effective saponification degree of D2EHPA in octane is larger than that in toluene at the same content of saponifier. The IR spectra indicate that the structure of organic phases varies significantly with the increase of saponification degree. The most water-in-oil microemulsion in the organic phase is formed at the 40% theoretical saponification degree. The water content and SAXS data of organic phase further verify this phenomenon. Solvent extraction results show that the saponified extractant can obviously improve extraction efficiency of cobalt. These results will be helpful for optimizing the saponification process of D2EHPA during metal extraction.

The processes of Zn2+ and Pb2+ extraction by bulk liquid membranes containing di (2-ethylhexyl) phosphoric acid and tri-n-octylamine during galvanostatic electrodialysis accompanied by electrodeposition of the metals were studied. The effects of the current density as well as of composition of the liquid membranes and aqueous solutions on the rate of zinc (II) and lead (II) transport were determined. It was demonstrated that a practically complete removal of zinc (II) and more than 90 % extraction of lead (II) from the feed solutions containing 0.01 M ZnSO4 or 0.01 M Pb (NO3)2 was achieved during 1.0 − 5.0 h of electrodialysis. A possibility of effective transfer of zinc (II) into dilute solutions of sulphuric, hydrochloric, perchloric and acetic acids was shown. Adherent zinc and lead coatings with a fine-grained structure have been deposited on the platinum cathode. More than 75% of zinc (II) and about 60% of lead (II) was deposited from solutions of sulfuric acid and perchloric acid, respectively.

The aim of this work was to develop new materials employing polymeric nanofibers modified with an organic extractant for the extraction of metals. For this purpose, nylon-6 nanofibers were modified with di-(2-ethylhexyl) phosphoric acid (DEHPA) for use in the selective extraction of zinc and nickel. The best extraction efficiencies were 85.5% for Zn and 4.6% for Ni, achieved under the following conditions: pH 2, solid:liquid (S:L) ratio of 1:40, and contact time of 7.5 min. In the stripping, the best efficiencies were 85.9% for Zn and 90.1% for Ni, using a concentration of HCl of 0.5 M, S:L ratio of 1:10, and contact time of 5 min. The nanofibers were evaluated in terms of their stability and capacity for reuse, and it was found that there was no loss of the DEHPA extractant from the nanofibers, while the extraction efficiency remained almost constant. Regarding to environmental aspects of the new technology, the results confirm that nanofibers exhibit the same efficiency of conventional liquid-liquid extraction, without the disadvantage of the use of organic solvents. In this way, this new technology brings an enormous gain in environmental terms, since it drastically reduces the use of hazardous substances.

In the leaching solution of high-sulfur bauxite roasted by sulfuric acid, a high concentration of aluminum presented along with titanium and iron. The present work was to remove Ti(IV) from the leach liquor by calcium alginate microsphere sorbent material (CA-P204) based on natural alginate impregnated with di-(2-ethylhexyl) phosphoric acid (D2EHPA) to purify leaching solution. Cation exchange and chelation make major contributions to the adsorption mechanism according to Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis. The results showed that Ti(IV) was successfully removed by the CA-P204 adsorbent from the Ti(IV)−Al(III)−Fe(III) ternary system with a dynamic column experiment. The removal rate of titanium was nearly 95% under optimal conditions and the maximum adsorption capacity was 66.79 mg/g at pH 1.0. Reusability of CA-P204 was evaluated over three consecutive adsorption/desorption cycles. The adsorption process was simple, low-cost, and had no waste discharge, suggesting that the CA-P204 was promising, efficient, and economical for removing Ti(IV) from high-sulfur bauxite leaching solution.

Owing to its chemical and pharmacological significances, the efficacy of reactive separation of protocatechuic acid (0.001–0.01 kmol m−3) from aqueous stream by means of tri-n-octylamine (TOA), di-...

Lanthanum nitrate distribution in three-component aqueous-organic systems with D2EHPA from acetate or acetic acid–acetate solutions has been studied, it has been shown that variation in sodium acetate concentration or composition of CH3COONa–CH3COOH mixture can affect metal distribution ratios. It has been found that extraction in three-component mixture of 1: 1: 1 composition (aqueous solution Ln(NO3)3 + CH3COONa + CH3COOH–D2EHPA in hexane–isopropyl alcohol) can provide lanthanide separation, which is dependent on the ratio of sodium acetate and acetic acid in aqueous phase and on D2EHPA concentration in organic phase. Lanthanide–lanthanum separation factors have been calculated for the extraction of lanthanide nitrates from acetic acid–acetate solutions.

The present investigation deals with the removal of uranium from a nitric acid waste solution (Raffinate solution: produce during yellow cake of uranium production) using the extraction chromatography technique (solvent impregnated material) ), where Tri-N-butyl phosphate (TBP) and Di-2-ethylhexyl phosphoric acid (D2EHPA) solvents were impregnated upon polyester sheet and charcoal respectively then the impregnated resin were tested for uranium removal. Thus, the factors affecting the impregnation process namely, solvent concentration, impregnation time, volume/mass ratio, impregnation temperature and diluents type were studied. Secondly the influences of initial uranium concentration, adsorption temperature, contact time, pH on the uranium adsorption on the prepared materials were studied. From the results the isotherm models also calculated to determine uranium adsorption behavior by the prepared TBP and D2EHPA impregnated polyester sheet and charcoal respectively. Both prepared materials were found to be fitted with Langmuir than Freundlich model isotherm.

Protocatechuic acid is used extensively in pharmacological and related industries which can also be obtained by fermentation. Reactive separation by means of reactive extractant is a favourable alternative to recover carboxylic acids from the aqueous dilute streams and the fermentation broth. In this paper, the reactive separation of protocatechuic acid were performed by D2EHPA (Di-(2-ethylhexyl) phosphoric acid) and TOA (tri-n-octyl amine) dissolved in MIBK (Methyl isobutyl ketone) at 298 K. Distribution coefficients, degree of extraction, complexation constants and loading ratio were estimated. The equilibrium for protocatechuic acid-extractant-diluent system was represented using Langmuir model, mass action law and relative basicity model. Results obtained from model were found to be close to experimental data. TOA was found more effective than D2EHPA for the recovery of protocatechuic acid having 5.39 as maximum distribution coefficient and 84.36% efficiency at 0.01 mol L−1 and 1.1437 mol L−1 concentration of protocatechuic acid and TOA respectively.

This work addresses the synergistic removal of nickel from the electroplating wastewater using a supported liquid membrane (SLM) process. The supported liquid membrane formulation consisting of Di-2-ethylhexyl phosphoric acid (D2EHPA), n-octanol, kerosene, and sulfuric acid as a carrier, synergist, diluent, and stripping agent, respectively. The effects of several significant parameters namely D2EHPA, n-octanol, and sulfuric acid concentrations as well as feed and stripping phases flow rates were investigated. Results revealed that n-octanol as a synergist significantly affected the removal efficiency of nickel since it can modify the D2EHPA molecules in the membrane phase. Besides, a kinetic model for the nickel ion transport across SLM revealed that the transport resistances due to the diffusion across the membrane ( Δ o r g ), transport resistances due to the diffusion through the aqueous boundary layer ( Δ a q ) , thickness of the aqueous diffusion layer ( d a q ), and diffusion coefficient of the nickel-carrier complex across the membrane ( D o r g ) were found to be 2.90 × 105 sm−1, 1.94 × 104 sm−1, 1.24 × 10−5 m and 7.20 × 10−10 m2s−1, respectively. Interestingly, an approach to a green process by incorporating palm oil as a diluent showed that it is feasible to be applied and offers a green SLM process in the future.

A study of the reaction mechanism and thermodynamic modeling of pentavalent vanadium V(V) extraction from NaVO3-H2SO4-H2O solutions using Di-(2-ethylhexyl) phosphoric acid (D2EHPA or HA) extractant was carried out. The effects of initial pH of the solution, extractant concentration, and temperature on the extraction of V(V) were examined. The stoichiometry of the extraction reaction was determined using the slope analysis method. The extracted species was shown to be VO2A. A thermodynamic modeling approach was proposed for the prediction of equilibrium concentrations and pH of the system based on the known initial concentrations and process temperature. In the presented approach, the non-ideality of both aqueous and organic phases was taken into account. The activity coefficients of all organic components were calculated using UNIQUAC-NRF model, while the Electrolyte-UNIQUAC-NRF model was employed to calculate the activity coefficients of ions in aqueous phase. The equilibrium constant of the extraction reaction and the unknown parameters of the models were adjusted through the regression of experimental data at 25 °C, 35 °C, and 45 °C. Adjusted parameters were used for the prediction of equilibrium vanadium concentration in organic phase and equilibrium pH of the aqueous phase. Both of regressed and predicted values were in very good agreement with the experimental data. Moreover, calculated standard molar enthalpy of the reaction indicated the endothermicity of extraction reaction between VO2+ and D2EHPA.

New saturated vapor pressure ( p sat ) data of organophosphorus extractants, di-(2-ethylhexyl) phosphoric acid (D2EHPA) and tributyl phosphate (TBP), were investigated in T = (383.8–546.2) K and p sat = (0.13–6.67) kPa using vacuum distillation method. The data was found to be a good fit with Antoine, August, Riedel and Wagner equation. Regression constants prove to be very useful in estimating p sat at operating temperature. Intermolecular hydrogen bonding affected D2EHPA having lower p sat in comparison with TBP. Thermodynamic properties of both molar enthalpy and molar entropy of vaporization were obtained using the Clausius-Clapeyron equation. As temperature increased, molar enthalpy and molar entropy of vaporization decreased showing a positive deviation from Trouton's rule. Using the relations of molar enthalpy and temperature, saturated liquid heat capacity was obtained. All data can be usefully employed for the design of a distillation column or evaporator for recycling of both extractants from organic wastewater.

It has been shown that the presence of small amounts of di-(2-ethylhexyl)phosphoric acid (below 6 mol % in the mixture of surfactants) in a sodium di-(2-ethylhexyl)phosphate–di-(2-ethylhexyl)phosphoric acid–decane–water system widens the region of microemulsion existence with respect water and decreases the slope of the dependence of hydrodynamic droplet diameter of on water-to-sodium di-(2-ethylhexyl) phosphate molar ratio. At di-(2-ethylhexyl)phosphoric acid concentrations in its mixture with sodium di-(2-ethylhexyl)phosphate higher than 6 mol %, the fraction of water bound with ions in microemulsion droplets decreases, the region of microemulsion existence narrows, specific conductance decreases, and the slope of the dependence of the hydrodynamic droplet diameter of on the water-to-sodium di-(2-ethylhexyl) phosphate molar ration increases.

In this study, separation of copper ion (Cu2+) from aqueous solution using two phosphorous based extractants (tri‑n‑butyl phosphate and di‑2‑ethylhexyl phosphoric acid) was aimed. The parameters monitored under the equilibrium study were initial copper concentration, extractant concentration, and pH. The copper concentration was taken in the range of 20 to 100 ppm, the extractant composition in the organic phase was varied from 10 to 40 vol% dissolving in toluene as an inactive diluent, and the pH effect was studied in the range of 1 to 11. The distribution coefficients were calculated, and a model equation was developed to estimate model parameters like the number of reacting molecules of the extractant and equilibrium constant using experimental results. In the kinetic study, the initial aqueous phase copper concentration, and the extractant concentration were changed, and initial rates of extraction were found out to develop a kinetic model and their parameters like rate constant and order of reaction.

In this paper, the flotation separation of hemimorphite from quartz was investigated by using di(2-ethylhexyl) phosphoric acid (DEHPA) as a collector. The results elucidated that DEHPA exhibited better flotation performances to hemimorphite than dibutyl phosphoric acid (DBP), tributyl phosphate (TBP), octanoic acid (OA) and palmitic acid (PA). And DEHPA also possessed good selectivity against quartz flotation and could realize the effective flotation separation of hemimorphite from quartz under pH 6.0–10.0. The adsorption and contact angle findings clearly indicated that DEHPA selectively adsorbed on hemimorphite, hardly on quartz. After DEHPA treatment, the hydrophobicity of hemimorphite was dramatically improved. Zeta potential suggested that DEHPA anion anchored on hemimorphite surfaces mainly through chemical bonds. FTIR inferred that DEHPA chemisorbed on to hemimorphite surfaces by formation of the Zn O bonds between the O atoms of the P( O)(OH) group and the surface zinc atoms, simultaneously with splitting the O H bonds of the P O H group. XPS gave clear evidences that the adsorbed DEHPA combined with Zn(II) species on hemimorphite surfaces to generate the Zn(II)-DEHPA surface complexes.

Interfacial formations of material based on metals di(2-ethylhexyl)phosphates of various metals exhibit hydrophobic properties. The contact angle of the surface, modified by the interfacial formations materials, could reach up to 140° depending on the nature of the solvent, the metal salt, the number of applications.

Saturated vapor pressure of the diluent (toluene, cyclohexane, hexane, heptane) in four binary diluent – di-(2-ethylhexyl)phosphoric (D2EHPA) acid systems was measured by the static method at T = (288.15, 298.15, and 308.15) K in a wide concentration range. Experimental data obtained were correlated with UNIQUAC thermodynamic model taking into account the existence of D2EHPA in the liquid phase in the form of a dimer. Excess molar volumes were determined for binary solutions of D2EHPA with toluene, cyclohexane, heptane in the temperature range of (288.15–308.15) K and hexane at (288.15 and 298.15) K using the vibrating tube densimeter. The Redlich–Kister type polynomial equation was applied to describe the volumetric properties of the solutions.

Protocatechuic acid has potential pharmacological significance, like antioxidant, antibacterial, and anticancer activity. The extraction of carboxylic acids from dilute aqueous phase is a topic of current interest to researchers. The present equilibrium study deals with the reactive extraction of protocatechuic acid from an aqueous solution by using di-(2-ethylhexyl)phosphoric acid (D2EHPA) in diluents, such as isobutyl acetate (IBA), toluene, and petroleum ether at isothermal conditions (298 ± 1 K). The physical extraction of protocatechuic acid with pure diluents is also carried out. The difference between the physical extraction and the reactive extraction was studied. The effects of acid concentration (0.001–0.01 mol·kg–1), extractant concentration (0.3445–3.1010 mol·kg–1), and type of diluent on the recovery of protocatechuic acid from aqueous solution were determined. KD values were obtained in the ranges of 1.14–4.03, 0.12–0.67, and 0.08–0.48 for D2EHPA in isobutyl acetate, toluene, and petroleum e...

This study demonstrates for the first time the possibility of selective separation of heavy, middle and light lanthanide ions, represented by Yb(III), Gd(III) and La(III), using a polymer inclusion membrane (PIM) composed of 45 wt% di-(2-ethylhexyl) phosphoric acid (D2EHPA) and 55 wt% poly(vinyl chloride) (PVC). Complete and selective extraction of these three lanthanide ions was achieved by varying the pH of the sulfuric acid feed solution (i.e. Yb(III) at pH 0.25, Gd(III) at pH 1.25 and La(III) at pH 2.25). The extracted ions were back-extracted completely into solutions containing sulfuric acid at concentrations of 7.0, 1.0 and 0.3 mol L −1 , respectively. A comprehensive study of the Yb(III) extraction system revealed that the Yb(III): (D2EHPA) 2 ratio in the extracted complex was 1:3, where (D2EHPA) 2 refers to the D2EHPA dimer. The corresponding thermodynamic extraction constant was determined to be 7.45 × 10 4 . Assuming the same stoichiometry for the La(III) and Gd(III) complexes, the thermodynamic extraction constants of these two lanthanides were determined on the basis of their extraction isotherms as equal to 0.776 and 81.2, respectively. The initial flux values for the three lanthanide ions studied ranged from 6.98 to 3.85 × 10 7 mol m −2 s −1 in the extraction experiments and from 12.4 to 5.76 × 10 7 mol m −2 s −1 in the back-extraction experiments.

Different separation techniques such as solvent extraction, ion exchange, and precipitation are often used for recovery of rare earth elements (REEs) from pregnant leach solutions obtained from acid leaching. Solvent extraction is generally accepted as the most appropriate commercial technology for separating REEs due to the need to be able to handle larger volumes of diluted pregnant solutions. This study focused on the development of selective separation of light and heavy REEs from the pregnant leach solution obtained from leaching of apatite ore in 1 M sulfuric acid (H2SO4) using solvent extraction. Three different commercial organophosphorus extractants (di-(2-ethylhexyl) phosphoric acid (D2EHPA), 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC88A) and tributyl phosphate (TBP)), and the influences of experimental parameters such as extractant concentration, organic/aqueous phase ratio, diluent type, pH, extraction time and stripping agent concentration were examined. Results showed that light REEs (LREEs) and heavy REEs (HREEs) in the pregnant leach solution were selectively separated with D2EHPA via a two-stage extraction process. In the first-stage of solvent extraction, >90% of (0.05 g/L) HREEs was extracted with 1.8 M D2EHPA in kerosene while the vast majority (>95%) of LREEs was remained in raffinate. In the second-stage, >93% (1.01 g/L) of LREEs was extracted from the raffinate with 1.8 M D2EHPA dissolved in kerosene at pH 1.6. HREEs (>95%) and LREEs (>90%) loaded with D2EHPA after the first and second-stage of extraction were stripped by 4 M H2SO4 and 1 M H2SO4 solutions, respectively. Distribution of middle rare earth elements (MREEs) was discussed through the extraction processes in this study.

Separation of rosmarinic acid by synergic reactive extraction using a mixture of two extractants (one of aminic and one of basic type) dissolved in solvents with different polarities has been studi...