PC-88A Concentration Research Articles

A comparative study of the solvent extraction of lanthanum(III) from different acid solutions

ABSTRACT Solvent extraction of lanthanum(III) using the organic extractant 2-ethylhexyl phosphonic acid mono-2-ethylhexylester (PC88A) diluted in kerosene from three different aqueous media (sulfuric, nitric and chloride) was investigated. Eh-pH and speciation diagrams suggested that free lanthanum ion (La(III)) species predominate under the experimental conditions studied in this paper. The effects of several parameters on the extraction of lanthanum including initial pH (1.5–7), initial La(III) concentration (0.08–1.35 mmol/L), PC88A concentration (10–90 mmol/L) and temperature (25–55°C) were evaluated. In general, both hydrochloric and nitric acids were found to be more effective than sulfuric acid in terms of higher extraction of lanthanum. The stoichiometry of the extraction reaction and also the equilibrium constant were calculated. The extraction of La(III) was significantly enhanced by increasing pH and PC88A concentration and was only slightly increased by increasing temperature. Stripping studies showed that 1 mol/L acid concentration is adequate for effective stripping of lanthanum from the loaded organic. The stoichiometry of the extraction reaction was also investigated using density functional calculations and found to be in reasonable agreement with the experimental results.

Selective Extraction of Scandium by a Long Alkyl Chain Carboxylic Acid/Organophosphonic Ester Binary Extractant

ABSTRACTThe organophosphorus extractant 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC88A) is widely used for solvent extraction of rare earth elements in an acidic leaching solution, but stripping of the loaded metals is difficult because of the high affinity between the metals and the extractant. Adding 100 times the concentration of neodecanoic acid (Versatic 10) to the extractant solution reduces the extraction ability for scandium (Sc) and enables quantitative stripping of the loaded Sc with a mild acidic solution, such as a 1 M mineral acid. The loading capacity is dependent on the PC88A concentration, so PC88A is the main species responsible for Sc extraction in the binary mixture. Nuclear magnetic resonance spectroscopy (NMR) of the organic phases suggests a potential interaction between the mixed extractants through the change in the hydrogen bonding. This causes an antagonistic effect and facilitates efficient Sc stripping from the extractant solution, so this method could be used for scandium recovery in industry.

Solvent extraction and separation of cerium(III) and samarium(III) from mixed rare earth solutions using PC88A

The solvent extraction of cerium(III) and samarium(III) from mixed solutions of all rare earth elements (REEs) except promethium using PC88A (2-ethyl hexyl phosphonic acid mono-2-ethyl hexyl ester), an acidic extractant, was investigated. The effects of aqueous equilibrium pH, various acids (sulfuric acid (H2 SO4), hydrochloric acid (HCl) and nitric acid (HNO3)), initial metal ion concentration and extractant concentration on the solvent extraction of Ce(III) and Sm(III) were systematically studied. From the experimental results, HNO3 and HCl were found to be the preflerred aqueous media for the solvent extraction of both Sm(III) and Ce(III). The most promising experimental conditions of pH, PC88A concentration and metal ion concentration were identified for the extraction of Ce(III) and Sm(III). Separation results showed that H2 SO4 at pH 2 provided the best separation between Sm(III) and Ce(III).

Transport Behavior of Divalent Lead Ions through Disphase Supplying Supported Liquid Membrane with PC-88A as Mobile Carrier

The transport behavior of Pb(II) through a novel disphase supplying supported liquid membrane (DSSLM) with 2-ethyl hexyl phosphonic acid-mono-2-ethyl hexyl ester (PC-88A) as the carrier in kerosene, polyvinylidene fluoride membrane(PVDF) as the support and HCl as the stripping agent, has been studied. The effects of organic-to-feed volume ratio (O:F), pH, initial concentration of Pb(II) and ionic strength in the feed solution, organic-to-strip volume ratio (O:S), concentration of HCl solution and PC-88A concentration in the supplying strip phase on transport of Pb(II) have also been investigated. The advantages of DSSLM campared to the traditional SLM were investigated. The system stability, the reuse of membrane solution and the retention of membrane phase were also studied. When initial Pb(II) concentration was 2.00 × 10-4 mol/L, the transport percentage of Pb(II) was up to 92.9% under the optimun conditions in 175 min. The kinetic equation was developed in terms of the law of mass diffusion and the theory of interface chemistry. The results were in good agreement with experimental results.

Stripping dispersion hollow fiber liquid membrane containing carrier PC-88A and HNO3 for the extraction of Sm3+

Stripping dispersion hollow fiber liquid membrane system (SDHFLM) containing feed phase adding acetate buffer solution and dispersion solution with HNO3 solution as the stripping solution and membrane solution of 2-ethyl hexyl phosphoric acid-mono-2-ethylhexyl ester (PC-88A) dissolved in kerosene, has been studied for the extraction of Sm3+. Many factors including pH value, volume ratio of membrane solution to stripping solution (O/W) and carrier concentration on Sm3+ extraction were investigated. Experimental results indicate that the optimum extraction conditions of Sm3+ were obtained as that PC-88A concentration was 0.120 mol/L, and O/W was 1.00 in the dispersion phase, and pH value was 4.80 in the feed phase. When initial Sm3+ concentration was 1.20 x 10(-4) mol/L, the extraction percentage of Sm3+ was up to 92.8% in 160 min. (

Chemical studies on uranium extraction from concentrated phosphoric acid by using PC88A and DBBP mixture

Liquid–liquid extraction of U (VI) from concentrated phosphoric acid by using (2-ethyl hexyl) phosphonic acid, mono (2-ethyl hexyl) ester (PC88A) and di-butyl butyl phosphonate (DBBP) has been investigated. The effect of different factors affecting the extraction process (PC88A concentration, DBBP concentration, shaking time, aqueous/organic phase ratio, phosphoric acid concentration and effect of diluents) have been investigated. The obtained data of temperature on the extraction showed that the enthalpy change is −17.15 kJ mol−1. Uranium was extracted from the strip liquor by using di (2-ethylhexyl) phosphoric acid and tri-octyl phosphine oxide mixture and finally converted to a high purity UO3 product using precipitation with hydrogen peroxide and heat treatment at 365 °C.

Stripping dispersion hollow fiber liquid membrane containing PC-88A as carrier and HCl for transport behavior of trivalent dysprosium

The transport of Dy 3+ through stripping dispersion hollow fiber liquid membrane system (SDHFLM) containing dispersion phase with HCl solution as stripping solution and 2-ethyl hexyl phosphoric acid-mono-2-ethyl hexyl ester (PC-88A) dissolved in kerosene as membrane solution, has been studied. Many factors of the interface chemical reaction and composition of the liquid membrane including pH value, initial concentration of Dy 3+, different ionic strength of feed phase, volume ratio of membrane solution to stripping solution (O/W), HCl concentration, carrier concentration, different stripping agents of dispersion phase, hydrodynamic characteristic (flow rates, stability) and hollow fiber structure parameters (inner diameter of fibers, membrane thickness, porosity, etc.) on Dy 3+ transport with SDHFLM were investigated. The advantages of SDHFLM compared to the traditional HFLM was investigated too. Experimental results indicated that the optimum transport conditions of Dy 3+ were that HCl concentration was 4.00 mol/L, PC-88A concentration was 0.150 mol/L, O/W was 0.5 in the dispersion phase, and pH value was 5.00 in the feed phase. Ionic strength had no obvious effect on transport of Dy 3+. When initial Dy 3+ concentration was 1.50 × 10 −4 mol/L, the transport efficiency of Dy 3+ was up to 95.4% in 170 min. The kinetic equation was developed in terms of the law of mass diffusion and the theory of interface chemistry. The results were in good agreement with the literature data.

Mathematical modeling of solvent extraction of uranium from sulphate media employing 2-ethylhexyl phosphonic acid-mono-2-ethylhexyl ester (PC88A) and its mixture with trioctylphosphine oxide (TOPO) as extractants

The extraction of U(VI) from sulphate medium with 2-ethylhexyl phosphonic acid-mono-2-ethylhexyl ester (PC88A, H2A2 in dimeric form) in n-dodecane has been investigated under varying concentrations of sulphuric acid and uranium. Slope analysis of uranium (VI) distribution data as a function of PC88A concentration suggests the formation of monomeric species, viz. UO2(HA2)2. This observation was further supported by the mathematical expression obtained during non-linear least square regression analysis of U(VI) distribution data correlating the percentage extraction (%E) and the acidity (Hi). A mathematical model correlating the experimental distribution ratio values of U(VI) (DU) with initial acidity (Hi) and initial uranium concentrations (Ci) was developed: \( D_{\text{U}} = 12.98( \pm 0.90)/\left\{ {C_{\text{i}}^{ - 0.75( \pm 0.05)} \times \left[ {H_{\text{i}} } \right]^{2} } \right\} \). This expression can be used to predict the concentration of uranium in organic as well as in aqueous phase at any Ci and Hi. The extraction data were used to calculate the conditional extraction constant (Kex) values at different acidities (2–7 M H+), uranium (0.02–0.1 M) and PC88A (0.2–0.6 M) concentrations. These studies were also extended for the extraction of U(VI) using synergistic mixtures of PC88A and TOPO from sulphate medium.

Studies on extraction behaviour of molybdenum (VI) from acidic radioactive waste using 2(ethylhexyl) phosphonic acids, mono 2(ethylhexyl) ester (PC-88A)/n-dodecane

This paper describes the studies on the extraction of molybdenum (VI) from aqueous nitric acid medium by (2-ethylhexyl) phosphonic acid, mono (2-ethylhexyl) ester (PC-88A). The extraction affecting parameters such as concentration of HNO3 in aqueous feed, effect of concentration of extractants, effect of diluents, and molybdenum concentration in the aqueous phase are investigated to optimize the extraction conditions for the quantitative separation of molybdenum from nitric acid medium. With increase of HNO3 concentration in aqueous phase, percentage extraction was found to be decreased in all the cases. Percentage extraction of molybdenum increases with increase in PC-88A concentration till the 0.15 M of PC88A, and after that it becomes constant. Kerosene and n-dodecane was found to be most suitable diluents. Among the various strippants used 0.2 M (w/v) solution of Na2CO3 and 0.2 M (w/v) solution (NH4)2CO3 are found to be the equally suitable for stripping of molybdenum from the loaded organic phase. The stripping of molybdenum from loaded organic layer by various reagents followed the order: (NH4)2CO3 >Na2CO3 >0.1 M sodium salt of EDTA >2 M NaOH >8 M HNO3. The optimized process conditions are employed to extract molybdenum (VI) from actual Davies–Gray waste as well as from diluted high level waste generated in the purex stream. More than 94% Mo(VI) was extracted from radioanalytical as well as from high level waste of purex process and quantitative recovery was achieved in both the cases when 0.2 M sodium carbonate was used as stripping agent.

Solvent extraction equilibrium of dysprosium(III) from nitric acid solutions with 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester

Abstract In view of the importance of solvent extraction of rare earth metals with the acidic organophosphorous reagent, the development of a chemically based model applicable to high concentration is desired. In the present study, the equilibrium distribution of dysprosium(III) between an aqueous nitric acid solution and 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC88A) was measured in the range of an initial aqueous dysprosium(III) concentration from 1.0×10 −3 to 1.0×10 −1 kmol/m 3 and PC88A concentration from 0.16 to 0.65 kmol/m 3 in Shellsol D70 as the diluent. The obtained data were analyzed using the chemically based model in order to correlate the equilibrium distribution ratios. In this model, dysprosium(III) was assumed to be extracted with the PC88A dimer as a 1:3 complex, the activities were considered for the aqueous species, and the effective concentration of the PC88A dimer was calculated using Alstad's empirical equation. As a result, the apparent extraction equilibrium constant was determined to be 253 (kmol·m −3) −2 with an excellent correlation between the experiment and calculation results in the wide range of the logarithm of the distribution ratio from −2 to 3.5. In conclusion, the methodology in this model would be effective for quantitative description of solvent extraction behavior of general rare earth elements as well as dysprosium.

Transport of yttrium metal ions through fibers supported liquid membrane solvent extraction

A novel idea of transport of yttrium (III) metal ions through fibers supported liquid membrane in two stage processes namely source to membrane and membrane to receiving phase has been proposed. The fibers supported liquid membrane was impregnated with different concentrations carrier. The experimental variables explored were concentration of yttrium (III) ions, pH of source phase, PC-88A concentration in membrane phase, acid concentration in receiving phase and stirring speed. The pre-concentration of yttrium (III) ions was investigated from the dilute solutions. The two-channel fibers supported liquid membrane solvent extraction was investigated for the transport of yttrium (III) ions from the source to membrane and membrane to receiving phase. The transport of yttrium (III) ions was observed through the fibers supported liquid membrane with capillary action.

Recovery of americium(III) from low acid solutions using an emulsion liquid membrane containing PC-88A as the carrier extractant

A liquid emulsion membrane (LEM) containing PC-88A (2-ethylhexylphosphonic acid-2-ethylhexyl monoester) as the carrier extractant and SPAN-80 as the surfactant was used to pre-concentrate Am3+ from dilute acid solutions. Out of the various stripping agents evaluated as the internal phase, 0.1M oxalic acid was found to be the most effective. The effect of various factors such as: external phase pH, equilibration time, PC-88A concentration, SPAN 80 concentration, phase volume ratio, etc. on Am3+ mass transfer was investigated. The emulsion was broken by the addition of solvents such as acetone and the actual mass transfer obtained after breaking the emulsion agreed well with that obtained by the difference method.

Use of a Surfactant Liquid Membrane Contactor for Zinc Uptake from an Acid Aqueous Effluent

A procedure for uptake of zinc ions from an acid aqueous effluent using a surfactant liquid membrane contactor (SLM) was studied. The liquid membrane was prepared by dissolving the extractant, PC-88A (an alkylphosphonic compound), used as mobile carrier, and Span-80, a surfactant, in kerosene. The SLM allowed selective and efficient metal transport from the feed solution to the metal-receiving liquor in experiments carried out in a batch-type stirred contactor at 30°C. A screening factor-type experimental design and a response-surface optimization design were developed to determine the variables that influence zinc removal. An analysis of variance was carried out on the experimental data which made it possible to model mathematically the metal transport system by means of a regression equation. A maximum value of 99.32% was measured for the extent of zinc extraction under the experimental conditions used in this study. The optimal values of the main statistically significant variables were the following: 4.45% w/w of PC-88A concentration, a double emulsion-stirring speed of 250 rpm and a multiple emulsion-stirring time of 45 minutes, all values close to the minimum levels studied. The alkylphosphonic extractant molecule plays a fundamental role in the process as metal-carrier although it has a lower interfacial activity than the surfactant. The surfactant stabilizes the emulsion by reducing the interfacial tension and avoiding the coalescense of droplets. However, it is not recommended to use an excess of surfactant in the membrane because it would compete with the extractant molecules for the sorption of active sites on the interface, increasing the interfacial resistance and lowering the efficiency of the metal transport process. These results shows the feasibility of removal and/or recovery of metal ions from effluents or any dilute aqueous solutions using this contactor based on a surfactant liquid membrane.