Dispersion-free Solvent Extraction Research Articles

Comparative dispersion-free solvent extraction of Uranium(VI) and Thorium(IV) by TBP and dialkyl amides using a hollow fiber contactor

Abstract Dispersion-free solvent extraction of U(VI) and Th(IV) from nitric acid medium was studied employing microporous hollow fiber membrane with several monoamide extractants, viz. N,N-di-2-ethylhexyl isobutyramide (D2EHiBA), N,N-dihexyl hexanamide (DHHA), N,N-dihexyl decanamide (DHDA) and N,N-dihexyl octanamide (DHOA), and the results were compared with those obtained with conventional TBP extractant. Effects of flow rate and feed metal ion concentration on the extraction rate were examined. The extraction was principally controlled by the distribution coefficient of the metal ions with the extractants. The studies were performed under different hydrodynamic conditions and the overall mass transfer coefficients of the extracting species were calculated and found to be independent of the flow rates. The overall extraction rates were governed by the viscosity and density of the organic phase. The separation factor between U(VI) and Th(IV) was excellent with branched chain monoamides, viz. D2EHiBA, followed by DHOA. The results indicated the selective recovery of Uranium in the presence of large concentrations of Thorium by monoamides in dispersion-free solvent extraction method. A mathematical model was employed for predicting the extraction behavior of metal ions, which gave an excellent match between the calculated and the experimental results.

Dispersion-Free Solvent Extraction of Cr(VI) from Acidic Solutions Using Hollow Fiber Contactor

The use of dispersión-free solvent extraction, through microporous hydrophobic membrane has been investigated. The hollow fiber contactor, with surface area of 1.4 m2 was used to extract Cr(VI) (0.005-0.12 g/L from aqueous sulphuric acidic media (pH 2.5-4.2 +/- 0.05). Several parameters such as extractant concentration, feed acidity and metal concentration in the initial aqueous solution were investigated. Results revealed that 15% v/v Cyanex 923 in Exxsol D-100 as organic phase and feed in the 2.5 pH range, gave optimum extraction (exceeding 95%) of Cr(VI) and it was possible to strip using 10 g/L hydrazine sulfate (also with recoveries exceeding 95%). In this step, Cr(VI) is immediately reduced to the less hazardous Cr(III) state. Results also showed that under the various experimental conditions, chromium(VI) extraction was rate-controlled by the interfacial reaction on the membrane surface. Typical overall mass transfer coefficients values are 4.2 x 10(-5) and 3.6 x 10(-6) cm/s for extraction and stripping operations, respectively.

Dispersion-free solvent extraction of U(VI) in macro amount from nitric acid solutions using hollow fiber contactor

The applicability of dispersion-free solvent extraction (DFSX), through microporous hydrophobic membrane has been studied. The hollow fiber membrane contactor, with surface area of ∼381 cm 2 was employed to extract U(VI) in macro concentration (35 g dm −3) from aqueous acidic solutions. Prior to deployment of this technique for recovery of U(VI) from oxalate supernatant waste, chemical parameters such as extractant concentration, feed acidity, concentration of U(VI) in feed were studied. The study revealed that 30% tri- n-butyl phosphate (TBP) in n-dodecane as an extractant and feed in 3 M HNO 3 gave an optimum extraction of U(VI) and it was possible to strip back utilizing 0.05 M HNO 3. It was established to recover more than 90% of U(VI) from oxalate supernatant waste, which was often generated from nuclear chemical facilities.

Application of Hollow Fiber Contactor in Nondispersive Solvent Extraction of Pu(IV) by TBP

Data on dispersion‐free solvent extraction (DFSX) of Pu(IV) from acidic nitrate media using microporous hydrophobic polypropylene hollow fiber membrane contactor with tri‐n‐butylphosphate (TBP) employing as an extractant are being presented. The DFSX operation was carried out with various concentration of TBP in n‐dodecane by passing acidic feed containing Pu (IV) through the tube side at the flow rate of 5.83 cm3 s−1 and organic extractant through the shell side at the flow rate of 1.53 cm3s−1. Extraction studies were performed under different hydrodynamic conditions and the overall mass‐transfer coefficient was evaluated with countercurrent flow condition. It was possible to extract and concentrate Pu(IV) from aqueous phase by employing this technique. For back extracting the Pu, uranous nitrate and hydroxylamine hydrochloride solution as strippants were examined, which flowed through the tube side (flow rate: 6.11 cm3 s−1) and the loaded organic was passed through the shell side with the flow rate of 1.66 cm3s−1. Results revealed that ∼80% of Pu(IV) from oxalate supernatant waste could be extracted by utilizing this technique.

Improved kinetics-based gold cyanide extraction with mixture of LIX79+TOPO utilizing hollow fiber membrane contactors

Dispersion-free solvent extraction of gold(I) (Au(CN) 2 −) from alkaline cyanide media was performed using porous hydrophobic hollow fibers with mixtures of membrane extractants. The organic extractant used for gold(I) extraction was LIX79 ( N, N′-bis(2-ethylhexyl)guanidine) alone and a mixture of trioctylphosphine oxide (TOPO)+LIX79 diluted with n-heptane. The mixture of LIX79+TOPO affords a better performance than LIX79 alone. It took 300 s to extract more than 95% gold with equimolar LIX79+TOPO (0.125 M), whereas pure LIX79 (0.375 M) took 1860 s to reach the same percentage level of gold extraction (over six times slower). The mass transfer coefficient’s ( K Au E) value was around four times higher with the equimolar mixture of 0.125 M LIX79+0.125 M TOPO than with LIX79/ n-heptane alone. Extraction of Au(CN) 2 − from alkaline cyanide solutions with TOPO alone was also observed, indicating that gold(I) complexation takes place probably by a solvation reaction mechanism (M +⋯Au(CN) 2·S n ). A model is presented which describes the extraction mechanism, indicating different rate-controlling steps. The validity of this model was evaluated with experimental data and was found to tie in well with theoretical values.

Dispersion-Free Solvent Extraction and Stripping of Gold Cyanide with LIX79 Using Hollow Fiber Contactors: Optimization and Modeling

This paper reports experimental data on hollow fiber dispersion-free membrane extraction (DFSX) of gold(I) from alkaline cyanide media using microporous hydrophobic polypropylene hollow fiber contactor. A recently developed new solvent extraction reagent, namely, LIX79 (Henkel Corporation), was employed as an extractant. The DFSX operation was carried out with 12% LIX79 in n-heptane by passing alkaline feed containing gold through the tube side and organic extractant through the shell side. Extraction studies were performed under different hydrodynamic conditions and mass correlations for the tube and shell side were presented for cocurrent and countercurrent flow conditions. A model is presented that identifies the different rate-controlling steps under various chemical and hydrodynamic experimental conditions in feed, organic, and membrane phases. The mass-transfer resistance resulting from a chemical extraction reaction at the surface was observed to be dominant during the entire extraction process. The validity of this model was evaluated with experimental data and found to tie in well with theoretical values. It was possible to separate and concentrate Au(I) (up to 400 mg/L) in the presence of other metal cyanide salts such as Fe(II), Cu(I), Ni(II), Ag(I), and Zn(II) (NaCN = 1000 mg/L) by employing this technique. The stripping of gold from LIX79 was accomplished efficiently by using NaOH, which flowed through the tube side (11.11 cm3/s) and the organic was passed through the shell side at (6.94 cm3/s).

Dispersion-Free Solvent Extraction of Thallium(III) in Hollow Fiber Contactors

Dispersion-free extraction of thallium(III) from NaCl/H2SO4 solution into butyl acetate has been studied using hydrophobic polypropylene and polyvinylidene fluoride hollow fibers of different effective lengths. The aqueous feed solution flowed inside the fibers and the organic phase was fed at the shell side. The influence of phase flow rates on the mass transfer coefficients was investigated, and correlations between the Sherwood and Graetz numbers were developed. The overall resistance to mass transfer is controlled by the feed-side mass transfer coefficient due to the high partition coefficient of HTlCl4 between the phases. The obtained results are discussed in terms of extraction efficiency, thallium flux through the interfacial area, and the length of the transfer unit as a function of the feed flow rate and the effective fiber length. The extraction efficiency was independent of the organic phase flow rate.

Membrane-Based Ethanol Extraction with Hollow-Fiber Module

Abstract The high energy requirements of the traditional separation of ethanol from fermentation liquors by distillation led us to seek a new energy-efficient separation method. Several alternatives, including absorption, molecular sieves, membrane separation processes, and liquid-liquid extraction processes, have been proposed and investigated (I). One of the most investigated separation techniques during the past few years has been membrane-aided solvent extraction (2–5). This dispersion-free solvent extraction process, which uses microporous membranes, overcomes such shortcomings of conventional liquid extraction as flooding and loadings. On the other hand, a technique with microporous hollow fibers may provide high mass transfer per unit volume since hollow-fiber modules contain an enormous surface area.

Hollow fiber solvent extraction: Performances and design

Dispersion-free solvent extraction from an actual process stream has been studied using microporous hydrophobic polypropylene Celgard® hollow fiber membranes in Liqui-Cel TM modules. Simultaneous extraction of two solute species from the same stream has been investigated using different hollow fiber modules with different packing fractions, surface areas and membrane types. Very high solute recoveries have been achieved in modules only 15 cm long. Mass transfer performances of a single module and modules-in-series have been characterized. For tube-side controlled extraction, mass transfer correlations are valid for a variety of modules suggesting easy scale-up. Experimentally obtained height of transfer unit (HTU) values as low as 3 cm suggest new perspectives in contacting equipment. A long term extraction study using a prototype module indicated no performance deterioration over 64 days. Alternate design strategies for extraction from a large scale stream have been analyzed.

Hollow fiber solvent extraction of pharmaceutical products: A case study

Dispersion-free solvent extraction using Celgard® microporous hydrophobic hollow fibers and flat membranes has been utilized for extraction/purification of fermentation-based pharmaceutical products. Extraction as well as back extraction has been studied using a pH swing procedure. Problems of emulsion formation, inherent in current processes, have been avoided to obtain stable dispersion-free operation. Very high solute recoveries and mass transfer rates have been obtained in the hollow fiber devices. Modular plant design using a series-parallel arrangement of this type of extractors and cost of existing dispersion-based devices indicate that these novel devices can compete effectively with commercial extractors.

Microporous Membrane Solvent Extraction

Abstract The versatility of the phenomenon of dispersion-free solvent extraction through immobilized aqueous-organic interface in a microporous hydrophobic membrane is demonstrated here. This technique has been used here for an organic-organic interface to extract aromatics from a hydrocarbon feedstock by a polar organic solvent. The phenomenon has been studied further with micropor-ous hydrophilic and composite hydrophobic-hydrophilic membranes. Operational modes and the influence of the membrane and boundary layer resistances for various solvent-solute-membrane systems have been studied for a CELGAKD (hydrophobic) and a CUPROPHAN (hydrophilic) membrane. Limited performance data for microporous hydrophobic CELGARD hollow fibers (X-20) are also presented.