Flat Sheet Supported Liquid Membrane Research Articles

Copper separation from nitrate/nitric acid media using Acorga M5640 extractant: Part II. Supported liquid membrane study

The facilitated transport of copper(II) from nitrate/nitric acid media through a flat-sheet supported liquid membrane (FSSLM) is investigated, using the commercially available oxime Acorga M5640 as ionophore, as a function of hydrodynamic conditions, concentration of copper (7.9×10 −5 to 1.3×10 −3 M) and H + (pH 1.0–2.0) and ionic strength in the feed solution, carrier concentration (5–40% v/v) in the membrane and support characteristics. The performance of the system is also compared using various diluents for the organic phase and against other available oxime extractants (MOC-55TD, LIX 860 and LIX 622). A model is presented that describes the transport mechanism, consisting of diffusion through a feed side aqueous diffusion layer, a fast interfacial chemical reaction, and diffusion of carrier and its metal complex through the organic membrane. The organic membrane diffusional resistance ( Δ o) and aqueous diffusional resistance ( Δ a) were calculated from the proposed model, and their values were 7.6×10 6 and 273 s/cm, respectively. It was observed that the copper flux across the membrane tends to reach a plateau at high concentration of copper or a low concentration of H + owing to carrier saturation within the membrane, and leads to a diffusion-controlled process. The values of the apparent diffusion coefficient ( D o a) and limiting metal flux ( J lim) were calculated from the limiting conditions and found to be 2.0×10 −8 cm 2/s and 2.3×10 −11 mol/cm 2 s, respectively. The values of the bulk diffusion coefficient ( D o,b) and diffusion coefficient ( D o) calculated from the model were 5.9×10 −9 and 1.6×10 −9 cm 2/s, respectively. The polymeric microporous solid support, Durapore GVHP 04700, was selected throughout the study as it gave the best performance.

Transport of chromium (VI) through a Cyanex 923–xylene flat-sheet supported liquid membrane

The present investigation deals with carrier-facilitated membrane transport of chromium (VI) from chloride media across a flat-sheet supported liquid membrane (FSSLM) using as organic reagent the phosphine oxide, Cyanex 923. The permeation of Cr (VI) has been studied under various experimental conditions: stirring speed of the source phase, initial metal and carrier concentrations, organic phase diluent, HCl concentration in the source phase, composition of the stripping phase and support characteristics. The mass transfer coefficient was calculated as 67 μm/s and the thickness of the aqueous boundary layer was calculated to be 15 μm. Chromium permeation and thus speciation across the membrane was also investigated, and the order found was: CrO 4 2−=Cr 2O 7 2−>Cr 3+.

Kinetic modelling of the active transport of copper(II) across liquid membranes using thiourea derivatives immobilized on microporous hydrophobic supports

The facilitated transport of CuII from chloride media through a flat-sheet supported liquid membrane (FSSLM) is investigated, using thiourea derivatives as ionophores, as a function of hydrodynamic conditions, concentration of copper (1–3×10-7 mol cm-3) and H+ (pH 0.1–2.5) in the feed solution, structure of carrier, carrier concentration (0.7–3×10-5 mol cm-3) in the membrane, strippant in receiving phase and support characteristics. A model is presented that describes the transport mechanism, consisting of diffusion through a feed aqueous diffusion layer, a fast interfacial chemical reaction, and diffusion of carrier and its metal complex through the organic membrane. The organic membrane diffusional resistance (Δo) and aqueous diffusional resistance (Δa) were calculated from the proposed model, and their values were 107×102 s cm-1 and 625 s cm-1, respectively. It was observed that the CuII flux across the membrane tends to reach a plateau at a high concentration of CuII or a low concentration of H+ owing to carrier saturation within the membrane, leading to a diffusion-controlled process. The values of the apparent diffusion coefficient (Doa) and limiting metal flux Jlim were calculated from the limiting conditions and found to be 2.9×10-6 cm2 s-1 and 1.4×10-9 mol cm-2 s-1, respectively. The values of the bulk diffusion coefficient (Do,b) and diffusion coefficient (Do) calculated from the model were 2.6×10-6 cm2 s-1 and 1.2×10-6 cm2 s-1. The polymeric microporous solid support, Durapure, was selected throughout the study as it gave the best performance.

EXTRACTION OF ALUMINUM FROM A PICKLING BATH WITH SUPPORTED LIQUID MEMBRANE EXTRACTION

ABSTRACT Large amounts of waste are produced yearly in the galvanic and chemical surface treatment industry. Bath liquids used in the various processes lose their function due to contamination. The spent bath liquids have to be replaced and treated prior to disposal, leading to high costs and a high environmental burden. In this paper, a proposed solution to the problem is investigated: the selective removal of the contaminant with supported liquid membrane extraction. The extraction of aluminum, a contaminant at high concentrations, from a pickling bath liquid with hydrofluoric acid and phosphoric acid as its main components has been carried out with the basic extractants Alamine 308 and Alamine 336 in a flat sheet-supported liquid membrane setup. Aluminum transport rates were obtained in the order of 10−6−10−5mol/(M2·s), which are normal values for this technique. The extraction was not completely selective as dissolved phosphorus was coextracted. In all experiments, precipitation took place on the surface of the liquid membrane and in the bulk of the strip phase. Increasing the stripping alkalinity from pH = 8 to pH = 13 reduced the amount of precipitation in the bulk of the strip phase but caused a substantial decrease in the aluminum flux. The precipitation prevents industrial application of the systems investigated.

EXTRACTION OF ALUMINUM FROM A PICKLING BATH WITH SUPPORTED LIQUID MEMBRANE EXTRACTION

ABSTRACT Large amounts of waste are produced yearly in the galvanic and chemical surface treatment industry. Bath liquids used in the various processes lose their function due to contamination. The spent bath liquids have to be replaced and treated prior to disposal, leading to high costs and a high environmental burden. In this paper, a proposed solution to the problem is investigated: the selective removal of the contaminant with supported liquid membrane extraction. The extraction of aluminum, a contaminant at high concentrations, from a pickling bath liquid with hydrofluoric acid and phosphoric acid as its main components has been carried out with the basic extractants Alamine 308 and Alamine 336 in a flat sheet-supported liquid membrane setup. Aluminum transport rates were obtained in the order of 10−6−10−5mol/(M2·s), which are normal values for this technique. The extraction was not completely selective as dissolved phosphorus was coextracted. In all experiments, precipitation took place on the surf...

Transport of Cesium from Reprocessing Concentrate Solutions through Flat-Sheet-Supported Liquid Membranes: Influence of the Extractant

Abstract The influence of the extractant on cesium transport from nuclear fuel reprocessing concentrate solutions to demineralized water through flat-sheet-supported liquid membranes (FSSLMs) was studied using four crown ethers of different lipophility: dibenzo-21-crown-7 (DB21C7), benzo-21-crown-7(B21C7). t-butylbenzo-21-crown-7 (tBuB21C7), and n-decylbenzo-21-crown-7 (nDecB21C7). The distribution coefficients of cesium show that the four crown ethers have similar extraction capacities which follow the sequence nDecB21C7 > tBuB21C7 > B21C7 > DB21C7. DB21C7 and B21C7 cannot be used in cesium transport experiments due to the low organic solubility of the former and the great tendency of the latter to form a third phase between the organic phase and the aqueous extraction phase. Of the other two crown ethers, nDecB21C7 leads to faster cesium transport than tBuB21C7 due to the stronger lipophilic character of the former; this allows a higher crown-ether concentration in the membrane to be obtained when nDecB21C7 is used.

Influence of the Extractant on Strontium Transport from Reprocessing Concentrate Solutions through Flat-Sheet Supported Liquid Membranes

Abstract The influence of the extractant on strontium transport through a flat-sheetsupported liquid membrane from nuclear fuel reprocessing concentrate solutions to demineralized water has been studied using two crown ethers of different lipophilicity: dicyclohexano-18-crown-6 (DC18C6) and di-tert-butylcyclohexano-18-crown-6 (DtBuC18C6). The distribution coefficients of strontium showed that DC18C6 is a better strontium extractant than DtBuC18C6 in the entire range of crown-ether concentration studied. No effect of association between the DC18C6 molecules was observed even at high concentrations. However, the strong lipophilic character of DtBuC18C6 led to a distribution coefficient of this extractant 10 times higher than the distribution coefficient of DC18C6. Thus, the membrane concentration of DtBuC18C6 was approximately 10 times higher than that of DC18C6. This leads to greater strontium permeability for DtBuC18C6, even though DC18C6 had a greater capacity for strontium extraction and a higher diffusion coefficient in the membrane due to the smaller molar volume of this crown ether. The precipitation of a white solid was observed when the synthetic concentrate was mixed with an organic phase containing DtBuC18C6 dissolved in n-hexylbenzene (0.7 mol·L−1 isotridecanol), causing a decrease of strontium permeability. In this case, DC18C6 had the greatest strontium permeability.

Stability of flat sheet supported liquid membranes in the transport of radionuclides from reprocessing concentrate solutions

The stability of a flat sheet supported liquid membrane (FSSLM) has been studied by using various kinds of diluents. The influence of several properties of the diluents on the stability of the SLM as well as on water transport have been analyzed. The high interfacial tensions and low water solubilities were the principal characteristics of the membrane solvents, together with their surface tension being lower than the critical surface tension of the support, which permits a long SLM lifetime. Under our own working conditions (osmotic pressure gradient across the membrane and the use of a solid support) a membrane lifetime of over 200 hr was attained by using membrane solvents with a water solubility lower than 12 g-l −1 and, simultaneously, a drop point of the SLM higher than 1.1 bar. These conditions could be obtained with isotridecanol or with aromatic diluents having aliphatic groups of six or more carbon atoms (like hexylbenzene) with a long chain alcohol as a phase modifier. Isotridecanol was found to be the best phase modifier (the most stable on an SLM). Measurements of water transport across the SLMs showed different stabilities for SLMs with 1-decanol, 4-nonylphenol or isotridecanol as phase modifiers, for which the SLM has a lifetime longer than 200 hr.

Carrier-mediated transport of uranyl ions across tributyl phosphate—dodecane liquid membranes

Carrier-facilitated transport of uranium(VI) against its concentration gradient from aqueous nitrate acidic solutions across an organic bulk liquid membrane (BLM) and flat-sheet supported liquid membranes (SLM) containing tributyl phosphate (TBP) as the mobile carrier and dodecane as the membrane solvent has been investigated. Extremely dilute to moderately concentrated uranyl nitrate solutions (ca. 10 −4 M) in 2 M HNO 3 generally constituted the source phase. With increasing carrier concentration in the organic membrane, both the amount of uranium that could be extracted into the membrane and the viscosity of the organic solution increased. These opposing effects resulted in maximum uranium permeation at ca.30% TBP in dodecane, while enhanced acidity of the strip side adversely affected the partitioning of the cation into the receiving phase. Among the several aqueous reagents tested, dilute ammonium carbonate (ca. 1 M) solution was the most efficient strippant. The stoichiometry of the urnium—TPB complex in this liquid membrane system was established to be UO 2(NO 3) 2·2TBP, which is in accord with that deduced on the basis of liquid—liquid distribution measurements.

Selection of Organic Phases for Optimal Stability and Efficiency of Flat-Sheet Supported Liquid Membranes

Abstract The efficiency and the stability of flat-sheet supported liquid membranes (SLMs) were studied in the case of the active transport of an amino acid, L-valine. Independent measurements on the organic phase (valine distribution, water concentration and viscosity) combined with the determination of some surface properties (interfacial tension and drop point) permit the description and prediction of the experimental permeability and stability of SLMs. The lifetime of the SLM was explained by taking into account diluent solubility in the aqueous phase, water concentration in the organic phase, interfacial tension between organic and feed phases, and drop point of the SLM. The experimental efficiency could be modeled by a mathematical expression involving the distribution coefficient of the solute and the viscosity of the organic solution.

Study of Uranium Removal from Groundwater by Supported Liquid Membranes

Abstract The separation of uranium from synthetic Hanford site groundwater by liquid-liquid extraction and by supported liquid membranes (SLM) was atudied. Bis(2,4,4-trimethylpentyl) phosphinic acid, H[DTMPeP], contained in the commercial extractant Cysnex 272, was selected for the membrane carrier because of its selectivity for uranium over calcium and magnesium. n-Dodecane was used as diluent and polypropylene membranea were used as the support. A water soluble complexing agent, 1-hydroxyethane-1,1-diphoaphonic acid, HEDPA, was used as atrlpping agent. The permeability coefficient of U(V1) was evaluated from a detailed study of the permeation of U(VI) through flat-sheet SLMs as a function of the membrane carrier concentration. The diffusion coefficient of the uranium complex in the organic phase was also evaluated from permeation experiments performed under loading conditions. Experiments were also carried out with Cs(II) and Fe(III) to measure the membrane selectivity for U(VI) over these two cations. ...