Patent Application
20100224030
1. Field of the Invention
The present invention relates to the removal and recovery of indium from feed solutions, such as process streams and waste waters, using supported liquid membrane technology.
2. Description of the Prior Art
Liquid membranes combine extraction and stripping, which are normally carried out in two separate steps in conventional processes such as solvent extractions, into one step. A one-step liquid membrane process provides the maximum driving force for the separation of a targeted species, leading to the best clean-up and recovery of the species (W. S. Winston Ho and Kamalesh K. Sirkar, eds., Membrane Handbook, Chapman & Hall, New York, 1992).
There are two types of liquid membranes: (1) supported liquid membranes (SLMs) and (2) emulsion liquid membranes (ELMs). In SLMs, the liquid membrane phase is the organic liquid imbedded in pores of a microporous support, e.g., microporous polypropylene hollow fibers (W. S. Winston Ho and Kamalesh K. Sirkar, eds., Membrane Handbook, Chapman & Hall, New York, 1992). When the organic liquid contacts the microporous support, it readily wets the pores of the support, and the SLM is formed.
For the extraction of a target species from a feed solution, the organic-based SLM is placed between two aqueous solutions—the feed solution and the strip solution where the SLM acts as a selective membrane for the transport of the target species from the feed solution to the strip solution. The organic liquid in the SLM contains an extractant, a diluent which is generally an inert organic solvent, and sometimes a modifier, and it is immiscible in the aqueous feed and strip streams.
SLMs have been investigated to remove metals, radionuclides, and rare earth metals from aqueous feed solutions in the scientific and industrial community. The removal of metals, including copper, zinc, cadmium, and palladium, with SLMs has been described (N. Aouad, G. Miquel-Mercier, E. Bienvenue, E. Tronel-Peyroz, G. Jerninet, J. Juillard, and P. Seta, “Lasalocid (X537A) as a Selective Carrier for Cd(II) in Supported Liquid Membranes,” J. Membrane Sci., 139, 167-174 (1998); J. A. Daoud, S. A. El-Reefy, and H. F. Aly, “Permeation of Cd(II) Ions through a Supported Liquid Membrane Containing Cyanex-302 in Kerosene,” Sep. Sci. Technol., 33, 537-549 (1998); J. Vander Linden and R. F. De Ketelaere, “Selective Recuperation of Copper by Supported Liquid Membrane (SLM) Extraction,” J. Membrane Sci., 139, 125-135 (1998); M. E. Campderros, A. Acosta, and J. Marchese, “Selective Separation of Copper with LIX 864 in a Hollow Fiber Module,” Talanta, 47, 19-24 (1998); M. Rovira and A. M. Sastre, “Modelling of Mass Transfer in Facilitated Supported Liquid-Membrane Transport of Palladium(II) Using Di-(2-ethylhexyl)Thiophosphoric Acid,” J. Membrane Sci., 149, 241-250 (1998); J. C. Lee, J. Jeong, J. T. Park, I. J. Youn, and H. S. Chung, “Selective and Simultaneous Extractions of Zn and Cu Ions by Hollow Fiber SLM Modules Containing HEH(EHP) and LIX84,” Sep. Sci. Technol., 34, 1689-1701 (1999); F. Valenzuela, C. Basualto, C. Tapia, and J. Sapag, “Application of Hollow-Fiber Supported Liquid Membranes Technique to the Selective Recovery of a Low Content of Copper from a Chilean Mine Water,” J. Membrane Sci., 155, 163-168 (1999)).
On the removal of radionuclides, Dozol et al. (J. F. Dozol, N. Simon, V. Lamaare, H. Rouquette, S. Eymard, B. Tournois, D. De Marc, and R. M. Macias, “A Solution for Cesium Removal from High-Salinity Acidic or Alkaline Liquid Waste: the Crown Calix[4]arenes”, Sep. Sci. Technol., 34, 877-909 (1999)) have described the use of the extractant, Calix[4]arenes monocrown or biscrown, blocked in 1,3 alternative cone conformation, in SLMs for the removal of cesium from high-salinity acidic or alkaline liquid waste. Kedari et al. (C. S. Kedari, S. S. Pandit, and A. Ramanujam, “Selective Permeation of Plutonium (IV) through Supported Liquid Membrane Containing 2-Ethylhexyl 2-Ethylhexyl Phosphonic Acid as Ion Carrier”, J. Membrane Sci., 156, 187-196 (1999)) have studied the selective permeation of plutonium (IV) through a SLM containing 2-ethylhexyl 2-ethylhexyl phosphonic acid as the ion carrier.
On the extraction of rare earth metals, Yaftian et al. (M. R. Yaftian, M. Burgard, C. B. Dieleman and D. Matt, “Rare-earth Metal-ion Separation Using a Supported Liquid Membrane Mediated by a Narrow Rim Phosphorylated Calix[4]arene,” J. Membrane Sci., 144, 57-64 (1998)) has reported the use of SLMs for europium, lanthanum, neodymium, praseodymium, and gadolinium.
One disadvantage of SLMs is their instability due mainly to loss of the membrane liquid (organic solvent, extractant, and/or modifier) into the aqueous phases on each side of the membrane (A. J. B. Kemperman, D. Bargeman, Th. Van Den Boomgaard, H. Strathmann, “Stability of Supported Liquid Membranes: State of the Art”, Sep. Sci. Technol., 31, 2733 (1996); T. M. Dreher and G. W Stevens, “Instability Mechanisms of Supported Liquid Membranes”, Sep. Sci. Technol., 33, 835-853 (1998); J. F. Dozol, J. Casas, and A. Sastre, “Stability of Flat Sheet Supported Liquid Membranes in the Transport of Radionuclides from Reprocessing Concentrate Solutions”, J. Membrane Sci., 82, 237-246 (1993)). The prior art has attempted to solve this problem through the combined use of SLM with a module containing two set of hollow fibers, i.e., the hollow-fiber contained liquid membrane (W. S. Winston Ho and Kamalesh K. Sirkar, eds., Membrane Handbook, Chapman & Hall, New York, 1992). In this configuration with two sets of microporous hollow-fiber membranes, one carries the aqueous feed solution, and the other carries the aqueous strip solution. The organic phase is contained between the two sets of hollow fibers by maintaining the aqueous phases at a higher pressure than the organic phase. The use of the hollow-fiber contained liquid membrane increases membrane stability, because the liquid membrane may be continuously replenished. However, this configuration is not advantageous because it requires mixing two sets of fibers to achieve a low contained liquid membrane thickness.
In ELMs, an emulsion acts as a liquid membrane for the separation of the target species from a feed solution. An ELM is created by forming a stable emulsion, such as a water-in-oil emulsion, between two immiscible phases, followed by dispersion of the emulsion into a third, continuous phase by agitation for extraction. The membrane phase is the oil phase that separates the encapsulated, internal aqueous droplets in the emulsion from the external, continuous phase (W. S. Winston Ho and Kamalesh K. Sirkar, eds., Membrane Handbook, Chapman & Hall, New York, 1992). The species-extracting agent is contained in the membrane phase, and the stripping agent is contained in the internal aqueous droplets. Emulsions formed from these two phases are generally stabilized by use of a surfactant. The external, continuous phase is the feed solution containing the target species. The target species is extracted from the aqueous feed solution into the membrane phase and then stripped into the aqueous droplets in the emulsion. The target species can then be recovered from the internal aqueous phase by breaking the emulsion, typically via electrostatic coalescence, followed by electroplating or precipitation.
The use of ELMs to remove metals, rare earth metals, and radionuclides from aqueous feed solutions has also been pursued in the scientific and industrial community. The ELMs for the removal of metals, including cobalt, copper, zinc, nickel, mercury, lead, cadmium, and silver, and for the removal of rare earth metals, including europium, lanthanum, and neodymium, have been described in detail (W. S. Winston Ho and Kamalesh K. Sirkar, eds., Membrane Handbook, Chapman & Hall, New York, 1992). The removal of metals including cobalt, nickel, cadmium, mercury, and lead with ELMs has been reported quite a lot in the literature (B. Raghuraman, N. Tirmizi, and J. M. Wiencek, “Emulsion Liquid Membranes for Wastewater Treatment. Equilibrium Models for Some Typical Metal-Extractant Systems,” Environ. Sci. Technol., 28, 1090-1098 (1994); T. Kakkoi, M. Goto, K. Sugimoto, K. Ohto, and F. Nakashio, “Separation of Cobalt and Nickel with Phenylphosphonic Acid Mono-4-tert-octylphenyl Ester by Liquid Surfactant Membranes,” Sep. Sci. Technol., 30, 637-657 (1995); R. S. Juang and J. D. Jiang, “Recovery of Nickel from a Simulated Electroplating Rinse Solution by Solvent Extraction and Liquid Surfactant Membrane,” J. Membrane Sci., 100, 163-170 (1995); H. Kasaini, F. Nakashio, and M. Goto, “Application of Emulsion Liquid Membranes to Recover Cobalt Ions from a Dual-component Sulphate Solution Containing Nickel Ions,” J. Membrane Sci., 146, 159-168 (1998); S. Y. B. Hu and J. M. Wiencek, “Emulsion-Liquid-Membrane Extraction of Copper Using a Hollow-Fiber Contactor,” AIChE J., 570-581 (1998)).
On radionuclides, the removal of strontium, cesium, technetium, and uranium has also been described in detail by Ho and Sirkar (W. S. Winston Ho and Kamalesh K. Sirkar, eds., Membrane Handbook, Chapman & Hall, New York, 1992). The extraction of strontium with the ELM technique has been investigated (I. Eroglu, R. Kalpakci, and G. Gunduz, “Extraction of Strontium Ions with Emulsion Liquid Membrane Technique”, J. Membrane Sci., 80, 319-325 (1993)).
One disadvantage of ELMs is that the emulsion swells upon prolonged contact with the feed stream. This swelling causes a reduction in the stripping reagent concentration in the aqueous droplets which reduces stripping efficiency. It also results in dilution of the target species that has been concentrated in the aqueous droplets, resulting in lower separation efficiency of the membrane. The swelling further results in a reduction in membrane stability by making the membrane thinner. Finally, swelling of the emulsion increases the viscosity of the spent emulsion, making it more difficult to demulsify. A second disadvantage of ELMs is membrane rupture, resulting in leakage of the contents of the aqueous droplets into the feed stream and a concomitant reduction of separation efficiency. Raghuraman and Wiencek (B. Raghuraman and J. Wiencek, “Extraction with Emulsion Liquid Membranes in a Hollow-Fiber Contactor”, AIChE J., 39, 1885-1889 (1993)) have described the use of microporous hollow-fiber contactors as an alternative contacting method to direct dispersion of ELMs to minimize the membrane swelling and leakage. This is due to the fact that the hollow-fiber contactors do not have the high shear rates typically encountered with the agitators used in the direct dispersion. Additional disadvantages include the necessary process steps for making and breaking the emulsion.
Thus, there has been a need in the art for an extraction process which maximizes the stability of the SLM membrane, resulting in efficient removal and recovery of metals, radionuclides, penicillin, and organic acids from the aqueous feed solutions. Ho recognized the need and invented the combined supported liquid membrane/strip dispersion process for the removal of chromium (W. S. Winston Ho, “Supported Liquid Membrane Process for Chromium Removal and Recovery”, U.S. Pat. No. 6,171,563 (2001)), metals (W. S. Winston Ho, “Combined Supported Liquid Membrane/Strip Dispersion Process for the Removal and Recovery of Radionuclides and Metals”, U.S. Pat. No. 6,328,782 (2001); W. S. Winston Ho, “Combined Supported Liquid Membrane/Strip Dispersion Process for the Removal and Recovery of Metals”, U.S. Pat. No. 6,350,419 (2002)), radionuclides (W. S. Winston Ho, “Combined Supported Liquid Membrane/Strip Dispersion Process for the Removal and Recovery of Radionuclides and Metals”, U.S. Pat. No. 6,328,782 (2001); W. S. Winston Ho, “Combined Supported Liquid Membrane/Strip Dispersion Process for the Removal and Recovery of Radionuclides”, U.S. Pat. No. 6,696,589 (2004)), and penicillin and organic acids (W. S. Winston Ho, “Combined Supported Liquid Membrane/Strip Dispersion Process for the Removal and Recovery of Penicillin and Organic Acids”, U.S. Pat. No. 6,433,163 (2002)). The synthesis of dialkyl monothiophosphoric acid extractants for the combined supported liquid membrane/strip dispersion process for the removal of metals has been reported (W. S. Winston Ho and Bing Wang, “Combined Supported Liquid Membrane/Strip Dispersion Process for the Removal and Recovery of Metals: Dialkyl Monothiophosphoric Acids and Their Use as Extractants”, U.S. Pat. No. 6,291,705 (2001)). But, none of these patents by Ho disclose the use of the combined supported liquid membrane/strip dispersion process for the removal and recovery of indium.
Thus, there is a need in the art for an extraction process which maximizes the stability and effectiveness of the SLM membrane for the efficient removal and recovery of indium from the aqueous feed solutions.
The present invention relates to a process for the removal and recovery of indium from a feed solution using a combined SLM/strip dispersion.
In one embodiment, the present invention relates to a process for the removal and recovery of indium from a feed solution which comprises the following steps. First, a feed solution containing indium is passed on one side of the SLM embedded in a microporous support material and treated to remove the indium by the use of a strip dispersion on the other side of the SLM. The strip dispersion can be formed by dispersing an aqueous strip solution in an organic liquid, for example, using a mixer. Second, the strip dispersion, or a part of the strip dispersion, is allowed to stand, resulting in separation of the dispersion into two phases: the organic liquid phase and the aqueous strip solution phase containing a concentrated indium solution.
The continuous organic phase of the strip dispersion readily wets the pores of a microporous support to form a stable SLM. The process of the present invention provides a number of operational and economic advantages over the use of conventional SLMs or solvent extraction.
Thus, it is an object of the present invention to provide an SLM process for the removal and recovery of indium which provides increased membrane stability.
It is another object of the invention to provide an SLM process having high indium removal and recovery.
It is yet another object of the present invention to provide an SLM process having improved recovery of indium to provide a concentrated strip solution of indium.
The present invention relates to a process for the removal and recovery of indium from a feed solution, such as waste waters or process streams. This new process employs a combination of a supported liquid membrane (SLM) and a strip dispersion.
In one embodiment, the present invention relates to a process for the removal and recovery of indium from a feed solution which comprises the following steps. First, a feed solution containing indium is passed on one side of the SLM embedded in a microporous support material and treated to remove the indium by the use of a strip dispersion on the other side of the SLM. The strip dispersion can be formed by dispersing an aqueous strip solution in an organic liquid, for example, using a mixer. Second, the strip dispersion, or a part of the strip dispersion, is allowed to stand, resulting in separation of the dispersion into two phases: the organic liquid phase and the aqueous strip solution phase containing a concentrated indium solution.
While any SLM configuration may be employed in the process of the invention, the preferred configuration employs a hollow fiber module as the liquid membrane microporous support. Such hollow fiber modules consist of microporous hollow fibers arranged in a shell-and-tube configuration. In the present invention, the strip dispersion is passed through either the shell side of the module or the tube side of the module, and the aqueous feed solution containing indium for extraction is passed through the opposing side of the module. The use of the hollow fiber system in the combined SLM/strip dispersion process allows constant supply of the strip dispersion as shown in
For the purposes of the invention, strip dispersion is defined as a mixture of an aqueous phase and an organic phase. The aqueous phase of the dispersion comprises an aqueous strip solution, while the organic phase comprises an extractant or extractants in an organic liquid. The dispersion is formed by the mixing of the aqueous and organic phases as shown in
In this SLM/strip dispersion system, there is a constant supply of the organic membrane solution, i.e., the organic phase of the strip dispersion, into the pores. This constant supply of the organic phase ensures a stable and continuous operation of the SLM. In addition, the direct contact between the organic and strip phases provides efficient mass transfer for stripping. The organic and strip phases can be mixed, for example, with high-shear mixing, to increase the contact area between the two phases.
Once removal of indium is complete, the mixer for the strip dispersion is stopped, and the dispersion is allowed to stand until it separates into two phases, the organic membrane solution and the concentrated strip solution. The concentrated strip solution containing indium is the product of this process.
The feed solution includes, but is not limited to, waste waters or process streams containing indium.
The microporous support employed in the invention is comprised of, for example, microporous polypropylene, polytetrafluoroethylene, polyethylene, polysulfone, polyethersulfone, polyetheretherketone, polyimide, polyamide, polyaramide, or mixtures thereof. The preferred microporous supports are microporous polypropylene and polytetrafluoroethylene hollow fibers.
The aqueous portion of the strip dispersion comprises an aqueous acid solution, such as a mineral acid. Examples of mineral acids useful in the present invention include, but are not limited to, hydrochloric acid (HCl), sulfuric acid (H2SO4), nitric acid (HNO3), and acetic acid (CH3COOH). The acid is present in a concentration between about 0.1 M and about 18 M. The preferred concentration for the acid solution is between about 1 M and about 6 M.
The continuous organic liquid phase into which the aqueous strip solution is dispersed contains an extractant or extractants. The extractant is capable of extracting indium contained in the feed solution. Typical extractants which are known in the art for extraction of indium from waste waters or process streams may be employed in the present strip dispersion.
The extractants include dialkyl phosphoric acids and alkyl phenylphosphonic acids. The dialkyl group of the dialkyl phosphoric acid is paraffinic (saturated) and has from 6 to 26 carbon atoms. The dialkyl phosphoric acids are selected from the group consisting of di(2-ethyl-hexyl)phosphoric acid (D2EHPA), di(2-butyl-octyl)phosphoric acid, di(2-hexyl-decyl)phosphoric acid, di(2-octyl-decyl/2-hexyl-dodecyl)phosphoric acid, di(2-octyl-dodecyl)phosphoric acid, di(hexyl)phosphoric acid, di(heptyl)phosphoric acid, di(octyl)phosphoric acid, di(nonyl)phosphoric acid, di(decyl)phosphoric acid, di(undecyl)phosphoric acid, di(dodecyl)phosphoric acid, di(tridecyl)phosphoric acid, di(tetradecyl)phosphoric acid, di(pentadecyl)phosphoric acid, di(hexadecyl)phosphoric acid, di(heptadecyl)phosphoric acid, di(octadecyl)phosphoric acid, di(nonadecyl)phosphoric acid, di(decadecyl)phosphoric acid, di(undecadecyl)phosphoric acid, di(dodecadecyl)phosphoric acid, di(tridecadecyl)phosphoric acid, di(tetrdecadecyl)phosphoric acid, di(pentadadecyl)phosphoric acid, di(hexadecadecyl)phosphoric acid, and mixtures thereof. The preferred dialkyl phosphoric acid is di(2-ethyl-hexyl)phosphoric acid (D2EHPA).
The alkyl group of the alkyl phenylphosphonic acid is paraffinic (saturated) and has from 6 to 26 carbon atoms. The alkyl phenylphosphonic acids are selected from the group consisting of 2-butyl-1-octyl phenylphosphonic acid (BOPPA), 2-hexy-1-decyl phenylphosphonic acid, 2-octyl-1-decyl/2-hexyl-1-dodecyl phenylphosphonic acid, 2-octyl-1-dodecyl phenylphosphonic acid, hexyl phenylphosphonic acid, heptyl phenylphosphonic acid, octyl phenylphosphonic acid, nonyl phenylphosphonic acid, decyl phenylphosphonic acid, undecyl phenylphosphonic acid, dodecyl phenylphosphonic acid, tridecyl phenylphosphonic acid, tetradecyl phenylphosphonic acid, pentadecyl phenylphosphonic acid, hexadecyl phenylphosphonic acid, heptadecyl phenylphosphonic acid, octadecyl phenylphosphonic acid, nonadecyl phenylphosphonic acid, decadecyl phenylphosphonic acid, undecadecyl phenylphosphonic acid, dodecadecyl phenylphosphonic acid, tridecadecyl phenylphosphonic acid, tetrdecadecyl phenylphosphonic acid, pentadadecyl phenylphosphonic acid, hexadecadecyl phenylphosphonic acid, and mixtures thereof. The preferred alkyl phenylphosphonic acid is 2-butyl-1-octyl phenylphosphonic acid (BOPPA).
The organic liquid of the present strip dispersion optionally comprises a hydrocarbon solvent or mixture. The hydrocarbon solvent or mixture has a number of carbon atoms per solvent molecule ranging from 6 to 18, preferably from 10 to 14. The hydrocarbon solvent includes, for example, n-decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane, isodecane, isoundecane, isododecane, isotridecane, isotetradecane, isoparaffinic hydrocarbon solvent (with a flash point of 92° C., a boiling point of 254° C., a viscosity of 3 cp (at 25° C.), and a density of 0.791 g/ml (at 15.6° C.)) or mixtures thereof.
The organic liquid of the present strip dispersion optionally contains a modifier to enhance the complexation and/or stripping of the target species. The modifier can be, for example, an alcohol, a nitrophenyl alkyl ether, a trialkyl phosphate or mixtures thereof. The alcohol can be, for example, hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol, tridecanol, tetradecanol, pentadecanol, hexadecanol, heptadecanol, octadecanol or mixtures thereof. The nitrophenyl ether can be, for example, o-nitrophenyl octyl ether (o-NPOE), o-nitrophenyl heptyl ether, o-nitrophenyl hexyl ether, o-nitrophenyl pentyl ether (o-NPPE), o-nitrophenyl butyl ether, o-nitrophenyl propyl ether or a mixture thereof. The trialkyl phosphate can be, for example, tributyl phosphate, tris(2-ethylhexyl)phosphate or mixtures thereof.
The organic liquid of the present strip dispersion comprises about 2 volume % to about 100 volume % (approximately 0.05M to 3M) extractant and about 0 volume % to about 20 volume % modifier in a hydrocarbon solvent or mixture. More preferably, the organic liquid of the present strip dispersion comprises about 5 volume % to about 40 volume % extractant and about 1 volume % to about 10 volume % modifier in a hydrocarbon solvent or mixture. Even more preferably, the organic liquid comprises 5 volume % to about 40 volume % extractant and about 1 volume % to about 10 volume % dodecanol in an isoparaffinic hydrocarbon solvent or in n-dodecane. All percentages are by volume unless specified otherwise.
The present invention has several advantages over conventional SLM technology for removal and recovery of indium from aqueous feed solution. These advantages include increased membrane stability, reduced costs, increased simplicity of operation, improved flux, and improved recovery for indium.
The present invention provides a constant supply of the organic membrane solution into the pores of the hollow fiber support for removal and recovery of indium from aqueous feed solution. This constant supply results in an SLM which is more stable than conventional SLMs, ensuring stable and continuous operation. This constant supply also eliminates the need for recharging membrane modules, which is required with conventional SLMs. Further, it eliminates the need for a second set of membrane modules for use during recharging of the first set of membrane modules. Thus, the present invention decreases not only operational costs but also the initial capital investment in the system. The present invention also increases simplicity of the removal operation.
The present invention provides direct contact between the organic/extraction phase and aqueous strip phase. Mixing of these phases provides an extra mass transfer surface area in addition to the area given by the hollow fibers, leading to extremely efficient stripping of the target species from the organic phase. This efficient stripping enhances the flux for the extraction of indium.
The present invention comprises a new type of SLM for removal and recovery of indium, and it provides increased flexibility of aqueous strip/organic volume ratio. This flexibility allows the use of a smaller volume of aqueous strip solution to obtain a higher concentration of the recovered indium in the aqueous strip solution. The concentrated strip solution is a valuable product for resale or reuse.
This invention is further illustrated by the following examples, which are not to be construed in any way as imposing limitations upon the scope thereof. To the contrary, it is to be clearly understood that reading the description herein may suggest various other embodiments, modifications, and equivalents to those skilled in the art without departing from the spirit of the present invention and/or the scope of the appended claims.
In all of the following examples, the supported liquid membranes (SLMs) with trip dispersion were used to extract indium from an aqueous feed solution to an organic solution, in which an aqueous strip solution was dispersed to continually strip the extracted indium. The SLM system consisted of a hollow-fiber membrane module (Liquid-Cel®, extra-flow 2.5×8, Membrana-Charlotte, USA), a feed solution tank, a feed pump (model 7592-50, Cole-Parmer, USA) to drive the feed solution into the polypropylene hollow fibers in the module, a strip dispersion tank with a mixer (SS-NZ-1000, Eyela, Japan) to well disperse the aqueous strip solution in the organic solution, and another pump (model 7553-70, Cole-Parmer, USA) to drive the water-in-oil dispersion into the shell side of the module. The hollow-fiber module was 6.35 cm (2.5 inches) in diameter and 20.3 cm (8 inches) in length, and it had a membrane surface area of 1.4 m2.
All of the following examples were run in the countercurrent mode with the feed solution passing through the tube side of the microporous polypropylene hollow fiber module whereas the strip dispersion passing through the shell side of the module. Indium in the feed solution was extracted to the organic solution in the membrane module, and the extracted indium was stripped into the dispersed strip solution both in the module and in the dispersion tank.
The aqueous feed solution, containing indium, was placed in the feed tank that was agitated by a magnetic stirring bar at a rate of 300 rpm. The strip solution, 5M HCl aqueous solution, was dispersed with a 2-bladed paddle (8.5 cm in diameter) at a rate of 300 rpm in the organic solution containing D2EHPA (Merck) as the extractant for indium in Isopar-L (ExxonMobil). The concentration of D2EHPA in Isopar-L was 0.6 M (20.5 vol %) for most of the experiments we performed unless specified otherwise. The organic solution also contained 2 vol % of 1-dodecanol (Merck), unless specified otherwise, as the modifier for the extractant. The total volume of the organic solution was 0.90 L (900 ml), and that of the strip solution was 0.12 L (120 ml) unless specified otherwise. Both of the feed and dispersion tanks were thermo-stated at 25° C.
The process was first started by passing the feed solution through the tube side of the hollow fiber module. After the hollow fibers were filled with the feed solution, the water-in-oil dispersion was pumped into the shell side of the module. To prevent the organic phase form passing through the pores of the hollow fibers into the feed solution, the pressure in the tube side was maintained at a positive pressure, i.e., 4 to 5 psi higher than that in the shell side unless specified otherwise. Both the feed and dispersion solutions were pumped from the tanks to the module and then recycled back to the tanks. The pumping rate for both streams was kept at 1 L/min.
During each experiment, samples from the feed and strip solutions were taken at certain timed intervals. The strip dispersion samples were allowed to stand until phase separation occurred. The aqueous phase from the strip dispersion sample was then collected. The aqueous phase samples from the strip dispersion samples and the feed solution samples were then analyzed to determine the indium concentrations by using an atomic absorption spectrophotometer (GBC 906, GBC, Australia) unless specified otherwise (for example, using an inductively coupled plasma (ICP) spectrometer).
Experiments with different feed compositions and volumes were carried out to investigate the performance of the process of SLM with strip dispersion. The performance maybe expressed in terms of indium recovery and concentrations in both the treated feed and strip solutions.
Feed Solution with 200 ppm In3+ in pH 1 H2SO4 of 15.5 L.
Feed Solution with about 180 ppm In3+ in pH 1 HNO3 of 1 L.
Feed Solution with about 190 ppm In3+ in pH 1 H2SO4 of 1 L
Feed Solution with about 160 ppm In3+ in pH 1 HCl of 1 L
Feed Solution with about 200 ppm In3+ in pH 1, 2 wt % H2C2O4 of 1 L
Feed Solution with about 200 ppm In3+ in pH 1, 2 wt % H2C2O4 of 1 L
Feed Solution with about 200 ppm In3+ in pH 1, 2 wt % H2C2O4 of 1 L
Feed Solution with 200 ppm In3+ in pH 1, 2 wt % H2C2O4 of 15.5 L
ITO Feed Solution with about 140 ppm In3+ and pH 0.9 of 15.5 L
Residual Electrolyte Feed Solution with about 11000 ppm In3+ and pH 0.9 of 0.5 L
Examples 1 to 10 have demonstrated that D2EHPA is an effective extractant in the supported liquid membranes (SLMs) with strip dispersion for the removal and recovery of indium from various aqueous feed solutions. These results of the SLMs with strip dispersion for indium are very much different from those for the metals and radionuclides disclosed in Ho's patents mentioned earlier (U.S. Pat. Nos. 6,291,705, 6,328,782, 6,350,419, 6,696,589) where D2EHPA was ineffective. Thus, these results disclosed in this present invention are unexpected in view of the prior art disclosed in the Ho's patents.
Feed Solution with 200 ppm In3+ in pH 1 H2SO4 of 1 L
