Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Reexamination Certificate
2000-02-04
2001-12-11
Mai, Ngoclan (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C210S682000, C210S687000, C210S688000, C210S643000, C210S651000, C423S008000
Reexamination Certificate
active
06328782
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the removal and recovery of radionuclides and metals from feed solutions, such as waste waters and process streams, using supported liquid membrane technology.
BACKGROUND OF THE INVENTION
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 semi-permeable membrane for the transport of the target species from the feed solution to the strip solution. The organic liquid in the SLM is immiscible in the aqueous feed and strip streams and contains an extractant, a diluent which is generally an inert organic solvent, and sometimes a modifier.
The use of SLMs to remove radionuclides from aqueous feed solutions has been long pursued in the scientific and industrial community. Nechaev et al. (A. F. Nechaev, V. V. Projaev, V. P. Kapranchik, “Supported Liquid Membranes in Radioactive Waste Treatment Processes: Recent Experience and Prospective”, in S. Slate, R. Baker, and G. Benda, eds.,
Proceedings of Fifth International Conference on Radioactive Waste Management and Environmental Remediation,
Volume 2, American Society of Mechanical Engineers, New York, 1995) have reported on the experience and prospective of using SLMs in radioactive waste treatment processes, and the transport of uranyl ion across SLMs has been studied extensively (J. P. Shukla and S. K. Misra, “Uranyl Ion Transport Across Tri-n-butyl Phosphate
-Dodecane Liquid Membranes”,
Proceedings of the International Symposium on Uranium Technology,
Bhabha Atomic Research Centre, Bombay, India, pp. 939-946, 1991; M. A. Chaudhary, “Separation of Some Metal Ions Using Coupled Transport Supported Liquid Membranes”, in H. Javed, H. Pervez, and R. Qadeer,
Modern Trends in Contemporary Chemistry,
Scientific Information Division PINSTECH, Islamabad, Pakistan, pp. 123-131, 1993).
Chiarizia et al. (R. Chiarizia, E. P. Horwitz, and K. M. Hodgson,
An Application of Supported Liquid Membranes for Removal of Inorganic Contaminants from Groundwater,
DOE Report No. DE92006971, 1991) have reviewed and summarized the results of an investigation on the use of SLMs for the removal of uranium and some inorganic contaminants, including technetium, from the Hanford site groundwater. Chiarizia (R. Chiarizia, “Application of Supported liquid Membranes for Removal of Nitrate, Technetium (VII) and Chromium (VI) from Groundwater”,
J. Membrane Sci.,
55, 39-64 (1991)) has described the separation of technetium (VII) and uranium (VI) from synthetic Hanford site groundwater using SLMs. Dozol et al. (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)) have studied the stability of flat sheet SLMs in the transport of radionuclides.
Recently, 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.
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 radionuclides from aqueous feed solutions has also been long pursued in the scientific and industrial community. The ELMs for the removal of radionuclides, including strontium, cesium, technetium, and uranium, have been described in detail (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 Techniq
Commodore Separation Technologies Inc.
Kilpatrick & Stockton LLP
Mai Ngoclan
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