Solvent extraction coupled transport

Solvent extraction Podbielniak extraction Membrane solvent extraction Coupled transport Minimum emulsification and associated entrainment loss Enhanced selectivity and concentration... 

Carrier facilitated transport processes often achieve spectacular separations between closely related species because of the selectivity of the carriers. However, no coupled transport process has advanced to the commercial stage despite a steady stream of papers in the academic literature. The instability of the membranes is a major technical hurdle, but another issue has been the marginal improvements in economics offered by coupled transport processes over conventional technology such as solvent extraction or ion exchange. Major breakthroughs in performance are required to make coupled transport technology commercially competitive. 

We report on a number of on-line chemical procedures which were developed for the study of short-lived fission products and products from heavy-ion interactions. These techniques combine gas-jet recoil-transport systems with I) multistage solvent extraction methods using high-speed centrifuges for rapid phase separation and II) thermochromatographic columns. The formation of volatile species between recoil atoms and reactive gases is another alternative. We have also coupled a gas-jet transport system to a mass separator equipped with a hollow cathode- or a high temperature ion source. Typical applications of these methods for studies of short-lived nuclides are described. 

Reverse osmosis also serves some of the waste management and resource recovery needs in the metals and metal finishing industry. Effluent streams from mining and plating operations containing heavy metals, acids, and other chemicals can be treated with reverse osmosis to recover both the metal as its salt, and purified water for reuse. For metal ion recovery from dilute solutions, however, reverse osmosis faces competition from conventional solvent extraction, membrane-based solvent extraction, and its variant, coupled transport (see Section V.F.3). 

The basic parameters of a facilitated, coupled transport are related to properties of the solute, carrier, and its solvent and membrane supports. These are individual and overall mass-transfer coefficients (in diffusional and chemical reactions kinetics regime), distribution constants, extraction, and couphng coefficients of forward extraction, Kq, and Kf p, respectively, and... 

In facilitated transport, unlike solvent extraction and other equihbrium stage wise processes, the overall mass transfer rate is not governed by the usual equihbrium considerations alone. Instead, the solute transport process is controlled by a combination of the diffusion rate and the complexation reaction rate and in case of coupled transport the solute can be transported against its concentration gradient thus opening up the possibilities of separation from even very dilute solute solutions. 

Baker R, Blume I. Coupled transport membranes. In Porter MC, ed. Handbook of Industrial Membrane Technology. Noyes Pubhcations, Park Ridge, NJ, 1990 511-558. Lo TH, Baird MHI, Hanson C. (Eds.). Handbook of Solvent Extraction. John WUey Sons, New York, NY, 1983. 

Complexing agents used in coupled transport membranes are usually diluted with a carrier solvent, typically a mixed aliphatic-aromatic hydrocarbon. We would generally expect the amount of metal extracted by the complexing agent solution to increase with increasing agent concentration, and this is usually the... 

Babcock, W.C., Baker, R.W., Kelly, D.J. LaChapelle, E.D. (1980c) Coupled transport membranes for uranium recovery. In International Solvent Extraction Conference, ISEC-80, 6012 September 1980, Liege, Belgium, pp. 80-90. 

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