HFSLM

Much effort has been expended in attempting to use membranes for separations. Reverse osmosis membranes are used worldwide for water purification. These membranes are based on size selectivity depending on the pores used. They do not have the ability to selectively separate target species other than by size. Incorporation of carrier molecules into liquid membrane systems of various types has resulted in achievement of highly selective separations on a laboratory scale. Reviews of the extensive literature on the use of liquid membrane systems for carrier-mediated ion separations have been published [15-20]. A variety of liquid membranes has been studied including bulk (BLM), emulsion (ELM), thin sheet supported (TSSLM), hollow fiber supported (HFSLM), and two module hollow fiber supported (TMHFSLM) types. Of these liquid membranes, only the ELM and TMHFSLM types are likely to be commercialized. Inadequacies of the remaining... 

However, ELMs are quite difficult to prepare and after transport, the oil droplets have to be separated and broken up to recover the receiving phase. Compared to the ELM, the BLMs are easier to operate. The supported liquid membranes (SLM) are categorized into two types of supports, namely, a flat-sheet supported liquid membrane (FSSLM) or a hollow fiber supported liquid membrane (HFSLM). Here a polymeric filter with its pores filled with the organic phase acts as membrane. The three different types of liquid membranes have already been schematically represented in Chapter 29. A schematic representation of a hollow fiber semp is shown in Figure 31.2. 

Transport of Pu(lV) from 3 M HNO3 solutions across Ahquat-336/ Solvesso-100 by HFSLM was studied. Permeability of Pu(IV) through a bundle of hollow fibers made up with 20 lumens, of 67 cm surface area, 9 cm length, and operated at a flow rate of 10 m /s on recycle mode was examined. More than 80% Pu from oxalate bearing wastes generated during reconversion process could be transported through 10% Aliquat-336/Solvesso-100 into hydroxylamine hydrochloride strippant in about three runs [167]. 

Lanthanide-actinide separation was also attempted by HFSLM (operated in the nondispersive extraction mode) method using diphenyldithiophosphinic acid derivatives. Geist et al. have employed a synergistic mixture of bis(chlorophenyl)-dithiophosphinic acid and TOPO in a hollow fiber module for the lanthanide-actinide separation [168]. About 99.99% Am... 

FIGURE 31.11 SEM pictures of the hollow fiber lumens used in an HFSLM study involving radioactive solutions, (a) Prior to irradiation (b) after irradiation. (Reproduced from Rathore, N.S., Sonawane, J.V., Gupta, S.K., Pabby, A.K., Venugopalan, A.K., Changrani, R.D., and Dey, P.K., Sep. Sci. Tech., 39, 1295, 2004. With permission.)... 

The last example shows that it is also feasible to use SLMs to remove and recover efficiently radioactive metals from nuclear process effluent. By using a microporous hydrophobic polypropylene hoUow-fiber supported Hquid membrane (HFSLM) consisting of extractant, tri-w-butyl phosphate (TBP) as carrier diluted with w-dodecane, actinides such as uranium (U) and plutonium (Pu) were removed [188]. It was concluded after modeling and evaluation of the process conditions that it is possible to remove more than 99% of U(VI) and Pu(IV) from process effluent in the presence of fission products when stripping reagent 0.1 M hydroxylamine hydrochloride in... 

Usapein P, Lothongkum AW, Ramakul P, Pancharoen U. Efficient transport and selective extraction of Cr(VI) from waste pickling solution of the stainless steel-cold rolled plate process using Aliquat 336 via HFSLM. Korean J Chem Eng 2009 26 791-798. 

FI CD RE 31.3 Schematic representation of the (a) hollow-fiber module, (b) fiow pattern in HFSLM, and (c) the HFSLM transport assembly. 

A schematic representation of HFSLM system is shown in Figure 31.3. A detailed description of Equation 31.4 has been given in the mass transfer modeling section, later in this chapter. 

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