Comparison of Liquid Membrane Processes for Metal Separations:  Permeability, Stability, and Selectivity

Abstract

A comparison of bulk, supported, and contained liquid membranes (BLM, SLM, and CLM) for metal separations with respect to permeability, stability, and selectivity is presented. The overall mass-transfer coefficient of magnitude order of 10-6 and 10-7 m s-1 was typically found for SLM/BLM and CLM, respectively. The SLM has the highest organic utilizing efficiency and the poorest membrane stability. Osmotic pressure across the membrane proves to be one of the major causes of SLM instability, and membrane pore elongation due to morphology changes reduces the SLM lifetime. The separation efficiency of liquid membranes can be enhanced by minimizing the organic inventory and maximizing the contact area between the aqueous phase and the organic membrane phase. However, this needs to be balanced against the improvement in stability of various liquid membrane configurations, which can be achieved by employing a significant organic inventory. The selectivity of liquid membranes mainly depends on the extractant used in the membrane phase and is similar to that of one-stage solvent extraction. The paper concludes with a technical comparison of the various liquid-membrane techniques.

Transport of Phenol Through Inclusion Polymer Membrane (Pim) Using Copoly(eugenol-Dvb) as Membrane Carriers

“…LM processes combine extraction and stripping into one single stage and thus non-equilibrium mass transfer characteristic where the separation is not limited by the equilibrium conditions [4]. The various configurations of LM include emulsion liquid membrane (ELM), bulk liquid membrane (BLM), contained liquid membrane (CLM), supported liquid membrane (SLM), electrostatic pseudo liquid membrane (ESPLIM) and polymer inclusion membrane (PIM) [2,5].…”

“…There are many reports on PIM as a modification of the SLM, due to the instability of the SLM for the compound carrier leakage [4,[6][7][8][9]. PIM is made from a solution containing a carrier compound, plasticizer and polyvinyl chloride (PVC) as a matrix polymer that forms a thin, stable and flexible film.…”

“…Finally, at the membrane/receiving solution interface, the complex dissociates and the target solute is released into the receiving solution, which is essentially the reverse of the process occurring at the source solution/membrane interface [5] PIM is usually evaluated using flux stability parameter [5]. Kim et al [13] and Levitskaia [14] using the calyx [6]arene and calyx [4]arene as carrier membrane to study the flux and lifetime. A variety of polymer membranes as the carrier has also been used in several studies with various methods of liquid membrane [15][16][17].…”

Extraction of phenol from aqueous effluent using triglycerides in supported liquid membrane

“…It may be explained based on the fact that the phenol can be transported through the membrane, when it is present in molecular or undissociated state in aqueous solution. Since the pK a value of phenol is 10, the phenol will be present in undissociated form for the pH values less than 10 [29,61,66]. The extent of dissociation was found to be the least when pH of the feed was maintained at 4.0, which resulted in the highest membrane mass transfer coefficient (3.50 Â 10 À6 m/s).…”

“…It was reported that the PTFE membranes are much more robust and have significant extended durability [61]. Three types of hydrophobic membranes (PTFE membrane pore size 0.45 mm and PP (polypropylene) membrane pore sizes 0.22 and 0.45 mm) were impregnated with coconut oil and subsequently used for phenol extraction.…”