A liquid membrane system consists of an aqueous feed containing metal ions, and a stripping solution. The liquid membrane is between the feed and stripping phases, and contains an organic carrier which reacts with the metal ions. The hollow fiber module contains many hollow fibers aligned horizontally, with the liquid membrane embedded inside them. The organic phase fills the pores of the fibers b
y capillary force. (Please see the pictures inside.) Generally, liquid membranes come either in an emulsion or a supported form. An emulsion liquid membrane (ELM) has a large transport area with a thin membrane; hence, there is a fast solute extraction. Several previous studies have investigated metal by ELM. However, ELM is unsuitable for widespread commercial application, and suffers from swelling instability of the inner phase. According to the supported liquid menrame(SLM), there are several types, including flat sheet(FSSLM), spiral(SPSLM), and hollow fiber(HFSLM). For these types, the organic phase or liquid membrane is embedded in the pores of the supporting material by capillary forces.Of all the aforementioned above, a hollow fiber supported liquid membrane(HFSLM) seem to be the most promising. It possesses several advantages over the traditional solvent extraction method, such as simultaneous one-step extraction and stripping, high selectivity, low extractant (carrier) and energy consumption, low capital and operating cost, large surface area to volume ratio, high mass transfer rate, resistance to flooding, and easy scale-up. For these reasons, HFSLM has been widely investigated for application in various fields: for instance, water treatment, and recovery of precious metals, rare earth metals, radioactive metals and biochemical substance.
