J. Chin. Inst. Chem. Engrs., Vol. 36, No. 5, 1-7, 2005 Selective Separation of Trivalent and Tetravalent Lanthanide from Mixture by Hollow Fiber Supported Liquid Membrane Ramakul Prakorn, Pattaweekongka Weerawat, Pancharoen Ura [1] Department of Chemical Engineering, Faculty of Engineering, Chulalongkorn University Bangkok, Thailand Hronec Milan Department of Organic Technology, Faculty of Chemical Technology University of Technology, Bratislava, Slovak Republic Abstract ─ The separation of tetravalent and trivalent lanthanide ions, Cerium (IV) and Neodymiun (III), respectively, from a sulfate solution through a liquid membrane was examined. TOA was used as carrier extractants and dissolved in kerosene. The liquid membrane was supported by hollow fiber microporous. Sodium carbonate was used as stripping solution. Pure tetravalent lanthanide, Cerium (IV) ions were obtained while trivalent, Neodymium (III), ions could not be extracted and stripped due to the different in form of trivalent and tetravalent lanthanide ions in sulfate solution. The transport system was studied as a function of several variables: concentration of sulfuric acid feed solution, concentration of TOA in liquid membrane, concentration of sodium carbonate in stripping solution, and flow rate of feed and stripping solution. The results indicated that the percentage of extraction is highly dependent on the concentration of sulfuric acid the feed solution and the concentration is 0.2 M for the maximum extraction. Percentage of extraction was enhanced when the concentration of TOA was increased. However, when the concentration of TOA was higher than 4% (v/v) the percentage of extraction was not increased because of the viscosity of liquid membrane. The percentage of extraction and stripping further increased when the concentration of sodium carbonate was increased until the sodium carbonate concentration was 1.25 M. The maximum percentage of stripping for Cerium (IV) of 71% and 100% selectivity was obtained. When the flow rate of feed or solution was increased the percentage of both extraction and stripping decreased due to resident time. Key Words : Lanthanide, Rare earth, Liquid membrane, Extraction [1] To whom all correspondence should be addressed INTRODUCTION Lanthanide or rare earth metal can be found in a large part of monazite and basnasite ores (Cotton et al., 1988). It has recently drawn considerable attention in various applications exploiting its fluorescent magnetic substances, optical glass, fiber optics, cata- lytic, laser property colorants for TV screen and in ceramic industries. Lanthanide metal is composed of tetravalent and trivalent metals. However, these met- als tend to come in a mixture form. Therefore, there has been a great interest in trying to purify these ele- ments. The liquid membrane, the liquid contains an ex- tractant or a carrier which has the potential for selec- tive permeation by using the facilitated transport mechanism (Gherrou and Kerdjoudi, 2002) has been widely applied to the extraction and stripping of metal ions because it is a combination of the extrac- tion unit and stripping unit of liquid-liquid-extraction process to single operation. This technique has been widely applied to the extraction and stripping of metal ions. In general, liquid membranes come either in an emulsion or a supported form. Emulsion liquid membrane (ELM) has a large transport area with a thin membrane (Ching-Yet and Pai-Zon, 1993). Hence there is a fast solute extraction. Nonetheless the complicated demulsification process for recovery of the concentrated solute as well as of the mem- brane liquid makes the Emulsion Liquid Membrane process very difficult to commercialize. In addition, ELM suffers from swelling instability of the inner phase. Mean while as for supported liquid membrane is held in porous structure which is usually in porous membrane. The metal is extracted into a pore liquid at the feed solution-membrane interface. At the stripping solution-membrane interface, the metal is extracted back and concentrated in the stripping so-