Chemical Engineering Journal 88 (2002) 37–44 Separation of zirconium and hafnium using hollow fibers Part I. Supported liquid membranes X.J. Yang a,b,∗ , A.G. Fane a , C. Pin b a UNESCO Center for Membrane Science and Technology, School of Chemical Engineering, The University of New South Wales, Sydney 2052, NSW, Australia b UMR 6524-CNRS, Université Blaise Pascal, 5 rue Kessler, 63038 Clermont-Ferrand, France Received 16 November 1999; received in revised form 29 August 2001; accepted 5 October 2001 Abstract A supported liquid membrane system using hollow fiber membranes as supports (HFSLM) has been studied for the separation of zirconium and hafnium, which are typical metal pairs with extreme similarity in chemistry. Tri-n-octylamine (TNOA) and trioctylmethyl ammonium chloride (Aliquat 336) were used as carriers. The effect on the transport and separation of Zr and Hf of HCl concentrations in the feed and stripping solutions, hollow fiber length, flow rate of aqueous phases was investigated. The mechanism of transport through the HFSLM is discussed. The controlling step for the liquid membrane process was the diffusion in the membrane, except at low flow rates. The HFSLM acquires a maximum Zr/Hf flux ratio of about 160, which is 20 times than that of a flat-sheet system reported previously. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Zirconium; Hafnium; Hollow fiber-supported liquid membrane; Transport; Separation 1. Introduction Zirconium (Zr) and hafnium (Hf) are two of the most important nuclear materials; the use of Zircaloy in the con- struction of fuel elements and other structural components in reactor cores meets many physical and technological re- quirements. One advantage of Zr in nuclear applications is its low thermal neutron capture cross-section (0.18 b/a), whereas Hf has 640 times higher neutron absorption. There- fore, the amount of Hf present in Zr has a direct effect on the efficiency of the reactor core and thus on the cost of pro- ducing nuclear power. Moreover, the total amount of Hf in the reactor core affects the reactor shutdown margin, a major safety concern. In other technical applications in geochem- istry and cosmochemistry, the precise measurement of the Hf isotopic ratio ( 176 Hf/ 177 Hf) is an important chronometering tool which requires pure Hf separated from the associated Zr. The chemical similarity of Zr and Hf, both in their metal- lic and compound states, is greater than that between any other homologous elements in the periodic table (the atomic and ionic radii of Zr and Hf are virtually identical; atomic radius: Zr = 1.45 Å, Hf = 1.44 Å; ionic radius: Zr 4+ = 0.74 Å, Hf 4+ = 0.75 Å) [1]. In recent years, the problem of ∗ Corresponding author. Present address: NSW Environment Protection Authority, P.O. Box 29, Lidcombe 1825, Australia. Fax: +61-2-9646-2755. E-mail address: yangj@epa.nsw.gov.au (X.J. Yang). Zr/Hf separation has acquired significant importance. The separation of Zr and Hf can be achieved in solvent extraction technology in multi-stages of two separate steps (extraction and stripping) using tri-n-butylphosphate (TBP) as extrac- tant [2,3]. These two processes can be combined in a single step by the use of a liquid membrane (LM), which poten- tially offers high selectivity in a single operation. However, the use of LMs for the difficult Zr and Hf separation has been very limited. Supported liquid membrane (SLM) using microporous membranes eliminates the major disadvantages of solvent extraction such as emulsification, flooding and loading limits, phase disengagement and large solvent in- ventory. Chaudry and Malik investigated transport of Zr(IV) [4] and Hf(IV) [5] through SLMs consisting of flat-sheet polypropylene microporous membranes impregnated with TBP–xylene. The maximum fluxes of 12.9 × 10 -6 mol/m 2 s (Zr) and 2 × 10 -6 mol/m 2 s (Hf) were found and a Zr/Hf flux ratio of about 8 was obtained at the optimized condi- tions of TBP concentration <2.93 M, HNO 3 concentration 5–6 M and temperature 10 ◦ C [5]. If a practical Zr/Hf process based on SLMs is to be developed, it is likely to use hollow fiber membranes as substrates. The hollow fiber-supported liquid membrane (HFSLM) is characterized by high sur- face/volume ratio and low organic extractant inventory and there has been no report on this approach for Zr/Hf sepa- ration. Liquid anionic exchangers such as tri-n-octylamine (TNOA) and tri-n-octyl-monomethyl ammonium chloride 1385-8947/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S1385-8947(01)00256-X