Concentration of europium(III) with supported liquid membrane containing a xylene solution of di-2-ethyihexyl phosphoric
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I.
INTRODUCTION
THE practical
application of solvent extraction to metal separation and concentration for the recycling of industrial metal resources and wastewater treating processes has been increasing at a rapid rate. One of the most important problems inherent in such processes is the large inventory of expensive extractants and solvents ,due to the very dilute metal solutions that result from the dissolution process. An alternative separation and concentration method which can potentially alleviate this problem is the use of liquid membrane technique. Liquid membranes containing extractants that complex with the metal ion and act as a mobile carrier can pump a specific metal from a region of low concentration into a region of high concentration. There are two types of liquid membrane: liquid surfactant membrane and supported liquid membrane. Liquid membrane processes of both types have been reported to be the promising recovery processes for metals from solutions, particularly dilute solutions. ~ In the practical application of supported liquid membranes for the recovery of metals, the use of hollow fiber membranes has been recommended because of their large membrane area per unit volume.: The elucidation of the mass-transfer mechanism for permeation through the liquid membrane is of practical importance in the selective separation and concentration of metal using a liquid membrane process, Most of the studies which have been carried out relate to the extraction of copper 3-H and uranium.~'.2-.4 There has been no report on the application of the liquid membrane technique to the extraction of rare earth metals. In this work, the separation and concentration of europium using a supported liquid membrane impregnated with di-2-ethylhexyl phosphoric acid (HDEHP) as a mobile carrier has been studied to clarify the permeation mechanism. TADAAKI NISHIKI, formerly Postdoctoral Fellow, Ames Laboratory, USDOE, is now Lecturer, Department of Chemical Engineering, University of Osaka Prefecture, Mozu-Umemachi, Sakai, Osaka, Japan. RENATO G. BAUTISTA is Group Leader, Ames Laboratory, USDOE, and Professor, Department of Chemical Engineering, Iowa State University, Ames, IA 50011. Manuscript submitted June 14, 1982.
METALLURGICALTRANSACTIONS B
The experiments were carried out to investigate the effects of a number of factors such as the concentration of europium in the aqueous solution and that of HDEHP in the membrane solution on the permeation rates of europium. The experimental results are then compared with a transport model for concentrating europium across the liquid membrane.
H.
THEORY
A. Model f o r Concentration of Europium
A liquid membrane containing HDEHP as a mobile carrier is shown in Figure 1. Europium ion in the feed solution contained in the left cell diffuses toward the interface (x = 0), where complex formation between europium ion (M 3+) and HDEHP (HX) occurs. HDEHP exists as the dimer (HX)2 in xylene.~5 The type of extractable complex species has been determined from the equilibrium distribution
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