Chemical equilibrium studies on the copper-sulfuric acid-kelex 100-xylene system
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INTRODUCTION
SOLVENT extraction processes are becoming more attractive in hydrometallurgical processing of ores because o f potentially low energy costs and minimization o f air pollutants. Typically, selective extraction of metal ions from multiple metal aqueous acidic 1,2 or ammoniacal3'4 leach solutions is required in order to obtain high purity solutions suitable for electrowining techniques. In these selective extraction processes, the interplay o f the chemical equilibria between the two phases and the kinetics o f interphase reactions determine the selectivity o f a given metal ion. It is shown by Fleming,1 that in the extraction Cu (II) and Fe (III) from acidic solutions by Kelex 100 (a highly branched/3-alkenyl-8-hydroxyquinoline) in xylene, the extraction kinetics o f copper are more rapid than those o f iron. However, the chemical equilibria favor the iron complex. To propose optimal design of such systems it is valuable to have a fundamental understanding o f the chemical equilibria and the mass transfer-chemical reaction steps. In regard to the chemical equilibria o f the copper system, fundamental studies are reported.5-8 Spink and Okuhara5 investigated the extraction o f copper into Kelex 100/120 as well as LIX63/65N/64N (an oxime-based acid chelating reagent), They compared the equilibrium data and concluded that the Kelexsystem effectively extracts copper at a l o w e r pH than LIX. Furthermore, the rate o f extraction with Kelexis considerably faster than with the LIX system. Flett et al6 studied the extraction o f copper by an alkylated 8-hydroxyquinoline in toluene. The results o f their equilibrium studies indicate that the slopes of the log D vs pH plots are anomalously low. They claimed that the low slopes are due to the changes o f the ionic strength and the activity coefficient associated with the bisulfate-sulfate equilibrium, the bisulfate-sulfate itself, and other ionic interactions. The equilibrium model these workers proposed is quite simplified. The metal distribution coefficient (D) is defined as [Cu]~/[Cu ++] instead o f [CU]or/[CU]Ar, and activity coefficients are not considered. Further, the aqueous phase equiC.K. LEE and L.L. TAVLARIDES are both with the Department of Chemical Engineering and Materials Science, Syracuse University, Syracuse, NY 13210. Manuscript submittedFebruary 8 , 1982. METALLURGICAL
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libria are not accounted for to estimate the correct copper ion concentration for use in their model. Bauer and Chapman8 investigated the equilibria o f the copper-sulfuric acidxylene-/3-alkenyl 8-hydroxyquinoline system. They used a statistical modeling procedure to correlate experimental data for the extraction o f copper from acid sulfate solution by Kelex 100 in xylene. In the model developed they assume that formation o f bisulfate and copper sulfate ion pairs should be nearly complete. Accordingly, they suggest that the ionic strength be calculated on the basis o f H÷ and HSO~as the predominant ions. Recently, Hoh and Bautista7 developed a chemically-based
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