J. Chem. Eng. Data 1986, 31, 4-11
4
EquSlbria In the System Coba)t/Di-2-ethylhexylphosphoric Acid/ Wa ter Mlchael A. Hughes' Schools of Chemical Engineering, University of Bradford, Bradford, West Yorkshire, BD7 IDP, England
Hou Sungshou
General Research Institute of Non-Ferrous, Ministry of Metallurgical Zndustry, Peking, China
The dicitrlbution of cobalt between varlous concentratlons of dE2-ethylhexylphosphorlc acld (DEHPA) and an aqueous phase has been studled. The concentratlons of DEHPA (= H.R.) range from 5 to 20% v/v. The temperature was 25 f 1 OC. A thermodynamic analysis of the equlltbrla Is reported. The average log K value Is -3.96 f 0.13. Actlvlty coeffklents are reported, and an Y ~ ~ Improved method for the calculation of Y ~ , ~ , ~In/ the organlc phase Is given.
I ntroductlon Since 1970 the methods of calculation of the activity coefficients of the aqueous electrolytes in high ionic strength medii involving the mul&o"nt system have been much improved due to the work done by Pltzer (7-7). The application of thermodynamics to equilibria in practical hydrometallurgical operations involving the aqueous phase is now possible. For the modelling of a practical liquid-liquid extraction equilibrium where a metal is distributed between an aqueous and organic phase it is also necessary to know the a c t i i of species in the organic phase: such data are generally not available Only a few papers on the thermodynamic modelling of the equilibrium distribution of metals with DEHPA have been published. ~ a e et s ai. ( 6 )reported on the extraction of uoZ2+ from the acidic perchlorate solutlon to n-hexane containing DEHPA. Information concerning the activity coefficients of the extractant was given. Brisk (7) studied the distribution of metals (Me2+ = Co2+, Ni2+, Cu2+)bewteen aqueous sulfate solution and a kerosene solution of DEHPA. The method of calculation of activity coefficients of the metals in the aqueous phase was based on the Guntelberg's modified Debye-Huckel equation. Therefore only the total ionic strength of the aqueous phase was considered in the calculation. The slope of the plot of (pH log a,z+(,,,) against the log D was found to be
