The solvent extraction of zinc chloride with di-n-pentyl pentaphosphonate

Abstract

The extraction of divalent zinc from aqueous solutions containing sodium chloride using di-n-pentyl pentaphosphonate [C 5H 11PO(OC 5H 11) 2] in kerosene has been investigated. Equilibrium data were in good agreement with equations of the form x/ y = a + bx, where coefficients a and b have been mathematically demonstrated to have a physicochemical meaning: a is the reciprocal of the distribution coefficient at infinite dilution and b is the reciprocal of the maximum loading capacity of the organic solution. By adjusting the extraction isotherms to such a type of equation by the least-squares method, the effects of chloride concentration in the aqueous phase and di-n-pentyl pentaphosphonate (DPPP) concentration in the organic phase were determined, showing that the extraction of divalent zinc from chloride solutions by DPPP proceeds according to the solvating reaction: Zn 2+(a) + 2Cl −(a) + 2 DPPP(o) ⇄ ZnCl 2· 2DPPP(o) where (a) and (o) represent aqueous and organic phases respectively. The extraction equilibrium constant of such a reaction was also determined, resulting in K EX = (30° C). Moreover, a mathematical model for the extraction reaction was established, allowing the calculation of equilibrium data as a function of the initial aqueous chloride concentration and organic DPPP concentration. Values of such data are given in comparison with experimental data and their perfect agreement demonstrates the validity of the theoretical model which will be used in a computer program for process flow-sheet simulation.