Full Length Research Paper

Extraction of zinc (II) by triphenylphosphite (TPP) in hydrochloric acid: Kinetics and mechanism

Alafara A. Baba* and F. A. Adekola

Department of Chemistry, University of Ilorin, P. M. B. 1515, Ilorin – Nigeria.

*Corresponding author. E-mail: baalafara@yahoo.com, alafara@unilorin.edu.ng.  Tel: +2348035010302.

Accepted 23 April, 2008

   Abstract

The extraction of Zinc (II) in chloride medium with triphenyl phosphite (TPP) in kerosene has been investigated under different experimental conditions in order to have a better understanding of the extraction mechanism. The extraction yield was found to depend on the concentrations of Zinc (II) and TPP, and pH. The extraction yield can easily be predicted based on an established linear expression. The effect of salting-out agents: LiCl, NaCl and NH₄Cl were also studied and they ranked NaCl<NH₄Cl<LiCl in increasing order of the extraction yield. This study suggests that Zn (II) forms a binuclear complex with TPP, according to the equation: . On the other hand, the stripping study showed that 0.5M HCl was satisfactory for the stripping of about 79.42% of zinc from the organic phase in a single stage. Finally, the findings on the possible re-use of TPP in kerosene showed that the TPP continuously losses its extraction ability with successive re-use. This has been attributed to its gradual degradation or transformations, and decrease in the number of co-ordination sites available for the divalent metal ion.

Key words: Zinc (II) extraction, triphenylphosphite, mechanism.