Kinetics of solvent extraction of metal ions with HDEHP—I Kinetics and mechanism of solvent extraction of Ti(IV) from acidic aqueous solutions with bis-(2-ethyl hexyl) phosphoric acid in benzene

Abstract

The rate of extraction of Ti(IV) from aqueous sulphuric acid solution into benzene with HDEHP [HDEHP = H 2 A 2 = bis-(2-ethyl hexyl)-phosphoric acid] and back extraction of the Ti(IV)-DEHP chelate from the benzene phase to an aqueous phase have been studied under various conditions. The distribution equilibria have also been investigated. The structure of the extracted species has been investigated by IR spectral data, molecular weight determination and phosphorous-titanium atom ratio determination. The extracted species has been shown to be [TiOA 2 ] 3 . From the extraction equilibrium studies, the reaction for the extraction of Ti(IV) has been proposed and the extraction equilibrium constant has been evaluated. The rate of forward extraction is proportional to [(TiO) +2 ] 3 , [H 2 A 2 ] (org) +3 and [H 2 SO 4 ] −3 , whereas the rate of backward extraction is proportional to [TiOA 2 ] (org) +1 , [H 2 A 2 ] (org) −1 and [H 2 SO 4 ] −1 . The rate determining step in the forward extraction involves the reaction of 3 atoms of titanium in a stable chain or ring with 3 molecules of HDEHP dimer molecules. The rate of backward extraction studies indicate that the rate determining step of the backward extraction involves the reaction of [TiOA 2 ] molecule with one molecule of H 2 SO 4 . The values of the equilibrium constants obtained from the equilibrium study and rate study are 10 (3.646±0.16) and 10 (10.604±0.194) respectively. The cause of this discrepancy has been explained.