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

Abstract

The rate of extraction of V(IV) from aqueous sulphuric acid solutions (0.5 mol dm −3 sulphate and 0.25 mol dm −3 acetate buffer) with HDEHP [HDEHP  H 2A 2  bis-(2-ethyl hexyl) phosphoric acid] in benzene and the back extraction of V(IV) from V(IV)-DEHP chelate in the benzene phase to aqueous sulphoric acid phase (0.5 mol dm −3 sulphate and 0.25 mol dm −3 sulphate and 0.25 mol dm −3 acetate) have been studied under various conditions. The rate expression for forward extraction can be written at (30 ± 1)°C as: − dC V A dt = −2.484 [H 2A 2] ( o) 0.5[H +] −1 (1 + 2.09 [Ac −]) (1 + 1.175 [SO 4 2−]) − (1 + 1.44 [NO 3 −]), and the backward extraction rate expression can be written as: − dC V O dt = 10 −0.6387 ( C V O ) [H 2A 2] ( o) −0.5 [H +] (1 + [NO 3 −]) −1 (1 + 0.5 [Ac −]) −1. In absence of the sulphate, acetate and nitrate ions, the formation of the 1:1 complex (VO 2+ + A − → VOA +) is the rate determining step in the forward extraction, whereas, the liberation of a DEHP − (A −) anion from the monomeric complex (VOA 2 → VOA + + A −) is the rate determining step in the backward extraction. The rate data is comparable with the equilibrium data.