Kinetics of solvent extraction of copper(II) by bis-(2, 4, 4-trimethylpentyl)phosphonic acid using the single drop technique

Abstract

The kinetics of the forward and backward extractions of copper(II) by the bis-(2,4,4-Trimethylpentyl) phosphonic acid process have been investigated using the single drop technique and flux (F)-method of data treatment. The (F)-equation for the forward extraction of Cu(II) from the sufate-acetato medium by bis-(2,4,4-trimethylpentyl) phosphinic acid can be represented by: Ff (kmol m-2 s-1) = 10-8.64 [CU2+](ini) [H+](int)-1 [H2A2](o)0.5 [HSO4-]1. Analysis of this equation gives, Ff (kmol m-2 s-1) = 10-4.88 [CuHSO4+] [A-]. An activation energy of ca. 13.7 kJ mol-1 indicates that the diffusions of CuHSO4+ and A- to the aqueous film of the interface (and not the chemical reaction between these two species to form CuHSO4.A) are rate controlling. The (F)-equation for the backward extraction of Cu(II) from the [CuHSO4A.HA] complex in the organic phase by an aqueous sulfate-acetato solution can be expressed as: Fb (kmol m-2 s-1) = 10-5.68 [CuHSO4A.HA](o) (1 + 103.67 [H+]-1)-1 [H2A2](0)-0.5 [SO42-]-1. Analysis of this equation results in two equations, Fb (kmol m-2 s-1) = 10-9.797 [CuHSO4A.HA](0) [A-]-1 [HSO4-]-1 and Fb (kmol m-2 s-1) = 10-8.127 [CuHSO4A.HA](o) [A-]-1 [SO42-]-1 at higher and lower aqueous acidities, respectively. Low activation energies (< 20 kJ mol-1) indicate that the stripping processes are diffusion controlling at both regions of H+ concentration. The value of Kex(rate) (kf/kb = 10-2.967) matches well with the Kex(eq) (10-3.19) value within the experimental limitations. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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Chemical Engineering and Technology

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