A New Method to Describe Two-Phase Solvent Extraction Based on Net Transport Potential Derived as Linear Combinations of Forward and Reverse Constituents

Abstract

With the view to avoiding the difficulties encountered in estimating thermodynamic activities of the multiple chemical species in two-phase liquid system, a set of forward, reverse, net and total transport potentials are defined to represent the chemical state of a transferring solute during transient using bulk concentrations. The net transport potential corresponds to that in the conventional two-film model of diffusion-controlled processes.

The overall driving forces of mass transport are redefined as the derivatives of the relevant transport potentials differentiated with respect to a state variable newly defined in terms of the bulk concentrations of the solute contained in both phases. Net and total quantities, i. e. transport potentials, overall driving forces and the molar fluxes are obtained as linear combinations of those for forward and reverse directions.

The topical features presented by these quantities and their mutual relations are discussed in detail. The experimental new overall transport coefficient for U(VI) varied in accord with the changes in the theoretical net transport potential and overall driving force. The present method permits describing the extractive mass transport consistently both to forward and reverse directions of transport.

KEYWORDS:

• solvent extraction
• transport potential
• overall driving force
• linear combination
• chemical potential
• TBP
• nitric acid
• uranium ions
• rhenium ions