Kinetics and Mechanism of the Interfacial Mass Transfer of Eu(III) in the System: Bis(2-ethylhexyl)phosphoric Acid,n-Dodecane-NaCl,Lactic Acid,Polyaminocarboxylic Acid,Water

Abstract

The rate laws which characterize the interfacial mass transfer of Eu³⁺ between aqueous phases containing a mixture of lactic acid and a polyaminocarboxylic acid (DTPA or HEDTA) and organic phases containing HDEHP in n-dodecane have been experimentally determined. The data demonstrate that in a wide range of stirring conditions the mass transfer process is entirely controlled by the rate of interfacial chemical reactions. A reaction mechanism where the four aqueous species, Eu³⁺, Eu—lactate, Eu—polyaminocarboxylate, and the mixed complex Eu—lactate—polyaminocarboxylate, are simultaneously reacting with the interfacially adsorbed HDEHP molecules has been worked out. This mechanism fully agrees with the experimental kinetic data. The rate constants which characterize most of the rate-determining steps have been calculated. Some practical implications of the faster mass transfer kinetics obtained with HEDTA are briefly discussed in relation to tervalent actinide-lanthanide group separations.