The dynamic interfacial tension for binary mixtures of hydrophobic metal ion extractants and a modifier were measured by using the drop volume technique. Four types of equimolar mixtures were considered: two chelating extractants: 2-hydroxy-5-nonylacetophenone oxime (HNAF) and beta-diketone (1-phenyldecan- 1,3-dion), two solvating extractants: trioctylphosphine oxide (TOPO) and tributyl phosphate (TBP), chelating and solvating extractants TOPO and beta-diketone, and the chelating extractant HNAF and the modifier (decanol). With the aid of the Ward and Torday equation the values of the diffusion coefficients of individual compounds and their equimolar mixtures were estimated. It was found that in the case of two types of investigated mixtures, i.e., HNAF + beta-diketone and HNAF + decanol the compound HNAF that was dominant in the mixed adsorbed monolayer and the more interfacially active also determined the kinetics of adsorption in mixed systems. In contrary to the mixture of two chelating reagents, in the case of a mixture of two solvating extractants the mixed system behaves like the less active, though dominant at the interface, reagent TBP. The same effect was observed in both of the considered diluents (toluene and octane). (c) 2005 Elsevier Inc. All rights reserved.