A synergistic extraction system consisting of sec-octylphenoxy acetic acid (CAl2, H(2)A(2)) and primary amine N1923 (B) for gallium(III), indium(III), and zinc(II) has been developed from chloride medium. Synergistic and antagonistic effects are observed for the title metals at low and high CAl2 concentration ratios, respectively. On the basis of the distribution ratios, the values of the separation factors are calculated and used for the discussion of the selectivities between gallium(III)/indium(III) and zinc(II). The synergistic extraction of zinc(II) with the mixtures has been investigated with the methods of slope analysis and constant mole. The synergistic adduct has been determined together with the equilibrium constant and thermodynamic constants. (C) 2011 Elsevier B.V. All rights reserved.