Amberlite LA-2 (a secondary amine) was studied for its ability to extract propionic acid at different amine concentrations. The extraction of propionic acid by Amberlite LA-2 dissolved in seven single solvents (cyclohexane, 2-octanone, toluene, methyl isobutyl ketone, isooctane, haxane and 1-octanol) was investigated under various amine concentrations at 298.15 K. Using Bizek's approach, two acids: amine complexes, (HO):(R2N) and (HO):(R2N)(2), are assumed to exist in the organic phase in case of proton-donating diluents, while the complexes (HO):(R2N) and (HO)(2):(R2N)(3) are suggested in the case of non-proton-donating diluents. Important data for design of separation units have been obtained as a result of batch experiments. These data are distribution coefficients (D), loading factors (Z), extraction efficiency (E) and overall extraction constants (K-11, K-12, K-23). The maximum removal of glycolic acid is 94.68% with MIBK and 0.93 mol L-1 initial concentration of Amberlite LA-2. (C) 2009 Elsevier B.V. All rights reserved.