Equilibrium of tartaric acid extraction from aqueous solutions with HOSTAREX A 324 (commercial tri-iso-octylamine) in iso-decanol/low aromatic kerosene mixtures, were studied as a function of acid, amine and iso-decanol concentrations at 25 degrees C. For interpretation of the equilibrium data the modified Langmuir isotherm was used. The values of the extraction equilibrium constants and the overall acid/amine ratios, assuring the best fit of the measured and calculated equilibrium acid concentrations, were determined. This simple model is a useful mathematical form for modelling including equilibrium parameters, as required in extraction equipment, and the model is valid for the aqueous phase acid concentration of less than 1 mol/l. The equilibrium data were also interpreted by a proposed mechanism of three reactions of complexation by which (1,1), (1,2) and (2,1) acid-amine complexes are formed. The optimum values of the corresponding equilibrium constants were determined. Kinetic measurements of the extraction pf tartaric acid from aqueous solutions with HOSTAREX A 324 in iso-decanol/low aromatic kerosene mixtures, were carried out in a highly agitated system (750 min(-1)) at 25 degrees C. The kinetic data were interpreted(1) by a formal elementary kinetic model, and (2) by using the proposed reaction mechanism. In both cases, very good fits between the experimental and calculated kinetic curves were obtained. Both of the kinetic models include equilibrium. The formal elementary kinetic model with the rate of the forward reaction being of the order of 0.7 with respect to the tartaric acid concentration in the aqueous phase and of 1.5 order with respect to the amine concentration, and the rate of the reverse reaction as first order with respect to the concentration of the acid-amine complex, could be suitable for the analysis and design of the process in dynamic conditions. The model based on the proposed mechanism is useful in elucidating the dependence of the participation of the individual complexes on the solvent phase composition as well as on the initial concentration of the acid in the aqueous phase.