The characteristics of adsorption of gallium and indium were measured by using a column, in which microcapsules containing 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester were packed. Firstly, adsorption isotherms for gallium and indium in the microcapsules were measured and analyzed according to Freundlich adsorption isotherm model, from which the saturation capacities were obtained and the operation lines for both metals were determined. Then, breakthrough curves for 5 mol/m(3) gallium and/or indium solution were measured using the column packed with the microcapsules. The effects of flow rate and pH of the feed solution on the characteristics of metal adsorption were investigated. When the flow rate decreased, the adsorption capacity of gallium became smaller, but that of indium was not changed at all. By selecting the pH of the feed solution, the separation of gallium from indium was achieved. However, the separation of indium from gallium was not completely achieved. In stripping operation, it was possible to separate both metals adsorbed in the column by selecting the hydrogen-ion concentration of the stripping solution. The breakthrough curves in the 5th run did not differ so much from that in the 1st run, whereby the loss of the extractant in the microcapsules was only about 0.01%. The theoretical equation of the breakthrough curve was established. The experimental data for each system were correlated to the calculated lines based on the predictive equation. (C) 2002 Elsevier Science B.V. All rights reserved.