The simultaneous removal of cationic and anionic radiotoxic nuclides such as Cs-137 and I-129 from radioactive liquid wastes has been studied. As an adsorbent material, the mixture of activated carbon and chabazite zeolite was used. The mixing ratio of 7:3 of activated carbon to chabazite in weight fraction was found to be optimum under the most conservative condition for the Cs+ and I- concentration ratio. Experimental data and surface analysis indicated that Cs+ adsorbed onto the activated carbon surface caused a synergistic effect on the adsorption of I-. The effect of background electrolytes, namely Na+ and Cl-, on the Cs+ isotherm was minute over the whole range of equilibrium concentrations, whereas that on the I- isotherm was greater at lower equilibrium concentrations. A dynamic model was proposed, based on surface diffusion and competitive adsorption. The breakthrough behaviors of Cs+ and I- in the column, charged with the mixed adsorbent, were predicted satisfactorily by the proposed dynamic model. (C) 1997 Elsevier Science B.V.