The rate equations and isotherms for two adsorption models have been formulated and discussed. The rate equations obtained have been compared to those of pseudo-first-order model and pseudo-second-order model, respectively. Calculated results indicated that the rate equations of single site model and dual site model could be approximated by those of pseudo-first-order model and pseudo-second-order model, respectively, in a limited ranges of the values of C(A.Se)(*) (or C(A.S2e)(*)), K* and t*. The adsorption isotherm of single site model has been found to be the same as that of Langmuir type. (C) 2008 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.