A general algorithm, named KINEQL, which may be applied to calculate the rate of adsorption of metal ions from aqueous solutions by hydrous oxides, was developed. The adsorption process is analyzed in terms of three separate but interacting phenomena : surface ionization, complex formation, and the presence of an electrostatic double layer adjacent to adsorbent surfaces. In this article, the first part of KINEQL, which calculates metal ion adsorption rates under the condition that rates are controlled by adsorption reactions, is described. Adsorption histories for cases with rapid as well as slow adsorption rates are calculated. In the case of rapid adsorption rates, adsorption mechanisms and rate constants obtained from the results of relaxation kinetic methods are used to calculate adsorption histories. Similar mechanisms are used in the case of slow adsorption rates, and the rate constants of the proposed mechanisms are obtained by matching model calculations with experimental results.