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Although the basic mass transfer of dissolved substances in water to a solid phase is often considered as a simple, partitioning process, in reality, several processes may indeed be taking place. Weber (1972) describes three consecutive steps in the adsorption of materials from solution by porous adsorbents. These include film diffusion, pore diffusion, and adsorption on the interior surface of the pore. A simple partitioning model does not account for these rate limiting processes: it is essentially an instantaneous transfer occurring upon the molecular contact with the solid. Hence, an equilibrium expression is used to describe this process. The simple partitioning model often breaks down when the question of desorption is raised. The equilibrium expression defining a partition coefficient or a distribution coefficient is predicated upon the assumption that the adsorption and desorption processes are essentially forward and reverse or completely reversible reactions. Many investigators including DiToro and Horzempa 1982) have shown this to not be the case. Debate as to whether adsorption/desorption is hysteretic or irreversible has occurred. It has even been suggested that the processes are indeed reversible but the experiments are flawed. What remains constant is that the elementary, reversible partitioning model is limited. Some investigators (Wang, et al. 1993) have proposed that sorption is a combination of two processes, adsorption and partitioning.The study described in this paper focuses on an aspect of the two process sorption mechanism model, namely experimentation to dilineate the two processes. It is hypothesized that the primary, or partitioning, process is very fast, described as an essentially equilibrium process. The secondary, or adsorption, process is slower and, thus, rate limiting. Long term batch adsorption experiments should show as rapid uptake by

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