An evaluation of single resistance transfer models in the sorption of metal ions by peat

The adsorption of Pb²⁺, Cd²⁺, Cu²⁺, Zn²⁺ and Al³⁺ onto peat has been studied using a system of standardised batch adsorbers under equilibrium and transient rate conditions. Models based on the assumption of a single external mass transfer resistance to adsorption have been developed to attempt to predict the concentration decay curves obtained experimentally, for several variable system parameters, under transient batch conditions. In this instance the single resistance is taken as that of film diffusion of the sorbate through the liquid film surrounding the sorbent particle. Two methods of determining the external mass transfer coefficient have been used, one based on the Weber model and the other on the Furusawa‐Smith model. Equilibrium data have been analysed and shown to conform to a linear Langmuir plot. The decay curves predicted by the models represented the experimental data very well, particularly at high sorbent masses. Under these conditions film diffusion appears to be the rate controlling step in the adsorption of metal ions by the peat. At low sorbent loadings, however, the influence of internal mass transfer is evident.