Elovich equation and modified second-order equation for sorption of cadmium ions onto bone char

The removal of cadmium ions from water by sorption onto bone char has been studied. Bone char, traditionally used for colour removal in sugar refining, is produced by the carbonisation of animal bone. Batch experiments were carried out to study the effects of initial cadmium ion concentration and bone char mass on the sorption rate. The experimental contact data were analysed using the Elovich model, previously used to describe the kinetics of gas adsorption on solids, and the Ritchie model, a modified second‐order kinetics equation. Initial analysis of the data, using the Ritchie model, was poor and therefore a modification was incorporated to make the Ritchie model predictions correlate the experimental data more accurately. Both the Elovich and modified Ritchie equations accurately predict the sorption capacity of cadmium on bone char, however, the sorption kinetics, derived from the differential forms of the two equations, were correlated better using the Elovich equation. © 2000 Society of Chemical Industry