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 c arried out to study the effects of initial cadmium ion concentration and bo ne char mass on the sorption rate. The experimental contact data were analy sed using the Elovich model, previously used to describe the kinetics of ga s adsorption on solids, and the Ritchie model, a modified second-order kine tics equation. Initial analysis of the data, using the Ritchie model, was p oor and therefore a modification was incorporated to make the Ritchie model predictions correlate the experimental data more accurately. Both the Elov ich 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 E lovich equation. (C) 2000 Society of Chemical Industry.