ANOMALOUS CADMIUM ADSORPTION IN FLOW INTERRUPTION EXPERIMENTS

Adsorption of cadmium (Cd) onto fine sand was investigated using batch (static) and steady flow (dynamic) experiments at pHs of 5.5, 6.0 and 6.5. For both types of experiment, adsorption of Cd onto sand was fou nd to increase with pH. In all experiments, greater adsorption of Cd w as found in flow experiments than in batch experiments. Flow interrupt ion was used to test whether nonequilibrium sorption occurred during t ransport of Cd. No concentration drop was observed immediately after t he resumption of flow. Instead, for all experiments, a consistent incr ease in effluent concentration was observed indicating that Cd was des orbed during the interruption period. This indicates the significance of velocity on adsorption/desorption of Cd onto the sand. The amount o f desorption was predicted by a transition from the dynamic to the sta tic sorption isotherm. (C) 1998 Elsevier Science B.V. All rights reser ved.