Multicomponent biosorption in fixed beds

The biosorption of Cu, Zn, Cd and Fe from multicomponent mixtures was studied in a flow-through column packed with Sargassum algal biosorbent in the Ca-form. The effects of competitive ion exchange such as the elution order of toxic metals from the column, and the concentration overshoots in column effluent were investigated both experimentally and by means of an ion exchange equilibrium column model (ECM). The ECM predicted, and the experiments confirmed, that from the feed containing Cu2+, Zn2+ and Cd2+, zinc broke through the column first, followed by cadmium and copper. When the binary mixtures containing 30 mg/l of Cu2+ and 4 mg/l of either Cd2+ or Zn2+ were passed through the column, the concentrations of Zn and Cd ions in the column effluent overshot the 4 mg/l feed concentration. The time interval between the overshoot of Zn and the breakthrough point of Cu was Significantly longer than that between the overshoot of Cd and the breakthrough point of Cu. However, Zn did not overshoot when the feed contained 50 mg/l of Cd and 4 mg/l of Zn. The ECM successfully predicted both the occurrence and the magnitude of the overshoots. The service time of a column treating multimetal mixtures was successfully predicted by combining the ECM with a mass transfer column model (MTCM). (C) 2000 Elsevier Science Ltd. All rights reserved.