Modelling the sorption of metals from aqueous solutions on goethite fixed-beds

The research on separation methods of toxic metals from wastewater streams is continuous and intensive and, among them, sorption processes are conside red of particular importance, mainly due to their effectiveness. The sorpti on of chromate anions and zinc cations from dilute aqueous solutions using a packed-bed (column configuration) of synthesised granulated goethite was investigated in the present study. The examined parameters during this inve stigation were the following: (1) the initial pH value of metal-laden aqueo us solution (two representative values at acidic pH, 3.5 and 5.0, were test ed); (2) the quantity of sorbent in the column, corresponding to bed height ; and (3) the influence of ethylene diamine tetra acetic acid (EDTA) additi on, a common, strong chelating agent. The Bed Depth-Service Time model has been applied to the sorption results in order to model the column operation . The removal efficiency of Cr(VI) anions by the sorptive column was found to be higher than that of Zn(II) cations. The presence of EDTA caused a cer tain decrease of removal efficiency for the case of hexavalent chromium, du e to competition for the same sorption sites, while the removal of divalent zinc was increased, due to variation of cation speciation. (C) 2001 Elsevi er Science Ltd. All rights reserved.