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 considered of particular importance, mainly due to their effectiveness. The sorption 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 investigation were the following: (1) the initial pH value of metal-laden aqueous solution (two representative values at acidic pH, 3.5 and 5.0, were tested); (2) the quantity of sorbent in the column, corresponding to bed height; and (3) the influence of ethylene diamine tetra acetic acid (EDTA) addition, 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 certain decrease of removal efficiency for the case of hexavalent chromium, due to competition for the same sorption sites, while the removal of divalent zinc was increased, due to variation of cation speciation.