Binding of divalent metal cations by sugar-beet pulp

The binding of divalent metal cations (Ca2+, Cd2+, Cu2+, Ni2+, Pb2+ and Zn2+) by sugar-beet pulp was studied. In the presence of 0.1 M NaNO3 the level of metal cation uptake was found to reach its maximum value very rapidly with the speed increasing both with the sugar-beet pulp concentration and with increasing initial pH of the suspension. Using a pH-metric method and by comparing binding isotherms drawn by measuring the free cation concentration after equilibration, a clear scale of decreasing selectivity was found as follows: Cu2+ similar to Pb2+ much greater than Cd2+ similar to Zn2+ > Ni2+ > Ca2+. Binding followed the Langmuir-type isotherm except for Ca2+ Adsorption may contribute to the binding phenomenon in addition to ion exchange, which may include electrostatic interactions and even chelation in the case of the more strongly bound cations. Sugar-beet pulp, which is cheap and highly selective, therefore seems to be a promising substrate to entrap heavy metals in aqueous solutions. Copyright (C) 1997 Elsevier Science Ltd. All rights reserved.