EFFECT OF IONIC STRENGTH AND MEDIUM COMPOSITION ON THE REMOVAL OF Pb2+ BY ALGINATE GEL BEADS. DPVASV AND ICP-OES MEASUREMENTS.

Abstract

The biosorption, i.e. a passive sequestering process by metabolically inactive biomass, shows a growing interest for toxic metal ions removal from contaminated aqueous solutions (1), such as municipal and industrial wastewaters. Since the sorption mechanism occurs mainly by ion exchange between the metal ion present in solution and the counter ion of the biopolymer (2), the efficiency of the sorption process largely depends on ionic strength and on the medium composition of solution containing the metal ion to be removed. In order to evaluate quantitatively the influence of ionic strength and medium on the metal removal process by the biomass, we report here results of a study on the sorption capacity of calcium in gel phase toward Pb2+ in aqueous solution in different simple (NaCl, NaNO3) and mixed [NaCl+CaCl2, NaCl+MgCl2, NaCl+Na2SO4) ionic media, in a wide range of ionic strength (0.05 < I/mol L -1 < 0.8), and at room temperature. Investigations were performed by evaluating the Pb2+ concentration in the solution after adsorption onto different amounts of calcium alginate gel beads over continuous time. Measurements of Pb2+ concentration were carried out by Differential Pulse Anodic Stripping Voltammetry (DP-ASV) and by Inductively Coupled Plasma Optical Emission Spectroscopy ICP - OES. To avoid the hydrolysis of the of Pb2+ ion, the solution containing the metal ion to be removed was kept at pH ~ 5. The pseudo second-order model was used to fit sorption process kinetic data(3). Sorption equilibrium was analysed using Langmuir and Freundlich isotherm models. Although both isotherm equations fitted properly the equilibrium data, Langmuir model seems to fit data slightly better than the Freundlich model.