The effect of montmorillonite clay in alginate gel beads for polychlorinated biphenyl adsorption: Isothermal and kinetic studies

Beads of alginate montmorillonite have been used as sorbent for polychlorinated biphenyls from aqueous solutions. The structure and the differences between the different beads were established by IR spectroscopy (FT-IR). The adsorption at 25 degrees C has been studied in a batch system, following its kinetics and assessing adsorbent dose, initial PCB concentrations, and pH effects. The results show that increasing the initial concentration of the PCBs and the adsorption time favored the adsorption. Adsorption isotherm data were modeled using Chapman, Freundlich and Langmuir adsorption isotherms and the appropriate parameters were calculated. Adsorption of trichlorobiphenyls on alginate-montmorillonite beads followed a Freundlich isotherm type model, while adsorption of tetra-, penta-, and hexachlorobiphenyls displayed a sigmoid-shaped (S-type) isotherm fitting the Chapman sigmoidal equation with the highest non-linear R-2 values among the three tested models. By comparing the percentage adsorptions using the same number of beads (same volumes), best removals were obtained by using alginate montmorillonite beads. Kinetic models were investigated to determine the mechanism of adsorption showing a best fit for the pseudo-second order model (R-2 from 0.998 to 0.982). Moreover, to underline the effect of montmorillonite in alginate gel beads, we have compared the isothermal adsorption curves between alginate montmorillonite and alginate beads. (C) 2014 Elsevier B.V. All rights reserved.