Clay minerals are one of
the potential good adsorbent alternatives to activated carbon because of their
large surface area and high cation exchange capacity. In this work the
adsorptive properties of natural bentonite and kaolin clay minerals in the
removal of zinc (Zn2+) from aqueous solution have been studied by
laboratory batch adsorption kinetic and equi- librium experiments. The result
shows that the amount of adsorption of zinc metal ion increases with initial
metalion
concentration, contact time, but decreases with the amount of adsorbent and
temperature of the system for both the ad- sorbents. Kinetic experiments
clearly indicate that adsorption of zinc metal ion (Zn2+) on bentonite
and kaolin is a two-step process: a very rapid adsorption of zinc metal ion to
the external surface is followed by possible slow decreas- ing intraparticle diffusion in the
interior of the adsorbent. This has also been confirmed by an intraparticle diffusion
model. The equilibrium adsorption results are fitted better with the Langmuir
isotherm compared to the Freundlich model. The value of separation factor, RLfrom Langmuir equation
give an indication of favourable adsorption. Finally from thermodynamic
studies, it has been found that the adsorption process is exothermic due to
negative ?H0 accompa- nied by decrease in entropy change and Gibbs free energy change (?G0).
Overall bentonite is a better adsorbent than kaolin in the the removal of Zn2+ from its aqueous solution.
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