Kinetic and Thermodynamics of the Removal of Zn2+ and Cu2+ from Aqueous Solution by Sulphate and Phosphate Modified Bentonite Clay
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Date
2010
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Publisher
Elsevier
Abstract
The modification of pristine Bentonite clay with sulphate and phosphate anions was found to increase
its cation-exchange capacity (CEC), adsorption capacity and overall pseudo-second order kinetic rate
constant for the adsorption of Cu2+ and Zn2+. Modification with sulphate and phosphate anion decreased
the specific surface area of pristine Bentonite clay. Phosphate-modified Bentonite clay was found to
give the highest adsorption capacity for both metal ions. The adsorption process was observed to be
endothermic and spontaneous in nature for both metal ions with Zn2+ being more adsorbed. Modification
with phosphate anion increased the spontaneity of the adsorption process. The effective modification
of pristine Bentonite clay with sulphate anion was confirmed from hypochromic shifts in the range of
13–18 cm−1 which is typical of physisorption while modification with phosphate anion was confirmed
by its hyperchromic shifts typical of chemisorption in the infrared red region using Fourier transformed
infrared spectroscopy (FTIR). Using the model efficiency indicator, kinetic data were found to show very
strong fit to the pseudo-second order kinetic model implying that the adsorption of Cu2+ and Zn2+ were
basically by chemisorption.
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Keywords
Bentonite, Phosphate, Sulphate, Thermodynamics, Kinetics, Adsorption