Removal of Lead and Cadmium from aqueous solution by Polyvinyl alcohol-modified Kaolinite clay: a novel nanoclay adsorbent.
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Date
2008
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Publisher
Multi-Science Publishing Co. Ltd
Abstract
Kaolinite clay was modified with polyvinyl alcohol (PVA) to
obtain a PVA–nano-clay adsorbent. X-Ray diffraction measurements of the
adsorbent showed no observable change in the d-spacing of its crystal lattice.
Scanning electron microscopy of the PVA-modified nano-clay adsorbent
indicated the presence of irregular crystal structures. Infrared spectroscopy
suggested that the PVA–nano-clay adsorbent basically possessed outer –OH
functional groups. This adsorbent was found to have an adsorption capacity of
56.18 mg/g for Pb2+ ions and 41.67 mg/g for Cd2+ ions. The adsorption data
obtained was well explained by the Diffuse Layer Model (DLM), which implies
that the adsorption of both metal ions onto the modified adsorbent was via an
inner-sphere surface complexation mechanism. The ∆H0 values for the
adsorption of both metal ions onto the PVA–nano-clay were –12.48 kJ/mol for
Pb2+ ions and –13.49 kJ/mol for Cd2+ ions, with both ions exhibiting negative
adsorption entropies. Data-fitting indicated that both the PVA–nano-clay and the
unmodified adsorbent possessed homogeneous and heterogeneous adsorption
sites. Virtually complete desorption (ca. 99%) of both metal ions occurred from
PVA–nano-clay within 3 min.