Removal of Pb(II) Ions from Aqueous Solutions by Kaolinite and Metakaolinite Materials

Aims: To study the sorption of Pb(II) ions from aqueous solutions by low cost adsorbent materials like kaolinite (KAO) and synthetic metakaolinite (MET) in order to validate the effects of pH, equilibrium contact time, adsorbent dose and adsorbate concentration. To investigate the sorption mechanism of Pb(II) ions on the surface of these two adsorbents through pseudo-first order, pseudo-second order, Elovich and intra-particle diffusion kinetic models.
Study Design: We used a batch sorption system at 27 ºC and operated at constant pH equal to 5.5.
Place and Duration of Study: Department of Chemistry, University of Dschang, Cameroon and Department of Inorganic Chemistry, University of Yaounde I, Cameroon, between July 2012 and September 2012.
Methodology: For each experiment (except otherwise stated), 0.5 g of adsorbent was measured and put into a 250-mL conical flask containing 20 mL of the Pb(II) ions at the desired concentration that ranged between 10 and 120 ppm and later on agitated, filtered and analyzed by UV-Visible spectroscopy.
Results: Equilibrium was attained after a contact time of 30 minutes both for KAO and MET. Maximum pHfor Pb(II) adsorption was at 5.5 and was therefore maintained at that value throughout. Maximum quantities adsorbed by each adsorbent were 2.37 mg/g for kaolinite and 1.34 mg/g for metakaolinite respectively. The most convenient model was the pseudo-second order, as per the linear regression coefficient values (r2). Equilibrium data were analyzed by Langmuir, Freundlich and Temkin adsorption models. It was inferred that the Langmuir and Temkin models (with very high r2 values) were most suited to describe the sorption of Pb(II) ions in aqueous solutions.
Conclusion: These results show that KAO and MET display lower efficiency for the removal of Pb(II) ions from aqueous domestic and industrial effluents than commercial activated carbon and others from diverse origins.