Adsorptive removal of Cd2+ , Cr 3+ and Cr 6+ using natural and synthetic goethite particles: Kinetics study

Abstract

The adsorption study of Cd2+
, Cr3+ and Cr6+ on natural goethite (NGT) and synthetic goethite (SGT) particles was
conducted using batch equilibrium assays to investigate the influence of agitation time on the adsorption process. The data
generated were thereafter fitted into six common kinetics models; pseudo-first order, pseudo-second order, Elovich, second
order, intra-particle diffusion and film diffusion models. Results showed a rapid uptake and reached equilibrium at 60
minutes for Cr3+
-SGT (qe = 29.84 mg/g), 90 minutes for Cd2+
-NGT (1.877 mg/g), Cd2+
-SGT (51.57 mg/g), Cr3+
-NGT (2.92
mg/g) and Cr6+
-NGT (2.372 mg/g), and 120 minutes for Cr6+
-SGT (19.035 mg/g). The adsorption kinetics revealed the order
of fittings: Pseudo-second order > Elovich > Second order > Pseudo- first order, as well as intra-particle diffusion > film
diffusion. Additionally, combined results of the kinetic modeling suggested that adsorption of the metal ions onto both
adsorbents followed chemisorption process and that the mechanism of the adsorption occurred either by a combination of
intra-particle and film diffusion, or that other processes occurred simultaneously with these two processes. The result of this
study therefore, could provide useful information on the sorption of these heavy metal ions on both goethite forms