Adsorption of Cu ions onto a 1.10 phenanthroline-grafted Brazilian bentonite

Abstract

The grafting, by chemical adsorption, of molecular 1.10-phenanthroline (OP) onto some Brazilian bentonite (montmorillonites) was studied to improve their adsorptive capacities to remove Cu ions from synthetic wastewater. The quantity of OP adsorbed was 112 mg g-1 of bentonite at pH 8.5 and no significant desorption was detectable in acidic or basic solutions. X-ray diffraction (XRD) spectra show that a complex type- is formed in which the OP molecules lay inclined in the clay interlayer. After the intercalation of OP, the adsorptive capacities of the natural bentonites increased by a factor of ten. Thus, adsorption of Cu ions, at optimal pH of 8.0±0.5, showed saturation values, which, calculated by the Langmuir model, yielded 110 mg of Cu ions g-1 of bentonite (3.5 meq g-1). The mechanisms of Cu uptake are ion-exchange adsorption onto untreated bentonite and ion exchange plus Cu2+ phenanthroline complexation (chemisorption) on the modified pillared clay. The desorption of Cu ions from OP clay revealed high uptake irreversibility and physical stability (of the adsorbent) either in strongly acidic or basic solutions. Thus, after acid treatment ~90% of the adsorbed Cu ions continued to be bound onto the OP-modified bentonite surface.