Pristine and activated bentonite for toxic metal removal from wastewater

Abstract

Natural bentonite clay (NBC) was activated using nitric acid (HNO3). Characterization techniques including FTIR, SEM, XRD and BET were employed to examine the morphology of NBC and ABC (activated bentonite clay) sorbents. Comparative application of ABC and NBC to remove heavy metals (Fe2+, Zn2+, Ni2+) from pharmaceutical effluents was investigated under various experimental conditions. The maximum proportional removal by ABC was 88.90, 81.80 and 75.50% at pH 8, and 63.90, 59.60, 58.70% at pH 10 for NBC, both for Zn2+, Fe2+ and Ni2+ respectively. The Freundlich multilayer adsorption model and pseudo-second-order kinetics best fit the experimental data, suggesting the formation of multiple adsorption layers via strong ionic and electrostatic interactions. Heavy metals adsorption is more favorable with ABC than NBC, due to the availability of more sorption sites and a larger specific surface. The thermodynamic parameters (ΔH°, ΔS°, and ΔG°) revealed that the adsorption is endothermic and spontaneous in nature for both ABC and NBC. HIGHLIGHTS Acid activation of bentonite clay using nitric acid was achieved in this study.; Enhanced morphology and physicochemical properties of pristine bentonite was observed.; Removal efficiency > 85% of recalcitrant heavy metals was obtained using modified bentonite.; Pre-oxidation of contaminated water using H2O2 enhanced clean-up efficiency.; Adsorption process was spontaneous, endothermic, and best described by multilayer sorption.;

Keywords

• adsorption
• bentonite clay
• heavy metals
• kinetics
• thermodynamics