Modification of bentonite by Al/Mg-polymeric hydroxy for Cu2+, Cd2+, and Pb2+ removal from aqueous solutions

A commercial bentonite was modified by Al/Mg-polymeric hydroxy, and its potential application of removing Cu2+, Cd2+, and Pb2+ from aqueous solution was also discussed. The modification did not change the bentonite microstructure, while the surface morphology becomes rough and the methyl and methylene groups appeared on the surface of modified bentonite (B-Al/Mg). Under acidic condition, the removal of Cu2+, Cd2+, and Pb2+ raised with the increase of initial pH of solutions, media dosage, and reaction temperature, and the efficacious contact times for Cu2+, Cd2+, and Pb2+ removal were 6 (Cu2+) and 8 h (Cd2+ and Pb2+). The Cu2+, Cd2+, and Pb2+ adsorption processes could be better described by Freundlich isotherm model and pseudo-second-order model. The intraparticle diffusion might be the rate-controlling step of Cu2+ and Pb2+ adsorption. The Cu2+, Cd2+, and Pb2+ adsorptions were heterogeneous, spontaneous, endothermic, and irreversible processes. The adsorptions of Cu2+ and Cd2+ were dominated by physisorption, while the chemisorption was dominant in Pb' adsorption. The results of column experiments suggested that B-Al/Mg had the potential application in purification of drinking water in practice because its removal of Cu2+, Cd2+, and Pb2+' was greater than activated carbons selected in this study, and the breakthrough times were up to 20-30 d. Simultaneously, the heavy metal concentrations of outlet were all less than the World Health Organization standard in breakthrough time. The dynamic adsorption of Cu2+, Cd2+, and Pb2+ was well described by bed-depth service time model. B-Al/Mg had the potential for commercial applications. For single heavy metal removal, the advised adsorption columns were column 4 (Cu2+ and Pb2+) and column 1 (Cd2+), and the column 5 was suggested for Cu2+, Cd2+, and Pb2+ competitive adsorption.