The potential of using nano-sized aragonite mollusk shell (nano-Bio-ARA) to remove Cd2+ from contaminated water was investigated by comparing the sorption kinetics and isotherms with the nano-sized calcite-type mollusk shell (nano-Bio-CAL) and nano-sized geological calcite (nano-Geo-CAL). Nano-Bio-ARA displayed extremely high sorption capacity to Cd2+ (8.91 mmol/g), much higher than nano-Bio/Geo-CAL, and many other natural or engineered materials. The results of thermodynamic experiments indicated that the sorption of Cd2+ on the nano-ARA was a spontaneous and endothermic process. The coexisting metals in the solution displayed competition effect to the sorption of Cd2+ on nano-Bio-ARA in the following order: Cu2+ > Cr3+ > Pb2+ > Zn2+ > Ca2+. EDTA impeded the sorption of Cd2+ on nano-Bio-ARA due to its strong chelating capacity to Cd2+ in the solution. The results demonstrate that nano-Bio-ARA is a potential high-effective material to treat Cd2+ contaminated water. (C) 2011 Elsevier Inc. All rights reserved.