Removal of Cd2+ from contaminated water by nano-sized aragonite mollusk shell and the competition of coexisting metal ions

► Nano-sized aragonite mollusk shells display high sorption capacity to Cd2+ in water. ► Epitaxial growth of otavite inhibits the sorption of Cd2+ on nano-sized calcite. ► Coexisting metals display competing effect in the order of Cu2+ > Cr3+ > Pb2+ > Zn2+ > Ca2+. ► Sorption of Cd2+ on the nano-ARA is a spontaneous and endothermic process.