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

The potential of using nano-sized aragonite mollusk shell (nano-Bio-ARA) to remove Cd(2+) 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 Cd(2+) (8.91mmol/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 Cd(2+) on the nano-ARA was a spontaneous and endothermic process. The coexisting metals in the solution displayed competition effect to the sorption of Cd(2+) on nano-Bio-ARA in the following order: Cu(2+)>Cr(3+)>Pb(2+)>Zn(2+)>Ca(2+). EDTA impeded the sorption of Cd(2+) on nano-Bio-ARA due to its strong chelating capacity to Cd(2+) in the solution. The results demonstrate that nano-Bio-ARA is a potential high-effective material to treat Cd(2+) contaminated water.