Sorption of toxic metals on sodium aluminosilicate (NAS)

The present study describes sorption of toxic metal ions viz: Hg2+, Pb2+, Cd2+, Zn2+ and As3+ onto synthesized sodium aluminosilicate. A series of experiments were carried out in different conditions. Time of equilibration was observed for 5 h through kinetic study. Sorption was found to be pH dependent. In the case of Hg2+, sorption was observed to be decreased by increasing the pH whereas it gradually increased with pH with respect to other metal ions. Sorption was observed to be decreased with the increase in metal ion concentration (10− 2 M to 10− 5 M) and the data was fitted well in Freundlich's isotherm. A thermodynamic study showed spontaneity of the sorption. Positive values of enthalpy and entropy indicate endothermic and increase in order of randomness at the solid–solution interface during sorption. A desorption study showed that distilled water has no capability of leaching metal ions in contrast with organic ones. The MINTEQA-2 software has been used for the aqueous speciation of the metal ions. Speciation data showed the presence of different species at different pH.