Revealing and elucidating chemical speciation mechanisms for lead and nickel adsorption on zeolite in aqueous solutions

Abstract

The removal of heavy metals from water is crucial for human health and the environment, and finding an appropriate adsorption material to achieve this goal is extremely desirable. In this study we reported zeolite as the adsorption material to remove the Pb2+ and Ni2+ from the aqueous solution and elucidated the chemical speciation using batch technique. The adsorption of these metals by zeolite was investigated in relation to pH, ionic strength, contact time, co-existing ions, and the temperature. Zeolite exhibited better adsorption capacities than several other adsorption materials, due to its larger specific surface area. The adsorption of Pb2+ and Ni2+ is influenced by ionic strength at pH < 7.0 and pH < 8 and is independent of the ionic strength at pH > 7.0 and pH > 8, respectively. The chemical speciation of Pb2+ and Ni2+ is regulated by outer- and inner-sphere surface complexation, respectively at low and high pH values,. The maximum adsorption capacity of Pb2+ and Ni2+ predicted from the Langmuir model was found to be 45.00 and 28.57 mg g–1 respectively at 303 K. The thermodynamic studies revealed the spontaneous and endothermic nature of adsorption process whereby zeolite displayed an efficient adsorption for both metals with increasing temperature. The findings are very useful in evaluating zeolite interactions in aqueous solutions with the chemical speciation of Pb2+ and Ni2+. From above findings, the zeolite can be recommended as an appropriate adsorbent to adsorb metal ions from aqueous solution.