Isothermal Modelling of Cd2+, Co2+, Fe2+, Mn2+, Ni2+, Pb2+ And Zn2+ Adsorptions onto Zeolitized Brick: Importance of Thermodynamic and Physical Characteristics of Cationic Metals in the Process

Poumaye N, Allahdin O, Lesven L, Wartel M and Boughriet A

Published on: 2021-08-09

Abstract

Brick containing metakaolinite was treated with sodium hydroxide in the aim to convert it into a composite of NaA and NaP zeolites and sand. This material was characterized by X-ray diffraction and scanning electron microscopy.  In single-metal systems, modified brick was used to remove Cd2+, Co2+, Fe2+, Mn2+, Ni2+, Pb2+ and Zn2+ ions from aqueous solutions. Modelling the experimentally measured data with Langmuir, Freundlich and Dubinin-Radushkevich (D-R) equations was conducted. The ability of alkali brick to uptake heavy metals followed the adsorption capacity order: Ni2+< Co2+ < Mn2+< Zn2+ ≈ Fe2+< Cd2+ < Pb2+.  Strong correlations were found between maximum adsorption capacity of alkali brick (determined from Langmuir model) toward metal cations and the ionic potential and hydration free energy of these ions, indicating the importance of both electrostatic forces and ionic diffusion through pores/channels of NaA and NaP zeolites in the adsorption mechanism. Metal hydration and medium fluidity were also found to be relevant factors influencing the ionic passage through zeolitic pores, and therefore the level of the adsorption capacity of the adsorbent. Chemical analysis of recovered (batch) solutions indicated that cationic exchanges between metallic species (Me2+) and the Na+ ions of sodic zeolites took place at the brick-water interface with molar ratios close to the stoichiometric one: 2 Na+/ 1 Me2+.