[SiO4] 4-and [AlO4] 5-linked to each other at corners by sharing their oxygen atoms in a three-dimensional network with numerous voids . This crystalline microporous alumina-silicate structure varies according to the configuration of the oxygen sharing , where Al 3+ isomorphous substitution for Si 4+ in the said framework results in a negative charge that is key in the adsorption of heavy metal cations . The adsorption efficiency is subject to several factors including zeolite crystal structure, pore sizes, quantity, adsorbate concentration, pH, contact time, and affinity to desired adsorbates .