Abstract

In this investigation, the removal of divalent heavy metals by two types of zeolites has been studied. The mechanism of cation exchange for
Cu2+, Ni2+, Cd2+ and Pb2+ on NaX Faujasite and Linde type A (LTA) zeolites was studied. Both zeolites are very efficient in divalent heavy
metals removal from water. Ion exchange isotherms were performed and the thermodynamic parameters were calculated as well. Kielland
plots showed that the order of selectivity is not the same for both the zeolites. For NaX it followed the following order Pb2+ > Cu2+ > Cd2+ >
Ni2+ while for LTA the order is Pb2+ > Cd2+ > Cu2+ > Ni2+. Exchange velocity (kw) and the radii of the hydrated metals ions are involved in
determining this order of selectivity.

Key words: NaX zeolite; LTA zeolite; exchange mechanism; heavy metals; selectivity.