Abstract
To improve ion-exchange capacity of zeolite towards Pb (II) ion, the sequent removal of free SiO2 using HF and of free Al2O3, CaO, Fe2O3, and MgO using EDTA solution has been performed. It was observed that the large amount of the metal ions can be dissolved from the zeolite without any significant damage to the structure of zeolite. The optimum condition was reached when 1.0 g zeolite was washed with 25 cm3 of 0.05 % (v/v) HF solution for 3 hours, and with 200 cm3 of 0.075 M EDTA solution at pH 5 for 50 hours. The HF washing improved the zeolite capacity in adsorbing Pb (II) ions from 87.7 mg g-1 to 95.2 mg g-1, and sequent washing using EDTA solution could further increase the capacity up to 135 mg g-1, which is comparable to that absorbed by synthetic mordenite, ca. 152 mg g-1.
