This study investigated the removal of cadmium and lead from Kermanshah oil refinery wastewater using Iranian clinoptilolite modified by HCl. HCl with a concentration of 5 M was used to modify zeolite. The results of Brunauer–Emmett–Teller analysis showed that the adsorbent specific surface area after the modification increased by more than six times. Moreover, the results of Fourier transform-infrared showed that the Si–O–Si groups were enhanced after the modification of the adsorbent. In addition, the results of X-ray diffraction and X-ray fluorescence analyses also showed that the modified adsorbent had better properties for adsorbing heavy metals. Afterward, we studied the use of Iranian clinoptilolite and modified Iranian clinoptilolite for the removal of cadmium and lead in an adsorbent bed. All the experiments were carried out in a continuous adsorbent bed with a volume of 330 ml at the ambient temperature. The effects of the operational variables (initial concentration of heavy metals, wastewater flow rate, and adsorbent dose) on the adsorption rate were investigated. The results indicated that, when the concentration of heavy metals and the adsorbent dose were the maximum and the flow rate was at the lowest level, the highest level of Cd and Pb removal was achieved using either adsorbents. However, the modified adsorbent had a higher ability to remove heavy metals. In optimal operating conditions and in the presence of the modified adsorbent, the removal of cadmium and lead from the wastewater was 85.9% and 98.9%, respectively.
