Investigation on the lead adsorption capacity of Iranian natural zeolite: modifications, structural effects, adsorption isotherms, kinetics, and mechanism studies

Clinoptilolite (NZ) as a natural and cost-effective adsorbent, modified with two different methods. At the first stage, by sodium chloride solution to obtain NaCl-modified natural zeolite (NaCl-MNZ), then sodium dodecyl sulfate (SDS) was used to modify NaCl-MNZ (SDS-MNZ). Along with NZ, NaCl-MNZ, and SDS-MNZ, commercial NaY zeolite was also used for removing lead cations from synthesized wastewater. The adsorption of SDS molecules on the outer surface of zeolite was confirmed by FTIR and the specific surface area of the SDS-MNZ was decreased due to the coverage of smaller pores by anionic surfactant molecules. The zeta potential measurements also revealed that the modification process has decreased the surface charge of the zeolite significantly, which was favorable for the adsorption of Pb2+ cations and improved clinoptilolite performance. The non-linear adsorption kinetics and isotherms are best described by the pseudo-first-order and Sips model, respectively. The maximum adsorption capacity of lead ions were 25.8435, 39.5992, 38.5454, and 101.0240 (mg/g) for NZ, NaCl-MNZ and SDS-MNZ and NaY, respectively. The results indicated that the adsorption capacity of natural zeolites modified with NaCl and SDS were approximately 35% and 33% higher than that of the clinoptilolite alone.