Removal of cationic and oxyanionic heavy metals from water using hexadecyltrimethylammonium-bromide-modified zeolite

The objective of this study was to develop a dual-electronic adsorbent using hexadecyltrimethylammonium (HDTMA)-modified NaY zeolite. HDTMA-modified zeolite (HMZ) possesses a positive charge on the external surface and a negative charge on the micropore surface, and therefore it simultaneously adsorbs cationic (Cu2+, Zn2+, Ni2+, Pb2+, and Cd2+) and oxyanionic (MnO4-, Cr2O72-) metal ions. The surface properties of NaY zeolite and HMZ were characterized according to scanning electron microscopy and Fourier transform infrared spectroscopy. The specific surface area, the elemental composition, and cation-exchange capacities were also examined. The obtained data were fitted with three types of kinetic adsorption models, pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. The amount of test metal ions adsorbed and the absorption mechanisms were illustrated. Moreover, competitive adsorption between cations and oxyanions was discussed. The results demonstrated that the HMZ behaved as a dual-electronic adsorbent. The pseudosecond- order kinetic equation exhibited the optimal fitting result. Ion exchange and complexation were regarded as primary mechanisms, and the adsorption capacities of cations and oxyanions followed the order Pb2+> Cu2+> Zn2+> Ni2+ and Cr2O72- > MnO4-, respectively. In addition, Pb2+ and Cr2O72- were dominant species during competitive adsorption.