Copper(II)–Humic Acid Adsorption Process Using Microporous-Zeolite Na-X

There is a need to develop effective and inexpensive methods for removal of heavy metals from contaminated water in developing countries. In this study, a novel microporous, microcrystalline, zeolite-type X high silica (NaX-500) sorbent was synthesized using hydrothermal method followed by calcination at 500 °C. Its sorption capacity to remove Cu(II) was tested in reconstituted water with and without humic acid (HA). Fourier transform infrared spectroscopy, chemical elemental composition, scanning electron microscopy, N₂ adsorption–desorption measurement and X-ray diffraction analyses confirmed that NaX-500 has a micro-crystalline structure with micrometer-sized pores and a specific area of about 336 m²/g. The results showed that sorption of Cu(II) below 20 mg/L was described by pseudo-first-order kinetic model and above 500 mg/L by the second order model, whereas Dubinin–Radushkevich model (for all cases R² values > 0.810) described best the sorption of copper(II) on NaX-500. The presence of HA was found to influence the adsorption efficiency as copper formed a complex with zeolite–HA, thus improving the adsorption capacities. This study shows that, the newly developed material is rapid and effective for the removal of copper from contaminated water both at low and moderate concentrations including from water with moderate concentration of humic substances.