Characterization of Natural Zeolite and Determination of its Ion-exchange Potential for Selected Metal Ions in Water

The growing demand for clean and safe water calls for alternative water treatment methods and materials. In this work, characterization of natural zeolite samples and evaluation of their potential to remove heavy metals from water were done. Zeolite samples sourced from Mount Elgon, Uganda were characterized using X-ray Fluorescence Spectroscopy (XRF), X-Ray diffraction (XRD), Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM/EDX) and Fourier-Transform Infrared Spectroscopy (FTIR). Stock solutions of Pb(II), Zn(II) and Cr(VI) ions prepared from their salts were spiked into distilled water for the study. The ion exchange capacities of the selected ions were studied at various pH, ion exchanger dosage, initial metal ion concentration and contact time. Isothermal and kinetic models were used to evaluate the ion exchange process. Results revealed the zeolite samples composed of 39.74 wt.% SiO 2 , 16.69 wt.% Al 3 O 2 , 11.51 wt.% CaO and 8.54 wt.% Fe 2 O 3 as major mineral constituents. The composition implies that samples have a Si/Al ratio ranging from 2.27 to 2.60 suitable for ion exchange of heavy metals. The major phase in the mineral is laumontite whose Ca 2+ ions are exchanged for cations such as heavy metals during the ion exchange processes. The maximum removal efficiencies were found at pH 6 (99% and 92.1%) for Pb(II) and Zn(II), respectively, while at pH 2 (85.5%) for Cr(VI). The maximum uptake according Langmuir model were 7.59 mg/g, 7.4 mg/g and 5.50 mg/g for Pb(II), Zn(II) and Cr(VI) ions, respectively. The pseudo-second-order equation fitted well the process for all metal ions investigated. Highlights Removal efficiencies of Pb 2+ , Zn 2+ and Cr 6+ on laumontite zeolites were 99%, 92.1% and 85.5%. Respective exchange capacities for Pb 2+ , Zn 2+ , Cr 6+ were 7.59, 7.40 and 5.50 mg/g. The Ion exchange processes fitted Langmuir and pseudo-second-order models.