Magnetic zeolite-polymer composites for Cu(II) and Cr(III) removal from aqueous solutions

Abstract

The objective of this study was to investigate the removal of Cu(II) and Cr(III) from aqueous solution using magnetic zeolite-polymer composites as adsorbents. Zeolite A was synthesized using sodium aluminate, sodium metasilicate and sodium hydroxide. Field emission scanning electron microscopy (FESEM) showed a hexahedron shape of zeolite A with a feret diameter of 2.04 ± 0.31 μm. Energy dispersive X-ray spectrometer (EDS) pattern demonstrated that oxygen (O), silicon (Si) and aluminum (Al) are the major elements of zeolite A. X-ray fluorescence (XRF) spectrometer analysis indicated that SiO2 (41.6 %) and Al2O3 (37.0 %) are the primary constituents of zeolite A. X-ray diffraction (XRD) pattern of zeolite A indicated the peaks corresponding to characteristic peaks of zeolite A and the BET surface area of zeolite A was 12.5 m2/g. Magnetic zeolite-polymer composites were synthesized using zeolite A, synthesized iron oxides, polyvinylidene fluoride, polyvinyl alcohol, dimethyl sulfoxide. The FESEM images showed a bead shape of the composite with a feret diameter of 3.21 ± 0.21 mm. According to EDS analysis, iron (Fe), carbon (C), fluorine (F), oxygen (O), silicon (Si), aluminum(Al) and sodium (Na) are evident elements of the composites. The swelling ratios (%) of the composites were within ±3 % at the pH 2, 7 and 9. Batch experiments were performed to investigate the Cu(II) and Cr(III) removal using the composites. The effect of composites dose on Cu(II) and Cr(III) removal was examined and the composites dose was determined to 2.5 g in 30 mL solution. Kinetic batch experiments showed that both Cu(II) sorption and Cr(III) sorption on the composites arrived at equilibrium in 4 hours. Equilibrium batch experiments demonstrated that the maximum adsorption capacities of the composites were 3.90 mg/g for Cu(II) and 2.04 mg/g for Cr(III). Batch experiments were also conducted to observe the effects of solution pH and temperature on the removal of Cu(II) and Cr(III). For both Cu(II) and Cr(III), adsorption capacities were the lowest when the solution pH was 2. And the metal adsorption by adsorbent increased at higher pH condition. Thermodynamic test indicated that Cu(II) and Cr(III) sorption on the composites occurred more rapidly with increasing temperature, implying the endothermic nature of sorption process. The results of repeated use of the composites showed that treatment with NaCl solution leads the regeneration of composites and treatment with HCl solution causes desorption only. From tracer experiment using fluorescein, the coefficient of determination (R2) between observed values and theoretical values was 0.988. And the adsorption capacities of the composites in reactor experiment were 1.08 mg/g for Cu(II) and 0.971 mg/g for Cr(III). This study demonstrated the applicability of magnetic zeolite-polymer composites for the removal of Cu(II) and Cr(III) from water.