Adsorption of hexavalent chromium onto magnetic natural zeolite-polymer composite

• MZ-PPy with improved density was successfully synthesized for Cr(IV) removal.
• Improved adsorption capacity was achieved using MZ-PPy.
• The sorption kinetic data fitted well to the pseudo-second order model.
• Equilibrium data followed the Langmuir isotherm model.
• MZ-PPy can be used in two cycles without loss of capacity.

Magnetic natural zeolite-polypyrrole (MZ-PPy) composite was prepared for enhanced removal of hexavalent chromium [Cr(VI)] from aqueous solution. The structure and morphology of the prepared adsorbent was analyzed with the Fourier transform infrared (FTIR), field-emission microscope (FE-SEM), energy dispersive X-ray (EDX), high resolution transmission electron microscope (HR-TEM) and X-ray diffraction (XRD). The effects of magnetic zeolite loading within the composite, initial pH, sorbent dosage, temperature and Cr(VI) concentration on Cr(VI) removal efficiency were investigated. Up to 99.99% removal efficiency was obtained when the pH was 2 and the initial Cr(VI) concentration was 300 mg/L. The sorption kinetic data fitted well to the pseudo-second order model and isotherm data fitted well to the Langmuir isotherm model. The maximum adsorption capacity determined from the Langmuir isotherm increased from 344.83 to 434.78 mg/g as the temperature was increased from 25 °C to 45 °C. Thermodynamic parameters revealed that the adsorption process is spontaneous and endothermic in nature. The results further indicated that the adsorption capacity is decreased in the presence of SO42− ions. The adsorption–desorption studies indicated that MZ-PPy retained its original Cr(VI) sorption capacity up to two consecutive cycles.