Synthesis and characterization of amidoximated polyacrylonitrile/organobentonite composite for Cu(II), Zn(II), and Cd(II) adsorption from aqueous solutions and industry wastewaters

A new adsorbent, polyacrylonitrile/organobentonite composite with amidoxime functionality was prepared using in situ intercalation polymerization technique and characterized by Fourier transform infrared spectroscopy, X-ray diffraction pattern, scanning electron microscopy, surface area analyzer, thermogravimetry, and potentiometric analysis. The adsorption of Cu(II), Zn(II), and Cd(II) ions was, examined by batch-equilibrium technique with respect to the initial pH, adsorbent dose, ionic strength, contact time, and initial metal concentration. Adsorption-complexation, in addition to ion exchange, must be involved in the sorption process. Maximum adsorption of 99.8% Cu(II), 98.9% Zn(II), and 97.4% Cd (II) with 2 g/L of the adsorbent was observed at pH 6.0 for an initial metal concentration of 25 mg/ L. The kinetic data were reasonably correlated with pseudosecond-order kinetic equation. An increase of ionic strength on the medium caused a decrease in metal adsorption, indicating the occurrence of outer-sphere surface complex mechanism for the metal. The equilibrium isotherm data were analyzed using Langmuir, Freundlich, and Scatchard isotherm models; however, the Langmuir model was found to provide the best correlation. The maximum monolayer adsorption capacity was 77.43, 65.40, and 52.61 mg/g for Cu(II), Zn(II), and Cd(II) ions, respectively, at 30 degrees C. The adsorption efficiency toward heavy metals removal was tested using different industry wastewaters. Acid regeneration was tried for several cycles with a view to recover the adsorbed metals and also to restore the adsorbent to its original state.