Adsorption behaviour of trivalent chromium on amine-based polymer aniline formaldehyde condensate

An amine-based polymer, aniline formaldehyde condensate (AFC) was coated on silica gel and used as an adsorbent for removal of trivalent chromium [Cr(III)] in aqueous environment. A comparative study with mixed metal solutions containing Cu(II), Cd(II), Pb(II), Cr(III) and Ni(II) showed that adsorption was in the order of Cu(II) > Ni(II) > Cr(III) > Pb(II) > Cd(II). Comparative adsorption of mixed metal ions by AFC was according to preferences dictated by the hard–soft theory of acids and bases and ligand exchange rate of metal ions. It was observed that in mixed metal solution Cr(III) adsorption by AFC though thermodynamically favoured with high binding constant, however, limited kinetically. Cr(III) adsorption by AFC increased with pH achieving maximum removal of 80% at pH 6. Formation of multidentate coordinate bond between [CrOH]2+ and [Cr(OH)2]1+ and deprotonated amine group (–NH2) of AFC was probable mechanism for removal of Cr(III) in aqueous environment. Adsorption of Cr(III) on AFC followed Lagergren’s second order kinetic model and Langmuir–Freundlich’s isotherm model with maximum monolayer coverage of 30.77 mg/g (0.57 mmol/g). Electromagnetic paramagnetic resonance and energy dispersive X-ray spectra confirmed the presence of trivalent chromium ion on surface of AFC coated silica gel.