Adsorption of Co(II) and Ni(II) by EDTA- and/or DTPA-modified chitosan: Kinetic and equilibrium modeling

The aim of the present study was to investigate the adsorption properties of surface modified chitosans in the aqueous solutions containing Co(II) and/or Ni(II) ions. For this purpose, the ligands of ethylenediaminetetraacetic acid (EDTA) or diethylenetriaminepentaacetic acid (DTPA) were immobilized onto polymer matrices of chitosan. Adsorption of Co(II) and Ni(II) by prepared adsorbents was investigated in batch techniques. The effects of pH, functional group, contact time, and the concentration of metals were studied. Metal uptake by EDTA-chitosan was 63.0 mg g−1 for Co(II) and 71.0 mg g−1 for Ni(II) and by DTPA-chitosan 49.1 mg g−1 for Co(II) and 53.1 mg g−1 for Ni(II). The adsorption efficiency of studied adsorbents ranged from 93.6% to 99.5% from 100 mg L−1 Co(II) and/or Ni(II) solution, when the adsorbent dose was 2 g L−1 and solution pH 2.1. The kinetics of Co(II) and Ni(II) on both of the modified chitosans followed the pseudo-second-order model but the adsorption rate was also influenced by intraparticle diffusion. The equilibrium data was best described by the Sips isotherm and its extended form was also well fitted to the two-component data obtained for systems containing different ratios of Co(II) and Ni(II). Nevertheless, the obtained modeling results indicated relatively homogenous system for Co(II) and heterogeneous system for Ni(II) adsorption.