Kinetic and thermodynamic study of Cd(II), Co(II) and Zn(II) adsorption from aqueous solution by NiO

The kinetics of Zn(II), Co(II) and Cd(II) sorption onto NiO is studied at different temperatures (303-323 K). The applicability of the various kinetic models is tested to determine the mechanism of the sorption reaction. The kinetics of the metal ion adsorption on NiO is best described by pseudo first order model. The time required to reach the adsorption equilibrium is dependent on the temperature and nature of metal cation. The increase in the extent of the metal cation adsorption with temperature is due to the increase in number of active sites on the surface of adsorbent. The values of activation energy determined from Arrhenius equation are observed to be 43.7, 32.7 and 29.4 kJ/mol for Zn(II), Co(II) and Cd(II) respectively. The energy of activation is found to follow the trend: Zn(II) > Co(II) > Cd(II) which is parallel to selectivity shown by the NiO towards these metal ions. The thermodynamic parameters of activation indicate that Cd(II), Co(II) and Zn(II) adsorption onto the NiO is the entropy driven ion exchange mechanism. (C) 2011 Elsevier B.V. All rights reserved.