Treatment of nickel ions from contaminated water by magnetite based nanocomposite adsorbents: Effects of thermodynamic and kinetic parameters and modeling with Langmuir and Freundlich isotherms

Co-precipitation procedure was applied in order to obtain different kinds of magnetic nanocomposite adsorbents for the removal of Ni(II) ions from aqueous solution. Prepared nanoadsorbents were characterized by using Fourier transform infrared spectroscopy, X-ray diffractometer, field emission scanning electron microscopy, transmission electron microscopy and the thermogravimetric analysis. The average sizes of nanoparticles were found to be 60 +/- 10 nm. Adsorption studies of heavy metal ions were carried out by batch experiments. Several factors effecting the adsorption of Ni(II) ions on the surface of magnetic nanoadsorbents such as pH (2-12), temperature (293-333 K), contact time (10-60 min), adsorbent dose (0.04-0.24g), shaking rate (100-750 rpm) and initial concentration of analyte (10-100 mg L-1) were studied. The maximum adsorptive removal percentage of Ni(II) ions onto magnetite-citric acid was found to be about 96% at pH 8, temperature 313 K, contact time 50 min, adsorbent dose 0.2 g, shaking rate 500 rpm and initial Ni(II) ions concentration 25 mg L-1. The maximum adsorption capacity for Ni(II) ions was obtained 46.513 mg g(-1) by using citric acid-magnetite as the best nanoadsorbent. The equilibrium adsorption data were well fitted to Langmuir and Freundlich isotherm models, with a better fitting to the Langmuir model for magnetite-citric acid adsorbent. A positive value (39.754 kJ mol(-1)) of enthalpy change (Delta H-0) suggests that the adsorption process was endothermic. Negative values of Gibbs free energy (Delta G(0)) reveal the feasibility and spontaneity nature of the adsorption process and the adsorption kinetics of Ni2+ was found to follow a pseudo-second-order kinetic model. Obtained results clearly showed that magnetite based nanoadsorbents could be efficient, cost-effective and safe adsorbents for the removal of Ni(II) ions from aqueous solution. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.