Kinetic, isotherm and thermodynamic investigations of Cu2+ adsorption onto magnesium hydroxyapatite/ferroferric oxide nano-composites with easy magnetic separation assistance

A novel magnetic nano-composite was synthesized by a simple method of coprecipitation through embedding ferroferric oxide into magnesium hydroxyapatite (MgHAp/Fe3O4) to remove Cu2+ from aqueous solution. The obtained adsorbent was characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), Brunauer-Emmett-Teller (BET) surface area measurement and Fourier transform infrared spectroscopy (FTIR). Mg2+ and Cu2+ possess the same electrical charge and similar ionic radius, which is especially beneficial to their exchange in hydroxyapatites. Static adsorption experiments indicated that the maximal immobilization capacity of Cu2+ reached to 305 mg/g on the optimum adsorption conditions (dosage of 0.32 mg/mL, contact time for 90 min, pH at 5.9 and temperature at 25 degrees C). Adsorption kinetics including the pseudo-first order and pseudo-second order kinetic models were researched and the data fitted better with the pseudo-second order kinetic model (R-2 = 0.99). For adsorption isotherms, Freundlich isotherm was proved to be the best correlation (R-2 > 0.99) compared with the Henry and Langmuir isotherms. The thermodynamic parameters (Delta G < 0, Delta S =4338 J/mol/K, Delta H = 7.006 kJ/mol) indicated that it was a spontaneously endothermic reaction. Furthermore, the well anti-interference and stability properties of the MgHAp/Fe3O4 adsorbent were confirmed through the interference experiment of coexistent metal cations and desorption experiment, respectively. (C) 2014 Elsevier B.V. All rights reserved.