Environmental contamination of heavy metals has become a worldwide problem and a special attention has been given to them because of their high toxicity, non-biodegradability and accumulation in the food chain. Heavy metals, even at trace level, are very harmful for human beings. Thus, the removal of heavy metals from water systems is a very critical and essential topic and has attracted a considerable attention .Among these techniques, adsorption as a cost-effective technology offers flexibility in design and operation, and in many cases it will generate high-quality treated effluent. In addition, a lot of adsorbents can be regenerated by desorption processes of ease of operation, for multiple use. A novel nanocomposite was synthesized featuring magnetic properties, and was used for the removal of Pb(II) as a toxic heavy metal from aqueous solutions. The obtained magnetic bionanocomposite was characterized using SEM, BET, FTIR, XRD, TGA, EDX and VSM. The effects of temperature, contact time, Pb(II) concentration, pH value of the solution and adsorbent dosage on the adsorption capacity of the nanocomposite were investigated. The kinetics data of adsorption process were analyzed by the models of pseudo-first order, pseudo-second order, the Elovich and intra-particle diffusion. The adsorption kinetics was well described by the pseudo-second order equation. The adsorption isotherms were more accurately fitted by the Langmuir equation and the maximum theoretical Pb(II) adsorption capacity of the nanocomposite was found to be 136.99 mg/g at pH 6 and 333 K. The negative Gi free energy values of adsorption illustrated the spontaneity of the adsorption of Pb(II) ions on the nanocomposite. The magnetic nanocomposite gave a saturation magnetization value of 9.50 emu/g, therefore, it was efficiently separated from the solution by a fast and simple magnetic separation process. Desorption of the Pb(II) ions from the nanocomposite was achieved by using 0.01M HNO 3 , CaCl 2 and NaCl solutions. A rotatable central composite design (CCD) and the RSM were used to conduct and to analyze the experiments, respectively. A two-mass transfer resistance model, consisting of the homogeneous solid diffusion model combined with the external mass transfer resistance, was applied to fit the experimental kinetic data of an agitated batch adsorption system and a parabolic dependence of the driving force on the particle radius was considered.
