Adsorption Behaviors Of Heavy Metal On Multi-walled Carbon Nanotube-hydroxyapatite Composites

Multi-walled carbon nanotube-hydroxyapatite composites (MWCNT-HAP) were synthesized and employed as sorbent to study the sorption characteristic of Pb(Ⅱ), Cd(Ⅱ) and Cu(Ⅱ) from single-and multi-metal[Pb(Ⅱ)+Cd(Ⅱ)+Cu(Ⅱ)] solutions using batch experiments. The effect of dosage of adsorbent, pH, ionic strength, contact time, initial concentration of heavy metals and temperature were investigated. The following conclusions can be obtained from the results analysis of the present study:(1) Under the same conditions, the adsorption capacity of lead, cadmium and copper onto MWCNT-HAP composites follows the sequence of Pb(Ⅱ)> Cu(Ⅱ)> Cd(Ⅱ). With an increase in the adsorbent dose, the adsorption capacity of lead, cadmium and copper decreases, and the removal rate is significantly increased. The optimum pH value for the adsorption of lead, cadmium and copper onto MWCNT-HAP composites is 4-6.(2) The removal of cadmium to MWCNT-HAP composites is strongly dependent on ionic strength, and the adsorption of lead and copper is independent of ionic strength.(3) In the multi-metal [Pb(Ⅱ)+Cd(Ⅱ)+Cu(Ⅱ)] competitive system, the adsorption capacities of MWCNT-HAP composites for Pb(Ⅱ), Cu(Ⅱ) and Cd(Ⅱ) are found to be 751.88, 130.65 and 117.36mg/g.(4) The kinetics adsorption of Pb(Ⅱ), Cd(Ⅱ) and Cu(Ⅱ) from single-and multi-metal[Pb(Ⅱ)+Cd(Ⅱ)+Cu(Ⅱ)] solutions onto MWCNT-HAP composites confirm that the adsorption is a rapid process and can reach an equilibrium at 120min. The kinetics data are fitted to pseudo-second-order kinetic model reasonably well.(5) The adsorption process of Pb(Ⅱ), Cd(Ⅱ) and Cu(Ⅱ) onto MWCNT-HAP composites is endothermal and spontaneous, and in favor of higher temperature. The adsorption isotherms of lead and copper are better explained by the Langmuir model. Langmuir model and Freundlich model can describe the adsorption of cadmium onto MWCNT-HAP composites very well.