Modifying hydroxyapatite nanoparticles with humic acid for highly efficient removal of Cu(II) from aqueous solution

Hydroxyapatite (HAP) could be a kind of potential low cost and biocompatible adsorbent for potentially toxic metals due to its special chemical composition and crystal structure. Humic acid (HA) modified HAP nanoparticles (HAP/HA) was prepared to adsorb Cu(II) ions from aqueous solution. The obtained materials were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscope (SEM). Then, batch experiments were carried out to investigate the possible adsorption mechanisms of Cu(II) ions onto HAP/HA nanoparticles. Results illustrated that the adsorption capacity of the modified HAP for Cu(II) was improved significantly as compared to that of the bare HAP. Kinetic experiments revealed that the pseudo-second-order model exhibited the best correlation with the adsorption data. Equilibrium data were best described by Sips model, and the estimated maximum adsorption capacity of HAP/HA was 58.42 mg/g at 313 K, displaying higher efficiency for Cu(II) removal than previously reported adsorbents. Cu(II) removal could be decreased in the presence of coexisting cations. (C) 2015 Elsevier B.V. All rights reserved.