Adsorption of heavy metals from aqueous solutions by magnetic barium hydroxyapatite nanoparticles

Magnetic barium hydroxyapatite (Fe3O4@BaHAP) nanoparticles were synthesised and used as a sorbent for the removal of several heavy metal ions from aqueous solutions. The sorbent characterisation was performed by scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), vibrating-sample magnetometer (VSM) and Fourier transform infrared spectroscopy (FTIR) techniques. A homemade device, named continuous collection of magnetic sorbent (CCMS), was designed for efficient removal of heavy metal ions from aqueous solutions and simultaneous collection of the sorbent by a permanent magnet at the end of the process. Results of BET analysis show that average pore diameter, average pore width, pore volume and specific surface area of the Fe3O4@BaHAP NPs were 10.9 nm, 11.6 nm, 0.16 cm3/g and 55.7 m2/g, respectively. Influential parameters on the removal efficiency were investigated and optimised using a central composite design method. The optimised values for solution pH, sorbent amount, stirring and circulating times were 6.2, 150 mg, 13 and 25 min, respectively. Magnetic BaHAP nanoparticles were shown to have higher removal efficiency than BaHAP or Fe3O4 alone. Under optimised conditions, adsorption capacities for Pb2+, Cr3+, Cd2+ and Cu2+ were 99.0, 66.5, 91.2 and 92.1 mg/g, respectively. The results demonstrated that the synthesised magnetic BaHAP nanoparticles can effectively remove several metal ions from contaminated water sources.