Adsorption, recovery, and regeneration of Cd by magnetic phosphate nanoparticles.

Adsorption plays an important role in removing cadmium (Cd2+) from water, and magnetic adsorbents are increasingly being used due to their ease of separation and recovery. Magnetic Fe3O4-coated hydroxyapatite (HAP) nanoparticles (nHAP-Fe3O4) were developed by co-precipitation and then used for the removal of Cd2+ from water. The properties of these nanoparticles were characterized by transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and magnetization curves. Experiments were conducted to investigate the effects of adsorption and mechanisms. Results illustrated that kinetic data were well fitted by a pseudo-second-order model. The adsorption capacity of nHAP-Fe3O4 was 62.14 mg/g. The mechanisms for the adsorption of Cd2+ on nHAP-Fe3O4 included rapid surface adsorption, intraparticle diffusion, and internal particle bonding, with the ion exchange with Ca2+ and chemical complexation being the most dominant. The regeneration efficiency and recovery rate of nHAP-Fe3O4 eluted by EDTA-Na2 after the fifth cycle were 63.04% and 40.2%, respectively. Results revealed that the feasibility of nHAP-Fe3O4 as an adsorbent of Cd2+ and its environmental friendliness make it an ideal focus for future research.