Adsorption mercury, cobalt, and nickel with a reclaimable and magnetic composite of hydroxyapatite/Fe3O4/polydopamine

In the current investigation, the adsorptive performance of hydroxyapatite (HAp) was improved by using Fe3O4 magnetic nanoparticles and polydopamine (PDA) and was applied to eliminate Hg(II), Co(II), and Ni(II). The tests of XPS, XRD, EDX, FTIR, TGA, and VSM were applied to identify the HAp/Fe3O4/PDA structure and adsorption mechanisms. Based on the finding, pH was of the most effective variables in the elimination process and the highest yield was determined at pH 6 for all studied metals. The equilibrium data followed the Langmuir and Freundlich models (R2 > 0.9). According to isotherm modeling, Hg(II), Co(II), and Ni(II) removal using HAp/Fe3O4/PDA has a physical mechanism. The highest elimination capacity (qm) for Hg(II), Co(II), and Ni(II) was set at 51.73 mg/g, 49.32 mg/g, and 48.09 mg/g, respectively. The effect of contact time had a good consistency with the findings of the Weber and Morris kinetic, as the process was done in two steps. The Gibbs free energy parameter revealed that the abatement process is spontaneous and its spontaneity degree decreases with elevating temperature. Various analyzes were used to explore the characteristics of the HAp/Fe3O4/PDA composite. In summary, HAp/Fe3O4/PDA had an effective capability to remove toxic metals from distilled water and landfill leachate. [Display omitted] •Hydroxyapatite (HAp) was magnetically composited with Fe3O4 and polydopamine (PDA).•The crystalline and mesoporous adsorbent of HAp/Fe3O4/PDA had a BET area > 37 m2/g.•The highest metal removal efficiency (> 92%) was obtained at pH 6.•The highest elimination capacity for Hg, Co, and Ni was obtained > 48 mg/g.•HAp/Fe3O4/PDA was used to remove metals from a landfill leachate.