A Novel Cross-Linked Magnetic Hydroxyapatite/Chitosan Composite: Preparation, Characterization, and Application for Ni(II) Ion Removal from Aqueous Solution

In this study, a novel magnetic hydroxyapatite/chitosan composite (HA/Fe3O4/CS) prepared from steel slag, shrimp shells, and bovine bones, and then cross-linked with a green tea extract was used as an adsorbent for Ni(II) ion removal from aqueous solution. Various techniques (SEM, FTIR, XRD, VSM) were used to characterize the adsorbent. Batch experiments were conducted to investigate the adsorption properties of Ni(II) ions on HA/Fe3O4/CS. The optimum conditions for the adsorption process were studied in detail. The adsorption isotherm, mechanism, kinetics, and thermodynamics were further discussed. Besides, the desorption and reusability of the adsorbent were evaluated for further applications. The results indicated that the HA/Fe3O4/CS composite has the potential application for removal of Ni(II) ions from aqueous solution with a maximum adsorption capacity of 112.36 mg/g at optimal conditions (pH of 6, contact time of 60 min, room temperature, and adsorbent dose of 3 g/L). The adsorption process of Ni(II) on HA/Fe3O4/CS was feasible, spontaneous, exothermic, and more favorable at lower temperature. Adsorption isotherm and kinetics were suitable to be described by the Langmuir model and pseudo-second-order kinetic equation, respectively. Recycling results confirmed that the HA/Fe3O4/CS composite maintains a great reusability potential for five consecutive cycles with Ni(II) removal efficiency of greater than 85%. The adsorbent can be easily regenerated by using HCl and EDTA solutions. The overall study revealed that the magnetic hydroxyapatite/chitosan composite can be applied as a low cost, environmental friendly, and highly efficient adsorbent for removal of Ni(II) ions from wastewater because of its high adsorption capacity, easy recovery, and good reusability.