Synthesis of NaAlSiO₄ Hollow Microspheres as Absorbents for the Removal of Heavy Metal Ions from Wastewater

In this study, NaAlSiO₄ hollow microspheres for Ni(II) and Cd(II) removal from wastewater were synthesized through a solvothermal method combined with calcination treatment. The hollow microspheres were characterized by SEM, TEM, DSC, XRD, FT-IR, and N₂ adsorption/desorption analyzer. The average diameter of microspheres was approximately 2 ± 0.5 μm, and the average pore size was approximately 20 ~ 60 nm. The removal ability was evaluated under different conditions, including various pH values, metal ion concentrations, and adsorption times. Results show that the adsorption capacity of the NaAlSiO₄ hollow microspheres depends on the surface area and the content of hexadecyl trimethyl ammonium bromide for Ni(II) and Cd(II), respectively. The maximum adsorption capacity calculated from Langmuir models was 297.11 mg/g for Ni(II) and 449.71 mg/g for Cd(II). The adsorption isotherm and kinetic fitting preferably agree with the Langmuir isotherm model with monolayer coverage. The Ni(II) adsorption efficiency was still more than 95% (Cd(II) adsorption efficiency significantly decreased to 23%) after four cycles, suggesting the high reusability of the hollow microspheres for Ni(II). The successful removal of Ni(II) and Cd(II) from water samples demonstrates the great potential of the proposed NaAlSiO₄ to remediate Ni(II) and Cd(II) polluted water in environmental remediation.