Melamine sponge loading improves the separation performance of magnetic hydroxyapatite for Pb(Ⅱ) adsorption

Magnetic materials as adsorbents for wastewater treatment have attracted considerable attention because of the ease of separation of adsorbents for reuse. However, the efficient separation of magnetic materials, particularly nanoscale materials, remains challenging. Therefore, in this study, we developed an innovative method to enhance the separation performance of magnetic hydroxyapatite (MP) using melamine sponge (MS) loading. It was found that, although the magnetic moments of MP decreased from 15.54 emu/g to 11.51 emu/g after MS loading, MS-loaded MP (MPMS) exhibited better magnetic separation performance than MP. The analysis of adsorption isotherms suggests that the theoretical maximum adsorption capacity of Pb2+ at an initial pH of 4.85 using MPMS was 139.28 mg/g. Combined with adsorption kinetics and thermodynamics analysis, adsorption was categorized as a chemical, heterogeneous, and endothermic process. Moreover, in the adsorption mechanism, cation exchange, electrostatic interaction, dissolution/precipitation, and surface complexation mechanisms contributed 70.96%, 4.39%, 6.10%, and 18.55%, respectively, to the total Pb2+ removal under the experimental conditions. Hence, we provide a quick and low-cost solution for enhancing the downstream separation of magnetic adsorbents for reuse.