One-step removal of anionic/cationic heavy metal ions from wastewater by magnetic amphoteric adsorbent

Simultaneous treatment of wastewater containing anionic and cationic pollutants in an easy-to-operate and environmentally friendly manner is a formidable challenge in environmental remediation. This work designed a low-cost and high-efficient amphoteric adsorbent Fe3O4/Mg-Al LDOs/AlS (SMA) for the simultaneous removal of Cr (VI) and Cu (II) pollutants from wastewater in one step. SMA is prepared with waterworks aluminum-containing sludge (AlS) from typical municipal engineering waste as the base material and loaded with magnetic nanoparticles to enhance recycling process after adsorption. SMA exhibits large specific surface area (similar to 418 m(2)/g), thereby providing sufficient adsorption active sites. Adsorption studies indicate that the adsorption of SMA toward two pollutants conforms to the pseudo-second-order kinetic model, while the Langmuir model is used to simulate the adsorption isotherm. The maximum adsorption capacity is calculated to be 235.3 mg/g for Cr (VI) and 669.2 mg/g for Cu (II). Thermodynamic studies reveal the process's spontaneous nature. The main adsorption mechanisms involve electrostatic attraction, surface complexation, isomorphic replacement, and chemical precipitation. Notably, SMA exhibits excellent adsorption performance in a wide pH range and water system containing multiple anions and cations. Moreover, the strong magnetic property facilitates easy separation and recovery through an external magnetic field, maintaining stable adsorption performance even after five cycles. Therefore, this study provides a win-win strategy for promoting environmental safety, not only proposing feasible approaches for the high value-added utilization of waste sludge, but also efficiently addressing the purification problem of complex anionic and cationic coexisting wastewater.