Novel preparation of sludge-based spontaneous magnetic biochar combination with red mud for the removal of Cu2+ from wastewater.

[Display omitted] • Alternative methods for the resource utilization of municipal sludge and red mud. • Ammonium oxalate was applied to the activation of sludge and red mud for the first time, which provided amino functional groups and reduction. • Fe 2 O 3 in the red mud is reduced to Fe 3 O 4 and Fe0 during co-pyrolysis, biochar obtained in situ magnetization. • The actual adsorption capacity of adsorbent SRMBC-750 was 242.62 mg/g, which exhibited excellent adsorption capacity for Cu2+. In this study, municipal sludge and red mud were used as raw materials to prepare spontaneous magnetic biochar (SRMC-750) for the adsorption of Cu2+ from wastewater. The experimental findings demonstrated that the maximum actual adsorption capacity was 242.62 mg/g at 25 °C and pH 5. The adsorption process followed the pseudo-second-order kinetic model and the Freundlich isotherm model. The potential adsorption mechanisms were electrostatic attraction, complexation, cation-exchange, and "cation-π". After five adsorption cycles, SRMBC-750 still had 75% removal efficiency for Cu2+. Overall, SRMBC-750 provides a potential pathway for the removal of Cu2+ from wastewater. [ABSTRACT FROM AUTHOR]