Metallic oxides derived from red mud efficiently loaded onto distillers grains biochar enhancing the removal of Pb(Ⅱ)/Zn(Ⅱ) from wastewater

Background As common toxic heavy metals, the combined pollution of Pb(II) and Zn(II) is difficult to remove simultaneously due to the competition between ions, so it is necessary to develop an efficient synergistic treatment strategy. Method The study involved synthesizing functional biochar by co-pyrolyzing DGs with RM, followed by a comprehensive evaluation of its Pb(II)/Zn(II) adsorption capabilities in aqueous environments. Significant findings Multidimensional characterization results confirmed that DGs and RM were well combined, where red mud-derived functional material, such as oxygen-containing functional groups and metallic oxides, successfully loaded onto the distillers' grains-based biochar. Further, the surface properties were also remarkably modified, such as the pore structure and specific surface area were improved, the alkalinity was increased, and magnetic properties were introduced. These modified properties were identified as crucial factors governing Pb(II)/Zn(II) adsorption efficiency. The red mud-modified biochar (RM-DC) exhibited significantly enhanced adsorption capacities for Pb(II) (294.335 mg g -1 ) and Zn(II) (41.456 mg g -1 ) at ambient temperature, representing notable improvements over the pristine biochar (185.038 and 25.038 mg g -1 , respectively). The conformity to both pseudo-second-order kinetics and the Langmuir-Freundlich isotherm model suggests that the adsorption process is characterized by chemical adsorption and multimolecular layer formation. The adsorption of both Pb(II) and Zn(II) on RM-DC was determined to be endothermic and spontaneous. Pb(II) immobilization proceeded through combined surface precipitation, complexation, ion exchange, and electrostatic attraction, while Zn(II) removal was predominantly achieved via ion exchange and electrostatic interactions. RM-DC exhibited promising adsorption capability in treating authentic acid mine drainage, highlighting its potential for practical wastewater purification. This study explores a new way to reuse the industrial bulk solid wastes and provides a highly efficient strategy for heavy metal elimination.