In-situ utilization of As(III) enhances selective recovery of heavy metals from acid mine drainage by hydroxyl-enriched Fe-Mn binary oxide

As(III), a common pollutant in acid mine drainage (AMD), can provide potential active sites for the adsorption of heavy metals on adsorbents. In this study, Pb(II), As(III), and Cu(II) were sequentially recovered from AMD using hydroxyl-enriched Fe-Mn binary oxide (O-FMO) via the in-situ utilization strategy of As(III). The results showed that the prepared O-FMO demonstrated better adsorption performance under acidic conditions than FMO. O-FMO exhibited an outstanding selectivity (＞99.6%) for the removal of Pb(II) and As(III) via the generation of insoluble As-Pb complex in AMD and the immobilized Pb and As could be subsequently separated using respective acid and alkaline solutions. Furthermore, the recovered O-FMO containing residual As could promote the selective removal of Cu(II) (Selectivity ＞98.4 %) from the treated AMD. Mechanism analysis revealed that the oxidized As(V) on the O-FMO played a dominant role in promoting metals adsorption via electrostatic interaction and complexation. Pb(II) can directly form a generally stable complex with H3AsO4 (As(V)) under acidic conditions, thereby replacing the Cu(II) and Cd(II) which only form acid-soluble complexes with H2AsO4-1 (As(V)). Besides, metal electronegativity affects the traits and the formation sequence of As-metal complexes. Hence, the recovery of metal(loid)s (purity > 98.4 %) from AMD following the order: Pb(II), As(III), and Cu(II) could be achieved by reutilizing O-FMO. This work offers a unique approach for AMD remediation by utilizing pollutants to treat pollution.