Amorphous Mn-La oxides immobilized on carbon sphere for efficient removal of As(Ⅴ), Cd(Ⅱ), and Pb(Ⅱ): Co-adsorption and roles of Mn species

Simultaneous removal of cation (e.g., Pb(Ⅱ), Cd(Ⅱ)) and oxyanion (e.g., As(Ⅴ)) heavy metals have attracted increasing interest for adsorption applications due to the complexity of heavy metal polluted groundwater. Manganese-lanthanum binary oxides immobilized on hydrothermal carbonization carbon (Mn x La 1-x @HTCC) were therefore rationally designed in this work, and the Mn-La oxides immobilized on HTCC exhibited more uniform dispersion compared to bulk phase. In single adsorption systems, superior adsorption of different heavy metals could be achieved by tuning the molar ratio of Mn to La, and Mn leaching was reduced by ∼ 75% compared with Mn@HTCC (without La doping). In the coexisting systems, the simultaneous presence of As(Ⅴ) and Pb(Ⅱ) greatly enhanced adsorption of both two heavy metals, while competition was observed in the coexistence of As(Ⅴ) and Cd(Ⅱ). By analyzing the “release-readsorption” phenomenon of Mn and the variation of Mn valence during adsorption, the different roles of Mn species in the removal of three heavy metals were proposed. Finally, high-speed flow adsorption column experiments confirmed that the Mn x La 1-x @HTCC composite can effectively and continuously adsorb heavy metals accompanied by trace Mn leaching content. Overall, this study indicates the potential of Mn-La carbon composites as a novel adsorbent in groundwater remediation.