Enhanced removal of heavy metal ions from aqueous solution using manganese dioxide-loaded biochar: Behavior and mechanism

In this study, a redox precipitation method was used to load manganese dioxide (MnO2) nanoparticles on biochar (BC) (BC@MnO2) pyrolyzed from the invasive water hyacinth, and the adsorption of Cd(II),Cu(II), Zn(II), and Pb(II) was investigated. Several techniques were used to characterize the adsorbents. The results revealed that the BC surface was covered by many intertwined thin amorphous MnO2 nanosheets, which significantly increased its specific surface area and pore volume. The adsorption of heavy metal ions by BC was negligible, whereas the MnO2-containing adsorbents exhibited a high capacity for adsorbing heavy metal ions. However, the MnO2-normalized adsorption amount decreased with increasing MnO2 load and was largely unchanged at MnO2 loads of 26.6% to 30.2%. The capacity for adsorbing heavy metal ions of BC@MnO2 was pH-dependent, but the adsorption affinity was unaffected by coexisting ions. Column tests revealed that BC@MnO2 with a load of 26.6% had a high capacity for removing heavy metal ions from simulated and real electroplating wastewater. Therefore, BC@MnO2 with a load of 26.6% shows promise as a regenerable adsorbent for removing heavy metal ions from water/wastewater. This study could lay an essential foundation to develop a win-win strategy for heavy metal ions removal from wastewater using biochar derived from water hyacinth.