Tunnel manganese oxides prepared using recovered LiMn2O4 from spent lithium-ion batteries: Co adsorption behavior and mechanism

The purpose of this study was to investigate Cobalt (Co) removal from wastewater using synthesized manganese oxides from the recovered LiMn2O4. An efficient ultrasonication leaching method was utilized to recycle LiMn2O4 from spent lithium-ion batteries (LIBs). The recovered LiMn2O4 was used to synthesize tunnel λ-MnO2, γ-MnO2 and β-MnO2 by acid leaching and hydrothermal methods. Meanwhile, Li+ in the supernatant was recycled by the precipitation of Li3PO4. Subsequently, for the synthesized tunnel MnO2, various characterizations and sodium hydroxide titration in NaNO3 solution were performed. The effect of sorption studies presented the uptake of Co increased with the pH increasing from pH ~1 to pH ~8 and the isothermal sorption at pH ~6 showed that γ-MnO2 possessed the highest uptake amount 0.44 meq/g, and the highest distribution coefficient 2.5 × 105 mL/g. Moreover, γ-MnO2 was found without Mn3+/Mn2+ leached during the sorption process. The ion exchange-surface complexation model was adopted to study the titration, effect of pH and isotherm sorption on the ion exchange reaction mechanism of Co adsorption. Overall, this work provides an economically feasible and environmentally friendly method to recycle the spent LIBs and the γ-MnO2 synthesized from the recovered LiMn2O4 was proved to be promising adsorbents for Co removal. [Display omitted] •Cathode/anode were recycled by ultrasonication with dilute NaOH/water.•Tunnel MnO2 were synthesized using recovered LiMn2O4.•γ-MnO2 without Mn3+/Mn2+ leached during the Co sorption process.•Primary ion-exchange and sorption reactions happened on MnO2 surfaces.•SsOCo+ was the main sorption species from the Co2+ and SsONa sites andSsO- sites reactions.