Biochars from modified sugarcane bagasse for manganese removal from mining effluents

Abstract

Biochars from sugarcane bagasse (non-treated or pretreated with NaOH or H3PO4) were obtained at different pyrolysis temperatures (400 or 500 °C) and applied as adsorbents for removal of Mn(II) from aqueous solution. A detailed adsorption study of Mn(II) on the biochars was performed and mechanisms of Mn(II) removal were elucidated. The biochar with better adsorption performance was applied for Mn(II) removal from mining effluents. The pretreatment of biomass with NaOH and the lower pyrolysis temperature (400 °C) increased the number of basic oxygenated groups on the surface of adsorbent, favoring the Mn(II) adsorption. The biochar pretreated with base (up to 98% removal) was nearly twice more efficient for Mn(II) removal than that pretreated with acid. FTIR and XPS results showed that complexation between oxygenated groups and the metal is an important mechanism of adsorption. XRD and XPS results indicated the formation of MnO and cation exchange as other mechanisms for Mn removal. DFT calculations suggested that CO and C-OH groups on the biochar can favor a direct interaction between active carbons on BC surface and Mn(II). The biochar with best adsorption performance reached up to 65.8% of Mn(II) uptake from real mining effluent, showing the feasibility of using BC from sugarcane treated with NaOH to remove Mn from complex effluents. Practicality of employing the material was evaluated by reusability assays and cost estimations. Our findings point advance in the field of biochar application for Mn removal and reveal the importance of application of these materials in real conditions.