Functional biochar fabricated from waste red mud and corn straw in China for acidic dye wastewater treatment

Red mud (RM) is an industrial waste that needs proper disposal without incurring hazards to the environment. In this study, we used RM and corn straw (CS) to fabricate functional biochar composites (FBCs) via pyrolysis. We fully characterized the changes in morphology and composition on the preparation of FBCs at different pyrolytic temperature and the gaseous products during pyrolysis. It was found that a porous structure was generated on CS, endowing FBCs with the ability to remove dyes in water. Moreover, CaO was created through the decomposition of CaCO3 in RM at ~700 °C, suggesting that FBCs could be used to neutralize the acidic wastewater. Hence, FBCs showed excellent performance in treating acidic dye wastewater, a common industrial wastewater with high contents of acid and dye and for which disposal is laborious. Additionally, FBCs exhibited magnetism because magnetic zero-valent iron was generated by the reduction of ferric oxide in RM with the CS gaseous product (CO) during pyrolysis. This work provided a dual-win strategy for waste recyclability and wastewater treatment, and the proposed method may have potential applications. [Display omitted] •FBC was fabricated from solid wastes of red mud and corn straw via pyrolysis.•The mechanism of structural transformation was investigated.•FBC could remove dyes and alleviate acid upon treatment with acidic dye wastewater.•FBC was collectable by magnet after wastewater treatment.•A dual-win strategy to recycle solid wastes and remedy acidic dye wastewater.