A green strategy from waste red mud to Fe0-based biochar for sulfadiazine treatment by peroxydisulfate activation

Zerovalent iron (Fe 0 )-based biochar (Fe 0 -BC) has attracted wide attention in activating persulfate to eliminate antibiotics. In this study, the waste red mud (RM) was successfully used as an iron precursor to prepare Fe 0 -BC (RMIS 1:1 ) via co-pyrolysis strategy, which was confirmed with remarkable capacity in peroxydisulfate (PDS) activation. The removal efficiency of sulfadiazine (SDZ) was 99.7% in RMIS 1:1 /PDS system in 20 min, with k obs of 0.3001 min −1 . Both free radicals (SO 4 − , OH, and O 2 − ) and non-free radicals ( 1 O 2 ) were responsible for SDZ degradation, in which the SO 4 − and O 2 − played the dominant roles. Four SDZ degradation pathways were provided according to the intermediates identified by Q-TOF-MS. Furthermore, the ECOSAR prediction implied that the intermediates have less eco-toxicity than SDZ. Compared with PDS concentration and RMIS 1:1 dosage, the initial SDZ concentration had stronger effect on its degradation. Co-existed Cl − slightly improved SDZ degradation rate, while other anions (NO 3 – /SO 4 2− /HCO 3 – /CO 3 2– ) and humic acid exhibited different levels of inhibition on SDZ removal. Moreover, RMIS 1:1 /PDS maintained acceptable degradation ability for practical pharmaceutical wastewater. The electrical energy per mass of SDZ was about 2.24 kWh/(g·SDZ) by RMIS 1:1 /PDS, lower than that produced in any other advanced oxidation processes that have been reported so far. In summary, this study reported a green strategy for Fe 0 -BC preparation from RM, which was valuable for both waste resource recycling and environmental remediation.