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

Zerovalent iron (Fe0)-based biochar (Fe0-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 Fe0-BC (RMIS1:1) via co-pyrolysis strategy, which was confirmed with remarkable capacity in peroxydisulfate (PDS) activation. The removal efficiency of sulfadiazine (SDZ) was 99.7% in RMIS1:1/PDS system in 20 min, with kobs of 0.3001 min−1. Both free radicals (SO4−, OH, and O2−) and non-free radicals (1O2) were responsible for SDZ degradation, in which the SO4− and O2− 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 RMIS1:1 dosage, the initial SDZ concentration had stronger effect on its degradation. Co-existed Cl− slightly improved SDZ degradation rate, while other anions (NO3–/SO42−/HCO3–/CO32–) and humic acid exhibited different levels of inhibition on SDZ removal. Moreover, RMIS1:1/PDS maintained acceptable degradation ability for practical pharmaceutical wastewater. The electrical energy per mass of SDZ was about 2.24 kWh/(g·SDZ) by RMIS1:1/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 Fe0-BC preparation from RM, which was valuable for both waste resource recycling and environmental remediation.