Synergistic upcycling of sewage sludge and rice straw into magnetic biochar for enhanced Sb(V) removal: Adsorption performance and mechanisms

The widespread use of antimony (Sb) in textile catalysis has led to wastewater contamination dominated by Sb(OH) ₆ ^- , which is difficult to remove using conventional treatments. This study presented a sustainable waste-to-value strategy for the synergistic upcycling of sewage sludge and rice straw into a magnetic biochar (MBC) for Sb(V) removal. The optimized MBC, M _0.3 -S/R(4:1)-BC, was synthesized through co-pyrolysis combined with iron co-precipitation, yielding a composite with enhanced specific surface area, abundant oxygen-containing functional groups and well-dispersed iron oxide particles, achieving a high Sb(V) removal efficiency of > 90% at a low dosage of 0.5 g/L within a wide pH range (pH 4 ~ 10). The adsorption process followed the pseudo-second-order and Langmuir models with a maximum adsorption capacity of 47.50 mg/g, was spontaneous and endothermic. Spectroscopic analysis and density functional theory (DFT) calculations revealed that the mechanism was primarily governed by strong chelation with -Fe-O-Fe groups ( E _ads = -367.36 eV), aided by ligand exchange with -COOH groups ( E _ads = -103.65 eV), hydrogen bonding with -OH/-NH ₂ groups and π-π interactions with aromatic rings. The MBC retained 72% of adsorption efficiency after five regeneration cycles and demonstrated effective Sb and P elimination in real textile wastewater, highlighting the practical promise of this synergy-driven, waste-derived adsorbent for sustainable water treatment.