Dual activation of persulfate by microwave-triggered composite modified biochar: Synergistic PAHs degradation and self-buffered pH control in soil remediation

The activation process of persulfate (PS) often leads to the production of hydrogen ions, causing soil acidification and potential secondary pollution risks. This work developed a composite modified biochar loaded with potassium ferrate (KFe@KBC). A microwave-assisted KFe@KBC-activated PS system was established to simultaneously remediate benzo[a]pyrene (BaP, a model of PAHs) contaminants and mitigate soil acidification. Results showed that ferrate loading introduced Fe–O bonds and created a multivalent iron environment on KFe@KBC, suggesting the possible involvement of ferrate-derived intermediate iron species in the oxidation process..Under the most favorable conditions identified by a triangular radar chart-based comparative evaluation (microwave power: 490 W; PS concentration: 0.8 mol/L; KFe@KBC dosage: 4 wt%; K 2 FeO 4 loading: 4 wt%; soil moisture content: 20%), the removal efficiency of BaP reached 98.92%, and the soil pH stabilized at approximately 6.91. The remediation process transformed compact soil into a more porous structure, with increased silt and clay content, enhancing aeration and water retention properties. BaP degradation proceeded through radical-induced ring-opening and chain-cleavage reactions, eventually mineralizing into CO 2 and H 2 O. Electron paramagnetic resonance and radical quenching experiments identified SO 4 • − , •OH, O 2 • − , and 1 O 2 as the primary active species driving degradation through combined radical and non-radical pathways. Besides, toxicity prediction indicated significantly reduced toxicity and accumulation potential of degradation products.