Enhanced adsorption of heavy metals from sludge incineration flue gas by activated boron nitride: the critical role of SO2

Non‑carbon adsorbents with excellent thermal stability are urgently needed for heavy metal control in sludge incineration flue gas. In this study, activated boron nitride (A-BN) with a high specific surface area (1308 m 2 /g) was synthesized via an organic precursor method. The effects of typical flue gas components (O 2 , CO 2 , SO 2 ) on the adsorption performance of A-BN for Zn, Cu, Pb and Cd in sludge incineration flue gas was systematically investigated. The results showed that O 2 (6 vol%) slightly enhanced the heavy metal adsorption capacity of A-BN, increasing the total adsorption capacity for the four heavy metals from 137.83 mg/g to 193.41 mg/g, while CO 2 exerted a slight inhibitory effect with the total adsorption capacity reduced to 129.66 mg/g. Notably, SO 2 demonstrated a significant promoting effect. At the optimal concentration of 700 ppm and the optimal adsorption temperature of 400 °C, the total adsorption capacity reached 545.20 mg/g, corresponding to a 2.81-fold increase compared to that in the simulated flue gas without SO 2 . The promotion mechanism was elucidated: SO 2 , in the presence of O 2 and trace moisture, is converted into surface sulfate and bisulfate species (SO 4 2− /HSO 4 − ), which serve as new polar active sites that enhance heavy metal chemisorption and sulfation. A-BN exhibits excellent SO 2 tolerance, high adsorption capacity, and rapid adsorption kinetics (reaching equilibrium within approximately 40 min), demonstrating great potential as a novel non‑carbon adsorbent for controlling heavy metal emissions in sludge incineration flue gas.