Efficient capture and detoxification of gaseous arsenic trioxide from flue gas using silicomanganese alloy dust

This study aims to develop efficient capture materials for gaseous arsenic trioxide (As₂O₃(g)) that can prevent arsenic poisoning in selective catalytic reduction (SCR) systems and reduce atmospheric arsenic emissions from coal-fired power plants. One kind of metallurgical dust from a silicomanganese alloy plant (named as SiMnD) was found to be cost-effective and environmentally friendly for As₂O₃(g) removal from flue gas for the first time. The sorbent showed excellent performance for gaseous arsenic trioxides capture with a good capacity of 13.82 mg/g at 450 °C in 60 min, which was better than the other reported metal oxides at high temperature. The As₂O₃(g) capture capacity in 12-h continuous test reached as high as 118.16 mg/g without penetration, and the sorbent showed good long-term durability and pretty good resistance to high concentrations of nitric oxide (NO), sulfur dioxide (SO₂) and carbon dioxide (CO₂). The sorbent also exhibited good recyclability even after five regeneration cycles. Nearly 92% of As₂O₃(g) was transformed into manganese (II) pyroarsenate (Mn₂As₂O₇), manganese arsenate (MnAsO₄) and diarsenic pentoxide (As₂O₅) after capture with lower toxicity. The results of Toxicity Characteristic Leaching Procedure (TCLP) and five-step sequential extraction demonstrated that spent SiMnD exhibited low arsenic bioavailability, indicating reduced environmental mobility of arsenic species. Trimanganese tetroxide (Mn₃O₄) and blythite (Mn₃Mn₂(SiO₄)₃) were the most essential active component for As₂O₃(g) removal and detoxification. The optimal As₂O₃(g) capture temperature of SiMnD was 450 °C which was suitable to be applied before SCR with little operating cost. SiMnD was proved to be one excellent capture and detoxification agent for As₂O₃(g) in flue gas at a lower temperature with promising application prospects.