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.