Arsenic removal from coal-fired flue gas by MnO2 coated magnetic flower-like Fe3O4 composites: Experimental and DFT study

The gaseous arsenic (mainly As2O3) emitted from coal combustion has become another highly toxic volatile pollutant of concern after mercury. Unlike high-temperature arsenic removal technology, injecting adsorbents before dust collectors has more industrial application prospects, where the development of high-performance arsenic removal adsorbents at low temperatures (100–200 °C) is the core. This work developed a magnetic recyclable MnO2 coated magnetic flower-like Fe3O4 (FL-Fe3O4) composites (Fe3MnxOy) adsorbent. It shows the prepared FL-Fe3O4 has both adsorption and catalytic effects on As2O3 removal from the flue gas. The As2O3 removal amount and efficiency of Fe3MnxOy reaches their maximum at 102.96 μg/g and 55.04 % at Mn/Fe molar ratio of 1 (Fe3Mn3Oy) where the comprehensive effect of the adsorption, oxidation, and fixation of As2O3 on Fe3MnxOy gets to optimal. Lattice oxygen plays an important positive role in the arsenic removal process and O2 can continuously supplement it. Priority adsorption of SO2 will consume lattice oxygen and convert it into SO42-, which inhibits the As2O3 removal by Fe3Mn3Oy. Finally, the influence mechanism of MnO2 coating and SO2 on As2O3 removal by Fe3MnxOy was deeply revealed based on density functional theory calculations. The finding has a vital promoting effect on the industrial application of flue gas arsenic removal technology.