LAUSR

Abstract The mechanism of MW irradiation for the enhancement of the long-term stability of arsenic (As) in FeSO4-treated realgar tailings was studied. The efficiency of As stabilization reached 99.5% in the MW-FeSO4-air system, 1.35–fold of that in the FeSO4-air system (71.8%). The increased As stability in realgar tailings was attributed to the enhanced transformation of more stable Fe–As minerals (e.g. symplesite) from unstable Ca/S–As minerals (pharmacolite and realgar). The oxidation of realgar was accelerated by reactive oxygen species (ROS) through the activation of molecular oxygen with FeII of FeSO4 due to the MW athermal effect in the MW-FeSO4-air system. H+ ions from realgar oxidation and FeSO4 hydrolysis facilitated the dissolution of pharmacolite. The released As was captured by the formed ferric oxyhydroxide. “Hot spots” on FeSO4 in MW field initiated the microstructural evolution to Fe–As crystalline minerals due to the MW thermal effect. The introduction of FeSO4 and oxygen promoted the generation of ROS and “hot spots” in MW field, which contributed to the transformation from Ca/S–As minerals to Fe–As crystalline minerals and was of great significance for the long-term stability of As in realgar tailings.