Long-term stabilization of realgar tailings via enhancing mineralogical transformation with microwave and FeSO₄...

The stabilization of realgar tailings is extensively employed to reduce the contamination from arsenic (As) leaching to the environment. The high efficiency of realgar oxidation and the formation of stable As-bearing minerals are crucial for the long-term stability of realgar tailings. Herein, the mineralogical transformation of labile As-bearing minerals, i.e., realgar and stabilization mechanisms of realgar tailings with microwave (MW) and FeSO₄ treatment were studied. Firstly, the activation of O₂ by FeSO₄ was enhanced and the generation of reactive oxygen species (ROS) was accelerated through MW treatment. Additionally, the mineralogical transformation to pararealgar due to "hot spots" on FeSO₄ under MW irradiation enhanced the oxidation of realgar. Pararealgar exhibited higher electrons delocalization and electron-donating ability compared than realgar based on density functional theory (DFT) calculations. Furthermore, the formation of stable As-bearing minerals in tailings was promoted after MW and FeSO₄ treatment, including crystalline Fe-As minerals and amorphous Ca-Fe-As minerals. Consequently, successful stabilization of realgar tailings was achieved with the As leachability <0.1 mg L^-1, which was below the Chinese standard limit (1.2 mg L^-1) for pollution control on the hazardous waste landfill. With 365 days of curing, the leachability of As in tailings furtherly decreased, demonstrating the long-term effectiveness of MW and FeSO₄ treatment. The long-term stability of realgar tailings was attributed to the increased proportions of crystalline Fe-As minerals and amorphous Ca-Fe-As minerals. Overall, this study provided a novel stabilization strategy toward realgar tailings as well as As-bearing mining wastes by using MW and FeSO₄ treatment.