Microwave-assisted arsenic removal and the magnetic effects of typical arsenopyrite-bearing mine tailings

• A novel microwave technique is used to remove arsenic (As) from intractable arsenopyrite-bearing mine tailings.
• Fe3O4 and Fe2O3 are optimized microwave-absorbing agents that assist arsenic removal.
• The magnetic effect increases with the As-removal efficiency.
• Arsenic can be separated from the tailings in the form of As (elemental form).
• Arsenopyrite and pyrite are converted into valuable pyrrhotite and magnetite.

A novel method for removing arsenic (As) from intractable arsenopyrite (FeAsS)-bearing mine tailings was investigated that used a microwave technique. Although the tailings were poor microwave absorbers, absorption was indirectly assisted by adding various microwave-absorbing materials (MAMs), including MnO2 (oxidant), C (reductant), Fe3O4 and Fe2O3. The results revealed that the type of MAM and the microwave runtime significantly affected the efficiency of As-removal from the tailings and the magnetic effects of the reaction residuals. Compared with MnO2 and C, the best As-removal efficiencies of the tailings and the magnetic effects of the reaction residuals were obtained using Fe3O4 (90.12%, 24997.03 × 10−8 m3/kg, in 4 min) and Fe2O3 (92.10%, 19774.73 × 10−8 m3/kg, in 14 min). In addition, their As-removal efficiencies positively contributed to the magnetic effects, which increased with the microwave runtime. The obtained products were characterized by using a variety of analytical techniques (e.g., SEM, EDAX and XRD). Overall, Fe2O3 and Fe3O4 underwent similar As-removal pathways and magnetic products. Arsenic was mainly removed in the form of As (elemental form) and AsS in the oxygen-free atmosphere, and As2O3 was removed in the oxidizing atmosphere. Meanwhile, the arsenopyrite (FeAsS) and pyrite (FeS2) in the tailings, mixed with Fe2O3 or Fe3O4, were mainly converted into valuable pyrrhotite (Fe1−xS and FeS) and magnetite (Fe3O4) in the oxygen-free atmosphere. This study provides a feasible and environmentally friendly method for removing arsenic from tailings (or minerals), regardless of their microwave-absorbing properties.