Recyclable Naturally Derived Magnetic Pyrrhotite for Elemental Mercury Recovery from Flue Gas

Abstract

Magnetic pyrrhotite, derived from the thermal treatment of natural pyrite, was developed as a recyclable sorbent to recover elemental mercury (Hg0) from the flue gas as a cobenefit of wet electrostatic precipitators (WESP). The performance of naturally derived pyrrhotite for Hg0 capture from the flue gas was much better than those of other reported magnetic sorbents, for example Mn–Fe spinel and Mn–Fe–Ti spinel. The rate of pyrrhotite for gaseous Hg0 capture at 60 °C was 0.28 μg g min–1 and its capacity was 0.22 mg g–1 with the breakthrough threshold of 4%. After the magnetic separation from the mixture collected by the WESP, the spent pyrrhotite can be thermally regenerated for recycle. The experiment of 5 cycles of Hg0 capture and regeneration demonstrated that both the adsorption efficiency and the magnetization were not notably degraded. Meanwhile, the ultralow concentration of gaseous Hg0 in the flue gas was concentrated to high concentrations of gaseous Hg0 and Hg2+ during the regeneration process, which facilitated the centralized control of mercury pollution. Therefore, the control of Hg0 emission from coal-fired plants by the recyclable pyrrhotite was cost-effective and did not have secondary pollution.