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.