Magnetic pyrrhotite, derived from the thermal treatment of natural pyrite, was developed as a recyclable sorbent to recover elemental mercury (Hg) from the flue gas as a cobenefit of wet electrostatic precipitators (WESP). The performance of naturally derived pyrrhotite for Hg 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 Hg capture at 60 °C was 0.28 μg g min and its capacity was 0.22 mg g 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 Hg capture and regeneration demonstrated that both the adsorption efficiency and the magnetization were not notably degraded. Meanwhile, the ultralow concentration of gaseous Hg in the flue gas was concentrated to high concentrations of gaseous Hg and Hg during the regeneration process, which facilitated the centralized control of mercury pollution. Therefore, the control of Hg emission from coal-fired plants by the recyclable pyrrhotite was cost-effective and did not have secondary pollution.

Goethite, one of the most thermodynamically stable iron oxides, has been extensively researched especially the structure (including surface structure), the adsorption capacity to anions, organic/organic acid (especially for the soil organic carbon) and cations in the natural environment and its potential application in environmental protection. For example, the adsorption of heavy metals by goethite can decrease the concentration of heavy metals in aqueous solution and immobilize; the adsorption to soil organic carbon can decrease the release of carbon and fix carbon. In this present overview, the possible physicochemical properties of the goethite surface contributing to the strong affinity of goethite to nutrients and contaminants in natural environment are reported. Moreover, these chemicals adsorbed by goethite were also summarized and the suggested adsorption mechanism for these adsorbates was elucidated, which will help us understand the role of goethite in natural environment and provide some information about goethite as an absorbent. In addition, the feasibility of goethite used as catalyst carrier and the precursor of NZVI was proposed for removal of environmental pollution.

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