H₂S-Modified Fe–Ti Spinel: A Recyclable Magnetic Sorbent for Recovering Gaseous Elemental Mercury from Flue Gas as a Co-Benefit of Wet Electrostatic Precipitators

Abstract

The nonrecyclability of the sorbents used to capture Hg 0 from flue gas causes a high operation cost and the potential risk of exposure to Hg. The installation of wet electrostatic precipitators (WESPs) in coal-fired plants makes possible the recovery of spent sorbents for recycling and the centralized control of Hg pollution. In this work, a H 2 S-modified Fe–Ti spinel was developed as a recyclable magnetic sorbent to recover Hg 0 from flue gas as a co-benefit of the WESP. Although the Fe–Ti spinel exhibited poor Hg 0 capture activity in the temperature range of flue gas downstream of flue gas desulfurization, the H 2 S-modified Fe–Ti spinel exhibited excellent Hg 0 capture performance with an average adsorption rate of 1.92 μg g –1 min –1 at 60 °C and a capacity of 0.69 mg g –1 (5% of the breakthrough threshold) due to the presence of S 2 2– on its surface. The five cycles of Hg 0 capture, Hg 0 recovery, and sorbent regeneration demonstrated that the ability of the modified Fe–Ti spinel to capture Hg 0 did not degrade remarkably. Meanwhile, the ultralow concentration of Hg 0 in flue gas was increased to a high concentration of Hg 0, which facilitated the centralized control of Hg pollution.