Light irradiation inhibits mercury adsorption by mineral sulfide sorbent.

• Amalgam plays an important role in the Hg0 immobilization process by CuS. • Light irradiation excited electron transfer on the Cu-terminated sites of CuS. • Light irradiation inhibited the formation of Cu amalgam and subsequent Hg0 capture. • Light irradiation in ESPs may limit Hg0 removal by mineral sulfide sorbents. An applicable way of mineral sulfide based remediators such as copper sulfide (CuS) for effective abatement of elemental mercury (Hg0) from coal-fired flue gas is to inject them prior to electrostatic precipitators (ESPs), in which light irradiation widely exists because of the corona discharge. A systematical investigation of Hg0 removal by CuS sorbent under light irradiation was conducted for the first time. The results show that light irradiation significantly inhibited the Hg0 removal efficiency of the CuS sorbent. The normalized Hg0 concentration at the reactor outlet even quickly increased from 0 to 0.45 once a lamp was turned on. Light irradiation excited a transfer of electrons on the Cu-terminated sites from inner Cu 3d orbit to outer Cu 4s orbit, and hence inhibited the formation of copper amalgam, which was supposed to be a key step in Hg0 immobilization by the CuS sorbent. Moreover, light irradiation accelerated the decomposition of copper amalgam to Hg0 which re-emitted to the gas flow. With these novel insights into the role of light irradiation concerning Hg0 removal over mineral sulfides, this work can provide guidance for selecting and adopting proper mineral sulfides in real-world coal combustion conditions to replace traditional activated carbons. [ABSTRACT FROM AUTHOR]