Nanosized Cu-In spinel-type sulfides as efficient sorbents for elemental mercury removal from flue gas

Mercury emitted from human activities has received increasing attention because of its extreme toxicity, persistence and bioaccumulation. The development of highly-efficient sorbent with abundant active sites that exhibit high affinity toward Hg⁰ is the key challenge for elemental mercury capture at low temperature. Herein, Cu-In spinel-type sulfides were synthesized through a hydrothermal synthesis. The Hg⁰ removal performance of Cu_xIn_2-xS₂ sorbents was evaluated in the temperature range of 75 °C to 175 °C. The synthesized Cu_xIn_2-xS₂ sorbents showed excellent performance for Hg⁰ removal at low temperatures, which perfectly matches the optimal temperature of flue gas at the downstream of desulfurization system. Hg⁰ removal efficiency of Cu_xIn_2-xS₂ sorbents significantly improved as the Cu proportion increased. CuInS₂ sorbent showed superior mercury removal performance, the mercury removal efficiency reached 99.6% at 125 °C. O₂ and NO showed a slight inhibition on Hg⁰ capture. The coexistence of SO₂ and H₂O showed no obvious negative effects on Hg⁰ removal. The CuInS₂ sorbent displayed a superior tolerance to SO₂ and H₂O. TPD and XPS analyses demonstrated that the adsorbed mercury mainly existed in the form of mercuric sulfides (HgS). Hg⁰ adsorption over CuInS₂ sorbent occurred via the Mars-Maessen mechanism. In this mechanism, Hg⁰ vapor was physically adsorbed on CuInS₂ sorbent and then converted to HgS. This study provides future potential for applying Cu_xIn_2-xS₂ sorbents to capture gaseous mercury at low temperature.