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

Highlights: • Cu_xIn_2-xS₂ sorbents were used to remove Hg⁰ from coal-fired flue gas. • About 99.6% Hg⁰ removal efficiency was achieved for CuInS₂ sorbent at 125 °C. • CuInS₂ exhibited a superior tolerance to SO₂ and H₂O during Hg⁰ removal. • Chemisorption mechanism is responsible for Hg⁰ adsorption on CuInS₂ sorbent. 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.