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

Abstract

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 CuxIn2-xS2 sorbents was evaluated in the temperature range of 75 °C to 175 °C. The synthesized CuxIn2-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 CuxIn2-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 CuxIn2-xS2 sorbents to capture gaseous mercury at low temperature.