Establishing a self-supporting system of H2S production from SO2 with induced catalytic reduction process for mercury capture with super-large enrichment

Abstract

Various sulfur (S) species in the environment possess different functions or adverse impacts, which highly depend on their existing states and forms. In a typical nonferrous smelting industry, the high concentration of SO2 is excrescent and needs further field upcycling, while such industry encounters a desperate shortage of sulfidation reagents (e.g., H2S or CuS) that are used for Hg0 capture in flue gas. Therefore, on-site reduction of SO2 to H2S or CuS for Hg0 capture is a feasible method to realize simultaneous SO2 upcycling and Hg0 immobilization. However, the low activity and rapid deactivation in direct reduction of SO2 with CO (DCRP) restrict actual application. To resolve the problems, an induced catalytic reduction process (ICRP) is established by refluxed partial COS to form nascent sulfurs (Sx*, x < 8), then Sx* is reduced to COS with CO. Subsequently, the obtained COS can be readily hydrolyzed to H2S. Results indicated that COS reduced SO2 showed five times higher rate than CO, which can significantly decrease the ramp from 400 to 375 °C. Moreover, it also can alleviate sulfation poison by COS induced effect because of preferential reaction sequence of SO2 with COS. Thus, the mechanism in ICRP was reasonablely transformed to mixed Mvk and E-R mechanism while DCRP was Mvk mechanism. Then, COS was readily hydrolyzed to H2S at 300 °C. Finally, the yielded H2S in-situ activated CuS exhibit a superior Hg0 capture performance with an adsorption capacity about 32.4 mg/g(CuS), which is 80 times higher than primitive CuS because of generated Sn2- in the presence of SO2 and H2O. This ICRP proved to be helpful in establishing a self-supporting system of H2S for SO2 reuse and Hg0 immobilization with super-large enrichment in nonferrous smelting industries.