Novel Synergistic Effect of Fe and Mo in FeMoS_x/TiO₂ for Recovering High Concentrations of Gaseous Hg⁰ from Smelting Flue Gas: Reaction Mechanism and Kinetics

Abstract

There is a high demand for developing a more effective and environment-friendly technology to substitute the complicated and hazardous Boliden–Norzink technology for recovering gaseous Hg0 from smelting flue gas. In this work, a low-cost and reproducible sorbent (FeMoS x /TiO2) was developed to recover gaseous Hg0 from smelting flue gas. FeMoS x /TiO2 exhibited a superior ability for capturing high concentrations of Hg0, with an adsorption rate of 72.2 μg g–1 min–1 and a capacity of 41.8 mg g–1 at 60 °C. These were generally larger than the sums of those of FeS x /TiO2 and MoS x /TiO2. The kinetic model of Hg0 adsorption by FeS x /TiO2, MoS x /TiO2, and FeMoS x /TiO2 were constructed according to the adsorption mechanism. Then, the structure–activity relationship of FeMoS x /TiO2 for Hg0 capture was determined by comparing the kinetic parameters. The intrinsic adsorption of Hg0 by MoS x /TiO2 (i.e., physically adsorbed Hg0 was oxidized by MoS3 to HgS) was inhibited marginally after FeS x was incorporated. However, another Hg0 adsorption route (i.e., physically adsorbed Hg0 was oxidized by FeS2 to HgS) appeared on FeMoS x /TiO2. Its rate was significantly higher than that of FeS x /TiO2. Thus, a novel synergistic effect of Fe and Mo in FeMoS x /TiO2 for Hg0 capture was observed.

Different Design Strategies for Metal Sulfide Sorbents to Capture Low Concentrations of Gaseous Hg0 in Coal-Fired Flue Gas and High Concentrations of Gaseous Hg0 in Smelting Flue Gas

“…Meanwhile, Table shows that the amount of S 2 2– on sulfureted Mo/FeTiO x decreased by approximately 26% after Hg 0 capture, while the amount of S 2– on sulfureted Mo/FeTiO x increased by 91%. This suggests that the active S species on sulfureted Mo/FeTiO x for the oxidation of Hg 0 physically adsorbed was mainly S 2 2– in MoS 3 /FeS 2 , , which was consistent with the mechanism of Hg 0 adsorption onto sulfureted FeTiO x . , Therefore, Hg 0 adsorption onto both sulfureted Mo/FeTiO x and sulfureted Mo/FeTiO x is approximately expressed as follows ,, …”

“…The S content was determined with temperature-programmed oxidation of S species to SO 2 (SO 2 -TPO) . SO 2 -TPO was conducted on a fixed-bed microreactor, and the gaseous SO 2 concentration was monitored online by a Thermo Fisher Scientific ANTARIS infrared gas analyzer.…”

“…Gaseous Hg 0 capture was performed on the fixed-bed microreactor. ,− The concentrations of Hg 0 in simulated CFG and simulated SFG after the primary treatment of condensation were 110 and 4300 μg m –3 , respectively, which were provided by purging N 2 through a Hg permeation tube placed in a water bath at different temperatures. The mass used for capturing low concentrations of gaseous Hg 0 was 5 mg, the gas flow was 500 mL min –1 , and the mass hourly space velocity (MHSV) was 6.0 × 10 6 cm –1 g –1 h –1 .…”

“…In our previous work, sulfureted FeTiO x , sulfureted HPW/γ-Fe 2 O 3 , and MoS x @γ-Fe 2 O 3 were developed as reproducible sorbents to recover low concentrations of gaseous Hg 0 from CFG at low temperatures (40–100 °C) as a co-benefit of wet electrostatic precipitators. Meanwhile, CuS x /TiO 2 , MoS x /TiO 2 , FeMoS x /TiO 2 , FeWS x /TiO 2 , sulfureted V 2 O 5 –MoO 3 /TiO 2 , and sulfureted FeTiO x were developed as reproducible sorbents to recover high concentrations of gaseous Hg 0 from SFG at low temperatures. The requirement for the sorbents to capture low concentrations of gaseous Hg 0 from CFG is quite different from that to capture high concentrations of gaseous Hg 0 from SFG.…”

“…As the Hg 0 concentration in SFG is relatively high, the sorbents may reach the adsorption saturation rapidly. Therefore, both the adsorption rate and adsorption capacity of the sorbents for capturing high concentrations of gaseous Hg 0 are concerned . As a result, the design strategy of metal sulfides for capturing low concentrations of gaseous Hg 0 from CFG may be different from that for capturing high concentrations of gaseous Hg 0 from SFG.…”