Mechanistic insights into HgCl2 adsorption over zinc sulfide: The role of inherent sulfur and newly-formed zinc chloride

Divalent mercury (Hg 2 + , mainly as HgCl 2 ) dominates the mercury species discharged from cement kiln flue gas , however, achieving effective control remains challenging. Herein, zinc sulfide (ZnS) was applied for HgCl 2 removal from cement kiln flue gas , showing superior adsorption performance among metal sulfides. ZnS achieved an unprecedented adsorption capacity of 426.1 mg ·g −1 at an optimal temperature of 160 °C, nearly 300 times higher than its Hg 0 adsorption capacity. The typical flue gas components (O 2 , H 2 O, NO and SO 2 ) displayed insignificant adverse effects on HgCl 2 adsorption. Such intriguing observation was ascribed to the inherent sulfur (S 2 2- and S 2- ) and newly-formed zinc chloride (ZnCl 2 ). The S 2 2- and S 2- sites facilitated the conversion of HgCl 2 into β-HgS and α-HgS, respectively. The HgCl 2 dissociation resulted in chlorination of ZnS to form ZnCl 2 which accelerated the initial HgCl 2 adsorption process . The moderate binding energy of HgCl 2 on the Zn sites of ZnCl 2 facilitated the migration of intermediate adsorption products to the S sites of ZnS to form HgS. This work not only provided a promising alternative to commercial activated carbons (ACs) for HgCl 2 removal from cement kiln flue gas, but also proposed new insights to guide the design of HgCl 2 adsorbents. Synopsis A high-efficient HgCl 2 removal strategy for cement kiln flue gas was developed, and the role of inherent sulfur and newly-formed ZnCl 2 in HgCl 2 adsorption over ZnS was proposed for the first time.