Mechanistic insights into mercury removal by FeCl3-modified ZnS: Role of oxidation and sulfur activation

ZnS has attracted considerable attention for its superior Hg⁰ adsorption in flue gas purification, though further performance enhancement remains challenging. This study proposes an efficient FeCl₃ impregnation strategy combined with high-surface-area ZnS to significantly improve Hg⁰ adsorption. Through liquid-phase impregnation, Fe³⁺ and Cl⁻ were introduced onto the surface of high surface area ZnS. Fe³⁺ oxidizes the surface S^2- of ZnS to the more active S₂^2- species, which subsequently reacts with Hg⁰ to form HgS. Meanwhile, Fe³⁺ can also promote Hg⁰ oxidation to Hg²⁺, enhancing the overall Hg⁰ adsorption performance. Cl⁻ enhances the adsorption capacity by adjusting the electronic environment and increasing active site activity. The FeCl₃-modified ZnS achieved an Hg⁰ adsorption capacity of 40.54 mg·g⁻¹, 34 times higher than unmodified ZnS, with improved adsorption rates and strong resistance to flue gas interference. This modification strategy enables stable operation in harsh industrial environments like cement kilns while reducing adsorbent dosage and operational costs. The FeCl₃ impregnation strategy is not only applicable to ZnS but also extendable to a variety of sulfide materials with well-developed porous structures, thereby offering a novel technological pathway for the development of highly efficient and cost-effective adsorbents.