Unveiling the Halogenation-Induced Formation of Hg 3 Se 2 X 2 (X = Cl, Br, and I) Compounds for Multiphase Mercury Cycling.

The interaction between mercury (Hg) and inorganic compounds, including selenium (Se), sulfur (S), and halogens (X = Cl, Br, or I), plays a critical role in the global mercury cycle. However, most previously reported mercury compounds are susceptible to reduction, leading to the release of elemental mercury (Hg 0 ) and causing secondary pollution. In this study, we unveil a groundbreaking discovery that underscores the vital role of halogenation in creating exceptionally stable Hg 3 Se 2 X 2 compounds. Through the dynamic interplay of Hg, Se, and halogens, an intermediary stage denoted [HgSe] m [HgX 2 ] n emerges, and this transformative process significantly elevates the stabilization of mercury. Remarkably, halogen ions strategically occupy pores at the periphery of HgSe clusters, engendering a more densely packed atomic arrangement of Hg, Se, and halogen components. A marked enhancement in both thermal and acid stability is observed, wherein temperatures ascend from 130 to 300 °C (transitioning from HgSe to Hg 3 Se 2 Cl 2 ). This sequence of escalating stability follows the order HgSe < Hg 3 Se 2 I 2 < Hg 3 Se 2 Br 2 < Hg 3 Se 2 Cl 2 for thermal resilience, complemented by virtually absent acid leaching. This innovative compound formation fundamentally alters the transformation pathways of gaseous Hg 0 and ionic mercury (Hg 2+ ), resulting in highly efficient in situ removal of both Hg 0 and Hg 2+ ions. These findings pave the way for groundbreaking advancements in mercury stabilization and environmental remediation strategies, offering a comprehensive solution through the creation of chemically stable precipitates.