Sulfide-occluded zeolite X for effective removal of Hg²⁺ from aqueous systems

Occluding sulfides into zeolite pores is a novel strategy to remove aqueous Hg species completely through cooperation between adsorption and precipitation reactions. For its practical application, it is urgent to maximize Hg²⁺ removal capacity of sulfide-occluded zeolite as well as to increase the removal rate. This study demonstrates that sulfide-occluded zeolite X showed the highest Hg²⁺ removal capacity, a value of 344.83 mg/g, among sulfide-occluded zeolites surely due to its largest window and pore sizes leading to diverse occluded sulfide species. It was revealed that large window size facilitated smooth diffusion of occluded sulfides onto the crystal surfaces to result in enhancement of both the capacity and the rate of Hg²⁺ removal. Notably, the sulfide-occluded zeolite X performed a complete removal of aqueous Hg²⁺ even in seawater where high concentrations of salt ions are present. In addition, any critical concentrations of residual total sulfur were not found in the decontaminated solutions. Therefore, zeolite X occluded with sulfides could be applied to practical Hg²⁺ removal from various Hg-contaminated aqueous systems.