Dual-functional Sites for Selective Adsorption of Mercury and Arsenic ions in [SnS4]4-/MgFe-LDH from Wastewater

Highlights: • [SnS₄]^4-/MgFe-LDH composite was newly reported. • Simultaneous removal of mercury and arsenic ions with different active sites. • Mercury can be recycled after the adsorption experiment. Heavy metals existed as multiple types in wastewater, enhanced the difficulty for disposal, and aroused huge environmental issues. High selective adsorption of the most hazardous heavy metals is one important method for water purification and resource utilization. In this study, we assembled the [SnS₄]^4- clusters and MgFe-based layered double hydroxide (LDH) to synthesize the [SnS₄]^4-/LDH composites, to capture mercury and arsenic ions simultaneously. The results indicated that such composite exhibited excellent mercury and arsenic removal performance with higher than 99% removal efficiency at a wide pH range. The uptake of mercury was ascribed to the [SnS₄]^4- clusters sites while the arsenic removal was mainly due to the existence of Fe site in LDH composite. The inserted [SnS₄]^4- clusters can enlarge the surface areas and create a hierarchical pore channel due to the increased interlayer spacing of LDH, which can enhance the adsorption capacity. The different adsorption mechanisms were also indicated by dynamic analysis. Pseudo-second-order kinetic model was more suitable for both Hg(II) and As(III) adsorption in the dual-heavy metal solution, and neither Langmuir isotherm model nor Freundlich isotherm model fitted the Hg(II) and As(III) adsorption in the mixed solution. The adsorption progress was influenced due to the coexistence of another heavy metal. Besides, mercury can be collected from the spent materials using a thermal-heating method. Such composite exhibits promising potential for mercury recycling.