Iron-derived solid redox system for effective and sustainable sulfur recovery from sulfide-bearing wastewater

Elemental sulfur recovery from sulfide-bearing wastewaters presents a promising strategy for achieving both a sustainable elemental sulfur supply and pollutant removal. However, existing methods face low efficiency or heavy chemical usage, limiting their practicality. Here, we report an iron-derived solid redox sulfur recovery system, capable of efficiently converting sulfides to elemental sulfur and separating elemental sulfur from the iron catalysts (ferrihydrite) via simple gravity-based methods. Using iron-derived solid redox system, we achieve a record sulfide removal rate of 102.9 ± 3.1 kg m^-3 d^-1 with an elemental sulfur selectivity of 93.5 ± 0.9%. The produced elemental sulfur is then efficiently separated from the solid mixture through a hydraulic sorting process, attaining 97.7 ± 0.2% purity. Mechanistic analysis identifies the iron and sulfur species governing the solid redox process and elucidates that the separation behavior of elemental sulfur is likely a result of surface-state-dependent elemental sulfur agglomeration and repulsion between elemental sulfur and iron flocs. Moreover, we verify the effectiveness of iron-derived solid redox system in recovering elemental sulfur from two real wastewaters and estimate the economic benefits of elemental sulfur recovery to exceed 180 United States dollars per ton. This work suggests a practical approach to enable sulfide-bearing wastewaters as a sustainable source for elemental sulfur supply efficiently and cost-effectively.