Photooxidation of Fe(II) to schwertmannite promotes As(III) oxidation and immobilization on pyrite under acidic conditions. (1st September 2022)

• Record Type: Journal Article
• Authors: Liu, Lihu; Guo, Diman; Qiu, Guohong; Liu, Chengshuai; Ning, Zengping
• Is Part Of: Journal of environmental management. Volume 317(2022)
• Publication Date: 2022-09-01
• Subjects: Sulfide mineral -- Reactive oxygen species -- Arsenic -- AMD -- Sunlight -- Schwertmannite; Environmental policy -- Periodicals; Environmental management -- Periodicals; Environment -- Periodicals; Ecology -- Periodicals; 363.705
• DOI: 10.1016/j.jenvman.2022.115425
• Languages: English
• ISSNs: 0301-4797

Abstract

Abstract: Pollution of arsenic (As) in acid mine drainage (AMD) is a universal environmental problem. The weathering of pyrite (FeS2 ) and other sulfide minerals leads to the generation of AMD and accelerates the leaching of As from sulfide minerals. Pyrite can undergo adsorption and redox reactions with As, affecting the existing form and biotoxicity of As. However, the interaction process between As and pyrite in AMD under sunlight radiation remains unclear. Here, we found that the oxidation and immobilization of arsenite (As(III)) on pyrite can be obviously promoted by the reactive oxygen species (ROS) in sunlit AMD, particularly by OH. The reactions between hole-electron pairs and water/oxygen adsorbed on excited pyrite resulted in the production of H2 O2, OH and O2 −, and OH was also generated through the photo-Fenton reaction of Fe 2+ /FeOH 2+ . Weakly crystalline schwertmannite formed from the oxidation of Fe 2+ ions by OH contributed much to the adsorption and immobilization of As. In the mixed system of pyrite (0.75 g L −1 ), Fe 2+ (56.08 mg L −1 ) and As(III) (1.0 mg L −1 ) at initial pH 3.0, the decrease ratio of dissolved total As concentration was 1.6% under dark conditions, while it significantly increased to 69.0% under sunlight radiation. The existence of oxygen or increase in initial pH from 2.0 to 4.0 accelerated As(III) oxidation and immobilization due to the oxidation of more Fe 2+ and production of more ROS. The present work shows that sunlight significantly affects the transformation and migration of As in AMD, and provides new insights into the environmental behaviors of As. Graphical abstract: Image 1 Highlights: Sunlight accelerates As(III) oxidation and immobilization on pyrite in AMD. OH plays an important role in the photooxidation of As(III). Schwertmannite formed from Fe 2+ oxidation facilitates As immobilization. Excited pyrite and photo-Fenton reaction of Fe(OH) 2+ contribute to OH formation.