title: Reductive removal of selenate by zero-valent iron: The roles of aqueous Fe(2+) and corrosion products, and selenate removal mechanisms.
abstract: Batch tests were conducted to investigate the roles of dissolved Fe(2+) and corrosion products, and the involved mechanisms in selenate (Se(VI)) removal by zero-valent iron (ZVI). The results showed that insignificant Se(VI) removal (4-7.5%) was observed in the presence of ZVI or Fe(2+) alone. However, external supply of dissolved ferrous ion dramatically enhanced Se(VI) removal in the presence of ZVI. Selenate removal efficiency increased with increasing Fe(2+) concentration. Selenate removal sustained only if Fe(2+) was supplied continuously. Both sequential extraction experiments and XPS analysis showed that selenate was reduced step by step, with elemental selenium and adsorbed selenite as the dominant reductive products. Selenite and elemental selenium could be further reduced to selenide, with continuous Fe(2+) supply and sufficient reaction time. In the ZVI-Se(VI)-Fe(2+) system, ZVI was the major electron donor for selenate reduction. Fe(2+) functioned as electron donor as well and was consumed with a Fe(2+):Se stoichiometry of ∼1:1. It also facilitated the transformation of the passive layer of iron coatings to a medium (e.g., magnetite) favoring electron transfer and thus enhanced selenate reduction. Iron corrosion products were media for electron transfer and reactive interfaces for selenium adsorption and reduction. These findings provided a new approach to overcome ZVI surface passivation for long-term application.
authors.affiliation: Department of Environmental Engineering, College of Hydraulic & Environmental Engineering, China Three Gorges University, Yichang 443002, China; Department of Biological and Agricultural Engineering, Texas A&M University, College Station, TX 77843, USA. Electronic address: bolong8111@gmail.com.
authors.forename: Cilai
authors.initials: C
authors.lastname: Tang
authors.affiliation: Department of Biological and Agricultural Engineering, Texas A&M University, College Station, TX 77843, USA.
authors.forename: Yong H
authors.initials: YH
authors.lastname: Huang
authors.affiliation: Department of Biological and Agricultural Engineering, Texas A&M University, College Station, TX 77843, USA.
authors.forename: Hui
authors.initials: H
authors.lastname: Zeng
authors.affiliation: College of Resources and Environment, Northwest A&F University of China, Yangling 712100, China.
authors.forename: Zengqiang
authors.initials: Z
authors.lastname: Zhang
mesh_terms: D000327:Adsorption; D002852:Chromatography, Ion Exchange; D003343:Corrosion; D007501:Iron / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D010084:Oxidation-Reduction; D056951:Photoelectron Spectroscopy; D020887:Selenious Acid / Q000737:chemistry*; D013054:Spectrophotometry, Atomic; D013056:Spectrophotometry, Ultraviolet; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification / Q000379:methods*; D014961:X-Ray Diffraction
chemical_list: D014874:Water Pollutants, Chemical; D007501:Iron; D020887:Selenious Acid
keywords: Corrosion products; Ferrous ion; Removal mechanism; Selenate; Zero-valent iron