title: The reductive immobilization of aqueous Se(IV) by natural pyrrhotite.
abstract: The interaction of Se(IV) with natural pyrrhotite was investigated at pH conditions ranging from acidic to nearly neutral. The results indicate that the reduction rate can be described in terms of a pseudo-first order reaction. At pH ∼4.0 to ∼5.0, the rate decreased with increasing pH. Unexpectedly, at pH ∼5.0, the rate increased with increasing reaction time. This response was also observed at pH ∼6.0. Two different reaction mechanisms were proposed to explain pyrrhotite oxidation by Se(IV). Because pyrrhotite is acid-soluble and can be attacked by both Fe(3+) and protons, direct reduction by the released aqueous sulfide dominates the reaction at low pH, whereas the cyclic oxidation of aqueous Fe(2+) adsorbed on pyrrhotite surfaces becomes predominant at high pH. Phosphate, which can be irreversibly bound to Fe(3+) intermediates even under acidic conditions, can significantly decrease the reaction rate by an order of magnitude at pH ∼4.5. In contrast to the thermodynamic calculations and the predicted prevalence of FeSe based on previous reports of aqueous Se(IV) reduction by synthetic mackinawite or troilite, only Se(0) was observed as the reaction product in this study. This observation confirmed that a slow reaction favors the formation of Se(0) rather than iron selenides.
authors.affiliation: Beijing National Laboratory for Molecular Sciences, Fundamental Science Laboratory on Radiochemistry & Radiation Chemistry, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.
authors.forename: Bin
authors.initials: B
authors.lastname: Ma
authors.affiliation: Beijing National Laboratory for Molecular Sciences, Fundamental Science Laboratory on Radiochemistry & Radiation Chemistry, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China; Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-sen University, Zhuhai, 519082, China; CAS Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China. Electronic address: kangmingliang@gmail.com.
authors.forename: Mingliang
authors.initials: M
authors.lastname: Kang
authors.affiliation: Beijing National Laboratory for Molecular Sciences, Fundamental Science Laboratory on Radiochemistry & Radiation Chemistry, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.
authors.forename: Zhong
authors.initials: Z
authors.lastname: Zheng
authors.affiliation: CAS Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China.
authors.forename: Fanrong
authors.initials: F
authors.lastname: Chen
authors.affiliation: Beijing National Laboratory for Molecular Sciences, Fundamental Science Laboratory on Radiochemistry & Radiation Chemistry, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.
authors.forename: Jinglin
authors.initials: J
authors.lastname: Xie
authors.affiliation: Environmental Geochemistry Group, ISTerre, University of Grenoble I, 38041 Grenoble, France.
authors.forename: Laurent
authors.initials: L
authors.lastname: Charlet
authors.affiliation: Beijing National Laboratory for Molecular Sciences, Fundamental Science Laboratory on Radiochemistry & Radiation Chemistry, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China. Electronic address: liucl@pku.edu.cn.
authors.forename: Chunli
authors.initials: C
authors.lastname: Liu
mesh_terms: D058085:Iron Compounds / Q000737:chemistry*; D007700:Kinetics; D008903:Minerals / Q000737:chemistry*; D010084:Oxidation-Reduction; D056951:Photoelectron Spectroscopy; D012643:Selenium / Q000737:chemistry*; D013440:Sulfides / Q000737:chemistry*
chemical_list: D058085:Iron Compounds; D008903:Minerals; D013440:Sulfides; D012643:Selenium
keywords: Kinetics; Nuclear waste disposal; Pyrrhotite; Reductive immobilization; Selenite