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Vertical variability of arsenic concentrations under the control of iron-sulfur-arsenic interactions in reducing aquifer systems

Pi, Kunfu ; Wang, Yanxin ; Postma, Dieke ; Ma, Teng ; Su, Chunli ; Xie, Xianjun

Journal of Hydrology, June 2018, Vol.561, pp.200-210 [Periódico revisado por pares]

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  • Título:
    Vertical variability of arsenic concentrations under the control of iron-sulfur-arsenic interactions in reducing aquifer systems
  • Autor: Pi, Kunfu ; Wang, Yanxin ; Postma, Dieke ; Ma, Teng ; Su, Chunli ; Xie, Xianjun
  • Assuntos: Arsenic Variability ; Redox Zonation ; Fe-S-As Interactions ; Reactive-Transport Model ; Groundwater ; Geography
  • É parte de: Journal of Hydrology, June 2018, Vol.561, pp.200-210
  • Descrição: Keywords Arsenic variability; Redox zonation; Fe-S-As interactions; Reactive-transport model; Groundwater Highlights * High-As groundwater with low Fe(II) is identified in sulfate-reducing aquifers. * Depth-dependent redox zonation accounts for the vertical variability of aqueous As. * SO.sub.4.sup.2- reduction contributes to limited aqueous Fe(II) and decoupled Fe(II) and As. * Fe-S-As interactions control the dynamic solid/aqueous-phase As re-partitioning. Abstract High spatial variability of arsenic (As) concentration in geogenic As-contaminated groundwater has been commonly observed worldwide, but the underlying reasons remain not well understood. Selecting a sulfate-containing, As-affected aquifer at the Datong Basin, northern China as the study area and combining hydrogeochemical investigation and sediment extraction with reactive transport modeling, this work elucidated the roles of Fe-S-As interactions in regulating the vertical variation of As concentration in the groundwater. Dissolved As concentration varied between 0.05 and 18 [mu]mol/L, but generally increased in the depth of 20--25 m and then decreased in 25--30 m. The high-As groundwater contained low Fe(II) (<0.007 mmol/L) and up to 15 [mu]mol/L sulfide, in contrary to the S/SE Asian deltas/floodplains where high Fe(II) and As jointly occur in the groundwater devoid of sulfate reduction. The reductive dissolution of As-bearing Fe(III) oxides coupled to the degradation of organic matter with an estimated maximum rate of 0.22 mmol C/L/yr, mainly accounted for the depth-dependent increase of As concentration in the upper part of the shallow aquifer (<25 m deep). However, the decreasing reactivity of Fe(III) oxides together with the increase of pH over depth rendered the majority of electrons being transferred to sulfate reduction. The Fe(II) sulfides formed as a consequence not only helped to restrict the build-up of Fe(II) in the groundwater but also probably co-precipitated As to prompt As decrease in the depth of 25--30 m. Arsenite adsorbed on remaining Fe(III) oxides and newly-formed Fe(II) sulfides is another important pool of As in the aquifer, which varies in response to the extents of Fe(III)-oxide and sulfate reduction and consequently alters As distribution coefficient between the solid and the aqueous phases. This study highlights the importance of coupled geochemical cycling of Fe, S and As for As mobilization and reveals how it regulates As partitioning between groundwater and sediments. Author Affiliation: (a) School of Environmental Studies & State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, 430074 Wuhan, China (b) Ecohydrology Research Group, Department of Earth and Environmental Sciences and Water Institute, University of Waterloo, Waterloo, Canada (c) Geological Survey of Denmark and Greenland, Oster Voldgade 10, DK-1350 Copenhagen, Denmark * Corresponding authors. Article History: Received 31 December 2017; Revised 13 March 2018; Accepted 18 March 2018 (miscellaneous) This manuscript was handled by G. Syme, Editor-in-Chief Byline: Kunfu Pi (a,b), Yanxin Wang [yx.wang@cug.edu.cn] (a,*), Dieke Postma (c), Teng Ma (a), Chunli Su (a), Xianjun Xie [xjxie@cug.edu.cn] (a,*)
  • Idioma: Inglês

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