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Decreased Electron Transfer between Cr(VI) and AH 2 DS in the Presence of Goethite
Author(s) -
Tomaszewski Elizabeth J.,
GinderVogel Matthew
Publication year - 2018
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2017.08.0316
Subject(s) - goethite , electron transfer , chemistry , environmental chemistry , electron , environmental science , physics , nuclear physics , adsorption
9,10‐Anthraquinone‐2,6‐disulfonic acid (AQDS) is commonly used as a model species to examine the influence of quinones on different biogeochemical cycles. The reduced form of this quinone, AH 2 DS, can donate electrons to the toxic metal species Cr(VI), leading to the precipitation of less soluble Cr(III) phases. Due to the environmental abundance of Fe(III) (oxyhydr)oxides, such as goethite (α‐FeOOH), it is important to study the role of these mineral phases on the electron transfer reaction between AH 2 DS and Cr(VI). In this study, this electron transfer reaction is examined in the presence and absence of goethite at three different ratios of AH 2 DS/Cr(VI). Ultraviolet‐visible spectroscopy is used to qualitatively assess the oxidation state of AQDS during reactions with goethite. Iron K‐edge and Cr K‐edge X‐ray absorption spectroscopy are used to examine the role of goethite in electron transfer and identify Cr(III) phases that form. Goethite inhibits the extent of Cr(VI) reduction to Cr(III), most notably at the highest ratio of AH 2 DS/Cr(VI) investigated. Production of semiquinone radical species may limit electron transfer and decrease the yields of Fe(II) and Cr(III), both in the presence and absence of goethite. Understanding abiotic electron transfer reactions that occur in systems with multiple redox active species is important to determine the contribution of abiotic redox reactions to Fe biogeochemical cycling in natural soils. Core Ideas Goethite inhibits the reduction of Cr(VI) to Cr(III) in the presence of AH 2 DS. Semiquinone radical production probably leads to a decrease in reducing equivalents. X‐ray absorption spectroscopy shows no Fe x Cr x (OH) 3 phases form in Cr(VI) reduction.