Matocha C J, Karathanasis A D, Rakshit S, Wagner K M
Department of Agronomy, University of Kentucky, N-122 Agricultural Science Center-North, Lexington, KY 40546-0091, USA.
J Environ Qual. 2005 Aug 9;34(5):1539-46. doi: 10.2134/jeq2005.0002. Print 2005 Sep-Oct.
Laboratory and field investigations have clearly demonstrated the important role of reduced iron (Fe(II)) in reductive transformations of first-row transition metal species. However, interactions of Fe(II) and copper (Cu) are not clearly understood. This study examined the reduction of Cu(II) by Fe(II) in stirred-batch experiments at pH 5.2 and 5.5 as influenced by chloride (Cl-) concentration (0.002-0.1 M), initial metal concentration (0.1-9.1 mM), and reaction time (1-60 min) under anoxic conditions. Reduction of Cu(II) to Cu(I) by dissolved Fe(II) was rapid under all experimental conditions and the stability of the products explains the driving force for the redox reaction. Under conditions of low [Cl-] and high initial metal concentration, >40% of total Cu and Fe were removed from solution after 1 min, which accompanied formation of a brownish-red precipitate. X-ray diffraction (XRD) patterns of the precipitates revealed the presence of cuprite (Cu2O), a Cu(I) mineral, based on d-spacings located at 0.248, 0.215, 0.151, and 0.129 nm. Fourier transform infrared (FTIR) spectroscopy corroborated XRD data for the presence of Cu2O, with features located at 518, 625, and 698 cm(-1). Increasing [Cl-] stabilized the dissolved Cu(I) product against Cu2O precipitation and resulted in more Fe precipitated from solution (relative to Cu) that appears to be present as poorly crystalline lepidocrocite (gamma-FeOOH). This process may be important in anoxic soil environments, where dissolved Fe(II) levels can accumulate.
实验室和现场调查已清楚地证明了亚铁（Fe(II)）在第一排过渡金属物种还原转化中的重要作用。然而，Fe(II)与铜（Cu）之间的相互作用尚不清楚。本研究在缺氧条件下，通过搅拌批次实验，考察了在pH值为5.2和5.5时，氯化物（Cl-）浓度（0.002 - 0.1 M）、初始金属浓度（0.1 - 9.1 mM）和反应时间（1 - 60分钟）对Fe(II)还原Cu(II)的影响。在所有实验条件下，溶解的Fe(II)将Cu(II)还原为Cu(I)的过程都很快，产物的稳定性解释了氧化还原反应的驱动力。在低[Cl-]和高初始金属浓度条件下，1分钟后溶液中>40%的总Cu和Fe被去除，同时形成棕红色沉淀。沉淀的X射线衍射（XRD）图谱显示存在赤铜矿（Cu2O），一种Cu(I)矿物，其d间距位于0.248、0.215、0.151和0.129 nm。傅里叶变换红外（FTIR）光谱证实了XRD数据中Cu2O的存在，其特征峰位于518、625和698 cm(-1)。增加[Cl-]可稳定溶解的Cu(I)产物，防止其沉淀为Cu2O，并导致更多的Fe从溶液中沉淀出来（相对于Cu），这些Fe似乎以结晶度较差的纤铁矿（γ-FeOOH）形式存在。这一过程在缺氧土壤环境中可能很重要，因为那里溶解的Fe(II)水平可能会积累。
