School of Earth & Environment, University of Leeds, UK.
Langmuir. 2010 May 4;26(9):6593-603. doi: 10.1021/la903935j.
The mechanism of green rust sulfate (GR-SO(4)) formation was determined using a novel in situ approach combining time-resolved synchrotron-based wide-angle X-ray scattering (WAXS) with highly controlled chemical synthesis and electrochemical (i.e., Eh and pH) monitoring of the reaction. Using this approach,GR-SO(4) was synthesized under strictly anaerobic conditions by coprecipitation from solutions with known Fe(II)/Fe(III) ratios (i.e., 1.28 and 2) via the controlled increase of pH. The reaction in both systems proceeded via a three-stage precipitation and transformation reaction. During the first stage,schwertmannite (Fe(8)O(8)(OH)(4.5)(SO(4))(1.75)) precipitated directly from solution at pH 2.8-4.5. With increasing pH (>5), Fe(2+) ions adsorb to the surface of schwertmannite and catalyze its transformation to goethite (alpha-FeOOH) during the second stage of the reaction. In the third stage, the hydrolysis of the adsorbed Fe(2+) ions on goethite initiates its transformation to GR-SO(4) at pH >7. The GR-SO(4) then continues to crystallize up to pH approximately 8.5. These results suggest that with an Fe(II)/Fe(III) ratio of < or = 2 in the initial solution the structural Fe(II)/Fe(III) of the GR-SO(4) will be close to that of the starting composition.
采用一种新颖的原位方法，结合时间分辨同步加速器基广角 X 射线散射（WAXS）与对反应的高度受控化学合成和电化学（即 Eh 和 pH）监测，确定绿锈硫酸酯（GR-SO(4)）的形成机制。使用这种方法，通过控制 pH 值的增加，从具有已知 Fe(II)/Fe(III) 比（即 1.28 和 2）的溶液中通过共沉淀合成严格厌氧条件下的 GR-SO(4)。在这两个系统中，反应通过三个阶段的沉淀和转化反应进行。在第一阶段，在 pH 2.8-4.5 下，schwertmannite（Fe(8)O(8)(OH)(4.5)(SO(4))(1.75)）直接从溶液中沉淀出来。随着 pH 值的增加（>5），Fe(2+)离子吸附到 schwertmannite 的表面，并在反应的第二阶段催化其转化为针铁矿（α-FeOOH）。在第三阶段，吸附在针铁矿上的 Fe(2+)离子的水解在 pH>7 时引发其向 GR-SO(4)的转化。然后，GR-SO(4)继续在 pH 约 8.5 结晶。这些结果表明，在初始溶液中 Fe(II)/Fe(III) 比<或=2 的情况下，GR-SO(4)的结构 Fe(II)/Fe(III)将接近起始组成。
