Institute for Building Materials (IfB), ETH Zurich, Stefano-Franscini-Platz 3, 8093, Zurich, Switzerland.
Paul Scherrer Institute, Nuclear Energy and Safety Department, Laboratory for Waste Management, 5232, Villigen, PSI, Switzerland.
Chemosphere. 2023 Sep;335:138955. doi: 10.1016/j.chemosphere.2023.138955. Epub 2023 May 22.
Whilst the oxidation of Fe(II) in aerobic conditions has been studied thoroughly, an in-depth knowhow on the fate or stability of Fe(II) in solutions with near-neutral pH under anaerobic conditions is still lacking. Here, we experimentally investigated the kinetics of Fe(II) oxidation in solutions with pH ranging between ∼5 and 9, under aerobic (when solutions were in equilibrium with atmospheric oxygen) and anaerobic conditions (when the dissolved oxygen concentration was ∼10 mol/L), by colorimetric means. Experimental results and thermodynamic considerations presented here, show that Fe(II) oxidation in anaerobic conditions is first-order w.r.t. [Fe(II)], and proceeds with set of parallel reactions involving different hydrolysed and non-hydrolysed Fe(II) and Fe(III) species, similar to that observed in aerobic conditions. However, in the absence of oxygen, the cathodic reaction accompanying the anodic oxidation of Fe(II), is the reduction of HO (l) releasing H (g). Hydrolysed Fe(II) species oxidise much faster than Fe and their concentrations increases with pH, leading to increased Fe(II) oxidation rates. Additionally, we also show the importance of the type of buffer used to study Fe(II) oxidation. Therefore, for the oxidation of Fe(II) in near-neutral solutions, the speciation of Fe(II) and Fe(III), the presence of other anions and the pH of the solution are critical parameters that must be considered. We anticipate that our results and hypothesis will find use in reactive-transport models simulating different processes occurring in anaerobic conditions such as corrosion of the steel in concrete structures, or in nuclear waste repositories.
虽然在有氧条件下已经对 Fe(II) 的氧化进行了深入研究，但对于近中性 pH 值条件下无氧条件下 Fe(II) 的命运或稳定性，我们仍然知之甚少。在这里，我们通过比色法实验研究了 pH 值在 5 到 9 之间的溶液中，在有氧（当溶液与大气氧平衡时）和无氧（当溶解氧浓度约为 10 mol/L 时）条件下 Fe(II)氧化的动力学。本文提出的实验结果和热力学考虑表明，无氧条件下的 Fe(II)氧化在动力学上是一级的，涉及一系列平行反应，涉及不同水解和非水解的 Fe(II)和 Fe(III)物种，类似于有氧条件下的反应。然而，在没有氧气的情况下，伴随 Fe(II)阳极氧化的阴极反应是 HO(l)的还原，释放出 H(g)。水解的 Fe(II)物种比 Fe 氧化得更快，并且它们的浓度随 pH 值的增加而增加，导致 Fe(II)氧化速率增加。此外，我们还表明了用于研究 Fe(II)氧化的缓冲剂类型的重要性。因此，对于近中性溶液中 Fe(II)的氧化，Fe(II)和 Fe(III)的形态、其他阴离子的存在和溶液的 pH 值是必须考虑的关键参数。我们预计，我们的结果和假设将在模拟无氧条件下发生的不同过程的反应输运模型中得到应用，例如混凝土结构中钢的腐蚀或核废料储存库。
