Institute for Building Materials, ETH Zürich, 8093 Zürich, Switzerland.
Empa Concrete & Asphalt Labortory, 8600 Dübendorf, Switzerland.
Environ Sci Technol. 2023 Oct 24;57(42):16097-16108. doi: 10.1021/acs.est.3c05260. Epub 2023 Oct 12.
The transformation of 2-line ferrihydrite to goethite from supersaturated solutions at alkaline pH ≥ 13.0 was studied using a combination of benchtop and advanced synchrotron techniques such as X-ray diffraction, thermogravimetric analysis, and X-ray absorption spectroscopy. In comparison to the transformation rates at acidic to mildly alkaline environments, the half-life, , of 2-line ferrihydrite reduces from several months at pH = 2.0, and approximately 15 days at pH = 10.0, to just under 5 h at pH = 14.0. The calculated-first order rate constants of transformation, , increase exponentially with respect to the pH and follow the progression log = log + ·pH. Simultaneous monitoring of the aqueous Fe(III) concentration via inductively coupled plasma optical emission spectroscopy demonstrates that (i) goethite likely precipitates from solution and (ii) its formation is rate-limited by the comparatively slow redissolution of 2-line ferrihydrite. The analysis presented can be used to estimate the transformation rate of naturally occurring 2-line ferrihydrite in aqueous electrolytes characteristic to mine and radioactive waste tailings as well as the formation of corrosion products in cementitious pore solutions.
采用台式和先进的同步辐射技术（如 X 射线衍射、热重分析和 X 射线吸收光谱），研究了碱性 pH 值≥13.0 的过饱和溶液中二水合羟高铁矾向针铁矿的转变。与在酸性到弱碱性环境中的转变速率相比，二水合羟高铁矾的半衰期 ，在 pH 值为 2.0 时从几个月减少到 pH 值为 10.0 时的约 15 天，在 pH 值为 14.0 时减少到不到 5 小时。转变的计算一级速率常数 ，随 pH 值呈指数增加，遵循 log = log + ·pH 的规律。通过电感耦合等离子体光学发射光谱法同时监测水溶液中的 Fe(III)浓度，证明了（i）针铁矿可能从溶液中沉淀出来，以及（ii）其形成受到二水合羟高铁矾相对较慢的再溶解的限制。所提出的分析可用于估算在与矿山和放射性废物尾矿以及水泥基孔隙溶液中腐蚀产物的形成有关的特征性水溶液电解质中天然存在的二水合羟高铁矾的转变速率。
