Helmholtz-Zentrum Dresden-Rossendorf, Institute of Resource Ecology, Bautzner Landstraße 400, 01328 Dresden, Germany.
Institute of Radioecology and Radiation Protection, Leibniz Universität Hannover, Herrenhäuser Straße 2, 30419 Hannover, Germany.
Environ Int. 2020 Mar;136:105425. doi: 10.1016/j.envint.2019.105425. Epub 2020 Jan 31.
In this study the complexation of U(VI) with orthosilicic acid (HSiO) was investigated between pH 3.5 and 5 by combining electrospray ionization mass spectrometry (ESI-MS) and laser-induced luminescence spectroscopy. The ESI-MS experiments performed at a total silicon concentration of 5 · 10M (exceeding the solubility of amorphous silica at both pH-values) revealed the formation of oligomeric sodium-silicates in addition to the UOOSi(OH) species. For the luminescence spectroscopic experiments (25 °C), the U(VI) concentration was fixed at 5 · 10M, the silicon concentration was varied between 1.3 · 10-1.3 · 10M (reducing the formation of silicon oligomers) and the ionic strength was kept constant at 0.2 M NaClO. The results confirmed the formation of the aqueous UOOSi(OH) complex. The conditional complexation constant at 25 °C, log *β = -(0.31 ± 0.24), was extrapolated to infinite dilution using the Davies equation, which led to log *β = -(0.06 ± 0.24). Further experiments at different temperatures (1-25 °C) allowed the calculation of the molal enthalpy of reaction ΔH = 45.8 ± 22.5 kJ·mol and molal entropy of reaction ΔS = 152.5 ± 78.8 J·K·mol using the integrated van't Hoff equation, corroborating an endothermic and entropy driven complexation process.
在这项研究中，通过结合电喷雾电离质谱（ESI-MS）和激光诱导发光光谱法，研究了 U(VI)与正硅酸（HSiO）在 pH 3.5 至 5 之间的络合作用。在总硅浓度为 5·10M（在两个 pH 值下均超过无定形硅的溶解度）的 ESI-MS 实验中，除了 UOOSi(OH)物种外，还发现了聚合的硅酸钠的形成。对于发光光谱实验（25°C），将 U(VI)浓度固定在 5·10M，硅浓度在 1.3·10-1.3·10M 之间变化（减少硅低聚物的形成），离子强度保持在 0.2 M NaClO 不变。结果证实了含水 UOOSi(OH)络合物的形成。在 25°C 时的条件络合常数，log *β=-(0.31 ± 0.24)，使用 Davies 方程外推至无限稀释，得到 log *β=-(0.06 ± 0.24)。在不同温度（1-25°C）下的进一步实验允许使用积分范特霍夫方程计算摩尔焓变ΔH=45.8±22.5 kJ·mol和摩尔熵变ΔS=152.5±78.8 J·K·mol，证实了一个吸热和熵驱动的络合过程。
