Institut de Chimie des Milieux et des Matériaux de Poitiers (IC2MP), UMR 7285, Université de Poitiers, CNRS, HydrASA, F-86073, Poitiers, France.
Orano Environmental R&D Dpt, 125 avenue de Paris, 92320, Châtillon, France; Centre de Géosciences, MINES Paris, PSL University, 35 rue St Honoré, 77300, Fontainebleau, France.
Chemosphere. 2023 Oct;338:139497. doi: 10.1016/j.chemosphere.2023.139497. Epub 2023 Jul 12.
The colloidal transport of trace (Fe, Al, Ba, Pb, Sr, U) and ultra-trace (Ra) elements was studied in a mining environment. An original approach combining 0.45 μm filtered water sampling, the Diffusive Gradient in Thin films (DGT) technique, mineralogical characterization, and geochemical modelling was developed and tested at 17 sampling points. DGT was used for the truly dissolved fraction of the elements of interest, while the 0.45 μm filtration includes both colloidal and truly dissolved fractions (together referred to as total dissolved fraction). Results indicated a colloidal fraction for Al (up to 50%), Ba (up to 86%), and Fe (up to 99%) explained by the presence of submicrometric grains of kaolinite, barite, and ferrihydrite, respectively. Furthermore, the total dissolved Ra concentration in the water samples reached up to 10-25 Bq/L (1.2-3.0 10 mol/L) at 3 sampling points, while the truly dissolved aqueous Ra concentrations were in the mBq/L range. Such high total dissolved concentrations are explained by retention on colloidal barite, accounting for 95% of the total dissolved Ra concentration. The distribution of Ra between the truly dissolved and colloidal fractions was accurately reproduced using a (Ra,Ba)SO solid solution, with values of the Guggenheim parameter a close to ideality. Ra sorption on ferrihydrite and kaolinite, other minerals well known for their retention properties, could not explain the measured colloidal fractions despite their predominance. This illustrates the key role of barite in such environments. The measured concentrations of total dissolved U were very low at all the sampling points (<4.5 10 mol/L) and the colloidal fraction of U accounted for less than 65%. U sorption on ferrihydrite could account for the colloidal fraction. This original approach can be applied to other trace and ultra-trace elements to complement when necessary classical environmental surveys usually performed by filtration on 0.45 μm.
在采矿环境中研究了痕量（Fe、Al、Ba、Pb、Sr、U）和超痕量（Ra）元素的胶体迁移。开发并测试了一种结合 0.45μm 过滤水采样、薄膜扩散梯度（DGT）技术、矿物学特征和地球化学模型的原始方法，在 17 个采样点进行。DGT 用于感兴趣元素的真正溶解部分，而 0.45μm 过滤则包括胶体和真正溶解部分（统称为总溶解部分）。结果表明，由于高岭石、重晶石和水铁矿等亚微米颗粒的存在，Al（高达 50%）、Ba（高达 86%）和 Fe（高达 99%）的胶体部分得到了解释。此外，在 3 个采样点，水样中总溶解 Ra 浓度高达 10-25 Bq/L（1.2-3.0 10-9mol/L），而真正溶解的 Ra 浓度在 mBq/L 范围内。如此高的总溶解浓度是通过胶体重晶石的保留来解释的，这占总溶解 Ra 浓度的 95%。使用（Ra，Ba）SO4 固溶体可以准确再现 Ra 在真正溶解和胶体部分之间的分布，Guggenheim 参数 a 值接近理想值。尽管 Ferrihydrite 和 Kaolinite 等其他以保留性能而闻名的矿物质对 Ra 具有吸附作用，但它们不能解释所测量的胶体部分。这说明了重晶石在这种环境中的关键作用。在所有采样点，总溶解 U 的浓度都非常低（<4.5 10-9mol/L），U 的胶体部分不到 65%。Ferrihydrite 对 U 的吸附可以解释胶体部分。这种原始方法可以应用于其他痕量和超痕量元素，以补充通常通过 0.45μm 过滤进行的经典环境调查。
