In this study, the release of elements and in particular U from five Austrian orthogneiss and granite samples into a CO₂-bearing solution was investigated to describe the initial phase (24 h) of leaching focusing on the impact of ferrous (hydro)oxide formation. Experiments were conducted at ambient temperature by flushing CO₂:N₂ gas through the reactive solution (pH_initial ~ 4.3) at a liquid:solid ratio of 10:1 with and without a reducing agent. The chemical evolution of the leaching solution was dominated by incongruent dissolution of silicates showing a parabolic kinetic behavior due to protective surface formation most likely caused by precipitation of amorphous Fe^III/Al hydroxides. However, the relative distribution of Ca, Mg and Sr in the leaching solution excellently traced the individual bulk rock composition. The mobilization of U was highly prevented under oxidizing conditions by sorption onto ferrous (hydro)oxides, which were precipitating through ongoing silicate leaching. Therefore, the leaching behavior of individual U-bearing minerals was less relevant for U release. At reducing conditions, the above elements were accumulated in the solution, although an oversaturation regarding U^IVO₂ was calculated. This indicates its inhibited formation within the experimental run time. The composition of experimental leaching solutions did not reflect analyzed groundwater compositions from investigated local rock-type aquifers indicating that reaction rate constants of siliceous rocks significantly differ between values found in nature and in the laboratory. Change in active mineral surface areas with ongoing weathering, accumulation of secondary precipitates, leached layer formation and given reaction time are key factors for distinct elemental release.

中文翻译：

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Orthogneiss和花岗岩（奥地利）中的铀和多种元素释放：相对于地下水成分的实验方法

在这项研究中，研究了从5个奥地利原镁和花岗岩样品中的元素（尤其是U）向含CO _2的溶液中的释放，以描述浸出的初始阶段（24小时），重点是氧化亚铁（氢）的形成。在环境温度下，通过在 有或没有还原剂的情况下，以10：1的液/固比将CO ₂：N ₂气体冲洗通过反应溶液（pH_初始值约为4.3），以进行实验。浸出液的化学演化主要由硅酸盐的不溶性溶解决定，硅酸盐的溶解性表现为抛物线动力学行为，这归因于保护性表面的形成，这很可能是由非晶态Fe ^III的沉淀引起的。/氢氧化铝。但是，Ca，Mg和Sr在浸出液中的相对分布极好地追踪了各个块状岩石的成分。在氧化条件下，通过吸附到（氢）氧化亚铁上来防止U的动员，氧化亚铁是通过不断的硅酸盐浸出而沉淀的。因此，单个含U型矿物的浸出行为与U释放无关。在还原条件下，尽管有关U ^IV O _2的过饱和，上述元素仍在溶液中积累被计算了。这表明其在实验运行时间内的形成受到抑制。实验浸出溶液的成分并未反映出所研究的当地岩质含水层的分析地下水成分，表明硅质岩的反应速率常数在自然界和实验室中发现的数值之间存在显着差异。活性矿物表面积的变化与持续的风化，次生沉淀物的积累，沥滤层的形成以及给定的反应时间是元素释放不同的关键因素。