²²⁶Ra is an important contributor to naturally occurring radioactive materials (NORM) and also considered in safety cases related to the disposal of spent nuclear fuel in a deep geological repository. Recrystallization and solid solution formation with sulfates is regarded as an important retention mechanism for ²²⁶Ra. In natural systems sulfates often occur as (Ba,Sr)SO₄. Therefore, we have chosen this solid solution at the Ba-rich end for investigations of the ²²⁶Ra uptake. The resulting ²²⁶Ra-solubility in aqueous solution was assessed in comparison with a thermodynamic model of the solid solution-aqueous solution system (Ba,Sr,Ra)SO₄ + H₂O. The temperature and composition of the initial (Ba,Sr)SO₄ solid solution were varied. Measurements of the solution composition were combined with microscopic observations of the solid and thermodynamic modeling. A complex recrystallization behavior of the solid was observed, including the dissolution of significant amounts of the solid and formation of metastable phases. The re-equilibration of Ba-rich (Ba,Sr)SO₄ to (Ba,Sr,Ra)SO₄ leads to a major reconstruction of the solid. Already trace amounts of Sr in the solid solution can have a significant impact on the ²²⁶Ra solubility, depending on the temperature. The experimental findings confirm the thermodynamic model, although not all solids reached equilibrium with respect to all cations.

中文翻译：

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重结晶并吸收226 Ra到富含Ba（Sr）SO4的固溶体中

²²⁶ Ra是自然产生的放射性物质（NORM）的重要贡献者，并且在与在深部地质处置库中处置乏核燃料有关的安全案例中也考虑到了Ra。重结晶和用硫酸盐形成固溶体被认为是²²⁶ Ra的重要保留机制。在自然系统中，硫酸盐通常以（Ba，Sr）SO _{4的形式出现}。因此，我们在富Ba端选择了这种固溶体来研究²²⁶ Ra的吸收。与固溶-水溶液体系（Ba，Sr，Ra）SO ₄ + H ₂的热力学模型比较，评估了所得的²²⁶ Ra在水溶液中的溶解度。O.初始（Ba，Sr）SO ₄固溶体的温度和组成有所变化。溶液组成的测量与固体和热力学模型的微观观察相结合。观察到固体的复杂的再结晶行为，包括大量固体的溶解和亚稳相的形成。富含Ba的（Ba，Sr）SO ₄与（Ba，Sr，Ra）SO ₄的重新平衡导致固体的重大重构。固溶体中已经存在痕量的Sr会对²²⁶产生重大影响Ra的溶解度，取决于温度。实验结果证实了热力学模型，尽管并非所有固体都相对于所有阳离子达到平衡。