Institute of Energy and Climate Research (IEK-6)-Nuclear Waste Management and Reactor Safety and ‡Central Institute of Engineering, Electronics and Analytics, ZEA-3 Analytics, Research Centre Jülich GmbH , 52425 Jülich, Germany.
Environ Sci Technol. 2014 Jun 17;48(12):6620-7. doi: 10.1021/es405502e. Epub 2014 May 29.
A combined macroscopic and microanalytical approach was applied on two distinct barite samples from Ra uptake batch experiments using time of flight-secondary ion mass spectrometry (ToF-SIMS) and detailed scanning electron microscopy (SEM) investigations. The experiments were set up at near to equilibrium conditions to distinguish between two possible scenarios for the uptake of Ra by already existent barite: (1) formation of a Ba1-xRaxSO4 solid solution surface layer on the barite or (2) a complete recrystallization, leading to homogeneous Ba1-xRaxSO4 crystals. It could be clearly shown that Ra uptake in all barite particles analyzed within this study is not limited to the surface but extends to the entire solid. For most grains a homogeneous distribution of Ra could be determined, indicating a complete recrystallization of barite into a Ba1-xRaxSO4 solid solution. The maxima of the Ra/Ba intensity ratio distribution histograms calculated from ToF-SIMS are identical with the expected Ra/Ba ratios calculated from mass balance assuming a complete recrystallization. In addition, the role of Ra during the recrystallization of barite was examined via detailed SEM investigations. Depending on the type of barite used, an additional coarsening effect or a strong formation of oriented aggregates was observed compared to blank samples without Ra. In conclusion, the addition of Ra to a barite at close to equilibrium conditions has a major impact on the system leading to a fast re-equilibration of the solid to a Ba1-xRaxSO4 solid solution and visible effects on the particle size distribution, even at room temperature.
采用飞行时间二次离子质谱（ToF-SIMS）和详细扫描电子显微镜（SEM）研究，对两个来自 Ra 吸收批实验的不同重晶石样本进行了宏观和微观综合分析。实验在接近平衡条件下进行，以区分 Ra 通过已存在的重晶石吸收的两种可能情况：（1）在重晶石上形成 Ba1-xRaxSO4固溶体表面层；（2）完全再结晶，导致 Ba1-xRaxSO4同质晶体。可以清楚地表明，在本研究中分析的所有重晶石颗粒中，Ra 的吸收不仅限于表面，而是扩展到整个固体。对于大多数晶粒，可以确定 Ra 的均匀分布，表明重晶石完全再结晶为 Ba1-xRaxSO4固溶体。从 ToF-SIMS 计算的 Ra/Ba 强度比分布直方图的最大值与从质量平衡计算的预期 Ra/Ba 比值相同，假设完全再结晶。此外，还通过详细的 SEM 研究检查了 Ra 在重晶石再结晶过程中的作用。与不含 Ra 的空白样品相比，根据使用的重晶石类型，观察到额外的粗化效应或强烈的定向聚集体形成。总之，在接近平衡条件下向重晶石中添加 Ra 会对系统产生重大影响，导致固体快速重新平衡到 Ba1-xRaxSO4固溶体，并对粒径分布产生可见影响，即使在室温下也是如此。
