Uptake of Ra during the Recrystallization of Barite: A Microscopic and Time of Flight-Secondary Ion Mass Spectrometry Study

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• 作者：Martina Klinkenberg ; Felix Brandt ; Uwe Breuer ; Dirk Bosbach
• 刊名：Environmental Science & Technology
• 出版年：2014
• 出版时间：June 17, 2014
• 年：2014
• 卷：48
• 期：12
• 页码：6620-6627
• 全文大小：468K
• 年卷期：v.48,no.12(June 17, 2014)
• ISSN：1520-5851

文摘

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 Ba_1鈥?i>xRa_xSO₄ solid solution surface layer on the barite or (2) a complete recrystallization, leading to homogeneous Ba_1鈥?i>xRa_xSO₄ 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 Ba_1鈥?i>xRa_xSO₄ 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 Ba_1鈥?i>xRa_xSO₄ solid solution and visible effects on the particle size distribution, even at room temperature.