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

Abstract

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.

Retention of 226Ra by barite: The role of internal porosity

“…Ra-free reference experiments (Klinkenberg et al, 2014). In this previous work, only very little changes of the outer shape and size of the barite particles were observed, leading to the conclusion that the uptake of Ra must be related to internal processes.…”

“…In this previous work, only very little changes of the outer shape and size of the barite particles were observed, leading to the conclusion that the uptake of Ra must be related to internal processes. The spatial resolution of the ToF-SIMS analysis provided in the same study allowed for the distinction between a surface layer and the Ra uptake into the crystal volume (Klinkenberg et al, 2014). Ra was clearly identified within the barite crystal volume.…”

“…However, the pathways enabling the Ra uptake into barite and the temporal evolution of the Ra distribution within the newly formed solid-solution remained unclear. The studies of Brandt et al (2015) and Klinkenberg et al (2014) are forming the basis for the here presented results. As the study of Brandt et al (2015) provides the complete and detailed description of the evolution of the Raconcentration, the solution chemistry is only briefly covered here.…”

210Pb and 210Po in Geological and Related Anthropogenic Materials: Implications for Their Mineralogical Distribution in Base Metal Ores

“…For example, Al Attar et al [114] report barite-strontianite solid solution and hokutolite [(Ba,Pb)SO4] as the main mineral components of radionuclide-containing scales associated with oil production. Extensive solid solution between isostructural Ba-and Ra-sulphates (so called radiobarite, (Ba,Ra)SO4 [165][166][167][168][169][170][171][172][173][174] has been modelled, and a number of natural occurrences have been documented e.g., [175,176]. In a detailed mineralogical insight into radionuclide host phases, Landa and Bush [79] document intense alpha particle activity associated with the presence of 210 Pb within micron-scale inclusions of anglesite within laths of gypsum.…”

Radionuclide behaviour in the natural environment

“…Barite is known as a very significant sink for Ra in TENORM sites. Ra is not only incorporated during neoformation of BaSO 4 by coprecipitation and solid-solution (2009) formation, but apparently is also incorporated in part when in contact in a barite suspension being at or close to macroscopic equilibrium with aqueous solution (Klinkenberg, Brandt, Breuer, & Bosbach, 2014). Model approaches to describe the interplay of adsorption, entrapment, and solid-solution formation of trace elements and RNs have recently been proposed in the literature (Heberling et al, 2014;Thien, Kulik, & Curti, 2014).…”