Recrystallization of 223Ra with barium sulfate

Studies of Mineral Nucleation and Growth Across Multiple Scales: Review of the Current State of Research Using the Example of Barite (BaSO4)

“…Experimental studies demonstrate sulfate minerals can incorporate a variety of potentially harmful elements, either via thermodynamically driven uptake in the form of a solid solution at low supersaturations or via coprecipitation at high supersaturations. Barite forms isostructural solid solutions by incorporating radium, ,,,,− selenium, arsenic, strontium, , chromium, , and lead. , On the basis of microscopic and spectroscopic studies, these elements incorporate into the barite lattice rather than simply adsorb to the surface. The cations (Ra 2+ , Pb 2+ , Sr 2+ ) substitute isostructurally for the Ba 2+ cation, whereas the anions (HAsO 4 2– , CrO 4 2– , SeO 4 2– ) substitute for the SO 4 2– ion, thus forming solid solutions.…”

“…162 Despite the existence of the three different recrystallization models, homogeneous, heterogeneous, and the modified homogeneous, it is not clear under what conditions each of them is valid, as the example of radium uptake into barite demonstrates. Recrystallization experiments with barite in contact with a solution containing radium can exhibit behavior explained by the original homogeneous model 25 or the heterogeneous model 30 or exhibit a transient kinetic behavior, 33,173 though most recent experiments can be explained using a modified homogeneous model. 162 Most of these studies 25,33,162,173 used the same barite powder as starting material; however, pretreatment of the powders (e.g., pre-equilibration times and separation of particle fine fractions) varied between the different experimental studies.…”

“…However, due to a lack of available and reliable thermodynamic data, it was unclear whether a homogeneous radiobarite solid solution would form or if only a partial equilibration near the surface was expected. This caused several groups to investigate the reaction of pre-equilibrated barite particles in an aqueous solution with radium, ,, which mimics the situation in which barite has precipitated from spent fuel by reacting with sulfate-containing groundwater or where barite is present within the backfill material, e.g., in the bentonite which is to be used in the Swiss repository . All studies showed a significant uptake of radium which could not be explained by merely surface adsorption.…”

Recrystallization and Uptake of 226Ra into Ba-Rich (Ba,Sr)SO4 Solid Solutions

“…Such solid solutions are ubiquitous in natural systems-most minerals in nature are mixtures of elements on the molecular scale rather than pure compounds. Recent studies [11][12][13][14][15][16][17][18] have shown that the formation of a (Ba,Ra)SO 4 solid solution significantly reduces the solubility of 226 Ra in aqueous systems. Rapid uptake via co-precipitation [11][12][13] as well as the slower recrystallization process can lead to this solid solution [14][15][16][17][18].…”

“…Recent studies [11][12][13][14][15][16][17][18] have shown that the formation of a (Ba,Ra)SO 4 solid solution significantly reduces the solubility of 226 Ra in aqueous systems. Rapid uptake via co-precipitation [11][12][13] as well as the slower recrystallization process can lead to this solid solution [14][15][16][17][18]. Recrystallization of BaSO 4 in the presence of 226 Ra has been considered to be relevant with respect to nuclear waste disposal [19] as well as to ore processing [20,21], where barite was also observed to take up 226 Ra from the process solutions.…”