Nucleation and growth kinetics of RaxBa1-xSO4 solid solution in NaCl aqueous solutions
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Output type: Journal article
Author list: Rosenberg Y., Sadeh Y., Metz V., Pina C., Ganor J.
Publisher: Elsevier
Publication year: 2014
Journal: Geochimica et Cosmochimica Acta (0016-7037)
Volume number: 125
Start page: 290
End page: 307
Number of pages: 18
ISSN: 0016-7037
eISSN: 1872-9533
URL: http://api.elsevier.com/content/abstract/scopus_id:84888062026
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Open access status: closed
Abstract
Co-precipitation of Ra and Ba in barite (i.e., the formation of a RaBaSO solid solution) has long been established as an important process that has the potential to control Ra concentration. This process is commonly described by a distribution model. Ample studies have shown that the key parameter of this model, the partition coefficient, varies in the range of 1-2 as a function of temperature, salinity and precipitation kinetics of the RaBaSO solid solution. This roughly twofold change in the partition coefficient may lead to large differences in the concentration of dissolved Ra.The present study systematically investigated the co-precipitation kinetics of the RaBaSO solid solution from aqueous solutions up to 5.9 molkgH2O-1 NaCl, circum-neutral pH and at ambient temperature. Laboratory batch experiments designed to follow the nucleation of the RaBaSO solid solution and the co-precipitation kinetics of Ba and Ra from aqueous solutions which were initially supersaturated with respect to barite (degree of supersaturation, β=20±2).The following empirical law describes the dependence of the activity-based partition coefficient, KD,barite″, on the degree of supersaturation, β:KD,barite″=(1.99±0.05)-(0.58±0.06)·log(βbarite).This empirical law is in good agreement with other literature data. The outcomes of the empirical law are compared to the prediction of a model for the nucleation of two-dimensional islands. © 2013 Elsevier Ltd.
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