期刊
CHEMICAL GEOLOGY
卷 497, 期 -, 页码 1-17出版社
ELSEVIER SCIENCE BV
DOI: 10.1016/j.chemgeo.2018.08.009
关键词
Radium uptake; Recrystallization; (Sr,Ba,Ra)SO4 solid solution; Barite; Celestine; Ternary solid solution thermodynamics
资金
- German Federal Ministry of Education and Research (BMBF) ImmoRad project [02NUK019C]
- German Federal Ministry of Education and Research (BMBF) ThermAc project [02NUK039D]
Solid solution formation between RaSO4 and other isostructural sulfates has been known for a long time as a process potentially controlling Ra concentrations in aquifers. Here, we measured the Ra uptake in the Sr-rich corner of the ternary (Sr,Ba,Ra)SO4 solid solution - aqueous solution (SS-AS) system by equilibrating SrSO4, BaSO4 and mixed (Sr,Ba)SO4 solids with Ra-bearing aqueous solutions for up to 1302 days at 90 degrees C at a solid/liquid ratio of 5 g/L. The recrystallization experiments were combined with electron microscopy studies of the solids. The evolution of the solid and aqueous phases was interpreted based on thermodynamic modelling applying a recently revised thermodynamic dataset for the (Sr,Ba,Ra)SO4 + H2O system. The recrystallization process involved several metastable phases, starting from the least soluble, Ba- and Ra-rich precipitates and ending with Sr-rich solids, whose compositions approached the predicted equilibrium states. The composition and the time evolution of metastable phases were correlated with changes in the computed supersaturation functions. Particularly, the formation of Ra-Ba- and Sr-rich rims on primary barite grains in the experiment with the mechanical mixture of 99% of celestine and 1% of barite has been explained by combining calculated supersaturation conditions with considerations of structural misfit. A key result was the observed final Ra-aq concentration which is about one order of magnitude lower compared to the initial concentration, implying an efficient uptake into the newly formed solid phases. These concentrations appeared to be just slightly lower than those predicted by the thermodynamic calculations, implying that the complete SS-AS equilibrium was close to be reached in Sr-rich systems in the recrystallization experiments lasting for about 3.5 years.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据