无序的晶体结构和碳酸异常高溶解度的碳酸
Artem V Matyskin1, Burçak Ebin1, Stefan Allard1
1Nuclear Chemistry and Industrial Materials Recycling Group, Energy and Materials Division, Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Kemivägen 4, SE-41296 Gothenburg, Sweden.
Inorganic chemistry
|July 21, 2023
概括
碳酸-226的合成和特征. 它的较高溶解度相比witherite支持Ra丰富阶段的混乱性质,适用于纯RaCO3.
科学领域:
- 放射化学 放射化学是指辐射化学.
- 固态化学 固态化学
- 地质化学 地质化学
背景情况:
- -226 (226Ra) 是核废物的关键放射性同位素.
- 了解化合物的可溶性和结构对于安全处置至关重要.
- 在某些废物场景中,碳酸 (RaCO3) 预计将成为主要的固体相.
研究的目的:
- 为了合成和描述-226碳酸盐 (RaCO3).
- 在不同的条件下确定RaCO3的可溶性.
- 为碳酸相提供结构性见解.
主要方法:
- 在室温下合成-硫酸盐 (226Ra0.76Ba0.24SO4).
- 使用X射线粉末衍射 (XRPD) 和扩展的X射线吸收细结构 (EXAFS) 进行表征.
- 在25.1°C以不同的离子强度进行过低和过和的溶解性研究.
主要成果:
- 分数结晶产生了两个阶段:一个主要的富含Ra的阶段 (Ra(Ba) CO3) 和一个较小的富含Ba的阶段 (Ba(Ra) CO3).
- 主要的Ra(Ba) CO3阶段表现出一个无序的碳酸氧结构,直接空间*ab initio*建模证实了这一点.
- 确定Ra(Ba) CO3的可溶性积 (log10 *K*sp0) 为 -7.5(1),显著高于矿 (-8.56).
- EXAFS数据表明,是由9个氧气协调的,平均Ra-O键距离为2.885(3) Å,Ra2+的离子半径为1.545(6) Å.
结论:
- 合成的富含Ra的阶段 (Ra ((Ba) CO3) 明显比矿更容易溶解,与其无序的结构一致.
- 对于Ra ((Ba) CO3的发现适用于纯RaCO3,表明其流动性比以前假设的更高.
- 确定Ra2+的离子半径和结构障碍是影响其地球化学行为的关键因素.
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