The effect of magnesium on the local structure and initial dissolution rate of simplified UK Magnox waste glasses
The effect of magnesium on the local structure and initial dissolution rate of simplified UK Magnox waste glasses
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DOI：
10.1016/j.jnoncrysol.2018.03.002
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发表时间：
2018-10
影响因子：
3.5
通讯作者：
Rui Guo;C. Brigden;S. Gin;S. Swanton;I. Farnan
中科院分区：
文献类型：
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作者：
Rui Guo;C. Brigden;S. Gin;S. Swanton;I. Farnan
模拟英国Magnox放射性废玻璃制备了一系列简化玻璃，并测定了镁的存在对玻璃结构和初始溶解速度的单独影响。这些玻璃的碱土含量(Ca/Mg)为6.5 摩尔%，Si、B和Na的相对比例接近于25 重量%的模拟马格诺废旧玻璃。每种简化玻璃的宏观性质相似，只是不同的是钙镁比不同。简化镁端元玻璃(不含钙)和全组分模拟玻璃的25 MG魔角旋转核磁共振(MAS核磁共振)谱相似，与两种玻璃中相似的镁局域环境一致。简化玻璃系列的11B MAS核磁共振谱显示，随着镁含量的增加，三配位B([3]B)的量有系统地增加。与钙相比，镁对四配位B([4]B)的电荷平衡有明显的变化。然而，浸出物的11B核磁共振测量表明，额外的[3]B并不是优先从含镁的样品中浸出的。尽管钙镁替代引起了玻璃的结构变化，但初始溶解速率(R0)在误差范围内与钙镁比保持不变。这表明，长期浸出实验中测得的含镁废玻璃的耐水性比含钙的SON68玻璃差，不是由玻璃中的初级结构效应引起的。
A series of simplified glasses were prepared to mimic the United Kingdom's Magnox radioactive waste glasses and determine the separate effect of the presence of Mg on the glass structure and the initial dissolution rate. These glasses had an alkaline earth (Ca/Mg) content of 6.5 mol% and relative ratios of Si, B and Na similar to 25 wt% waste loaded Magnox waste glass simulant. Each simplified glass had similar macroscopic properties, differing only in Ca/Mg ratio.25Mg magic angle spinning nuclear magnetic resonance (MAS NMR) spectra of the simplified Mg endmember (MgEM) glass (with no Ca) and the full-component simulant glass were similar, consistent with the similar Mg local environments in both glasses.11B MAS NMR spectra of the series of simplified glasses showed a systematic increase in the amount of three-coordinated boron ([3]B) with increasing amounts of Mg. A clear change in the charge balancing of four-coordinated boron ([4]B) by Mg compared with Ca is observed. However,11B NMR measurements of the leached material showed that the additional[3]B was not preferentially leached from the Mg containing samples. Despite the structural changes in the glass induced by Ca/Mg substitution, initial dissolution rates (r0) remained invariant, within error, with Ca/Mg ratio. This indicates that the poorer aqueous durability of Mg-containing Magnox waste glass measured experimentally in long-term leaching experiments, compared with SON68 glass containing Ca, is not caused by a primary structural effect in the glass.