Zhang Yingjie, Lu Kimbal T, Wei Tao, Karatchevtseva I, Zheng Rongkun
Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia.
School of Physics and Advanced Materials, University of Sydney, Ultimo, New South Wales 2007, Australia.
Dalton Trans. 2023 Dec 5;52(47):17942-17953. doi: 10.1039/d3dt03078d.
Alkaline earth metal ions play an important role in the formation of secondary uranium minerals due to their abundance in the Earth's crust. Although uranium oxide hydrate (UOH) minerals and synthetic phases with calcium, strontium and barium ions have been investigated, their counterparts with magnesium ions are much less studied. In this work, synthetic UOH materials with magnesium ions have been investigated with three new compounds being synthesised and characterised. Compound Mg(HO)(HO)[(UO)O(OH)] (U-Mg1 with a U : Mg ratio of 3 : 1) crystallises in the monoclinic 2/ space group having a layered crystal structure, constructed by β-UO layers with 6-fold coordinated Mg ions as interlayer cations. Compound NaMg(HO)[(UO)O(OH)] (U-Mg2p with U : Mg : Na ratios of 6 : 1 : 2) crystallises in the triclinic 1̄ space group having a layered structure, constructed by a unique type of uranium oxide hydroxide layer containing both α-UO and β-UO features, with alternating layers of 6-fold coordinated Mg and 6-/8-fold coordinated Na interlayer cations. Compound NaMg(HO)[(UO)O(OH)] (U-Mg2n with U : Mg : Na ratios of 8 : 1 : 2) crystallises in the triclinic 1̄ space group having a corrugated layer structure, constructed by a unique type of uranium oxide hydroxide layer with mixed 6-fold coordinated Mg and 7-fold coordinated Na interlayer cations. The structural diversity in the UOH-Mg system was achieved by adjusting the solution pH using NaOH, highlighting the importance of solution pH control and the additional Na ions in the formation of UOH phases. The extra structural flexibility offered by the Na ions emphasizes the opportunity for synthesising UOHs with dual-cations to further improve our understanding of the alteration products of spent nuclear fuel under geological disposal.
碱土金属离子在地壳中含量丰富，在次生铀矿物的形成过程中发挥着重要作用。尽管已对氧化铀水合物（UOH）矿物以及含钙、锶和钡离子的合成相进行了研究，但含镁离子的同类物研究较少。在这项工作中，对含镁离子的合成UOH材料进行了研究，合成并表征了三种新化合物。化合物Mg(HO)(HO)[(UO)O(OH)]（U-Mg1，U:Mg比例为3:1）结晶于单斜2/空间群，具有层状晶体结构，由β-UO层构成，6配位的Mg离子作为层间阳离子。化合物NaMg(HO)[(UO)O(OH)]（U-Mg2p，U:Mg:Na比例为6:1:2）结晶于三斜1̄空间群，具有层状结构，由一种独特类型的铀氧化氢氧化物层构成，兼具α-UO和β-UO特征，6配位的Mg和6/8配位的Na层间阳离子交替排列。化合物NaMg(HO)[(UO)O(OH)]（U-Mg2n，U:Mg:Na比例为8:1:2）结晶于三斜1̄空间群，具有波纹层结构，由一种独特类型的铀氧化氢氧化物层构成，层间阳离子为6配位的Mg和7配位的Na混合。通过用NaOH调节溶液pH值实现了UOH-Mg体系的结构多样性，突出了溶液pH值控制以及额外的Na离子在UOH相形成中的重要性。Na离子提供的额外结构灵活性凸显了合成双阳离子UOH以进一步加深我们对地质处置下乏核燃料蚀变产物理解的机会。
