Polymorphic transformations of titanium oxides contribute to economic uranium mineralization in sandstone

Geology Pub Date : 2024-03-20 DOI:10.1130/g51982.1
Shuo Yin, Zhaobin Yan, Jiali Fu, Wen Zhang, Hong Liu, Fei Xia, Qingfei Wang
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Abstract

Sandstone-hosted uranium (U) deposits provide a significant U resource for nuclear energy worldwide. Driven by redox reactions, tetravalent uranium-bearing minerals are commonly associated with reductants (e.g., pyrite and organic matter). However, numerous observations have revealed that tetravalent uranium-bearing minerals can spatially coexist with chemically stabilized titanium oxides in sandstone-hosted U deposits, requiring a complementary mechanism to interpret these findings. We present a new model based on in situ texture, trace-element content, and titanium isotopic ratio, as well as polymorph type and related transformation for titanium oxides from the Yaojia Formation of the southwestern Songliao Basin in northeast China. Specifically, in our model, abundant nanopores were generated during the spontaneous transformation of anatase to rutile, producing a porous material for hexavalent U adsorption. Facilitated by a U-rich source rock, adsorbed U in porous titanium oxide from the lower Yaojia Formation was up to several thousand parts per million. In order to minimize surface energy, a subsequent decrease in surface area by merging small pores is inevitable. When the evolved surface area was small enough, hexavalent U would be desorbed and subsequently transformed to tetravalent U by local reductants, forming uraninite nanoparticles on the surface of U-rich rutile with relatively large pores. Our newly proposed mechanism not only contributes to a better understanding of economic U mineralization in sandstone, but also suggests that U occurred as uranium oxide instead of brannerite in sandstone-hosted U deposits, providing a nano-mineralogical perspective required for industrial processing.
钛氧化物的多态转化促进了砂岩中的经济铀矿化
砂岩型铀(U)矿床为全球核能提供了重要的铀资源。在氧化还原反应的驱动下,四价铀矿物通常与还原剂(如黄铁矿和有机物)伴生。然而,大量观察结果表明,在砂岩型铀矿床中,四价铀矿物可以与化学稳定的钛氧化物在空间上共存,这就需要一种补充机制来解释这些发现。我们根据中国东北松辽盆地西南部姚家地层钛氧化物的原位质地、痕量元素含量、钛同位素比值以及多晶型和相关转化,提出了一个新的模型。具体而言,在我们的模型中,锐钛矿向金红石矿的自发转化过程中产生了丰富的纳米孔隙,从而形成了可吸附六价铀的多孔材料。在富铀源岩的作用下,下姚家地层多孔氧化钛中的铀吸附量高达百万分之几千。为了最大限度地降低表面能,通过合并小孔隙而减少表面积是不可避免的。当演化的表面积足够小时,六价铀将被解吸,随后在局部还原剂的作用下转化为四价铀,在孔隙相对较大的富铀金红石表面形成铀矿石纳米颗粒。我们新提出的机制不仅有助于更好地理解砂岩中的经济铀矿化,而且还表明在砂岩孕育的铀矿床中,铀是以氧化铀而非糠酸盐的形式出现的,为工业加工提供了所需的纳米矿物学视角。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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