Degradation and ion exchange mechanisms in metatorbernite-type (Cu(UO2)2(XO4)2.8H2O, X=As, P) minerals; implications for remediation of radiochemical

本项目旨在了解变质橄榄岩型矿物的结构、稳定性及降解机理。偏铁闪矿(Cu（UO2)2(PO4)2 8H2O）及其类似的砷酸盐偏铁闪矿(Cu（UO2)2(AsO4)2 8H2O）是由铀矿（铀矿）蚀变形成的常见次生铀矿物。在自然和人为污染的环境中，这两种矿物都被认为是铀的重要宿主。因此，了解这些矿物相的稳定性对于制定旨在防止有毒元素（再）释放到环境中的保留和修复策略至关重要。偏镁铝辉石和偏镁铝辉石是层状矿物，由磷酸铀酰/砷酸盐片和含有水配位铜（II）离子的水合夹层组成。两端成员相Cu(UO2)2(PO4)2-x(AsO4)x 8H2O， 0x2之间存在完全的固溶体。通过一系列的浸出实验，我们发现固溶体的稳定性与组成有关，富as相的稳定性较低，特别是在u浸出方面。为了理解这种基于成分的稳定性的原因，我们已经开始对矿物结构进行深入的研究。铀和砷所表现出的主要x射线散射意味着以前的研究无法通过实验确定氢原子在晶格中的位置，仅使用x射线技术。我们的分析包括同步加速器粉末x射线衍射、单晶x射线衍射、中子粉末衍射、红外光谱和计算方法的结合。我们的工作旨在提出一种新的稳钙辉石固溶体结构模型，并将这一知识应用于观察到的稳定性差异。

This project aims to understand the structure, stability and degradation mechanisms of metatorbernite type minerals. Metatorbernite (Cu(UO2)2(PO4)2 8H2O), and its arsenate analogue metazeunerite (Cu(UO2)2(AsO4)2 8H2O), are common secondary uranium minerals that result from the alteration of uranium ore (uraninite). Both minerals are considered significant hosts for uranium in natural and anthropogenically contaminated environments. Understanding the stability of these mineral phases is therefore essential in the development of retention and remediation strategies aimed to prevent the (re)release of toxic elements into the environment.Metatorbernite and metazeunerite are layered minerals, comprised of uranyl phosphate/arsenate sheets with hydrated interlayers containing water coordinated copper(II) ions. A complete solid solution exists between the two end member phases: Cu(UO2)2(PO4)2-x(AsO4)x 8H2O, 0x2. Through a series of leaching experiments we have found that the stability of the solid solution is composition dependent, with As-rich phases exhibiting a lower stability, particularly with respect to U-leaching. To understand the reason(s) for this composition-based stability, we have begun an in-depth investigation into the mineral structure. Dominant X-ray scattering exhibited by uranium and arsenic has meant that previous studies have been unable to experimentally locate the position of hydrogen atoms within the crystal lattice using X-ray techniques alone. Our analysis includes a combination of synchrotron powder X-ray diffraction, single crystal X-ray diffraction, neutron powder diffraction, infrared spectroscopy, and computational methods. Our work aims to present a new structural model for the metatorbernite metazeunerite solid solution, and apply this knowledge to the observed stability differences.