Crystal Chemistry and Structural Complexity of the Uranyl Carbonate Minerals and Synthetic Compounds

Abstract

Uranyl carbonates are one of the largest groups of secondary uranium(VI)-bearing natural phases being represented by 40 minerals approved by the International Mineralogical Association, overtaken only by uranyl phosphates and uranyl sulfates. Uranyl carbonate phases form during the direct alteration of primary U ores on contact with groundwaters enriched by CO2, thus playing an important role in the release of U to the environment. The presence of uranyl carbonate phases has also been detected on the surface of “lavas” that were formed during the Chernobyl accident. It is of interest that with all the importance and prevalence of these phases, about a quarter of approved minerals still have undetermined crystal structures, and the number of synthetic phases for which the structures were determined is significantly inferior to structurally characterized natural uranyl carbonates. In this work, we review the crystal chemistry of natural and synthetic uranyl carbonate phases. The majority of synthetic analogs of minerals were obtained from aqueous solutions at room temperature, which directly points to the absence of specific environmental conditions (increased P or T) for the formation of natural uranyl carbonates. Uranyl carbonates do not have excellent topological diversity and are mainly composed of finite clusters with rigid structures. Thus the structural architecture of uranyl carbonates is largely governed by the interstitial cations and the hydration state of the compounds. The information content is usually higher for minerals than for synthetic compounds of similar or close chemical composition, which likely points to the higher stability and preferred architectures of natural compounds.

Investigations of the Cobalt Hexamine Uranyl Carbonate System: Understanding the Influence of Charge and Hydrogen Bonding on the Modification of Vibrational Modes in Uranyl Compounds

“…A H-bonding network within the tetramethylammonium uranyl tricarbonate compound has also been delineated, and again the uranyl oxo groups do not participate in additional intermolecular interactions with the hydrogen bond donors. 57 Within the guanidinium system, the trimeric species [(UO 2 ) 3 (CO 3 ) 6 ] 6– was the major species isolated, but [C(NH 2 ) 3 ] 4 [(UO 2 )(CO 3 ) 3 ] has also been reported by Fedosseev and co-workers. 58 In both cases, no hydrogen bonds were observed between the guanidinium cations and the uranyl oxo groups.…”

Crystallization of Uranyl Silicate Natroboltwoodite during an Experimental Dissolution of the Mineral Yttrialite-(Y): Crystal Structure and Raman Spectroscopy

“…Noteworthy, comparing complexity measures for natural minerals and synthetic uranyl silicates, the overall complexity of synthetic uranyl silicates is higher than for minerals, which is, for instance, a somewhat different trend than for other chemical groups, at least for sulfates and carbonates . For uranyl silicate minerals, if taking into account the swamboite-(Nd) average structure, the average complexity measure as I G,tot.…”

Structural and chemical complexity of minerals: an update

“…For some interesting applications of ladder diagrams to the analysis of uranyl minerals and inorganic compounds see Gurzhiy and Plášil (2019) and Gurzhiy et al (2019 and 2021).…”

“…The complexity of chemical composition and crystal structure are therefore fundamental characteristics of minerals that have high relevance to the understanding of their stability, occurrence and evolution. The universal quantitative measures of structural and chemical complexity were proposed in Krivovichev (2012, 2013, 2014; Krivovichev et al , 2018) on the basis of Shannon information theory and have been recognised as useful parameters for the analysis of various mineralogical and crystal chemical phenomena, from crystal-structure classifications to metastable crystallisation and mineral evolution (Tambornino et al , 2015; Christy et al , 2016; Varn and Crutchfield, 2016; Plášil et al , 2017; Plášil, 2018a, 2018b, 2018c; Ovchinnikov et al , 2018; Majzlan et al , 2018; Colmenero et al , 2019; Gurzhiy and Plášil, 2019; Gurzhiy et al , 2019, 2021; Hornfeck, 2020; Bindi et al , 2020; Majzlan, 2020; Mugnaioli et al , 2020; Sabirov and Shepelevich, 2021; Kaußler and Kieslich, 2021, etc.). The aim of this review is to summarise the recent findings in the field of structural and chemical complexity of minerals and to outline possible directions for its further development.…”