U6+ Minerals and Inorganic Compounds: Insights Into an Expanded Structural Hierarchy of Crystal Structures

The recent weathering of uraninite from the Červená vein, Jáchymov (Czech Republic): a fingerprint of the primary mineralization geochemistry onto the alteration association

“…Remarkable are zones of compreignacite aggregates (Fig. 3c, green) (Rosenzweig and Ryan 1977) are based upon the topology, which is distinct from that of protasite to which compreignacite also belongs (Burns 2005). Moreover, the Ca 2+ -content in studied phase probably corresponds with the mineral becquerelite, based upon the same topology as compreignacite.…”

Challenging conventional f-element separation chemistry – reversing uranyl(vi)/lanthanide(iii) solvent extraction selectivity

“…This ligand environment results in distorted pentagonal bipyramidal coordination around the central uranium atom, by far the most common geometric arrangement for 7-coordinate uranyl complexes. [15] The two imine nitrogen atoms are positioned respectively above and below the equatorial plane around the uranyl moiety (O1-U1-N1 = 85.22(8) o and O1-U1-N2 = 99.04(8) o ), resulting in the sulfonated salicylidene units also siting above and below the equatorial plane in a 'stepped' conformation. This tetradentate ligand binding and stepped conformation has also been observed for three previously structurally coordinated salen complexes, UO2(salen)(MeOH), UO2(salen)(EtOH) and UO2(salen)(TPPO) (TPPO = triphenylphosphine oxide).…”

The role of potassium atoms in the formation of uranyl selenates: the crystal structure and synthesis of two novel compounds

“…Understanding the formation of natural and synthetic uranium phases is important for modelling of alteration processes occurring in the uranium deposits and geological radioactive waste repositories (Finch et al 1999). Nowadays seven uranyl selenites are known as mineral species (Burns 2005;Krivovichev and Plášil 2013), whereas no uranium selenates have been found in nature to date. This can be explained by both high solubility of uranyl selenates in aqueous solutions and easy reduction of Se 6+ to the Se 4+ state under common natural conditions (Charykova et al 2010(Charykova et al , 2012Krivovichev et al 2011aKrivovichev et al , 2012.…”

“…Synthetic members of the uranyl selenate group display an outstanding structural diversity. There are more than 120 purely inorganic or organically templated inorganic uranyl selenates (Burns 2005;Krivovichev et al 2007;Krivovichev and Plášil 2013). Most of the uranylcontaining compounds, in particular uranyl selenate structures, are layered due to the specific coordination of U(VI) atoms (Burns et al 1997).…”