Tubular Chains, Single Layers, and Multiple Chains in Uranyl Silicates: A2[(UO2)Si4O10] (A = Na, K, Rb, Cs)

2016 ◽  
Vol 16 (9) ◽  
pp. 5268-5272 ◽  
Author(s):  
Hsin-Kuan Liu ◽  
Chun-Chi Peng ◽  
Wen-Jung Chang ◽  
Kwang-Hwa Lii
Keyword(s):  
Uranyl Silicates

Alteration of Natural Uranyl Oxide Hydrates in Si-Rich Groundwaters: Implications For Uranium Solubility

1991 ◽  
Vol 257 ◽  
Author(s):  
R.J. Finch ◽  
R.C. Ewing
Keyword(s):  
Corrosion Products ◽  
Dissolved Silica ◽  
Uranyl Phosphates ◽  
Uranyl Silicates ◽  
Solid Phases ◽  
And Control

ABSTRACTThe uranyl oxide hydrates are common initial corrosion products of uraninite (nominally U02+x) during weathering. In the presence of dissolved silica these early-formed phases alter to uranyl silicates (most commonly soddyite, U2SiO8-2H2O, and uranophane, CaU2Si2O11·6H2O). Uraninite, however, usually contains radiogenic Pb, and the earlyformed Pb-poor uranyl oxide hydrates alter incongruously to uranyl silicates plus Pb-enriched uranyl oxide hydrates such as curite. Similar to dissolved silica, radiogenic Pb may also serve to limit the mobility of U in nature by fixing U in solid phases. Curite may also play an important role in the formation of uranyl phosphates, which are significantly less soluble than the uranyl silicates, and control U solubility in many groundwaters associated with altered U ore.

Flux Synthesis of Salt-Inclusion Uranyl Silicates: [K3Cs4F][(UO2)3(Si2O7)2] and [NaRb6F][(UO2)3(Si2O7)2]

2009 ◽  
Vol 48 (17) ◽  
pp. 8357-8361 ◽  
Author(s):  
Cheng-Shiuan Lee ◽  
Sue-Lein Wang ◽  
Yen-Hung Chen ◽  
Kwang-Hwa Lii
Keyword(s):  
Flux Synthesis ◽  
Uranyl Silicates

State of uranyl silicates MII(HSiUO6)2 ·6H2O (MII=Mn, Co, Ni, Cu, Zn) in aqueous solutions

2013 ◽  
Vol 298 (1) ◽  
pp. 519-529 ◽  
Author(s):  
Oxana Nipruk ◽  
Nikolay Chernorukov ◽  
Natalya Zakharycheva ◽  
Elena Kostrova
Keyword(s):  
Aqueous Solutions ◽  
Uranyl Silicates

FTIR characterization of amorphous uranyl-silicates

2008 ◽  
Vol 253 (3-4) ◽  
pp. 136-140 ◽  
Author(s):  
D. Gorman-Lewis ◽  
S. Skanthakumar ◽  
M.P. Jensen ◽  
S. Mekki ◽  
K.L. Nagy ◽  
...  
Keyword(s):  
Ftir Characterization ◽  
Uranyl Silicates

The Alteration of Uraninite to Clarkeite

1992 ◽  
Vol 294 ◽  
Author(s):  
Robert J. Finch ◽  
Rodney C. Ewing
Keyword(s):  
North Carolina ◽  
Ground Water ◽  
Low Temperatures ◽  
Atomic Ratio ◽  
Granitic Rocks ◽  
Mole Percent ◽  
Chemical Zoning ◽  
Sheet Structure ◽  
Uranyl Silicates ◽  
Important Constituent

ABSTRACTThe oxidative alteration of uraninite by alkali-bearing, hydrothermal (200-400° C) solutions in granitic rocks produces the rare mineral clarkeite. The general formula for Na-clarkeite is{(Na,K)6-y-z(M2+PM3+qM4+r)y(□1+z-xPbx)}[UO2)7-xOt0]·nH2O. z ≈ p+2q+3r.The terms in square brackets designate the sheet structure; the other elements and vacancies (0) occur in interlayer sites. Clarkeite can accommodate Ca, Sr, Ba, Y, Th, and lanthanides. Thus, clarkeite is a potential actinide and fission product host. The replacement of uraninite by clarkeite occurs in the solid state and results in the loss of one-half of the uranium from uraninite. As U decays to Pb, the radiogenic Pb enters interlayer vacancies in clarkeite. This destabilizes the structure and clarkeite eventually decomposes to wölsendorfite, (Pb,Ca)2U2O7·2H2O, or curite, Pb3U8O27·3H2O.Clarkeite from Spruce Pine, North Carolina is zoned compositionally, with a K-rich core (atomic ratio K:Na:Ca = 1.0 : 0.11 : 0.12) surrounded by Na-clarkeite (Na:K:Ca = 1.0 : 0.03 : 0.03), rimmed and veined by Ca-clarkeite (Ca:Na:K = 1.0 : 1.25 : 0.05). Volumetrically, Na-clarkeite is the most important constituent. The chemical zoning reflects the disparate chemistries of K+, Na+, and Ca2+. Na-clarkeite and Ca-clarkeite are structurally similar, but have different sheet structures. The solubility of K in Na-clarkeite is less than five mole percent and is due to the different sizes of Na+ and K+ ions. The K-phase may not be related structurally to clarkeite.Exposed to ground water at low temperatures, clarkeite alters to the uranyl silicates, uranophane and kasolite. The alkalis are leached by ground water. The fate of Th, Y, and lanthanides from clarkeite is uncertain.

Formation of Secondary Uranium Minerals in the Koongarra Deposit, Australia

1993 ◽  
Vol 333 ◽  
Author(s):  
Hiroshi Isobe ◽  
Rodney C. Ewing ◽  
Takashi Murakami
Keyword(s):  
Northern Territory ◽  
Accessory Mineral ◽  
Migration Behavior ◽  
Graphite Layer ◽  
Uranium Mineral ◽  
Oxidation Condition ◽  
Uranyl Phosphates ◽  
Alteration Processes ◽  
Uranyl Silicates ◽  
Uranium Minerals

ABSTRACTSecondary uranium minerals from the Koongarra deposit, Northern Territory of Australia, were examined in order to understand the formation and alteration processes of the uranium minerals and their relevance to the migration behavior of uranium, lead, calcium and rare earth elements in the weathered zone. In most of the secondary ore zone, the only stable uranium mineral was saléeite (Mg(UO2)2(PO4)2·10H20), occurring as euhedral platy crystals up to 1 mm in length in veins and at surfaces. Apatite (Ca5(PO4)3F), an accessory mineral of the host rock, has saléeite reaction rims, suggesting formation at the expense of apatite. Ca-uranyl phosphates, such as autunite (Ca(UO2)2(PO4)2·10H2O), were not identified, and Ca-rich uranyl silicates are also absent in the primary ore zone. Pb-bearing uranyl phosphates were found only in the graphite layer cross-cutting the secondary ore zone. In the graphite layer, the local low oxidation condition and high hydrocarbonate content of ground water have affected the formation of uranium minerals and the migration behavior of uranium.

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