Formation of CaUO₂(CO₃)₃²⁻and Ca₂UO₂(CO₃)₃(aq) complexes at variable temperatures (10–70 °C)

Abstract

The ternary complexation of calcium uranyl tricarbonate species, CaUO2(CO3)32− and Ca2UO2(CO3)3(aq), which are the predominant U(vi) complexes in groundwater and seawater, was investigated at variable temperatures from 10 to 70 °C.

Influence of Alkaline Earth Metal Ions on Structures and Luminescent Properties of NamMnUO2(CO3)3(4–m–2n)– (M = Mg, Ca; m, n = 0–2): Time-Resolved Fluorescence Spectroscopy and Ab Initio Studies

“…There was a direct evidence of the formation of ternary complexes CaUO2(CO3)3 2-and Ca2UO2(CO3)3 where the calcium ions enter the second coordination layer of the uranyl and interact with the carbonate ligands, as first reported by Bernhard et al, 25 and investigated later on by several groups. 8,19,21,[26][27][28][29][30][31] The luminescence of such complexes exhibits a hypsochromic shift of the whole spectrum by about 300 cm -1 compared with the free ion, when most other U(VI) compounds, like phosphates, silicates, hydroxides, or organic complexes, are showing a bathochromic shift. The blue-shifted luminescence of the triscarbonatouranyl(VI) entities results from the strong interaction of UO2 2+ with the carbonate ligands that bind the uranium atom with two out of their three oxygens in the equatorial plane of the uranyl ion, leading to a six-fold-coordinated uranyl structure.…”

“…Similar observations have been made with the less stable ternary MgUO2(CO3)3 2-and SrUO2(CO3)3 2complexes, 35,36 while the confirmation of the existence of the ternary Mg2UO2(CO3)3 complex is still discussed. 26,31,35 Quantum chemical modeling is an appropriate theoretical support for a better understanding of the luminescence of these ternary triscarbonatouranyl complexes with alkaline earth metal cations.…”

Determination of formation constants and specific ion interaction coefficients for CanUO2(CO3)3(4−2n)−complexes in NaCl solution by time-resolved laser-induced luminescence spectroscopy

“…4 The CanUO2(CO3)3 (4-2n)complexes have been studied since their first identification in a seepage water from a uranium mine in Saxony, Germany. 5 Since then, several analytical methods were used to explore their chemical structures and behaviour, such as time-resolved laser-induced luminescence spectroscopy (TRLS), [5][6][7][8][9][10][11] anion exchange method, 12,13 potentiometry -using Ca-specific electrode -, 14 ultraviolet-visible (UV-Vis) absorption spectroscopy, 15 and extended X-ray absorption spectroscopy (EXAFS). 7,8,[16][17][18] The interaction between Ca 2+ and UO2(CO3)3 4-seems slightly more important compared to the other alkaline earth elements,.…”

Visible-NIR absorption spectroscopy study of the formation of ternary plutonyl(vi) carbonate complexes

“…be 3.13 ± 0.2220 and 3.00 ± 0.2523 in previous work. Other chemical models presuming the formation of neutral Ca 2 PuO 2 (CO 3 ) 3 (aq) species show unsatisfactory spectrophotometric results with failures in the spectral fitting procedure (ESI,Fig.…”

“…Over the past two decades, the formation of ternary species (M x UO 2 (CO 3 ) 3 2x−4 , M = Ca 2+ and Mg 2+ ) has been intensively studied and the M x UO 2 (CO 3 ) 3 2x−4 complexes are the dominant aqueous U(VI) species in the presence of naturally abundant Ca 2+ and Mg 2+ ions in groundwater and seawater. [15][16][17][18][19][20][21][22][23][24][25] In addition to their overwhelming predominance in aqueous U(VI) species in natural waters, the ternary complexes are U(VI) species with significantly increased mobility resulting from decreased U(VI) sorption [26][27][28] and hindered reduction to immobile tetravalent uranium. [29][30][31][32] In a field study, the occurrence of Ca 2 UO 2 (CO 3 ) 3 (aq) was observed even in deep, reducing, Fe(II)-containing groundwater (E h -140 mV, ∼500 metres below sea level).…”