Determination of formation constants and specific ion interaction coefficients for Ca_nUO₂(CO₃)₃^(4−2n)−complexes in NaCl solution by time-resolved laser-induced luminescence spectroscopy

Abstract

The formation constants of CaUO2(CO3)32− and Ca2UO2(CO3)3(aq) were determined in NaCl medium at ionic strengths between 0.1 and 1 mol kgw−1 using time-resolved laser-induced luminescence spectroscopy (TRLS).

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

“…Therefore, the use of the 1800 lines mm -1 grating was required to probe the possible differences recorded at ambient temperature. Table 1 The aqueous compositions of prepared sample solutions calculated with published thermodynamic data from Shang et al 21 ., Lee et al 35 and Dong et al 29 No.…”

“…[10][11][12][13][14][15][16][17][18] The case of the carbonate species is particularly interesting. 8,13,15,[19][20][21] Both anionic complexes UO2(CO3)2 2and UO2(CO3)3 4-are characterized by an absorption spectrum shifted to longer wavelengths as compared with UO2 2+ aqua ion and its hydrolyzed species. 22,23 Meinrath et al…”

“…4 Conversely, recent works have shown that the use of modern TRLFS set-up allows measuring UO2(CO3)3 4at ambient temperature. 21,24 It has been shown that the U(VI) luminescence is increasing when alkaline earth metal ions are added into a solution that contains UO2(CO3)3 4-, i.e., in the presence of dissolved bicarbonate. The repartition of these species (and solids) can be described in e.g.…”

“…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.…”

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

“…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).…”