Hydrolysis of Uranyl(VI) in Acidic and Basic Aqueous Solutions Using a Noncomplexing Organic Base: A Multivariate Spectroscopic and Statistical Study

Abstract

In the field of actinide aqueous chemistry, this work aims to resolve some controversy about uranyl(VI) hydroxide species present in basic aqueous solutions. We revisit the Raman, IR, and UV-visible spectra with two new approaches. First, Raman, IR and UV data were recorded systematically from aqueous solutions with the noncomplexing electrolyte (C(2)H(5))(4)NNO(3) at 25 °C and 0.1 MPa ([U(total)] = 0.005-0.105 M) in H(2)O and D(2)O over a wide range of -log mH(D)(+) between 2.92 and 14.50. Second, vibrational spectra (IR and Raman) of basic solutions in H(2)O and D(2)O were analyzed using the Bayesian Positive Source Separation method to estimate pure spectra of individual species. In D(2)O solutions, the new spectroscopic data showed the occurrence of the same species as those in H(2)O. As observed for the wavenumber of the symmetric stretching mode, the wavenumber characteristic of the O═U═O antisymmetric stretching mode decreases as the number of OH(D)(-) ligands increases. These kinds of data, completed by (1) analysis of the signal widths, (2) persistence of the apparent exclusion rule between IR and Raman spectra of the uranyl species stretching modes, and (3) interpretation of the absorption UV-visible spectra, allow discussion of the chemistry, structures, and polynuclearity of uranyl(VI) species. In moderate basic solutions, the presence of two trimers is suggested. In highly basic solutions ([OH(-)] ≈ 3 M), the two monomers UO(2)(OH)(4)(2-) and UO(2)(OH)(5)(3-) are confirmed to be in good agreement with earlier EXAFS and NMR results. The occurrence of the UO(2)(OH)(6)(4-) monomer is also suggested from the more basic solutions investigated.

A luminescence line-narrowing spectroscopic study of the uranium(vi) interaction with cementitious materials and titanium dioxide

“…It is caused by a significant weakening of the axial UvO bonds upon sorption due to the increased electrondonating abilities of the ligands in the equatorial plane of the sorbed UO 2 2+ ions. 15,48,54 The broad luminescence bands indicate strong variation in the bonding environment of the sorbed UO 2 2+ ions. Fig.…”

“…2, spectrum a and b in the results section). The spacing (Δ) between E and the first line of this series, S 1 , results in values for ν s in the ground state as follows: ν s = ∼870 cm −1 for the UO 2 2+ aquo ion 47,48 and 700 cm −1 < ν s < 800 cm −1 for uranium minerals (silicates, carbonates) and UO 2 2+ sorbed species. 26 in an ill-defined coordination environment (e.g.…”

Electrochemical deposition of uranium oxide in highly concentrated calcium chloride

“…The charge transfer band was observed in the wavelength range less than 408 nm. The absorption spectrum in 6.9 M CaCl 2 containing UO 2 Cl 2 was different from that in the aqueous solution containing uranyl hydrolysis or oligomer species reported by Quiles et al [16]. The uranyl species in 6.9 M CaCl 2 does not form hydrolysis species even though H ?…”

Observations of surface-mediated reduction of Pu(VI) to Pu(IV) on hematite nanoparticles by ATR FT-IR

“…Theoretical work [25][26][27] estimates that the absorption peaks for the actinides will exhibit the following trend with respect to the wavelength assuming they are all in the same oxidation state: U > Np > Pu. Previous experimental work has measured the ATR FT-IR peak energies for U(VI), Np(V/VI), and Pu(VI) in aqueous solutions and confirmed this trend [25,[28][29][30]. The shift in peak location and shape, relative to the aqueous species, has been used to infer the mode (i.e.…”

“…The saturated KNO 3 (s) was prepared by mixing solid KNO 3 (s) (VWR) with DI water until until past the point of dissolution (its solubility, 316 g/L at 20 ∘ C). Experiments were also completed with 238 U(VI) and 237 Np(V) following the same method described for 242 Pu to confirm sorbed and aqueous absorption peaks determined previously experimentally [25,[28][29][30][31][32][33][60][61][62] and theoretically [25][26][27] Lefevre et al [33] previously noted that air-dried DRIFT samples reported equivalent results as their ATR FT-IR flow cell setup leading to the conclusion that Fe 2 O 3 -uranyl complexes were not modified by drying and Wijnja [63] reached similar conclusions for carbonate sorption to -Al 2 O 3 . It is expected that a hydration layer will remain at the mineral surfaces.…”