X-ray diffraction data for two new calcium uranium (VI) hydrates

Abstract

The X-ray powder diffraction patterns for two new synthetic calcium uranium (VI) silicate hydrate phases are reported. Ca1.5U6(OH)7O16·7H2O is orthorhombic, space group P*a*, with unit cell a=13.8949(14), b=12.0776(12), c=15.228(3) Å. The structure appears to be related to that of becquerelite. Ca2(UO2)2(Si2O5)3·10H2O was also indexed on an orthorhombic unit cell, a=12.075(3), b=15.406(6), c=26.043(6) Å. The Powder Diffraction File coverage of uranium-containing minerals which could, on the basis of their chemical formula, form in U-containing cements is also reviewed.

EXAFS investigation on U(VI) immobilization in hardened cement paste: influence of experimental conditions on speciation

“…In general, the distances deduced from EXAFS were consistent with those obtained from XRD [10,23,24,27]. Further, important aspects of the U(VI) coordination environment were confirmed, in particular the distance between U(VI) and the two axial oxygen atoms and the existence of a split equatorial oxygen shell.…”

“…Ca-uranate (CaUO 4 ·H 2 O) and uranophane (Ca(UO 2 ) 2 (SiO 3 OH) 2 ·5H 2 O) were synthesized by Moroni and Glasser [9] and their characterization is described elsewhere [9,10]. The CaUO 4 ·H 2 O sample was reported to be a hydrated calcium uranate [9] and initially named "phase X".…”

“…For example, the coordination number (N) of the first shell was held constant, simulating the axial oxygen atoms of the uranyl structure, as the X-ray absorption near edge structure (XANES) part of the spectra did not indicate any change in the redox state. In case of the U(VI) reference compounds, the coordination numbers of all neighboring atoms were held constant in accordance with the XRD data published in the literature [10,23,24,27]. For each fit, the threshold energy (ΔE 0 ) was linked for all shells and was allowed to vary as a global parameter.…”

“…The latter assumption implies that the path length and DW factor of each MS path is related to the SS axial oxygen path. The fitting approach was tested on several reference compounds (soddyite, becquerelite, α-uranophane, CaUO 3.8 and K-boltwoodite) based on the comparison of fitted data with the crystallographic distances reported in the literature [10,23,24,[27][28][29].…”

Synthesis of Calcium Monouranate Particles via an Aqueous Route

“…The XRD pattern of orange Ca2U3O11 particles (Figure 3b -25˚C) resemble a Ca-bearing endmember of the Ianthanite -Becquerelite -Compreignacite mineral group (Figure 3b diamonds) 21 formed under similar conditions with differing calcium content, suggesting structural isomorphology in the 0.25 ≤ [Ca/U] ≤ 1 range. During curing up to 700˚C (Figure 2a), the precipitates decompose to form spherical particles composed of crystalline calcium polyuranate (Ca2U3O11) (Figure 3b -700˚C, circles) via an initial 6wt.…”