Fossil Bioapatites with Extremely High Concentrations of Rare Earth Elements and Yttrium from Deep-Sea Pelagic Sediments

Abstract

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From Molecular Oxo-Hydroxo Ce Clusters to Crystalline CeO2

“…5) exhibits a shape very similar to the one of Ce(IV) in aqueous solution, with a slight broadening of the peaks B and C. This single peak A and B features were also observed in environmental conditions with Ce atoms sorbed at the manganese oxide surface. 90 These clusters exhibit short μ 3 oxygen atoms and a structure where the local geometry around the Ce atoms is similar to that of the surface cerium atoms of larger Ce clusters (i.e., Ce-{24} and Ce-{38}). 59 For this reason, these hexameric clusters might be considered as an intermediate step of Ce(IV) hydrolysis.…”

“…Regarding CeO 2 NPs, the Ce core /Ce total ratio was calculated geometrically by considering the NPs to be spheres with a single size distribution (with uncertainty associated with D (10) and D (90) determined for these nanoparticles), the cerium atoms to be homogeneously distributed in the particle and the cerium atoms that did not correspond to core atoms located on an outer sphere layer at 2.3 Å from the surface (corresponding to a typical Ce−O distance in CeO 2 38 ). These approximations led to the ratio: with R corresponding to the NP radius in nm.…”

Revealing the Incorporation of Cerium in Fluorapatite

“…It remains to be seen whether this finding can be extended to biogenic FAp, such as those occurring in marine sediments, which are prospective resources for REY. 80 Bioapatites from ocean-floor sediments have similar Ce L 3 -edge X-ray absorption near-edge structure (XANES) spectra as magmatic/hydrothermal FAp, 8 indicating that Ce is also trivalent. But XANES spectroscopy does not inform on the chemical form of REY, and therefore on ore enrichment processes that can be different for high-temperature magmatic/hydrothermal and low-temperature sedimentary deposits.…”

“…70−72 The Durango FAp was characterized previously by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and electron probe microanalysis (EPMA). 8 It contains 4890 mg/kg (ppm) Ce, 3340 mg/kg La, and 971 mg/kg Pr. The chemical composition of Imilchil FAp is reported in Table S2.…”

“…The site occupancy of a given REE can be apprised in principle by extended X-ray absorption fine structure (EXAFS) spectroscopy, as this technique is element-selective. However, a major roadblock in analyzing multielemental Earth materials by EXAFS is the overlap of the X-ray fluorescence lines from two or more elements, ,, and therefore its application to REE-containing natural apatites is unprecedented.…”