Dataset Information

Carbonate complexation enhances hydrothermal transport of rare earth elements in alkaline fluids.

ABSTRACT: Rare earth elements (REE), essential metals for the transition to a zero-emission economy, are mostly extracted from REE-fluorcarbonate minerals in deposits associated with carbonatitic and/or peralkaline magmatism. While the role of high-temperature fluids (100 < T < 500 °C) in the development of economic concentrations of REE is well-established, the mechanisms of element transport, ore precipitation, and light (L)REE/heavy (H)REE fractionation remain a matter of debate. Here, we provide direct evidence from in-situ X-ray Absorption Spectroscopy (XAS) that the formation of hydroxyl-carbonate complexes in alkaline fluids enhances hydrothermal mobilization of LREE at T ≥ 400 °C and HREE at T ≤ 200 °C, even in the presence of fluorine. These results not only reveal that the modes of REE transport in alkaline fluids differ fundamentally from those in acidic fluids, but further underline that alkaline fluids may be key to the mineralization of hydrothermal REE-fluorcarbonates by promoting the simultaneous transport of (L)REE, fluoride and carbonate, especially in carbonatitic systems.

SUBMITTER: Louvel M

PROVIDER: S-EPMC8933457 | biostudies-literature | 2022 Mar

REPOSITORIES: biostudies-literature

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Carbonate complexation enhances hydrothermal transport of rare earth elements in alkaline fluids.

Louvel Marion M Etschmann Barbara B Guan Qiushi Q Testemale Denis D Brugger Joël J Brugger Joël J

Nature communications 20220318 1

Rare earth elements (REE), essential metals for the transition to a zero-emission economy, are mostly extracted from REE-fluorcarbonate minerals in deposits associated with carbonatitic and/or peralkaline magmatism. While the role of high-temperature fluids (100 < T < 500 °C) in the development of economic concentrations of REE is well-established, the mechanisms of element transport, ore precipitation, and light (L)REE/heavy (H)REE fractionation remain a matter of debate. Here, we provide direc ...[more]

PMID: 35304459

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Project description:Abstract The interaction between rare earth element (REE)‐rich (La, Pr, Nd, Dy) aqueous solutions, dolomite (CaMg(CO3)2), and aragonite (CaCO3) at low temperature hydrothermal conditions (25–220 °C) is studied. The experiments result in the solvent‐mediated surface precipitation and subsequent pseudomorphic mineral replacement of the dolomite and aragonite seeds by newly formed REE‐carbonates. The host grains are replaced from periphery inward. The newly formed REE‐bearing carbonates in La‐, Pr‐, and Nd‐doped systems follow the crystallization sequence: lanthanite [REE2(CO3)3·8H2O] → kozoite [orthorhombic REECO3(OH)] → hydroxylbastnasite [hexagonal REECO3(OH)]. The interaction of Dy‐bearing solutions with dolomite results only in the crystallization of kozoite [orthorhombic DyCO3(OH)]. However, experiments with aragonite reveal a two‐step crystallization pathway: tengerite [Dy2(CO3)3·2‐3(H2O)] → kozoite [orthorhombic DyCO3(OH)]. The temperature, the dissolution rate of the host mineral, and the ionic radii of the REE3+ in question are found to control the kinetics of the replacement reaction, the polymorph selection, and the crystallization pathways toward bastnasite. The findings allow to gain a more in‐depth understanding of the formation REE‐bearing carbonates, particularly the mineral bastnasite, which is the main source of REEs for industry. This knowledge can be used to improve REE separation, exploration, exploitation methods, as well to produce carbonate minerals with tailored structures. The interaction of rare earth element (REE)‐bearing solutions and dolomite/aragonite results in solvent‐mediated surface precipitation and subsequent pseudomorphic mineral replacement of the host carbonate seeds by newly formed rare earth carbonates, following the crystallization sequence: lanthanite → kozoite → hydroxylbastnasite. The reaction is controlled by the temperature, ionic radii of the REE3+, and the solubility and dissolution rate of the host mineral.

Dataset Information

Carbonate complexation enhances hydrothermal transport of rare earth elements in alkaline fluids.

Publications

Carbonate complexation enhances hydrothermal transport of rare earth elements in alkaline fluids.

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