127-13 Stability of Rare Earth Carbonates and Implications for Ore Deposits and Extraction

Session: Mineralogy, Geochemistry, Petrology, and Volcanology Student Session

Presenting Author:

Godwin Agbanga

Authors:

Agbanga, Godwin Akotenvusi¹, Scharrer, Manuel², Burkmann, Konrad³, White, Christian⁴, Woodfield, Brian⁵, Navrotsky, Alexandra⁶

Abstract:

Rare earth elements (REEs) are in high demand for modern technology and crucial commodities due to high prices and unstable supply chains. They are essential in the green energy transition, consumer appliances, and military goods, and have applications in energy, defense, electronics, and ceramics. Most REEs are extracted from carbonates and phosphates bearing REEs. One promising avenue involves recycling aluminum-bearing waste sludges from aluminum production using supercritical CO₂, a technique that has shown potential for efficient REE extraction. To understand and model the fractionation and mobility between the REEs during ore mineral formation, as well as improve the extraction processes, it is essential to thermodynamically model the interactions among the REEs, CO₂, and H₂O phases. However, despite their importance, stable carbonate phases are not yet well thermodynamically characterized, creating a gap in our ability to fully constrain and predict the behavior of REEs under these conditions.

Experimental and geologic evidence in the REE-H₂O-CO₂ system points to five important REE carbonate phases (amorphous, lanthanite, tengerite, kozoite, and bastnaesite) at ambient to low temperature hydrothermal conditions (<250 °C). The amorphous phase forms as an intermediate phase during initial precipitation. At close to ambient conditions, the amorphous precursor transforms into the lanthanite phase for light REEs, while tengerite is formed for intermediate REEs and the amorphous phase remains present for the heavy REEs. At elevated temperatures, kozoite and bastnaesite become successively more stable form for most REEs. To investigate the thermodynamic quantities and to conclude on the influence of kinetic and thermodynamic factors for the formation of the different phases, enthalpies of formation were measured using both high-temperature oxide melt drop solution and acid solution calorimeters and absolute entropies were derived from low heat capacity measurements using a Quantum Design Physical Property Measurement System. Stability trends derived from both experimental results and thermodynamic calculations show that the formation of these carbonate phases highly depends on kinetic factors, on temperature, and the ionic radius of the REE. The thermodynamic properties also reveal crucial information on REE fractionation between carbonate phases indicative to natural and industrial processes.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7975

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