The genesis and chemistry of bastnäsite and rare earth carbonates vital for tech industry shown to be extremely complex

In the Wiley Open Access journal, Global Challenges, new research, "Chemical Textures on Rare Earth Carbonates: An Experimental Approach to Mimic the Formation of Bastnäsite," has unveiled the intricate factors that influence the genesis and chemistry of bastnäsite and rare earth carbonates vita for the tech industry and its hardware outputs.

Bill Loguidice May 31, 2024 1 min read

Secondary electron SEM images of the surface of calcite grains reacted with the PAAS solution at 80 °C showing the progressive replacement by REE carbonates (left: grain view, right: detailed view), after a,b) 24, c,d) 72 h, and e,f) 4 weeks.

In the Wiley Open Access journal, Global Challenges, research article, “Chemical Textures on Rare Earth Carbonates: An Experimental Approach to Mimic the Formation of Bastnäsite,” has unveiled the intricate factors that influence the genesis and chemistry of bastnäsite and rare earth carbonates vita for the tech industry and its hardware outputs. According to the Introduction, as rare earth elements (REE) are essential in many green technologies, they play a critical role in a more sustainable future. Further, there is a substantial risk to their supply as the availability of REE deposits with minable concentrations are limited. As such, a better understanding of the mechanisms controlling REE concentration in minerals would have applications in more efficient mining practices as well as REE separation techniques and recycling.

The abstract follows.

Secondary electron SEM images showing the series of replacement REE-bearing minerals observed on the surface of the host carbonate grains. a) Thin, platy lanthanite crystals on calcite at 21 °C after 12 weeks in PAAS solution. b) Detail of lanthanite with small (<1 µm) secondary kozoite crystals on aragonite at 21 °C after 8 weeks in PAAS solution. c) Spherulitic kozoite on aragonite at 80 °C after 1 week in PAAS solution. d) Detail of kozoite on aragonite at 80 °C after 1 week in non-PAAS solution. e) Hydroxylbastnäsite on aragonite at 210 °C after 24 h in non-PAAS solution. f) Detail of hydroxylbastnäsite on dolomite at 210 °C after 48 h in non-PAAS solution. g) Secondary replacement of hydroxylbastnäsite by cerianite on calcite at 210 °C after 24 h in non-PAAS solution. h) Detail of the early stages of nanocerianite formation on calcite at 210 °C after 24 h in non-PAAS solution.

Abstract

The interaction between multi-component rare earth element (REE) aqueous solutions and carbonate grains (dolomite, aragonite, and calcite) are studied at hydrothermal conditions (21–210 °C). The effect of ionic radii of five REEs (La, Ce, Pr, Nd, Dy) on solid formation are analyzed using two solution types: equal REE concentrations and concentrations normalized to Post Archean Australian Shale Standard (PAAS). The interaction replaces the host Ca–Mg carbonate grains with a series of REE minerals (lanthanite → kozoite → bastnäsite → cerianite). At 165 °C, equal concentration solutions promote kozoite crystallization, maintaining similar REE ratios in solids and solution. PAAS solutions result in zoned REE-bearing crystals with heterogeneous elemental distributions and discreet REE phases (e.g., cerianite). Chemical signatures indicate metastable REE-bearing phases transforming into more stable polymorphs, along with symplectite textures formed by adjacent phase reactions. Overall, experiments highlight the dependence of polymorph selection, crystallization pathway, mineral formation kinetics, and chemical texture on REE concentrations, ionic radii, temperature, time, and host grain solubility.