Chemical Textures on Rare Earth Carbonates: An Experimental Approach to Mimic the Formation of Bastnäsite.

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).

The role of fluocerite in the genesis of bastnäsite: mechanistic insights and transformation pathways.

Fluocerite is a rare earth element (REE) fluoride found as an accessory mineral in magmatic-hydrothermal REE ore deposits, including alkaline complexes and carbonatites, where it is often associated with REE-fluorocarbonates. This study investigates the crystallisation kinetics, mechanisms and energetics of fluocerite (REEF) and its role as a precursor phase of bastnäsite, one of the key minerals used for the extraction of REE. Fluocerite was synthesized by reacting pure fluorite (CaF) with La-, Ce- and Nd-bearing solutions at temperatures ranging from ambient to low hydrothermal (30-90 °C).

Impact of Rare Earth Elements on CaCO Crystallization: Insights into Kinetics, Mechanisms, and Crystal Morphology.

This study investigated the crystallization kinetics and mechanisms of calcium carbonate (CaCO) in the presence of rare earth elements (REEs) including lanthanum (La), neodymium (Nd), and dysprosium (Dy). Through a comprehensive approach utilizing UV-vis spectrophotometry, powder X-ray diffraction, and high-resolution electron microscopy, we examined the effects of REEs on CaCO growth from solution at varying concentrations and combinations of REEs. Our findings highlight that even trace amounts of REEs significantly decelerate the rate of CaCO crystallization, also leading to alterations in crystal morphology and mechanisms of growth.

The role of nanocerianite (CeO) in the stability of Ce carbonates at low-hydrothermal conditions.

The formation of cerianite (CeO) was investigated at low hydrothermal conditions (35-205 °C) two experimental settings: (1) crystallisation from solution experiments, and (2) replacement of Ca-Mg carbonates (calcite, dolomite, aragonite) mediated by Ce-bearing aqueous solutions. The solid samples were studied with a combination of powder X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared spectroscopy. The results revealed a multi-step crystallisation pathway: amorphous Ce carbonate → Ce-lanthanite [Ce(CO)·8HO] → Ce-kozoite [orthorhombic CeCO(OH)] → Ce-hydroxylbastnasite [hexagonal CeCO(OH)] → cerianite [CeO].