• Bakker, Wim Harry
• Deon, Fiorenza
• Van Ruitenbeek, Frank
• Dijkstra, Arjan

Abstract

Rare Earth Elements (REE) are essential for low-carbon energy solutions for the Energy Transition. Hyperspectral satellite- or UAV-based remote sensing of REE-resources, and proximal hyperspectral imagingspectroscopy (e.g., drill core imaging), such as drill core imaging, have a high potential as tools to support exploration, because of the unique spectral properties of the REE. However, to date, high-quality reflectance spectra of REE-minerals with controlled compositions are lacking.<br/><br/>To address this research gap, we synthesized a series of single-, dual- and mixed-REE minerals. These include hydrated phosphates (rhabdophane) and anhydrous phosphates (, monazite and , xenotime). We also synthesized La-Nd solid solution monazites to constrain the effect of Nd concentrations on the spectral properties, and calcite-monazite mixtures to simulate REE-bearing rocks. Recently we also succeeded in synthesizing single-REE carbonates (hydroxylbastnäsite). We also prepared calcite-monazite mixtures to simulate REE-bearing rocks. PProducts were confirmed by X-ray powder diffraction and structural refinement, and reflectance spectra in the wavelength range 350-2500 nm were measured.<br/><br/>The strong intensities of the absorption features found hold promise for REE-exploration by hyperspectral remote sensing. Moreover, the data confirm that most REE’s have a distinct spectral signature – including in the shortwave IR part of the spectrum. These signatures are largely independent of the host mineral, (because the 4f-electrons involved are relatively shielded). This contrasts with most other minerals, in which the excitation energies of electronic transitions in ions are strongly affected by the surrounding crystal field. This means that in the case of REE there exists a unique potential to detect chemical elements, or maybe even concentrations, rather than mineral (groups) by proximal and remote sensing techniques. There are, however, subtle spectral differences between minerals, e.g., monazite-(Nd) v. bastnäsite-(Nd), which can be resolved in imaging spectroscopy applications.

Topics

• mineral
• Carbon
• spectroscopy
• rare earth metal