Eudialyte is potentially one of the most important sources of lanthanides, particularly high-value heavy rare earths such as Dy, Tb and Y. Furthermore, it is a mineral that occurs in deposits in several locations in Europe, potentially providing European sources for these critical metals.
Anouk Borst’s paper on the structural state of lanthanides and yttrium in eudialyte has just been published in Mineralogical Magazine. This is an important paper that identifies exactly where in the structure the lanthanides are. This is more than academic interest – efforts are being made to make efficient extraction methods for the Zr, Nb and REE elements. Low temperature, energy efficient extraction methods often break a structure down into component parts that retain the local coordination that were inherited from the host. If REE are associated with the Zr site (as has been hypothesised), then they will potentially follow Zr during extraction. If the heavy and light REE are on different sites, there may be an opportunity to extract the high-value lanthanides from low value counterparts at the extraction stage.
The paper outlines the possible sites that lanthanides and yttrium might occupy in the eudialyte structure, then uses X-ray Absorption Fine Structure (XAFS) to determine it.
She studied Nd and Y to represent the light and heavy rare earth fractions respectively. Her results show that all the rare earths reside on the Ca site. This means that careful mineral processing is unlikely to separate out the heavy and light rare earth fractions at source. She presents a crystal lattice model to predict the behaviour of the rare earths she did not analyse directly. In doing so, she and her team provide the first direct evidence for the structural state of rare earths in what is potentially one of the most important future resources of one of the world’s most critical metal resources.