A generic flow sheet for REEs from a 2015 entitled "A review of hydrometallurgical flowsheets considered in current REE projects", produced for the British Columbia Geological Service.

Regardless ore body or clay, the flowsheets come together after the leach. The first shared step is the pimary removal of impurities. This is a huge area of research. For clays this is a pH adjustment that flocs the aluminum whilst leaving the REEs in solution; great in theory but fraught in practice where REE losses can be unacceptable high.

At present the Chinese can recover LREEs but not HREEs from carbonatite-hosted monazite. Yet as we all know, there's only small chemical differences between most REEs, so it begs the question: Why can they extract the one and not the other?

Answer: Concentration of impurities relative to REEs is the most important factor. Depleting unwanted metal ions by any number of current methods always results in the loss of some of the REEs. In the case of clays, the problem is manageable; in the case of hard rock ores, it appears it is not. It is the aluminum Al+3 in IACs that presents the main challenge, whereas Ca+2 is the main challenge in carbonatite C&L liquors. Among their main actions, these impurity elements consume expensive post-cracking chemicals and/or co-precipitate REEs (representing a loss of recovery).

As a result, at present the vast majority of HREEs come from low-grade clays whose leaching is done very gently (because the REE ions are held very loosely) thus resulting in much lower impurities, and this practice will continue until someone solves the challenges of current C&L. This is one area of research that Lynas might have made progress on.

A second area of active research is in the next shared flow sheet box: Crude REE recovery. Four methods are seen listed in the box; all are being looked at for the umpteenth time. A modification of the traditional double salt technique could be in the offing. I am looking for research on "direct SX" at this time.

A third area of active research is the next shared box, where the crude REE precipitate undergoes secondary impurity removal again driven by selective precipitation and/or other treatments. Selective removal of impurities from rare earth sulphuric liquor using different reagents - ScienceDirect

The point is to prepare a lowest-impurity highest-concentration feed for SX so as to contain consumables and environmental costs which quickly escalate with challenges posed by high impurities or low REE concentrations.

Full disclosure: Sadly, I am less hopeful for 2023 HREE production at the LAMP than I was just a month ago. That said, I am still not ready to join Dudley Kingsnorth in his investment.

GLTASH

Progress in green and efficient enrichment of rare earth from leaching liquor of ion adsorption type rare earth ores