Avalon admits it does not have metallurgy - Avalon Rare Metals Inc.

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Hydrometallurgical Testwork
The hydrometallurgical process is comprised of two main steps, an acid bake to initially break down the rare earth minerals most susceptible to chemical attack followed by a caustic crack of the residue of those minerals most resistant to chemical attack, mainly zircon. The filtrate from the acid bake step will be processed for the recovery of the mixed light rare earths and rare metals. It is expected that the recovery process will include purification of the solution using solvent extraction followed by double sulphate salt precipitation of the light rare earths using sodium sulphate, filtration to recover the rare earths, processing to remove iron from the double sulphate salt filtrate, then precipitation and filtration of residual heavy rare earths. As noted, the residue from the acid bake process will contain the ZrO₂, Nb₂O₅ and Ta₂O₅ and about half the heavy rare earths.

This is finally an admission that complex silicates have no repeat NO known hydro metallurgy and this is why

Double sulphate salt means they are using  P507 used by Chinese for their rare earth separation.
This solvent needs to be loaded with NaOH for both lights, mediums and heavies in order to improve its efficiency
When you mix a loaded solvent like P507 with rare earths in sulphate medium you precipitate double sulfate salt (Na,RE(SO4)2) which means you cannot load this solvent in a sulphate

Call the CEO up and ask him how you separate a double sulphate and listen to the double speak. The amswer is you cannot.

First to admit this is  Avalon, next will be  Quest,Tasman, Greenland Minerals and Matamec