Hi @mountainwashere that is a really interesting article. In terms of processing them from what I understand is that because the rare earth's have similar chemical properties and coexist in the same ore they are quite difficult to separate. That is perhaps where China has the edge perhaps?
btw are you sure Cerium Oxide is toxic? It's commonly used for polishing glass and gemstones :(. (Edit: there are 2 oxides, the other oxide Cerium III, is more toxic)
I came here to chime on in on the coexistence/separation issue. One of the biggest leads China has is that that infrastructure and expertise to deal with that issue, specifically, has a huge initial capital cost.
The source I found didn't specify, I'd assume it was the latter?