lanthanoids

The difference is that now much of it is separated from the other lanthanoids (a difficult and energy-intensive process) and concentrated in junkyards and landfills.

________________ † It isn't true that lanthanoids don't form ores at all; monazite and bastnäsite are ores of lanthanoids (as well as actinoids).

But this is very much not the case with landfill, in which the lanthanoids are conveniently separated not only from one another but from the hazardous actinoids — although cigarette-lighter flints have many lanthanoids, if you're mining catalytic converters, they'll be entirely free of both thorium and lanthanum.

Since the concentrations of many interesting elements are orders of magnitude higher than their natural concentrations in ores — particularly in elements like the lanthanoids which, as you point out, do not concentrate very much† — my naïve supposition is that landfill mining will be considerably cheaper.

My wifi hotspot is Actinoids, my spouse's is Lanthanoids.

My wifi hotspot is Actinoids, my spouse's is Lanthanoids.