Rare earths are found in thorium deposits and the thorium is radioactive waste from rare earth mining. Funny how plans come together, no?
Thorium main isotope, Th-232, accounts for 99.98% of all the Thorium in existence. That isotope has a half-life of 14 billion years.
(For comparison, Uranium has two chief isotopes: U-238, which accounts for 99.27% of all Uranium in existence, and with a half-life of 4.47 billion years; and U-235, with a natural occurence of roughly 0.7% and a half-life of 704 million years.)
Remember, the longer the half-life, the less radioactive and/or dangerous the isotope (generally speaking).
So Thorium is orders of magnitude safer than Uranium.
Of course, tailings from the mining of Rare Earths could contain who knows what - but as far as the Thorium is concerned, I would be far less worried about it than about the Uranium.
Regards,
P.S. Thorium is not fissile - i.e., cannot ordinarily be used to make nuclear bombs.