Rare Earths, Magnets, etc.
High intensity magnets are currently made with rare earth elements. REEs principally occur in monazite. According to this paper, there are 1e9 kg of thorium (and presumably rare-earth bearing) ores. Presume monazite ores, which are 5% to 10% thorium oxide, and 55% to 60% rare earth oxides.
The crustal abundance of rare earths is (presumably ppm by weight):
Element |
ppm |
frac |
AMU |
PO4 |
monaz |
Cerium |
60.0 |
0.2946 |
140 |
0.1191 |
0.0979 |
Yittrium |
33.0 |
0.1620 |
89 |
0.0836 |
0.0539 |
Lanthanum |
30.0 |
0.1473 |
139 |
0.0598 |
0.0490 |
Neodymium |
28.0 |
0.1375 |
144 |
0.0546 |
0.0457 |
Scandium |
20.0 |
0.0982 |
45 |
0.0666 |
0.0326 |
Praseodymium |
8.2 |
0.0403 |
141 |
0.0162 |
0.0134 |
Samarium |
6.0 |
0.0295 |
150 |
0.0114 |
0.0098 |
Gd Dy Yb Er |
14.2 |
0.0697 |
157 |
0.0263 |
0.0232 |
Eu Ho Tr Tm Lu |
4.3 |
0.0211 |
152 |
0.0081 |
0.0070 |
Total |
203.7 |
1 |
|
0.4458 |
0.3325 |
Fraction metals |
0.5542 |
||||
Fraction metals monazite |
0.3325 |
||||
The mass percentage assumes the mineral is a PO₄ phosphate (95 AMU ).
The crustal abundance is used here as a proxy for relative abundance in REE ores. Most of the REEs are not concentrated into ores, and arenot economically recoverable (we cannot afford to run the entire earth's crust through magnetic separation - not enough magnets!). None are concentrated in other solar system objects, none of which have plate tectonics and ocean-driven beneficiation.