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

total kg

Priuses

Cerium

60.0

0.2946

140

0.1191

0.0979

98e6

Yittrium

33.0

0.1620

89

0.0836

0.0539

54e6

Lanthanum

30.0

0.1473

139

0.0598

0.0490

49e6

5 million

Neodymium

28.0

0.1375

144

0.0546

0.0457

46e6

50 million

Scandium

20.0

0.0982

45

0.0666

0.0326

33e6

Praseodymium

8.2

0.0403

141

0.0162

0.0134

13e6

Samarium

6.0

0.0295

150

0.0114

0.0098

10e6

Gd Dy Yb Er

14.2

0.0697

157

0.0263

0.0232

2e6

Eu Ho Tr Tm Lu

4.3

0.0211

152

0.0081

0.0070

<1e6

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 are not 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.

Major deposits

MT

China

36

United States

13

Australia

India

World

99

Questionable source

A Prius uses 1 kg of neodymium in the motor, and 10 kg of lanthanum in the battery. There are enough reserves of rare earths worldwide to produce only 5 million Priuses of the current design.

Launch loop magnet rails will also require high-strength magnets. Those will be recycled, but some will be lost. Presuming we