Rare Earths Are Not Rare. Separating Them Is the Problem.
Neodymium is more abundant in the crust than lead. Cerium is more abundant than copper. The name is an eighteenth-century accident, and only half of it is still true.
Magnets and Motors · Part 4 — Limits and Supply · Chapter 10 · 17 min read
Neodymium is more abundant in the crust than lead. Cerium is more abundant than copper. The name is a historical accident from the eighteenth century, when they were found in scarce minerals and were difficult to isolate — and only the second half of that is still true.
28 ppm
Neodymium — more than lead
~1 %
Ionic radius gap between neighbours
100s–1,000+
Solvent extraction stages needed
60–80 %
Heavy rare earth cut by grain boundary diffusion
10.1 — More abundant than lead
If price tracked abundance those points would fall on a line. They do not, because the cost is in separation, not extraction. Rare earths occur together in the same minerals and must be split from one another.
10.2 — Why separation is so hard — the lanthanide contraction
Across the lanthanide series, 4f electrons shield the nuclear charge poorly, so effective nuclear charge climbs steadily and the ions contract: La³⁺ at 103 pm down to Lu³⁺ at 86 pm.
Adjacent neighbours therefore differ in ionic radius by roughly one per cent, and all sit in the same +3 oxidation state with the same outer configuration. Chemically they are almost the same element fifteen times over.
In plain English
Separation relies on solvent extraction, exploiting a partition coefficient that differs by a few per cent per stage — which means hundreds to over a thousand mixer-settler stages in cascade to reach magnet-grade purity. That is the plant, the capital, the chemical consumption and the waste stream that constitute the actual barrier.
10.3 — Processing, not mining
Important
Deposits exist in Australia, the United States, India, Brazil, Vietnam and Greenland. Separation capacity at scale is concentrated in a way that mining is not, and a separation plant takes the better part of a decade to permit and commission.
Opening a mine does not solve it.
10.4 — Five approaches, ranked by how proven they are
| Status | Approach | What it does |
|---|---|---|
| In production | Grain boundary diffusion | Cuts heavy rare earth use by 60–80 % for equal coercivity. Already standard on most automotive-grade magnets — see chapter 4. |
| In production | EESM | Zero magnets. BMW and Renault ship it at volume, so the remaining objections are cost and complexity, not feasibility. |
| In production | Induction | Zero magnets, fully mature. Costs 2–4 efficiency points, mostly at the light loads where vehicles spend their time. |
| Emerging | Ferrite-assisted SynRM | Ferrite instead of NdFeB in a reluctance rotor. Credible for cost-sensitive segments; watch the cold-demagnetisation behaviour from chapter 5. |
| Research | Ce substitution · MnBi · tetrataenite | Cerium is the cheap over-supplied lanthanide; MnBi’s coercivity rises with temperature; tetrataenite is a rare-earth-free iron-nickel phase. None at automotive scale. |
10.5 — Recycling
Technical framing
A traction motor contains 1 to 2 kg of magnet at roughly 30 wt % rare earth — a far richer concentration than any ore, in a known location, in a known chemistry.
The obstacles are collection, disassembly and demagnetisation rather than metallurgy. Direct reuse of intact magnets from end-of-life motors is the highest-value path and the target of most current work; hydrogen decrepitation is the leading route for breaking sintered magnets down into reusable powder.
Quick check: test yourself
1.A government announces a new rare earth mine to secure magnet supply. What has it not solved?
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2.Why does the lanthanide contraction make separation so expensive?
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3.Which single measure has cut heavy rare earth consumption most?
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Chapter summary
- ✓Rare earths are not rare — neodymium beats lead and cerium beats copper on crustal abundance. Price tracks separation difficulty, not geology.
- ✓The lanthanide contraction leaves adjacent elements about one per cent apart in ionic radius and identical in oxidation state, so separation needs hundreds to over a thousand cascade stages.
- ✓The bottleneck is therefore a plant, not a deposit, and a separation plant takes most of a decade to build.
- ✓Grain boundary diffusion, EESM and induction are the three proven ways to cut exposure; ferrite-assisted SynRM is emerging and Ce, MnBi and tetrataenite are research.
- ✓A traction motor is a richer rare earth deposit than any ore, and recycling it is a collection and disassembly problem rather than a metallurgical one.
Frequently asked questions
If rare earths are abundant, why are they expensive?+
Because the cost is in separation, not extraction. Rare earths occur together in the same minerals and must be split from one another, and the lanthanide contraction makes adjacent elements differ in ionic radius by roughly one per cent while sharing the same +3 oxidation state and outer configuration. Chemically they are almost the same element fifteen times over. Plot abundance against price and the points do not fall on a line, because price is a proxy for separation difficulty and demand rather than for how much is in the ground.
Why does opening a new mine not fix rare earth supply?+
Because the bottleneck is processing. Deposits exist in Australia, the United States, India, Brazil, Vietnam and Greenland. What is concentrated in a way that mining is not is separation capacity — and a separation plant takes the better part of a decade to permit and commission, because reaching magnet-grade purity needs hundreds to over a thousand mixer-settler stages in cascade, each exploiting a partition coefficient that differs by only a few per cent.
What are the credible ways to reduce rare earth exposure?+
In production today: grain boundary diffusion, which cuts heavy rare earth use by 60 to 80 per cent for equal coercivity and is already standard on most automotive-grade magnets; EESM, which uses no magnets at all and ships at volume from BMW and Renault; and induction, fully mature at a cost of 2 to 4 efficiency points. Emerging: ferrite-assisted synchronous reluctance, credible for cost-sensitive segments but with cold-demagnetisation behaviour to watch. In research: cerium substitution, MnBi whose coercivity rises with temperature, and tetrataenite, a rare-earth-free iron-nickel phase.
Is recycling motor magnets practical?+
The metallurgy is the easy part. A traction motor contains 1 to 2 kg of magnet at roughly 30 wt % rare earth — a far richer concentration than any ore, in a known location and a known chemistry. The obstacles are collection, disassembly and demagnetisation. Direct reuse of intact magnets from end-of-life motors is the highest-value path and the target of most current work; hydrogen decrepitation is the leading route for breaking sintered magnets down into reusable powder.
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Magnets and Motors is an original educational series on permanent magnets and electric machines. Datasheet ranges, temperature coefficients and efficiency figures are representative standard-condition literature values, not measurements of a specific product, and sources differ on several. Always verify against the specific magnet and lamination datasheets in use before making design, procurement or certification decisions.