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Material World
Element · Th

Thorium

A potential nuclear fuel that is several times more abundant than uranium and has never been commercialised.

Thorium is a weakly radioactive metal, more abundant in the crust than uranium and produced largely as an unwanted by-product of rare-earth mining, where monazite sand contains it in quantity. Producers have often had more of it than they could use or dispose of.

It is not itself fissile. Thorium-232 absorbs a neutron and transmutes to uranium-233, which is, and this is the basis of the thorium fuel cycle — a route repeatedly proposed as safer and more proliferation-resistant than the uranium cycle, and repeatedly not built at scale.

Uses

Thorium's historical civilian use was the gas mantle, where thorium dioxide glows brilliantly white when heated — a use now largely replaced because of the radioactivity.

Thorium dioxide's very high melting point made it a refractory and a component of high-quality optical glass for camera lenses, again mostly abandoned on radiological grounds. The prospective use is nuclear fuel, pursued in research programmes in India and China, where reactors designed around the thorium cycle are under active development rather than merely proposed.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

is used as

  • Nuclear fuel — application · not itself fissile — it breeds uranium-233

is extracted from

  • Monazite — mineral · historically the principal source of thorium, which substitutes into the rare earth site

is produced by

  • Solvent extraction and electrowinning — process · leached from monazite processing residues, and as an oxide rather than a metal — thorium is a by-product nobody currently wants, which is the difficulty rare earth operations keep running into

is an alternative to

  • Uranium — element · as nuclear fuel: thorium is three times as abundant, produces far less long-lived waste, and is not fissile — it has to be bred into uranium-233 first, which is why every thorium programme is a proposal and every uranium one is a power station

is found in

  • Monazite — mineral · substitutes within a solid solution — an individual specimen may hold little of it

Sources

  • Material World
    Our own writing
  • Wikidata
    Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)
  • PubChem
    US National Library of Medicine · Mixed — aggregated third-party content, rights retained by depositors
  • NIST — National Institute of Standards and Technology
    United States Department of Commerce · US Government work — public information, credit requested

Questions this page answers

Where it comes from, and what it becomes

Follow Thorium back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Upstream — what it comes from

  • Thorium → is produced by (leached from monazite processing residues, and as an oxide rather than a metal — thorium is a by-product nobody currently wants, which is the difficulty rare earth operations keep running into) → Solvent extraction and electrowinning → takes as input (in the low-grade and oxidised ores that flotation cannot economically treat, with bacteria oxidising the sulfide into a form the acid can attack) → Chalcopyrite
  • Thorium → is extracted from (historically the principal source of thorium, which substitutes into the rare earth site) → Monazite
  • Thorium → is produced by (leached from monazite processing residues, and as an oxide rather than a metal — thorium is a by-product nobody currently wants, which is the difficulty rare earth operations keep running into) → Solvent extraction and electrowinning → takes as input (a carbonate dissolves straight into acid, which is why an oxidised orebody goes to a leach pad and the sulfide beneath it goes to a smelter) → Malachite
  • Thorium → is produced by (leached from monazite processing residues, and as an oxide rather than a metal — thorium is a by-product nobody currently wants, which is the difficulty rare earth operations keep running into) → Solvent extraction and electrowinning → takes as input (leached with acid or alkali depending on the host rock, which is what decides the flowsheet of a uranium mill) → Uraninite

Downstream — what it becomes