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Material World
Element · Rh

Rhodium

The most expensive of the precious metals, and almost all of it is in exhaust pipes.

Catalyst

Rhodium does one thing better than anything else: it reduces nitrogen oxides to nitrogen in a car's catalytic converter, in the presence of everything else an exhaust stream contains.

That single application consumes most of world production, and there is very little of it — rhodium is recovered as a minor fraction of platinum and nickel ores. When emissions standards tighten, demand rises against a supply that cannot respond, and the price has repeatedly exceeded gold's by a wide margin.

Uses

Rhodium is used almost entirely in catalytic converters, where it is uniquely effective at reducing nitrogen oxides to nitrogen. No cheaper substitute performs the same job as well, which is the reason its price has periodically exceeded gold's by a wide margin.

Its remaining uses are small and specialised: rhodium plating gives white gold jewellery its bright finish and protects silver from tarnish, and rhodium catalysts are used in the industrial synthesis of acetic acid and in hydroformylation.

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

is an alternative to

  • Platinum — element · complementary rather than substitutable — they catalyse different halves of the reaction

is produced by

  • Electrorefining — process · from the same slimes and the same platinum-group concentrate, and rarer in them than palladium by an order of magnitude

is used in

  • Catalytic converter — object · a fraction of a gram, doing the nitrogen oxide reduction that neither of the others does well — and worth enough on its own to make converter theft organised crime

is produced at

  • Bushveld Igneous Complex — place · as a co-product, and its price history is what a supply that cannot be expanded quickly looks like

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 Rhodium 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

  • Rhodium → is produced by (from the same slimes and the same platinum-group concentrate, and rarer in them than palladium by an order of magnitude) → Electrorefining → takes as input (as impure smelted anodes, around 99% copper, which is not pure enough for wire) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (as the element removed, not added) → Oxygen → is produced by (the largest output by tonnage, and the reason air separation units sit beside steelworks) → Air separation
  • Rhodium → is produced by (from the same slimes and the same platinum-group concentrate, and rarer in them than palladium by an order of magnitude) → Electrorefining → takes as input (as impure smelted anodes, around 99% copper, which is not pure enough for wire) → Copper → is extracted from (the principal copper ore worldwide) → Chalcopyrite
  • Rhodium → is produced by (from the same slimes and the same platinum-group concentrate, and rarer in them than palladium by an order of magnitude) → Electrorefining → takes as input (as impure smelted anodes, around 99% copper, which is not pure enough for wire) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (roasted to drive off sulfur, then reduced to copper) → Chalcopyrite
  • Rhodium → is produced by (from the same slimes and the same platinum-group concentrate, and rarer in them than palladium by an order of magnitude) → Electrorefining → takes as input (as impure smelted anodes, around 99% copper, which is not pure enough for wire) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (reduced with carbon to metallic tin) → Cassiterite
  • Rhodium → is produced by (from the same slimes and the same platinum-group concentrate, and rarer in them than palladium by an order of magnitude) → Electrorefining → takes as input (as impure smelted anodes, around 99% copper, which is not pure enough for wire) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (reduced with coke in a blast furnace) → Hematite
  • Rhodium → is produced by (from the same slimes and the same platinum-group concentrate, and rarer in them than palladium by an order of magnitude) → Electrorefining → takes as input (as impure smelted anodes, around 99% copper, which is not pure enough for wire) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (the phosphate rock charged to the electric furnace, with coke to reduce it and silica to take up the calcium) → Apatite

These are the most distinct paths back. Rhodium can be traced through others besides.

Downstream — what it becomes

  • Rhodium → is used in (a fraction of a gram, doing the nitrogen oxide reduction that neither of the others does well — and worth enough on its own to make converter theft organised crime) → Catalytic converter → is used as (the largest catalytic application by metal value there is) → Catalysis
  • Rhodium → is used as → Catalysis
  • Rhodium → is produced at (as a co-product, and its price history is what a supply that cannot be expanded quickly looks like) → Bushveld Igneous Complex