[SMM Flash] Iridium’s extreme physical and chemical properties make it one of the most difficult platinum-group metals (PGMs) to assay accurately. With a melting point of about 2,446°C and strong resistance to corrosion and conventional acids, iridium cannot be fully processed using the standard equipment and methods commonly used for gold, silver and other precious metals.
Conventional sampling can produce significant errors because iridium remains solid during normal furnace processing and its high density causes iridium-rich particles to settle at the bottom of crucibles. Standard lead fire assay can also lose iridium through slag, crucible and cupel interactions. Specialised techniques such as nickel sulfide collection, alkaline fusion and molten-salt chlorination are therefore required for reliable analysis.
The challenge is becoming increasingly important as iridium supply remains highly constrained. The metal occurs at extremely low concentrations in the Earth’s crust, is mainly recovered as a byproduct of other mining and has annual primary supply measured in only a few tonnes. With demand rising, particularly from PEM electrolyzers, accurate assaying is critical to maximise secondary recovery and ensure fair valuation of iridium-bearing materials.
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