Iridium is becoming a vital material in the shift to green hydrogen because its ability to withstand extreme heat, corrosion, and harsh electrochemical conditions makes it essential for several specialized industrial uses, particularly in proton exchange membrane (PEM) electrolyzers.
The same durability that contributes to iridium's industrial value also makes it difficult to sample, analyze, and recycle. With demand rising while supply remains highly limited, accurate analysis has become essential for both commercial transactions and establishing a reliable secondary market.
The biggest source of future demand for iridium is expected to be PEM water electrolysis. These electrolysis units split water into hydrogen and oxygen using electricity that is best produced from renewable sources. They can operate at high current densities and respond quickly to changes in wind and solar power, making them suitable for producing renewable hydrogen.
In a PEM electrolyzer, the oxygen evolution reaction occurs at the anode under highly acidic, strongly oxidizing conditions. In such an environment, most metals either corrode rapidly or lose their catalytic activity. Iridium oxide remains the best catalyst because it has both high electrochemical activity and the durability needed for long-term operation. Manufacturers are aiming at decreasing the amount of iridium used in each electrolyser. Catalyst loadings have already dropped significantly, and experimental systems are aiming for even greater reductions. Yet given the size of the hydrogen projects envisaged, the total demand could keep on increasing even though each system uses less metal.
Global primary iridium production is exceptionally small, generally estimated at only 7–8 metric tons annually. Approximately 80% of supply comes from South Africa, with additional production from Russia, Zimbabwe, and North America. Iridium is rarely mined as a primary product. It is recovered in small quantities as a byproduct of platinum, palladium, nickel, and copper production. As a result, its supply does not respond directly to its own market price. Even a substantial increase in iridium demand may not lead mining companies to extract more ore if the economics of the principal metals do not support higher production.
This byproduct dependency, combined with geographic concentration, leaves the market exposed to mine disruptions, processing interruptions, and geopolitical risk. It also increases the strategic importance of recovering iridium from spent catalysts, electrolyzer components, aerospace alloys, spark plugs, and other industrial materials.
Secondary recovery can ease pressure on primary supply, but iridium-bearing scrap is often complex and hard to value. In PEM electrolyzers, for example, iridium oxide is incorporated into catalyst-coated membranes containing fluorinated polymers. Conventional incineration can release hazardous and corrosive hydrogen fluoride, making straightforward thermal treatment unsuitable without sophisticated emissions controls.
Recyclers are therefore developing alternatives such as mechanical disassembly, catalyst decoating, solvent separation, and selective hydrometallurgical recovery. Once the iridium-bearing fraction has been separated, its concentration must be accurately established before the material can be purchased, refined, or settled commercially. This is where one of the market's less visible problems appears: many standard precious-metal assays are not reliable for iridium.
A valid assay starts with a representative sample. With iridium, obtaining one can be harder than the final instrumental measurement. Precious-metal scrap is often melted into a supposedly uniform liquid before taking a pin or dip sample. This approach works only when every component of the lot melts and mixes completely. Iridium's melting point is approximately 2,446°C, far above the operating range of many conventional refining and assay furnaces.
Other metals in the batch can melt while iridium remains as solid particles. Since iridium is extremely dense, these particles can sink to the bottom of the crucible. The melted material may appear to be uniform even though the iridium is strongly stratified. A sample taken from the top of the material can greatly underestimate the batch value. On the other hand, a sample that happens to include a concentrated particle may yield an unrealistically high value. In neither case does the result accurately reflect the shipment. For this reason, facilities that work with iridium must use sample-preparation techniques appropriate for refractory materials. The required method depends on the feed type and may include complete grinding and mixing, stepwise sampling, or specialized high-temperature melting equipment.
Lead fire assay remains one of the most reliable techniques for analyzing gold and silver and can, in some cases, be used for certain platinum-group metals. Iridium, though, is unlike the metals for which the method was developed. In a standard lead fire assay, the sample is fused with a flux, lead oxide, and a reducing agent; molten lead droplets gather the precious metals, which then settle to form a button. The button is then cupelled to remove the lead and leave a precious-metal bead for further analysis.
Gold and silver dissolve easily and combine with molten lead; iridium usually stays solid at the temperatures used in fire assay and does not form a uniformly mixed alloy with the collector, so recovery depends on whether individual particles are physically trapped in the lead.
Fine particles may remain suspended in the slag, become lodged in the crucible, or be lost into the porous cupel. Recoveries can therefore be low and inconsistent. Repeating the assay may produce different results because the underlying problem is not simply instrumental precision; it is incomplete and uneven collection. For a high-value metal, even a modest recovery error can create a substantial discrepancy between the material's actual content and what the supplier is paid.
Nickel sulfide fire assay is among the most established methods for collecting refractory platinum-group metals, including iridium, ruthenium, and osmium.
The sample is combined with a nickel compound, sulfur, reducing agents, and a flux. This produces a nickel sulfide matte with a high affinity for the PGMs. This matte separates from the lighter slag and forms a button containing the collected metals.
Once cooled, the button is crushed and dissolved in hydrochloric acid; most of the nickel sulfide matrix is removed, leaving a concentrated PGM residue for further digestion and instrumental analysis.
Nickel sulfide collection is usually better suited to iridium than to lead fire assay, but it takes more time and requires specialized knowledge and strict quality controls. Because nickel reagents may contain trace PGM contamination, reagent blanks must be measured carefully. Moreover, certain geological and industrial matrices may interfere with phase separation and therefore require modified fluxes or pretreatment.
Even when iridium has been concentrated, it usually must be put into solution before the final measurement can be carried out; ordinary open-vessel aqua regia digestion often cannot dissolve it completely. Microwave-assisted high-pressure digestion overcomes this limitation by heating the acids in sealed, pressure-resistant vessels; the higher temperature and pressure increase reaction rates and enable stronger digestion conditions than open-beaker methods.
The acid used must suit the sample; for geological materials and slags, hydrofluoric acid is needed to decompose silicates, and for concentrated PGM residues, treatment with mixtures of hydrochloric and nitric acids under pressure may be used. Because these reagents and conditions are dangerous, carry out digestion only with appropriate equipment and by following strict safety procedures. After dissolution, iridium can be determined by ICP-OES or ICP-MS; ICP-MS has very high sensitivity, but matrix elements remaining from nickel, copper, bismuth, or other collectors can interfere by suppressing signals or causing interferences. Methods such as tellurium coprecipitation and ion-exchange separation can eliminate these matrix components before the final measurement.
As PEM electrolyzer production increases, the limited availability of iridium will make secondary recovery increasingly necessary. However, recycling cannot operate efficiently without buyers' and sellers' confidence in the metal content of their materials. Accurate analysis requires more than a sensitive instrument; it starts with a representative sample and includes proper preconcentration, full digestion, control of interferences, and documented quality assurance. For many iridium-containing materials, the standard lead fire assay is not sufficient. Owners of suspected iridium-containing catalysts, alloys, or industrial scrap may benefit from having the material professionally evaluated before accepting a settlement based on conventional precious-metal methods. Phoenix Refining offers free assays for iridium-containing materials, helping suppliers establish metal content and determine an appropriate refining route before recovery.
