When Karl Karlovich Klaus isolated ruthenium in 1844, it was unlikely to become an industrial star. It's a rare metal; it's tough, brittle, and very difficult to work with on its own. To date, its only major industrial use has been as a small addition to other precious metals to improve wear resistance. That property led to its use in platinum and palladium alloys for jewelry, electrical contacts, and precision components. A very well-known application was in the fountain pen nib. From the 1940s, Parker offered "RU" nibs with a ruthenium-rich tipping material. The nib tip had to glide across the page for a long time without wearing away. For the recycler, though, a durable consumer product was a remarkable source of metal. Pens and jewelry would be stored, lost, or simply thrown away. Even when they were recovered, they contained very little ruthenium compared with the other metals they were made of. Early on, ruthenium scrap was essentially scattered among individual owners, and there was no real way to recover it in significant quantities.
Ruthenium's industrial importance increased significantly with the introduction of the dimensionally stable anode. These were used in processes such as chlor-alkali (the electrolysis of brine to produce chlorine and sodium hydroxide) and involved a very thin layer of ruthenium dioxide as a catalytic coating on a robust titanium substrate. The coating enabled the process to run efficiently and avoided the rapid consumption that plagued the older graphite anodes.
The app changed the scrap stream. A spent industrial anode is a big, obvious thing, owned by a company that has a vested interest in accounting for its valuable materials. The coating may have failed long ago, but the anode can still contain recoverable ruthenium. Specialist firms can strip off the old coating, recover the metal, and then reprocess the titanium base. Ruthenium therefore moved from the dispersed consumer scrap stream into a closed-loop industrial system where the manufacturer/operator knew where the metal was and could arrange its return.
From the 1990s on, the growth of digital storage created another major use for ruthenium. Its crystal structure makes it ideal as an extremely thin layer under the magnetic material on hard drive platters. That layer was key to the recording technologies that enabled the higher storage densities.
It requires high-purity ruthenium sputtering targets to feed a vacuum deposition process. The scrap story splits here. Used targets and the ruthenium deposited onto the production equipment stay in the factory, where they can be collected, reprocessed, and made into new targets. The ruthenium that ends up in the finished hard drive is a whole different proposition. It's in a very thin layer on the platter (a few nanometers thick). When that drive becomes e-waste, recyclers can recover most of the metals fairly easily, but the ruthenium in that ultra-thin layer is much harder to recover. The manufacturing process does generate a viable recycling stream. The end product is not readily recyclable.
Ruthenium's chemical versatility has also made it a key component in a range of catalysts for industrial synthesis. Spent catalysts, unused chemicals, and off-spec batches can be collected at the production site and sent back to the specialist refiners. Unlike a used pen or hard drive, you can often recover a significant amount of ruthenium from a single piece of equipment. Its catalytic properties have also attracted interest in clean energy applications, with researchers and manufacturers looking at ruthenium-based catalysts for water electrolysis (again often in combination with other metals to improve the durability). If such systems are widely deployed, the equipment's end of life would create another trackable scrap stream, similar to that of a spent industrial anode. The amount of recoverable metal will depend on equipment design and how easily mixed materials can be separated.
Ruthenium is now in advanced semiconductor manufacturing. As feature sizes shrink, the problems with using copper for interconnects become more acute: the barriers and liners around the copper take up too much of the space available for the conductor. Some research has explored ruthenium as a thin liner, and at the smallest dimensions, it could potentially be used as an interconnect material. It's also used as a protective coating on the mirrors in EUV lithography machines, a key enabler for making the most advanced chips. The purity requirements in these applications are very high, but you don't get it in any one convenient form. A fab generates a full range of waste streams from its processes: used deposition material, residue on the chamber walls, polishing waste, wastewater, and captured exhaust. Some streams can be collected as solids; others are ruthenium in a very dilute form among a host of other chemicals. The recovery process must be tailored to the specific process that generated the waste.
Ruthenium is produced primarily as a by-product of mining for the other platinum group metals. You can't just scale up the supply of ruthenium simply because demand increases for data storage, electronics, or clean energy applications. That puts secondary recovery in an increasingly important position. Over the 180 years we've looked at, the pattern is clear: ruthenium is easiest to recover when it's concentrated in an application, identifiable, and part of an industrial return stream. It's most difficult to recover when it's highly dispersed in consumer products or waste streams. The next big step forward in the use of ruthenium may be matched by an equally significant design advance to ensure that, when the metal has done its job, it can be captured.
