Ruthenium is one of the rarest elements in Earth’s crust. Its abundance in the bulk continental crust is estimated at 0.6 parts per billion. Like other PGMs, ruthenium rarely occurs in native metallic form. Instead, it is typically associated with other platinum group elements in base-metal sulfide deposits and chromite-bearing rocks.
The main ruthenium-bearing minerals include laurite, commonly represented as (RuOs)S₂, and ruarsite, RuAsS. Ruthenium can also occur in natural osmium–iridium–ruthenium alloys, where it may form up to 10–20% of the alloy composition. It is generally found as microscopic inclusions in minerals such as pentlandite, pyrrhotite, chalcopyrite, and chromite.
Unusual ruthenium enrichments have been reported in natural nuclear reactor zones, such as those discovered at Oklo and Bangombé in Gabon. In these deposits, ruthenium was generated as a nuclear fission product and can reach concentrations far higher than those found in ordinary geological settings. Ruthenium is also present in extraterrestrial materials, including chondrites, iron meteorites, and Martian meteorites, confirming its broader cosmochemical significance.
Ruthenium is produced almost entirely as a by-product during the extraction and refining of other platinum group metals. Its production depends strongly on mining operations targeting platinum, palladium, nickel, and copper. This by-product status makes ruthenium supply relatively inflexible: even if demand rises, production cannot easily be increased unless extraction of the main metals also expands.
The main primary producing region is South Africa, particularly the Bushveld Complex, which dominates global supply. Smaller quantities are produced in Zimbabwe from the Great Dyke and in Russia from the Norilsk-Talnakh nickel-copper sulfide deposits. Canada was formerly a supplier but has ceased production recently. Global primary ruthenium production remains relatively stable at around 30 tonnes annually, but demand is expected to continue increasing. Forecasts suggest that the global ruthenium market may reach approximately 45 tonnes by 2033, growing at a compound annual growth rate of about 3.6%. Recent data, however, already show a persistent supply-demand imbalance. Shortfalls of 3–4 tonnes per year occurred in 2023–2024, with projected shortages of around 8 tonnes in 2025.
This imbalance has affected prices. Ruthenium rose from approximately 18.5 USD/g in January 2025 to around 50 USD/g by January 2026, making it one of the strongest-performing metals of 2025. Despite this increase, ruthenium remains the least expensive of the platinum group metals.
Because of its supply concentration, technological importance, and limited substitutability, ruthenium has been classified as a critical or strategic metal by the European Union, the United States, Canada, and South Africa. In the EU criticality matrix, ruthenium has gradually gained greater economic importance and raised supply concerns, mainly because one producing region dominates.
Ruthenium-bearing ores can be grouped into three main categories. The first consists of ores mined primarily for PGMs, with nickel, copper, and cobalt as by-products; these are typical of South Africa and Zimbabwe. The second consists of nickel-copper sulfide ores, where PGMs are recovered as by-products, as in Russia and historically in Canada. The third includes miscellaneous ruthenium-bearing ores that are not currently mined economically.
The initial stages of primary production are designed to concentrate the platinum group metals. Ore is crushed and processed by flotation to produce a concentrate, which is then smelted. In some processes, magnetic separation is used to concentrate PGMs in a nickel-copper-iron metallic phase. Base metals such as copper, nickel, and iron are then dissolved, leaving a PGM-rich concentrate.
Another important source of PGM concentrates is anodic slime from nickel and copper electrorefining. These slimes can contain platinum, palladium, rhodium, iridium, ruthenium, silver, gold, selenium, tellurium, and other elements. Different refineries use different flowsheets, but most involve leaching, separation of major PGMs, purification, and final reduction to metallic products.
For ruthenium, hydrochloric acid with chlorine gas is commonly used to dissolve PGM concentrates. Ruthenium forms chloride complexes, such as hexachlororuthenate (RuCl₆²⁻). Its separation is often achieved by oxidative distillation. Strong oxidizing agents such as sodium chlorate or sodium bromate convert dissolved ruthenium into volatile ruthenium tetroxide, RuO₄. Osmium behaves similarly, forming volatile OsO₄. These tetroxides are swept out of solution by air and captured in a reducing hydrochloric acid scrubber, where ruthenium is converted back into soluble chloride complexes.
Ruthenium is then separated from osmium, usually by reoxidizing osmium to volatile OsO₄ while keeping ruthenium in solution. Final recovery is commonly achieved by precipitation with ammonium chloride to form ammonium hexachlororuthenate, followed by hydrogen reduction to metallic ruthenium. Alternatively, ruthenium can be precipitated as ammonium pentachloronitrosylruthenate and thermally decomposed to produce ruthenium sponge. Industrial ruthenium refining can achieve high recoveries, typically between 90% and 99.5%. However, the processes require strict safety controls because volatile ruthenium and osmium tetroxides are highly toxic, and chlorine oxide species can be explosive.
Although recycling of platinum group metals is already an established industrial practice, the urgency for ruthenium recycling is on the rise. One of the main reasons driving this trend is the limited primary supply of ruthenium, which is constrained by its nature as a by-product and the concentration of resources in only a few regions. Furthermore, the growing demand for ruthenium in various applications, such as catalysis, hydrogen technologies, semiconductors, data storage, and electronics, is significantly increasing its consumption.
Another factor contributing to this trend is the lack of viable substitutes for ruthenium. Its unique combination of catalytic, chemical, and physical properties makes it difficult to replace in many applications. Additionally, with recent price increases, recovering ruthenium from secondary sources has become more economically attractive due to its high value.
On the environmental front, many wastes containing ruthenium are hazardous or challenging to manage. Consequently, the recovery of this metal can help in reducing environmental impacts. Secondary sources often have ruthenium concentrations that are much higher than those found in natural ores, and they can possess simpler compositions. This characteristic makes them particularly appealing targets for hydrometallurgical recovery processes.
Membrane electrode assemblies are key components of fuel cells that use proton exchange membranes and water electrolyzers. They contain catalyst layers made from platinum group metals dispersed on carbon supports and separated by a polymer electrolyte membrane such as Nafion.
Ruthenium is used in these systems as an anode catalyst, especially for oxygen evolution reactions, and as an alloying component in platinum-based catalysts. Although the ruthenium content is usually much lower than the platinum content, spent fuel cells and electrolyzers represent an emerging secondary source.
A typical recycling strategy involves manually separating the membrane electrode assembly, delaminating the catalyst layers, and treating the ruthenium-bearing catalyst by hydrometallurgical or pyrometallurgical methods.
Several advanced approaches have been studied. One way is to soak the membrane support in a mixture of alcohol and water to separate the PtRu nanoparticles, and then soak it in hydrochloric acid with hydrogen peroxide and aluminum chloride. Ruthenium is then separated from platinum by converting it into volatile RuO₄, which is trapped in a reducing hydrochloric acid-alcohol solution. Ruthenium salts such as ammonium hexachlororuthenate can then be precipitated and reused as catalyst precursors.
Another route involves alkaline fusion with sodium hydroxide or sodium hydroxide/sodium nitrate mixtures, followed by hydrochloric acid leaching and solvent extraction using Cyanex 923. Ion exchange can be introduced to remove interfering elements such as tin and antimony before extraction. Ruthenium can then be isolated as ammonium hexachlororuthenate.
Electrochemical dissolution has also shown promise. Alternating potential waveforms, such as saw-tooth or square-wave regimes, can dissolve ruthenium and platinum much faster than conventional chemical leaching. Under optimized square-wave conditions in 1 M hydrochloric acid, up to 98% of ruthenium can be dissolved at room temperature in about one hour. These methods reduce acid consumption and can eliminate some pretreatment steps, making them attractive for future recycling processes.
Ruthenium catalysts are widely used in industrial hydrogenation, amination, oxidation, and Fischer–Tropsch reactions. They are often supported on porous oxides such as zirconia, alumina, silica, or carbon and may contain between 0.1% and 30% ruthenium. Because of these relatively high metal loadings, spent catalysts are among the most promising secondary ruthenium resources.
For example, Ru–Zn/ZrO₂ catalysts used in selective benzene hydrogenation may contain 5–15% ruthenium. One recovery strategy involves first removing zinc and zirconium, then enriching ruthenium in the residue. Zinc can be selectively leached with sulfuric acid, while zirconium can be removed after roasting with sodium bisulfate and water leaching. The ruthenium-rich residue can then be fused with sodium nitrate and sodium hydroxide to form sodium ruthenate, Na₂RuO₄. Subsequent oxidative distillation produces volatile RuO₄, which is trapped in a hydrochloric acid-alcohol solution to yield ruthenium chloride products.
Other approaches aim to produce high-purity ruthenium nitrosyl nitrate, Ru(NO)(NO₃)₃, from spent catalysts. Under optimized conditions, total yields above 90% have been reported. Microwave-assisted leaching has also been explored for Ru/Al₂O₃ catalysts. Hydrochloric acid leaching at an elevated temperature can dissolve up to 95% of ruthenium while limiting aluminum dissolution. Ruthenium can then be recovered from the leachate by cloud point extraction using surfactants and chelating agents. While promising, this method still requires improvement in selectivity and final metal isolation.
Ruthenium is also present in by-products from nickel and copper metallurgy, especially in converter matte, anode slimes, and selenium-tellurium residues. During nickel-copper matte leaching, ruthenium, rhodium, and iridium can precipitate into PGM concentrates. Studies have shown that matte iron content and oxygenated conditions strongly influence ruthenium recovery. Low-iron matte under oxygenated conditions can result in nearly complete ruthenium precipitation, while high-iron matte or non-oxygenated conditions lead to much lower recovery.
Ruthenium may also precipitate during iron hydrolysis from nickel sulfate solutions. At pH 4, ruthenium precipitation efficiencies of about 98% have been reported. Thiourea precipitation from later-stage matte leach solutions has achieved up to 87% ruthenium recovery. Copper anodic slimes provide another potential source. During sulfuric acid treatment, ruthenium can concentrate in selenium-tellurium residues. Subsequent alkaline treatment, acid dissolution, chlorination, roasting with sodium chloride, and oxidative distillation can produce ruthenium powder, although detailed overall recovery data are often lacking.
Bioleaching has also been investigated for low-grade PGM concentrates. Mixed cultures of thermophilic and mesophilic microorganisms can remove base metals such as copper, nickel, and cobalt. However, ruthenium extraction by subsequent cyanidation remains low because of ruthenium’s chemical inertness and slow complex formation.
Red mud, the major waste product of alumina production by the Bayer process, is generated in enormous quantities worldwide. It is primarily composed of iron, aluminum, silicon, titanium, calcium, and sodium oxides. Although typically treated as hazardous waste, red mud may contain valuable elements such as rare earths, scandium, gallium, and, in some cases, ruthenium.
One recent study identified approximately 0.1% ruthenium in red mud from an alumina factory in China. Acid leaching tests showed that phosphoric acid was the most effective leaching agent, followed by hydrochloric acid, sulfuric acid, and nitric acid. Under optimized conditions using 5 M phosphoric acid at 90 °C for six hours, more than 93% of ruthenium was dissolved.
However, the resulting solution contained only about 0.1 g/L ruthenium and large quantities of iron, aluminum, and calcium. Therefore, further separation and purification steps would be required before this route could become industrially viable.
Ruthenium recovery faces several scientific and industrial challenges. Its chemistry is complex because it forms multiple oxidation states and a wide range of chloride, nitrate, nitrosyl, oxide, and organometallic species. Some compounds, especially RuO₄, are volatile and highly toxic. Many recovery methods also require aggressive oxidants, strong acids, high temperatures, or complex downstream purification.
Future progress in utilizing secondary ruthenium resources will hinge on several key priorities. First, it is essential to identify and characterize ruthenium-rich waste streams to understand their potential fully. Concurrently, efforts should focus on improving selective leaching and separation methods to enhance the efficiency of recovery processes. Another important aspect is the reduction of reliance on toxic volatile RuO₄ pathways, where feasible, to promote safer alternatives. This includes the development of greener and safer extractants that can facilitate the extraction process without posing environmental risks.
Additionally, improving recovery methods from dilute solutions will be critical to guarantee that even small concentrations of ruthenium can be economically recovered. Integrating secondary feeds into existing PGM refineries will also be a significant focus, allowing for a more efficient use of resources. Finally, it will be necessary to evaluate both the economic and environmental performance of these processes at an industrial scale to ensure sustainable progress in this field.
Ruthenium is emerging as a strategically important metal for modern industry. Its applications in catalysis, clean energy, electronics, data storage, and high-performance computing are expanding, while primary supply remains limited and geographically concentrated. These factors have created growing concern over long-term availability and have strengthened the case for recycling.
Primary ruthenium production is well established, but its dependence on platinum, nickel, and copper mining constrains it. Secondary sources—including spent catalysts, membrane electrode assemblies, metallurgical by-products, red mud, industrial wastewaters, and even nuclear waste—offer important opportunities to supplement supply.
Among these, spent industrial catalysts appear to be the most promising near-term source because of their relatively high ruthenium content and compatibility with existing PGM refining systems. At the same time, innovative hydrometallurgical methods such as solvent extraction, ion exchange, adsorption, biosorption, electrochemical dissolution, and selective precipitation could expand recovery from more dilute and complex waste streams.
As demand continues to rise, ruthenium recycling will become not only economically attractive but also strategically necessary. Developing efficient, safe, and sustainable recovery technologies will be essential for securing future ruthenium supply and supporting the advanced technologies that increasingly depend on this rare and valuable metal.
