Ruthenium Recycling

Basic Properties

• Classification: A platinum group metal (PGM) and transition metal, grouped in Period 5 and Group 8 of the periodic table.
• Atomic mass: ~101.07 u.
• Physical state: A hard, brittle metal with a metallic luster; it is relatively dense and resistant to wear.
• Melting point: ~2334 °C (one of the highest among PGMs, surpassed only by iridium and osmium).
• Boiling point: ~4150 °C.
• Density: ~12.45 g/cm³ (similar to rhodium but less than platinum).
• Electrical conductivity: Moderate, with good thermal stability, making it useful in high-temperature electronics.

Chemical Behavior

• Chemically inert at room temperature, resistant to corrosion by most acids (including hydrochloric and sulfuric acid) and alkalis. It dissolves only in molten alkalis or strong oxidizing mixtures (e.g., nitric acid with hydrogen peroxide).
• Reacts with oxygen at high temperatures to form ruthenium dioxide (RuO₂) or volatile ruthenium tetroxide (RuO₄), the latter being a strong oxidizing agent.
• Exhibits a wide range of oxidation states (+2, +3, +4, +6, +8), with +3 and +4 being the most common, contributing to its diverse catalytic properties.

Occurrence & Extraction

• One of the rarest elements in Earth’s crust, with an average abundance of ~0.001 parts per million (ppm). It rarely occurs in its free form.
• Primarily found as a trace impurity in platinum ores (e.g., sperrylite) and nickel-copper sulfide ores, often alongside other PGMs. Major sources include South Africa, Russia, and Canada.
• Extracted as a byproduct during the processing of platinum or nickel ores. The complex extraction process involves crushing, froth flotation, smelting, and chemical separation (via solvent extraction or ion exchange) to isolate ruthenium from other PGMs.

Key Uses

• Catalysis: A major application. Ruthenium catalysts are used in industrial processes such as hydrogenation (e.g., converting vegetable oils to solids), oxidation reactions, and ammonia synthesis. They also play a role in fuel cells, facilitating hydrogen oxidation and oxygen reduction.
• Electronics: Used in thick-film resistors (due to its stable electrical resistance across temperatures) and as a coating for electrical contacts, enhancing durability and resistance to corrosion.
• Platinum alloys: Added to platinum (5–10% ruthenium) to increase hardness and wear resistance, used in jewelry, laboratory equipment, and spark plugs for high-performance engines.
• Electroplating: Thin ruthenium coatings provide wear and corrosion resistance for tools, medical devices, and aerospace components.
• Solar cells: Emerging applications in dye-sensitized solar cells, where ruthenium complexes act as light absorbers.

History & Economics

• Discovered in 1844 by Russian chemist Karl Ernst Claus, who isolated it from platinum ore residues. He named it “ruthenium” after Ruthenia, a historical term for the region encompassing modern-day Russia and Ukraine.
• Due to its rarity, ruthenium is a high-value metal, with prices tied to global supply (dominated by South Africa and Russia) and demand from electronics and catalysis industries.