Rhodium: the most expensive metal in the car

There is an element in Dmitrii Ivanovich Mendeleev's periodic table that is both a jewel and a critically important industrial material. Its number is 45, and its name is rhodium. It costs several times more than gold and platinum, it is incredibly rare and has unique catalytic properties that help make the air in cities cleaner. Today, rhodium is one of the most in-demand metals in the world, and its importance continues to grow.

Why is the element called "rhodium"?

The name rhodium comes from the Greek word ῥόδον (rhodon), which means "rose". The element received its name for the characteristic pink-red color of one of its first chemical compounds — rhodium chloride. The discoverer of the element, the English chemist William Wollaston, was impressed by the beauty of this shade and decided to immortalize this delicate connection with the flower in the name of the metal.

Why does rhodium have the atomic number 45?

The atomic number 45 means that there are 45 protons in the nucleus of a rhodium atom. In the periodic table, it is located in the ninth group (by the modern classification — 9) or the VIIIB group in the old classification, in the fifth period. Rhodium belongs to the "rhodium-palladium-silver" triad and is part of the so-called light group of platinum metals.

History of discovery: another metal from platinum ore

The history of the discovery of rhodium is similar to a detective story from the 19th century. In 1803, the English physician and self-taught chemist William Wollaston, already famous for the discovery of palladium, continued to study raw platinum that was brought from South America. He noticed that after extracting palladium, a dark-red substance with amazing properties remained in the solution.

Wollaston isolated a new substance through complex chemical reactions (dissolution in aqua regia, precipitation) and, after restoring it, obtained a powder of metallic rhodium. In 1804, he officially announced the discovery of a new metal in a report to the Royal Society. Initially, Wollaston obtained only a few grams of rhodium, remaining almost the only producer for a long time.

Uniqueness of rhodium: brilliance and durability

Appearance. Rhodium is a silver-white shiny metal with a strong blueish tinge. It has high reflectivity.

Chemical inertness. It is one of the most corrosion-resistant metals. It does not oxidize in the air even when heated to 600°C and does not dissolve in acids, including aqua regia. Rhodium is refractory (melting point 1963°C) and has high mechanical strength.

Catalyst. The main application of rhodium is based on its unique ability to accelerate chemical reactions. It is particularly effective in the neutralization of nitrogen oxides, making it indispensable in automotive catalysts.

Where rhodium is found

Rhodium is one of the rarest elements in the Earth's crust. Its content in the Earth's crust is estimated at 0.0000001%. It does not occur in the form of independent minerals, but is extracted as a byproduct of platinum and nickel ores. The main deposits of rhodium are located in South Africa, Russia (on the Kola Peninsula and in the Norilsk region), Canada, and Zimbabwe. The average price of rhodium is from 500 to 700 thousand dollars per kilogram, making it one of the most expensive metals in the world.

Application of rhodium in industry

Automotive catalysts. Approximately 80% of the rhodium produced is used here. Rhodium plays a key role in three-way catalytic converters: it converts toxic nitrogen oxides (NOx) into safe nitrogen and oxygen.

Chemical industry. Rhodium is used as a catalyst in the carbonylation reaction of methanol for the production of acetic acid. It is also used in the production of nitric acid and in the hydrogenation of organic compounds.

Glass industry and optics. Platinum-rhodium alloys are used for making vessels for boiling high-quality optical glass and glass fiber, as they are resistant to molten glass and do not stain it. Rhodium coating on searchlights and mirrors is distinguished by exceptional brightness and durability.

Jewelry. Rhodium plating is the process of coating jewelry made of white gold or silver with a thin layer of rhodium. This gives the ornaments an incredible brilliance, protects them from scratches, and prevents tarnishing. About 5-10% of rhodium is used in jewelry.

Electronics. Rhodium is used for coating electrical contacts and connectors in precision measuring equipment, as it is resistant to corrosion and the formation of oxide films. The thickness of the coating is usually 0.5–1 micron.

The future of rhodium: growing demand and search for alternatives

The future of rhodium is directly related to global environmental standards. With the transition to electric vehicles, the role of rhodium as a component of the catalyst for internal combustion engines may decrease. Some manufacturers are looking for ways to replace rhodium with cheaper metals, such as palladium. However, growing environmental requirements in developing countries support demand. Active development is taking place in the technology of secondary recovery of rhodium from spent catalysts. Rhodium continues to be indispensable in the glass and chemical industries.