This rare and expensive metal is now widely used in everyday life.
Many people believe that gold is the rarest and most expensive metal in the world. However, this is not accurate. In reality, there is a metal that is rarer than gold and is also the most expensive in the world: rhodium.
The prices of metals vary based on demand and accessibility. Due to its malleability, conductivity, durability, and attractive appearance, gold is among the most expensive metals globally.
The current price of gold is approximately $1,850 per ounce, which is still quite cheap compared to rhodium. As the most expensive precious metal and one of the rarest, the price of rhodium is around $10,300 per ounce.
Rhodium is a silvery-white metal belonging to the platinum group. It has a high reflective quality (up to 80% of light) and does not tarnish. Rhodium is hypoallergenic, harder than gold, and incredibly durable. Its name is derived from the Greek word “rhodon,” meaning rose color.
With its silvery-white appearance resembling silver, rhodium is very hard, has a high melting point, and excellent corrosion resistance. Rhodium does not easily react with oxygen, making it a precious metal and an ideal catalyst, resistant to both corrosion and oxidation. With an overall hardness and a melting point of 1,964 degrees Celsius, rhodium belongs to the platinum group along with platinum, palladium, osmium, iridium, and ruthenium. Its ability to withstand temperatures up to 600 degrees Celsius in water and air, as well as its insolubility in most acids, makes rhodium highly useful for cars, airplanes, electrical switches, resistors, and high-temperature thermocouples.
Rhodium is hypoallergenic, harder than gold, and extremely durable. Being a precious metal, rhodium resources on Earth are relatively scarce compared to other metals. Rhodium is present at a concentration of about 0.000037 ppm (1 ppm = 1 milligram/kg) in the Earth’s crust, while gold is much more abundant, around 0.0013 ppm, according to the Royal Society of Chemistry (RSC). Rhodium is primarily produced in Canada, South Africa, and Russia, often as a byproduct of nickel and copper ore refining, containing about 0.1% precious metal. Approximately 16 tons of rhodium are produced annually, with estimated reserves of 3,000 tons.
Rhodium (also known as Rhodi) was discovered in 1803 by William Hyde Wollaston, shortly after he discovered the compound palladium. At that time, he collaborated with Smithson Tennat in a commercial venture aimed at producing pure platinum for sale. Rhodi typically does not appear in its pure form but exists in compounds along with other substances in platinum or nickel ore.
After its discovery, Rhodi had limited applications mainly used for measuring temperatures up to 1,800 degrees Celsius due to its good stability in the temperature range of 1,300-1,800 degrees Celsius.
Car exhaust emission control system. (Photo: Bellingham Herald)
The first application of Rhodi was for electroplating for decorative purposes and as a corrosion-resistant coating. Later, the introduction of the three-way catalytic converter (also known as the exhaust emission control system) by Volvo in 1976 increased the demand for Rhodi. Previously, catalytic converters only used platinum or palladium, while the three-way catalytic converter used Rhodi to reduce emissions, converting harmful unburned hydrocarbons, carbon monoxide, and nitrogen oxides into less toxic gases. Notably, to remove nitrate compounds from exhaust, only Rhodi can do so without any substitutes.
Over time, the primary use of Rhodi has been in exhaust emission control systems. It is estimated that in 2012, approximately 30,000 kg of Rhodi was consumed, of which 81% (24,300 kg) was used in exhaust emission control systems. The remainder was mainly used in the glass and chemical industries.
Unlike other materials used in supercars and luxury vehicles, car manufacturers often use Rhodi even in low-end models. Since 1993, any gasoline vehicle has contained Rhodi in its exhaust emission control system.
Exhaust system structure on a car with an emission control system. (Photo: YourMechanic)
However, due to the high rarity of Rhodium and the complexities of extraction, it is considered one of the ten most expensive substances in the world. This means its value has skyrocketed over time. Since 2016, the price of Rhodium has increased fivefold, similar to palladium. The current price of Rhodium is approximately $29,400 per ounce (28.3 g), equivalent to over $1 million per kg, while gold is priced at only $1,700 per ounce.
The high price has led to an increase in thefts of exhaust emission control systems from cars in recent years. This component is easy to steal; thieves can act within just a few seconds using tools like jacks, wrenches, or saws.
Victims of these thefts are often vehicles parked in one place for extended periods. High-clearance vehicles like SUVs, pickups, and trucks are also targets due to their height, making it easy to crawl underneath for removal. Especially, later model Toyotas are targeted because they have higher clearance and the bolts connecting the catalytic converters are easier to detach.
On the other hand, not all exhaust emission control systems are constructed alike. Generally, older cars tend to use more metal, for example, the Toyota Prius or Nissan Frontier are hunted more often because they use fewer engines, meaning more catalysts are discarded, resulting in a higher amount of Rhodium.
To replace a stolen exhaust emission control system, owners must spend up to $4,100, and in some areas, they may face fines of $1,300 for exceeding permitted emission levels. When the exhaust emission control system is missing, the sound from the exhaust will be louder than usual, making it easy for the car owner to notice the loss.
Lock cage for catalytic converters made of steel wire. (Photo: Heycar).
Nevertheless, there are few ways to completely prevent catalytic converter theft. The simplest remedy is to park in a garage at home (if available) or in well-lit parking lots, monitored areas, or with an attendant, and engraving identification marks or license plates. In some places, mechanics suggest welding the tops of the bolts of the exhaust emission control system or using wire cages with locks to protect this component.
| A metal so expensive that few dare to use it This precious metal has also been used as a coating for jewelry and silverware since the 1930s. However, until now, rhodium has never been used to craft jewelry, even though it has a shiny and beautiful appearance. The simple reason is that rhodium rings and bracelets would be prohibitively expensive, and the material is too difficult to obtain. Thus, although it looks like silver, rhodium is only used for plating rather than as a primary material for jewelry due to impracticality. Being the most expensive precious metal in the world, those who “dare” to use it for jewelry plating are very rare. The most familiar example is the crown of the British monarch, which was plated with rhodium in 1858 to symbolize the luxury and power of the monarchy. Additionally, the electrical conductivity and stability of rhodium are also applied in the electronics industry. Components such as resistors, circuit boards, and hard drives cannot do without rhodium. Finally, rhodium is used as a catalyst in various chemical reactions in industry. Rhodium also appears in the chemicals industry. This world’s most expensive metal is essential in the synthesis of alkyl compounds, epoxy compounds, and aldehyde compounds. Rhodium is found in extremely limited quantities in the Earth’s crust. South Africa is the world leader in rhodium mining, followed by countries like Russia, Canada, and the United States. However, production in these countries is still significantly lower compared to South Africa. Rhodium is primarily traded in the international precious metals market. Buyers can purchase rhodium in the form of bars or coins from some brokers specializing in precious metals. However, due to its high value, rhodium purchases are often made in small quantities. Furthermore, rhodium is not as readily available for purchase as other precious metals like gold or silver. Additionally, rhodium is sold on the market at fluctuating prices depending on supply and demand. The automotive industry is the main customer purchasing rhodium for use in catalytic converters. Finally, a significant portion of rhodium is sold through recycling. Used catalytic converters are a source of this precious metal. |
