Rhodium

Rhodium Details

Rhodium Symbol: Rh

Rhodium Atomic Number: 45

Rhodium Atomic Weight: 102.905

What is Rhodium?

Rhodium is a chemical element that is found in alloys and compounds and as a free metal. It is hard, silvery-white in color, and lustrous and has a lower density and higher melting point (1970 C or 3578 F) than platinum. It is usually found in nickel and platinum ores and belongs to the platinum group metals together with platinum, iridium, osmium, palladium, and rhodium. It is a transition metal with paramagnetic properties and a face-centered structure. The name of the element means rose in Greek, and the metal was first discovered by the English chemist William Hyde Wollaston in 1803. He was also the first to isolate rhodium.

Properties and Isotopes
This is a rare precious metal that is found in ores together with gold, platinum, silver, and palladium. At temperatures of up to 600°C (1,112 °F), water and air have no effect on rhodium. It reacts with molten alkalis and concentrated sulfuric acid. The metal has radioisotopes and isotopes, and the most stable ones are rhodium-102 and rhodium-101. The isotopes are 9 in total. Many of the radioisotopes have a short half life of less than 30 minutes. The metal itself has several oxidation states, but the most commonly observed is +3.

Applications and Extraction
Rhodium has different industrial and commercial applications and is often used in alloys with iridium and platinum. Alloys are used to make products such as resistance and thermocouple wires, photograph needles, and pen nibs. In addition, alloys are used for the production of electrodes and furnace windings. Electrodes are also used for electrical contacts and spark plugs. Rhodium itself is used to control emissions and in the process of hydrogenation. Alloyed with other metals, it is incorporated in turbine engines, lab crucibles, and bushings. Optical instruments are also produced with the use of rhodium. In general, the element has many applications because it is resistant to corrosion, reflective, and can be alloyed with other metals. In addition, rhodium has good oxidation resistance. It is also used in alloys because it is very durable.

The element obtained from nickel and copper ores, which makes it a by-product. It is found in very low concentrations of up to 0.1 percent. During extraction, platinum, palladium, gold, and silver are removed to obtain rhodium. The process is complex and involves treatment with hydrochloric acid, sodium hydroxide, and sodium bisulphate. It is also treated with ammonium chloride and sodium nitrite. Burning and evaporation are required to obtain rhodium in pure form. In general, the extraction process is more complex due to the fact that it is found together with other precious metals. There are mining sites in Canada, South Africa, and other countries. There are deposits in Montana, the U.S. as well. Rhodium is mainly exported by Russia and South Africa, with a total production of 30 tonnes per year. It is more expensive than other precious metals such as gold.

Environmental and Health Affects
One risk to consider is that rhodium is flammable and is thus considered a fire hazard. It reacts with oxygen in the air. Airborne particles at high concentrations are harmful for human health. There is insufficient research to conclude whether exposure to rhodium and its isotopes is a health hazard, however. Given its scarcity, the element is not considered an environmental hazard. Laboratory tests on plants show that it is toxic in high concentrations. Its compounds are reactive, but the metal itself is harmless. In fact, some compounds have been found to be carcinogenic, but rhodium is a non-toxic material.

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