Rh, Rh

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Rhodium is found in platinum ores and is used in alloys with platinum and as a catalyst. It is abbreviated to Rh and has atomic number 45. It is one of the most expensive precious metals.

Rhodium chloride, rhodium fluoride, rhodium fluoride and rhodium fluoride are some examples. The lower oxidation states are only stable if ligands are present. Griffith, W. P. The Rarer Platinum Metals; John Wiley and Sons: NewYork, 1976; p 313.

The most stable radioisotopes are 101 Rh with a half-life of 3.3 years, 102 Rh with a half-life of 207 days, 102m Rh with a half-life of 2.9 years, and 99 Rh with a half-life of 16.1 days. Twenty other radioisotopes have been characterized with atomic weights ranging from 92.926 u ( 93 Rh) to 116.925 u ( 117 Rh). Most of these have half-lives that are less than an hour except 100 Rh (half-life: 20.8 hours) and 105 Rh (half-life: 35.36 hours). There are also numerous meta states with the most stable being 102m Rh (0.141 MeV) with a half-life of about 2.9 years and 101m Rh (0.157 MeV) with a half-life of 4.34 days. See isotopes of rhodium.

The primary decay product before 103 Rh is ruthenium and the primary product after is palladium. David R. Lide (ed.), Norman E. Holden in CRC Handbook of Chemistry and Physics, 85th Edition CRC Press. Boca Raton, Florida (2005). Section 11, Table of the Isotopes.

Diluted nitric acid dissolved all but palladium and rhodium, which were dissolved in aqua regia and the rhodium was precipitated by the addition of sodium chloride as . After washing with ethanol, the rose red precipitate was reacted with zinc forming rhodium metal.

This is known as rhodium flashing in the jewelry business. It also may be used in coating sterling silver in order to strengthen the metal from tarnish, as a result from the copper compound found in sterling silver. Solid (pure) Rhodium jewelry is very rare, because the metal has both high melting point and poor malleability (making such jewelry very hard to fabricate) rather than due to its high price.

It is found in platinum ores and obtained free as a white inert metal which is very difficult to fuse. Principal sources of this element are located in South Africa, in river sands of the Ural Mountains, and in North America, including the copper-nickel sulfide mining area of the Sudbury, Ontario region. Although the quantity at Sudbury is very small, the large amount of processed nickel ore makes rhodium recovery cost effective. The main exporter of rhodium is South Africa (> 80%) followed by Russia.

As of October 2007, rhodium costs approximately eight times more than gold, 450 times more than silver, and 27,250 times more than copper by weight. Rhodium's typical historical price is about $1,000/troy oz, http://periodic.lanl.gov/elements/45.html but in recent years, it has increased to about $4500/troy oz.

As a typical used fuel has 3% fission products by weight, it will contain about 400 grams of rhodium per ton of used fuel. The longest lived radioisotope of rhodium is 102m Rh which has a half life of 2.9 years, whereas the ground state ( 102 Rh) has a half life of 207 days., while rhodium is the least radioactive One kilogram of fission rhodium will contain 6.62 ng of 102 Rh and 3.68 ng of 102m Rh. As 102 Rh decays by beta decay to either 102 Ru (80%) (some positron emission will occur) or 102 Pd (20%) (gamma ray photons with about 500 keV are generated) and the excited state decays by beta decay (electron capture) to 102 Ru (gamma ray photons with about 1 MeV are generated). If the fission occurs in an instant then 13.3 grams of rhodium will contain 67.1 MBq (1.81 mCi) of 102 Rh and 10.8 MBq (291 Ci) of 102m Rh. As it is normal to allow used nuclear fuel to rest for about five years before reprocessing, much of this activity will decay leaving 4.7 MBq of 102 Rh and 5.0 MBq of 102m Rh. If the rhodium metal was then left for 20 years after fission, then the 13.3 grams of rhodium metal would contain 1.3 kBq of 102 Rh and 500 kBq of 102m Rh. At first glance, the rhodium might be adding to the resource value of reprocessed fission waste, but the cost of the separation of rhodium from other metals needs to be considered.

Lethal intake (LD 50 ) for rats is 12.6 mg/kg of rhodium chloride (RhCl 3 ).

In 1979 the Guinness Book of World Records gave Paul McCartney a rhodium-plated disc for being history's all-time best-selling songwriter and recording artist.

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