 Discovery Information
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| Who: William Wollaston |
| When: 1803 |
| Where: England |
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| Name Origin
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| Greek: rhodon (rose). Its salts give a rosy solution. |
| "Rhodium" in different languages. |
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| Sources
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| The industrial extraction of rhodium is complex as the metal occurs in ores mixed with other metals such as palladium, silver, platinum, and gold. Principal sources of this element are located in South Africa, in river sands of the Ural Mountains, in North and South America and also in the copper-nickel sulfide mining area of the
Sudbury, Ontario region. Obtained as a by-product of nickel production. Over 80% of the world's rhodium exports comes from South Africa. The annual production of rhodium is only around 20 tonnes.
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| Abundance
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| Universe: 0.0006 ppm (by weight) |
| Sun: 0.002 ppm (by weight) |
| Carbonaceous meteorite: 0.18 ppm |
| Earth's Crust: 0.0007 ppm |
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| Uses
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| The primary use of this element is as an alloying agent for hardening platinum and palladium. Used as a coating to prevent wear on high quality science equipment and with platinum to make thermocouples. Also used in headlight reflectors, telephone relays, fountain pen points and airplane spark plugs.
Sometimes used to give white gold extra shine.
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| History
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| Rhodium was discovered in 1803 by William Hyde Wollaston, soon after his discovery of palladium. They made this discovery in England using crude platinum ore that they presumably obtained from South America.
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| Their procedure involved dissolving the ore in aqua regia, neutralizing the acid with sodium hydroxide (NaOH). They then precipitated the platinum by adding ammonium chloride, NH4Cl, as ammonium chloroplatinate. The element palladium was removed as palladium cyanide after treating the solution with mercuric cyanide. The material that remained was a red rhodium(III) chloride: rhodium
metal was isolated via reduction with hydrogen gas.
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| Notes
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| Rhodium metal does not normally form an oxide, even when heated. Oxygen is absorbed from the atmosphere at the melting point of rhodium, but on solidification the oxygen is released. Rhodium has both a higher melting point and lower density than platinum. It is not attacked by acids: it is completely insoluble in nitric acid and dissolves slightly in aqua regia. A complete dissolution of rhodium in powder form is only obtained in sulfuric acid.
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| Rhodium has been used for honours, or to symbolize wealth, when more commonly used metals such as silver, gold, or platinum are deemed insufficient.
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| Hazards
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| Compounds that contain rhodium are not often encountered by most people and should be considered to be highly toxic and carcinogenic. Rhodium compounds can stain human skin very strongly. This element plays no biological role in humans.
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