Rhodium - Discovery, Occurrence, Production, Properties and Applications of Rhodium

Chemical Formula

Rh

Topics Covered

Background

Discovery

Occurrence

Production

Key Properties

Applications

Metallurgy

Jewellery

Background

Rhodium belongs to the platinum group metals. It is a silvery-white metal that is hard and durable that exhibits high reflectance.

When compared to platinum is has a lower density and a high melting point

Discovery

The discovery of rhodium has been attributed to William Hyde Wollaston who discovered it in England in 1803. He successfully isolated it from a crude ore shortly after having discovered palladium.

The name rhodium is derived from the Russian word “rhodon” which means rose.

Occurrence

Rhodium is found in its elemental form in North America. It is also found in association with nickel and copper in Canada and South Africa. The latter is the largest exporter of Rhodium.

Production

The production of rhodium is quite involved as it is usually found in ores along with metals such as platinum and palladium. Separation from such ores is quite complex. For this reason, rhodium is often produced as a by-product of other metals extraction, when its production becomes more economical.

Ores are treated to remove precious metals such as gold, silver, palladium and platinum. The resultant residue is melted using NaHSO4 and then treated to extract Rh2(SO4)3. Rhodium hydroxide is them precipitated out using sodium hydroxide. This is redissolved using hydrochloric acid to produce H3RhCl6. This is them treated with NaNO2 and NH4Cl which produces (NH4)3[Rh(NO2)6]. The precipitate is then dissolved in hydrochloric acid to produce pure (NH4)3RhCl6. This materials is then heated in a hydrogen atmosphere to yield rhodium metal.

Key Properties

         Rhodium is hard and durable

         It is silvery-white in appearance

         It has a high reflectivity

 

Property

 

Value

Symbol

 

Rh

Atomic Number

 

45

Atomic Weight

 

102.91

CAS Number

 

7440-16-6

Density

 

12.45g/cm3

Melting point

 

1964˚C

Boiling Point

 

3695˚C

Applications

Metallurgy

Rhodium is used as an alloying agent for precious metals such as platinum and palladium where its addition increases the hardness. These alloys are used in resistance furnace elements, thermocouples, bushings for glass fibre production and aircraft spark plug electrodes. These alloys are also commonly used in catalysts for a range of industrial applications.

Jewellery

Rhodium is also used in jewellery, where it is used to plate white gold via electrolytic deposition. In such applications, it imparts a ‘white’ colour.

 

Primary author: AZoM.com

 

Date Added: Jul 7, 2006 | Updated: Jun 11, 2013
Ask A Question

Do you have a question you'd like to ask regarding this article?

Leave your feedback
Submit