Palladium

Palladium: the essentials

 Brief description: ruthenium, rhodium, palladium, osmium, iridium, and platinum together make up a group of elements referred to as the platinum group metals (PGM).

Palladium is a steel-white metal, does not tarnish in air, and is the least dense and lowest melting of the platinum group metals. When annealed, it is soft and ductile. Cold working increases its strength and hardness. It is used in some watch springs.

At room temperatures the metal has the unusual property of absorbing up to 900 times its own volume of hydrogen. Hydrogen readily diffuses through heated palladium and this provides a means of purifying the gas.

This sample is from The Elements Collection, an attractive and safely packaged collection of the 92 naturally occurring elements that is available for sale.

Isolation

Isolation: it would not normally be necessary to make a sample of palladium in the laboratory as the metal is available commercially. The industrial extraction of palladium is complex as the metal occurs in ores mixed with other metals such as platinum. Sometimes extraction of the precious metals such as platinum and palladium is the main focus of a partiular industrial operation while in other cases it is a byproduct. The extraction is complex and only worthwhile since palladium is the basis of important catalysts in industry.

Preliminary treatment of the ore or base metal byproduct with aqua regia (a mixture of hydrochloric acid, HCl, and nitric acid, HNO₃) gives a solution containing complexes of gold and platinum as well as H₂PdCl₄. The gold is removed from this solution as a precipitate by treatment with iron chloride (FeCl₂). The platinum is precipitated out as (NH₄)₂PtCl₆ on treatment with NH₄Cl, leaving H₂PdCl₄ in solution. The palladium is precipitated out by treatment with ammonium hydroxide, NH₄OH, and HCl as the complex PdCl₂(NH₃)₂. This yields palladium metal by burning.

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