Ruthenium Production

Platinum processing wastes or sludge appearing after Cu/Ni electrolytic refinement may be used as ruthenium feedstock. Raw material smelted with barium or sodium peroxides Ba₂O₂/Na₂O₂ respectively are dissolved in water and treated by gaseous chlorine as a strong oxidizer. Yielded volatile ruthenium RuO₄ is sublimated by heating the solution, and then dissolved in hydrochloric acid. Ammonium hexachlororuthenate (NH₄)₂[RuCl₆] is then precipitated from the solution isolated and roasted yielding RuO₂ which tjen is reduced until pure metal by hydrogen. Ruthenium and its alloys are smelted in induction furnaces using ZrO₂ crucibles or in arc furnaces with Argon atmosphere.

It is also possible to extract ruthenium from used nuclear fuel; fission products of uranium, plutonium or thorium yielding 250 g per ton of wasted fuel elements.

Ruthenium may be conveniently prepared from osmiridium, which is an alloy of osmium and iridium containing small proportions of rhodium and ruthenium, the last named amounting in some cases to 6 per cent.

The alloy is heated to a white heat with four or five times its weight of zinc in a carbon crucible until the vapour of zinc ceases to be evolved. The friable mass left is crushed and heated with a mixture of barium dioxide and nitrate to about 900° C. in an earthenware crucible. On cooling, the powdered mass is treated with dilute hydrochloric acid, care being taken to keep the temperature down by immersion of the containing vessel in cold water. A fume-cupboard with a powerful draught is desirable in view of the presence of poisonous osmic tetroxide in the evolved vapours.

When the reaction has subsided, nitric and sulphuric acids are added, whereby barium sulphate is precipitated. The clear solution is decanted and distilled until one-quarter of its volume has been collected as distillate. This latter liquor is rich in osmium, and may be worked for that metal. The residue is evaporated to small bulk. Ammonium chloride and a small quantity of nitric acid are added, and the mixture evaporated to dryness on the water-bath. A violet-black crystalline solid is obtained which is washed with water half saturated with ammonium chloride until the filtrate is colourless. The insoluble residue consists of fairly pure ammonium chlor-iridate containing ruthenium, from which the spongy metals are obtained by ignition.

It now remains to separate out the ruthenium. This is accomplished by fusing with potassium hydroxide and nitrate, best in a silver crucible, and subsequently dissolving in water. The solution obtained has an orange-yellow colour in consequence of the presence of potassium ruthenate. This colour is removed by the addition of nitric acid, ruthenium oxide separating out. Ignition in a graphite crucible with a little chalk yields the free ruthenium, the chalk combining with any silicon, chromium, and osmium that may have been present.

Further purification may be effected by one or more additional fusions of the metal with potassium hydroxide and nitrate.

As obtained in this way the metal is not pure, but contains small quantities of alloyed elements such as osmium and iridium.

Chemically Pure Ruthenium, may be obtained1 from the foregoing by maintaining it, in the form of a fine powder, at a dull red heat in a current of oxygen for about three hours, whereby the osmium content is quantitatively oxidised to the volatile tetroxide, OsO₄, which is driven off. The ruthenium also undergoes partial oxidation, and is now reduced in a current of pure hydrogen. It is then fused, preferably in a silver vessel, with excess of potassium hydroxide and nitrate, cooled, and extracted with water. The orange-coloured solution, containing potassium ruthenate, is gently distilled in a current of chlorine whereby volatile ruthenium tetroxide is produced, and is absorbed in aqueous potassium hydroxide. Since all the osmium has been removed, the distillate of ruthenium tetroxide is exceedingly pure, for the residue contains no other metal yielding a volatile product under these conditions. Upon addition of absolute alcohol to the potash solution a black precipitate is obtained containing ruthenium in a more or less completely reduced condition, reduction being finally completed by ignition in a current of pure hydrogen.

Crystalline Ruthenium may be obtained by fusing the metal with excess of tin in a carbon crucible, whereby the compound, RuSn₃, is formed. Treatment with boiling hydrochloric acid removes the excess of tin, and the unattacked residue of RuSn₃ is ignited in a current of hydrogen chloride. The combined tin is thereby removed as a volatile chloride, leaving behind crystalline ruthenium. Cubic and fernlike crystals are obtained by ignition of the finely divided metal at a high temperature with borax and pyrites.