Iridium Mining

Iridium is a rare and dense metal found on the earth's crust by 0.0001ppm. It occurs in natural alloys with other noble metals in iridosmine (77% Iridium) and Platiniridum (75% iridium)

Mining:

Even though Iridium occurs in natural alloys, it isn't used for the commercial Iridium extraction. Iridium is extracted from the ores of copper sulfide and nickel as it contains iridium and other platinum group metals as impurities.The copper and nickel ore containing iridium are mined by surface mining and underground mining. The chalcocite and chalcopyrite are the ores which are mined mostly for extracting iridium.

In surface mining, open pit mining method is handled by drilling, blasting and benching of the open surface containing iridium ore particles. It is the widely used method in iridium mining.The underground mining of iridium is done in depth areas where the ores happens to be deep inside the earth's surface.

It is employed only by the condition where the deep dug iridium ores are high in quality and can compensate the expensive mining process. This method is not much used in the iridium mining.The iridium mining countries are South Africa, Russia, USA and Canada

Processing and extraction:

The collected ores of copper and nickel with Iridium is milled and crushed into small pieces. Then the crushed gangue undergoes roasting, smelting and finally electrolytic refining. In the electrolytic refining; the noble metals such as gold, silver, platinum, osmium, Iridium, ruthenium and non metals such as selenium and tellurium will settle down as anode mud inside the electrolytic cell.The anode mud is collected as the primary material for extraction of Iridium.

The anode mud is made into an aqueous solution by mixing sodium peroxide with it. Then the fused mixture is now made to react with aqua regia or chlorine with hydrochloric acid, in which the usage scale of acid is based on the composition of the mixture. After the reaction gold, platinum and other non metals will be dissolved in the concentrated acid mixture leaving Iridium, osmium, iridium and ruthenium as a solid residue within it. The solid residue is now treated with sodium bisulfate to remove rhodium from the mixture.

Now, the mixture remains of insoluble osmium-ruthenium-Iridium composite are treated with sodium oxide where the Iridium remains insoluble by producing water soluble osmium-ruthenium salts. Then the immiscible Iridium solution is isolated and reduced by hydrogen to produce Iridium metal as sponge. The sponge will be crushed and made into pure metal powder by powder metallurgical techniques.South Africa is the largest producer of Iridium by holding 80% of world production with it.

Definition

Iridium is the chemical component with atomic number 77. A very solid, brittle, silvery-white transition metal of the platinum family, iridium is the second densest component and is the most corrosion-resistant metal, even at temperatures as high as 2000 ?C. Although only firm molten salts and halogens are corrosive to solid iridium, finely divided iridium dust is much more reactive and can even be flammable. The most important iridium compounds in conditions of use are the salts and acids it forms with chlorine, though iridium also forms a number of organometallic compounds used in catalysis and in research.

Properties

A member of the platinum group metals, iridium is white, similar to platinum, but with a slight yellowish cast. Due to its stiffness, brittleness, and very high melting point, solid iridium is hard to machine, form, or work, and thus powder metallurgy is commonly employed instead. It is the only metal to maintain good mechanical properties in air at temperatures above 1600 ?C.