The production of osmium is very complex and usually takes place during the extraction of other metals, such as platinum or gold.

The starting material for osmium production is usually anode sludge from gold or nickel production. The anode sludge is dissolved in aqua regia, causing platinum and gold to dissolve. The other platinum metals and silver remain.

The silver forms insoluble silver chloride which can be separated by nitric acid and lead carbonate. Subsequently, sodium hydrogen carbonate is melted and leached out.

Rhodium is dissolved and removed as rhodium sulphate. The residue is melted down together with sodium peroxide, causing ruthenium and osmium to dissolve. Iridium remains in the insoluble residue.

Chlorine is added to the solution. This produces the volatile substances osmium tetroxide and ruthenium tetroxide.

After the addition of alcoholic caustic soda lye, only osmium tetroxide is dissolved and can therefore be separated from ruthenium tetroxide.

To obtain elemental osmium, it is precipitated as a complex with ammonium chloride.

Finally, hydrogen is reduced to metallic osmium.

OsO2(NH3)4Cl2 + 3 H2 → Os + 4 NH4+ + 2 Cl- + 2 OH-


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