Osmium Production
Osmium Production
Osmium is taken out from nickel-copper and copper-molybdenum platinum containing deposits. South Africa is one of the biggest suppliers. Platinoids are concentrated in copper and nickel electrolytic refining sludge from which 0.1 mass %. Osmium containing concentrate is obtained. Osmium is extracted by roasting on air at 800-900 °C. The gaseous phase which contains OsO4, SO2 and SeO2, is absorbed by 10% NaOH solution. It is neutralized until pH 8 and then precipitated by SO2. The sediment contains Na8[Os(SO3)6], it is treated by H2SO4 for SO2 removing and by oxidizer, e.g. Cl2 in the presence of NaOH. The yielded OsO4 is sublimated with its vapours absorbed by 20% alkali solution with Osmium concentration 60 g per liter. The solution is treated by methanol for reduction of yielded perosmate to the osmate, then by saturated solution KOH, after which K2[OsO2(OH)4] is precipitated. This salt is reduced by hydrogen then roasted at 930 °C and milled until fine powder containing 99.98% Osmium and iron, nickel and silicon impurities.
By another method the OsO4 alkali solution is treated by NH4Cl with Fremy's salt [OsO2(NH4)4]Cl2 as the output of the reaction. The salt then is roasted in hydrogen atmosphere at 700-800 °C which results with Osmium sponge. The sponge is milled and is purified from contaminations until 99.95% by exposing to fluohydric acid.