Rhenium: Ore Heated with Nitre Cake at 300 °C, Oxide Caught, Sulphide Reduced in Hydrogen at 1000 °C (Driggs, US 1,911,943)

Rhenium's highest oxide boils away at about 300 °C. Driggs heated rhenium-bearing ore with nitre cake under oxidising conditions so the oxide sublimed off, caught it in water, threw it down as sulphide and reduced that in hydrogen to rhenium powder. Result: rhenium metal powder, ready to press and sinter. Source: F. H. Driggs, US 1,911,943 (1933). Hydrogen sulphide is a deadly gas, and arsine may come off in the reduction. Picture: the patent flow sheet.