Leaching is done in long pressure vessels which are cylindrical (horizontal or vertical) or of horizontal tube form known as autoclaves. A good example of the autoclave leach process can also be found in the metallurgy of zinc. It is best described by the following chemical reaction:
This reaction proceeds at temperatures above the boiling point of water, thus creating a vapour pressure inside the vessel. Oxygen is injected under pressure, making the total pressure in the autoclave more than 0.6 MPa and temperature at 473-523 K .
The leaching of precious metals such as gold can be carried out with cyanide or ozone under mild conditions.