Pressure Leaching Plant

In 1981, the Pressure Leaching Plant at Trail became the first commercial application of direct leaching of zinc concentrates in the world. A second autoclave with 20% higher capacity was placed in service, to replace the original unit which will remain out of service for renovations. This plant has the capacity to treat 25% of the total zinc concentrate input.

Reground zinc concentrates are pumped into the autoclave with cell house acid and oxygen. The autoclave contents are mixed by five 75 kW agitators and conditions are controlled at 150ºC and 1.4 MPa. Elemental sulphur is separated from the plumbo-jarosite leach residue in a series of flotation cells. After remelting and hot filtration, the elemental sulphur is shipped to markets in rail tank cars. The slurry of zinc sulphate solution and leach residues is pumped to the Sulphide Leaching Plant for further processing.

The picture above shows the top of the Pressure Leach autoclave, with a view of the agitator motors, where zinc concentrate is dissolved to form zinc electrolyte.