Sulphide Leaching Plant

This plant leaches the zinc from 1300 t/d of Roaster zinc calcine and purifies the combined solutions from this plant and the Oxide and Pressure Leach plants.

Zinc calcine, leach solutions and cell house acid are mixed in 11 agitated tanks which are controlled to varied pH, from 1.7 to 3.5, by additions of cell house acid or calcine. Continuous pH monitoring is facilitated by submerged pH cells in controlled tanks.

After leaching, the acid leach slurry is distributed to four 24-m thickeners where the leach residues are separated from the clear zinc sulphate solution. The residues are filtered and washed before being pumped to the Lead Smelter for further processing to recover zinc and other metals. These recovered metals are recycled as a fume to the zinc circuit through the Oxide Leach Plant.

Clear zinc sulphate solution flows continuously from the thickeners to the zinc dust purification circuit. Solution flow rate from this circuit is approximately 450 m/h.

1 As seen above, an operator prepares to take a sample from the hot stage filter, which removes residues containing impurities from zinc electrolyte.