Roaster Plant

Zinc concentrate is converted to zinc calcine by burning the concentrate in fluid bed roasters. DOELL Two Lurgi Fluo-solid roasters and one suspension roaster treat 77% of the zinc concentrates and the remaining 23% are treated by the Pressure Leach Plant. Zinc calcine (ZnO), produced by burning the sulphide concentrates with air and direct oxygen addition, is the soluble zinc form which is the primary feed for the Leaching Plant. After discharging from the roasters, calcine is cooled, passed through a ball mill, and collected in cyclones and electrostatic precipitators before being pneumatically transported to two 3000 tonne silos located adjacent to the Leaching Plant.

The process gas discharging from the roasters, at 930ºC and containing 8% SO₂ gas, passes through heat recovery boilers which generate 4.1 MPa steam for process heating in other plants. Following the boilers, this gas is subjected to several cleaning and cooling steps and a mercury removal unit en route to the sulphuric acid plants.

To ensure maximum extraction efficiency of zinc, consistent production rates, and consistent environmental control, the entire plant is controlled by primary and secondary computer control system, located in a central control room.

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