COLOROBBIA Lead Oxide Division

Lead is abundantly available almost everywhere in the world under the form of sulphide, in the mineral called galena and in minerals of secondary importance such as cerussite, and anglesite. It is extracted throught roasting and reduction that consist in the conversion of lead to oxide and successive reduction with carbon coke in a furnace.

Another method foresees the roasting in a reverbatory furnace, with conversion of a part of the sulphide to oxide or sulphate; by removing the air and increasing the temperature, the initial lead sulphide combines with the sulphate and with the oxide, producing metallic lead and sulphur dioxide.

The waste material, recovered from the various industrial processes and thus fused, constitutes an important source of this metal. As the galena contains other minerals, impurities such as copper, zinc, silver and gold are present in the lead obtained.

The recovery of precious metals from lead minerals is important at least as much as its production. Silver and gold are recovered by the Parker process, during which a little quantity of zinc mixed with the fused lead, melts the precious metals. The fused alloy then rises to the surface and is removed, whilst the zinc is separated by distillation.

Impure lead is often purified by mixing fused lead in the presence of air, in this case the oxides of the metallic impurities rise to the surface and can be eliminated. The highest levels of purity are obtained electrolytically.

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