Primary smelting of lead

The sintered ore is then passed to the blast furnace, where it is mixed with coke together with various slags, silica, limestone and recycled lead from emission control devices. In the furnace, the lead is initially converted to oxides by injection of a blast of air. Subsequently the oxides are reduced by carbon and CO to metallic lead. A slag comprising mainly iron and calcium silicates is also formed. The liquid lead flowing from the furnace is about 94-98% pure, and is known as lead bullion. 

An oxidized impurity, or dross, is formed on the surface of the molten bullion, and this is removed as a solid scum. It amounts to 10-35% of the bullion, and contains many metallic impurities. Lead bullion is recovered from the dross by charging a dross reverberatory furnace with 60-70% by weight of dross accompanied by sulphur, coke and a flux. Typically the furnace has a capacity of about 130 tonne day of charge. This process causes an atmospheric emission of lead, predominantly in the form of sub-micrometer particles (see Table 5.2). 

The latter parts of the lead production process (Fig. 5.1) are those of refining the lead bullion. These are not major sources of lead emissions. Any process in 

Property Sintering Blast furnace Dross reverberatory 

Fugitive emissions also arise in the lead production processes, and estimates of their magnitude appear in Table 5.3. These are caused mainly by the sintering operations, lead ore concentrate handling and transfer, and zinc fuming furnace vents [1]. They are mostly of a relatively large particle size and cause environmental contamination within a range of up to about 1 km. 

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