Lead, blast-furnace smelting slags

Zinc Zinc is processed very similarly to copper and lead. The zinc is bound in the ore as ZnS, sphalerite. Zinc is also obtained as an impurity from lead smelting, in which it is recovered from the blast furnace slag. 

The lead concentrate must he roasted for effective removal of sulfur and then smelted in a blast furnace. Sulfur is mostly removed hy a sinter process. The galena concentrate or the ore itself, if its impurity content is low, is mixed with silica and other slag-forming reagents and roasted in sinter machines to produce lead oxide, lead silicate, and some metallic lead. The principal reactions are ... 

In lead smelting, the oxygen-enriched blast has been used in lead cupola and slag fuming furnaces. Oxygen enrichment of the copper blast furnace is also common. 

Limestone is widely used as a flux in the smelting of copper, lead, zinc and antimony from their ores. It is charged into the smelters with the concentrated ores. The limestone calcines and the resulting lime reacts with silica, alumina and other impurities to form a molten slag. The slag chemistry is similar to that in the blast furnace (section 11.1.3). 

Refining, a process of removing any impurities left after roasting or smelting, also can be done in a blast furnace. Iron, copper, and lead can be refined in oxidation reaction that removes impurities as an oxide slag or an oxide gas. Fire refining can separate... 

Direct smelting processes provide alternatives to the sinter plant-blast furnace above, up to the stage of crude bullion production, but still require the addition of refining operations to produce high-grade lead. Three alternatives have been evaluated - the Kivcet process, the QSL process and the Isasmelt process - as typical of the top submerged lance slag bath reactor. Evaluations are based on comparable feeds, predominantly lead concentrates with low residue inputs. 

In the example used for the basis of cost estimates in this chapter, the copper content of concentrates is 0.5 per cent and for a blast furnace slag of 0.15 per cent copper, recovery into matte would be around 80 per cent, which would yield 0.017 tonnes of copper matte containing 40 per cent copper per tonne of lead produced. Taking smelting charges and penalties at US 1000/t of contained copper and the LME copper prices at US 7500/t, the return for copper matte is US 44/t of lead produced. 

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