Lead Manufacturing process from Lead concentrates Before lead concentrate can be charged into Rotary furnace for smelting, it must be roasted to remove most of the sulphur and to agglomerate further the fine flotation products or fired directly in furnace. Various fluxing materials, such as limestone or iron ore, are mixed with the ore concentrate. The mix is spread on a moving grate, and air is blown through at a temperature of 1,100 °C. The sulphur, along with coke additions, serves as a fuel and is combusted to sulphur dioxide gas, which is usually recovered for the production of sulphuric acid as a by-product. A blast of air is admitted to the lower part of the furnace to aid combustion of the coke, generating a temperature of about 1,100 °C and producing carbon monoxide. This gas then reacts with the metallic oxides, producing carbon dioxide and molten metal. Non-metallic wastes form a slag with the fluxing materials. When reduction is complete, the furnace is tapped and the lead drawn off to flow into drossing kettles or molds.
At this stage, the semi-finished product, 95 to 97 percent lead and containing dissolved metallic and non metallic (oxide and sulphide) impurities, is known as base bullion. The bullion is maintained at a temperature just above its melting point, about 330 °C (626 °F). At this temperature, the solubility of copper in lead is very low, so that the copper content segregates and forms a scum, or dross, on the surface of the bath in the drossing kettle. After this is skimmed off, more copper and other impurities are brought to the surface by stirring sulphur and lead pyrite into the bath or by agitating it with submerged air lances. These impurities are also skimmed off, and the remaining base bullion is refined to yield lead of commercial quality. Sulphurous gases generated by the smelting process are tapped from the waste shaft to heat steam and to produce sulphuric acid as a by-product. Refining; The condensed bullion is loaded into Refining kettle, required chemicals are added to remove traces of zinc, iron, copper and antimony. All impurities are skimmed off, resulting in 99.97% lead, which is widely used commercial grade. Hot metal pump is used to fill the mould of a continuous caster which results into 30 kgs ingots.