The QSL Process has been developed to smelt lead sulphide concentrates as well as sulphate and mixed oxide-sulphate secondaries such as flue dusts, battery paste or lead-silver residues. As in conventional lead smelting, the gangue minerals contained in the raw materials are separated from the molten metal in the form of a fluid siliceous slag. Instead of two separate steps of sintering and blasting in a furnace, the QSL Process is a one-step process of continuous smelting of the charge, with the resulting pellets directly fed to the oxidation and reduction zones of the reactor. Sulphur dioxide gas emissions of about 15 to 25% by volume are utilized in the manufacture of sulfuric acid. Any sulphur contained in reduction coal or fuel is recovered, and the precipitated flue dust is directly recycled to the mixing section.