Introduction to Lead Metallurgy

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Lead metallurgy is the best medium for silver production: generally, the recovery rate of gold and silver using lead is over 95%, so the recovery of these metals is directly related to the production of lead. Currently, about 80% of the world’s primary crude lead is produced using the traditional sintering-blast furnace smelting process. Traditional methods are mature in technology and relatively reliable; however, their drawback is that during the sintering process for desulfurization and clumping, the SO2 concentration in the sintering flue gas is low, making it somewhat difficult to recover sulfur. Additionally, blast furnace smelting requires expensive metallurgical coke. To address the aforementioned problems, metallurgists conducted research on new lead smelting processes. Since the 1980s, new lead smelting methods such as the QSL process, flash smelting, TBRC top-blown converter process, and Kivsethan and Essa processes have emerged one after another. Among them, the QSL method is a new direct lead smelting process developed by the German company Lurgi in the 1970s. Although Canada, South Korea, and China acquired this patent to build plants, the production results were not very satisfactory ； Flash smelting has not yet been put into industrial production ； The TBRC method was developed by the Swedish company Boliden, but its operation is intermittent, and the furnace lining suffers severe corrosion ； The Kivset method was developed by the former Soviet Union’s Research Institute of Non-ferrous Metals. Numerous manufacturers have now adopted it for industrial production; it represents a new lead smelting process with advanced parameters and mature, reliable technology. However, this method requires high capital investment, and its benefits can be fully realized only in factories with large-scale production capabilities. The Essa lead smelting technology relies on an oxygen injection into the melt using a Cero submerged lance inserted from above. It creates a turbulent molten pool, allowing intense oxidation or reduction reactions to occur rapidly. In the first section, the high-lead slag produced by the smelting furnace is sent to the reduction furnace via a trough, while the flue gas generated from oxidation desulfurization is sent to the acid production system after dust removal. In the second reduction furnace, the crude lead produced and the slag are continuously discharged from the outlet and separated in a conventional pre-bed; the resulting flue gas is dust-removed before being emitted through a chimney. Isafah smelting process. This process flow is advanced; it has a wide range of compatibility with raw materials, and the production scale can be adjusted as needed, making it quite flexible. It features advanced performance parameters, and the SO2 concentration in the exhaust gases is high, which helps to address the issue of gas pollution during the production process ； At the same time, the smelting process is enhanced, resulting in high recovery rates for gold and silver, effective utilization of waste heat, and low energy consumption. It not only meets the requirements for the renovation of lead-silver smelting at Plant 308, but also can contribute to the advancement of silver-lead metallurgy production and technology in China; therefore, the Isa process is recommended as the preferred option for the lead smelting process in this project. Traditional blast sintering – the blast furnace method – presents certain difficulties in the production of acid from flue gas. Nevertheless, in recent years, large lead smelters such as those in Zhuzhou, Shenyang, and Jiyuan in China have still used this method for their expansion and renovation projects, owing to its advantages of fast construction, rapid commissioning, and quick achievement of full production capacity. There are two methods for refining crude lead: the thermal method and the electrolytic method. Generally speaking, the electrolytic method is effective for separating silver, gold, bismuth, and antimony; it achieves high recovery rates for metals such as lead and silver, offers favorable working conditions, and features a high degree of mechanization and automation. The disadvantage of the electrolytic method is that its capital investment is higher than that of the thermal method. The pyrological method requires the processing of a large number of intermediate products, resulting in high energy consumption and thus higher production costs compared to the electrolytic method. Given that the lead matte in this project contains large amounts of metals such as silver and bismuth, the conventional method for processing lead anode sludge involves a pyrometallurgical-electrolytic process to recover gold and silver, while the slag is subjected to reduction smelting to produce refined bismuth and other products. This process is simple, the technology is mature, and it is easy for workers to operate; however, the recovery rate of valuable metals is low. Antimony and lead volatilize in the form of oxides and end up in the smoke, which not only makes comprehensive recovery difficult but also causes secondary pollution.