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Lead smelting extracts lead from ores using heat and chemical reactions. The process dates back over 8,000 years and was done in open hearths and furnaces. Modern methods use controlled environments to minimize pollution. Recycled materials are also used in secondary lead smelting.
Lead smelting uses heat and chemical reactions to free lead from compounds it is bound to in lead ores. The mineral galena – lead sulfide (PbS) – is one of the main minerals used in the smelting process. First, lead is oxidized, freeing it from sulfur and binding it with oxygen, forming lead oxide (PbO). Then, oxygen is extracted from lead at high temperature, reducing the environment. This is done in the presence of carbon so that the oxygen combines with the carbon, leaving pure molten lead as the final product.
Archaeological evidence of lead smelting dates back over 8,000 years. The earliest known melting occurred in what is today’s Turkey. A lead pipe has been discovered at archaeological sites in Mesopotamia, ancient Persia and Egypt. The Romans used lead extensively for plumbing. Primitive lead smelting hearths and furnaces were used to extract lead from galena and were developed in many areas of the world where the ore has been found.
Ancient smelting was done using loads of lead ore and charcoal in open hearths and furnaces. High grade ores such as galena had to be used to recover sufficient quantities of lead. Pure, molten lead flowed from smelters, forming raw lead slabs for later use. This process has been used for thousands of years and was made possible by the relatively low temperatures required for lead smelting. Primitive smelting sites are still a source of lead pollution, as no efforts have been made to protect the soil from contamination.
Modern smelting methods use a controlled environment to maximize lead recovery and minimize lead pollution. Lead smelting is done using blast furnaces and rotary kilns, or a combination of both. Lead ores are mixed with coke, limestone and other materials and reduced in the furnace. Heavy molten lead settles to the bottom of the furnace, while other substances form lighter layers on top of the lead. Much of the pollution and waste is controlled, as many of the by-products of lead smelting are captured for later recovery and use.
The recovery of lead from recycled products is done by secondary lead smelting. Old pipes, batteries and other lead-containing materials are used instead of lead ores. The process of recovering recycled materials is similar to smelting lead from ore. Heat and carbon-containing compounds such as coke or charcoal are used in the reduction of lead oxides. Sulfur and other waste products are captured using lime, soda ash or similar materials.
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