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Plants for the production of lead are generally referred to as lead smelters. Primary lead production begins with sintering. Concentrated lead ore is fed into a sintering machine with iron, silica, limestone fluxes, coke, soda ash, pyrite, zinc, caustics or pollution control particulates. Smelting uses suitable reducing substances that will combine with those oxidizing elements to free the metal. Reduction is the final, high-temperature step in smelting. It is here that the oxide becomes the elemental metal. A reducing environment (often provided by carbon monoxide in an air-starved furnace) pulls the final oxygen atoms from the raw metal. Lead is usually smelted in a blast furnace using the carbon from the sintering machine to provide the heat source. As melting occurs, several layers form in the furnace. The molten lead layer sinks to the bottom of the furnace. A layer of the lightest elements, including arsenic and antimony, floats to the top and is referred to as the speiss. A "matte" layer also forms from the copper and metal sulfides. Finally, a layer of blast furnace slag, which contains mostly silicates, also forms. The speiss and the matte are usually sold to copper smelters where they are refined for copper processing. The slag is stored and partially recycled, if the metal content is sufficient. The lead from the blast furnace, called lead bullion, then undergoes the drossing process. The bullion is agitated in kettles then cooled to 700-800 degrees. This process results in molten lead and dross. Dross refers to the lead oxides, copper, antimony and other elements that float to the top of the lead. Dross is usually skimmed off and sent to a dross furnace to recover the non-lead components which are sold to other metal manufacturers. The Parkes process is used to separate silver or gold from lead. Finally, the molten lead is refined. Pyrometallurgical methods are usually used to remove the remaining non-lead components of the mixture, for example the Betterton-Kroll process and the Betts electrolytic process. The non-lead metals are usually sold to other metal processing plants. The refined lead may be made into alloys or directly cast.〔USEPA, Profile of The Nonferrous Metals Industry. EPA 310-R-95-010 as shown in ()〕 People who operate or work in such plants are also referred to as smelters. ==Lead ores== Galena, the most common mineral of lead, is primarily lead sulfide (PbS). The sulfide is oxidized to a sulfite (PbSO3) which thermally decomposes into lead oxide and sulfur dioxide gas. (PbO and SO2) The sulfur dioxide (like the carbon dioxide in the example above) is expelled, and the lead oxide is reduced. Anglesite, Cerussite, Pyromorphite, Mimetite and Wulfenite are other lead ores. Other elements frequently present with lead ores include zinc and silver.〔Nicole Fobi, MD, LEAD SMELTING International Review, Morehouse School of Medicine, Atlanta, GA May 15th, 2007〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Lead smelting」の詳細全文を読む スポンサード リンク
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