Plants for the production of lead are generally referred to as lead smelters. Primary lead production[ clarification needed ] 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 lead sinter produced in the sintering process and coke to provide the heat source. As melting occurs, several layers form in the furnace. A combination of molten lead and slag sinks to the bottom of the furnace, with a layer of the lightest elements referred to as speiss, including arsenic and antimony floating to the top of the molten material. The crude bullion and lead slag layers flow out of the 'furnace front' and into the 'forehearth', where the two streams are separated. The lead slag stream, containing most of the 'fluxing' elements added to the sintering machine (predominantly silica, limestone, iron and zinc) can either be discarded or further processed to recover the contained zinc.
The crude lead bullion, containing significant quantities of copper will then undergo 'copper drossing'. In this step elemental sulphur, usually in solid form is added to the molten crude lead bullion to react with the contained copper. A "matte" layer forms in this step, containing most of the copper originating from the crude lead bullion and some other impurities as metal sulfides. The speiss and the matte are usually sold to copper smelters where they are refined for copper processing.
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. [1]
People who operate or work in such plants are also referred to as smelters.
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. [2]
Most of the lead produced comes from secondary sources. Lead scrap includes lead-acid batteries, cable coverings, pipes, sheets and lead coated, or terne bearing, metals. Solder, product waste and dross may also be recovered for its small lead content. Most secondary lead is used in batteries.
To recover lead from a battery, the battery is broken and the components are classified. The lead containing components are processed in blast furnaces for hard lead or rotary reverberatory furnaces for fine particles. The blast furnace is similar in structure to a cupola furnace used in iron foundries. The furnace is charged with slag, scrap iron, limestone, coke, oxides, dross, and reverberatory slag. The coke is used to melt and reduce the lead. Limestone reacts with impurities and floats to the top. This process also keeps the lead from oxidizing. The molten lead flows from the blast furnace into holding pots. Lead may be mixed with alloys, including antimony, tin, arsenic, copper and nickel. It is then cast into ingots. [3] [4]
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Humans have been smelting lead for thousands of years, poisoning themselves in the process. Although lead poisoning is one of the oldest known work and environmental hazards, the modern understanding of the small amount of lead necessary to cause harm did not come about until the latter half of the 20th century. No safe threshold for lead exposure has been discovered—that is, there is no known amount of lead that is too small to cause the body harm.
The US Centers for Disease Control and Prevention and the World Health Organization state that a blood lead level of 10 μg/dL or above is a cause for concern; however, lead may impair development and have harmful health effects even at lower levels, and there is no known safe exposure level. [5] Authorities such as the American Academy of Pediatrics define lead poisoning as blood lead levels higher than 10 μg/dL.
Lead smelters with little pollution controls contribute to several environmental problems, especially raised blood lead levels in the surrounding population. The problem is particularly significant in many children who have grown up in the proximity to a lead smelter. [6]
The earliest known cast lead beads were thought found in the Çatalhöyük site in Anatolia (Turkey), and dated from about 6500 BC. They were later identified in fact to be made from cerussite and galena, minerals rich in, but distinct from, lead. [7] Ancient smelting was done using loads of lead ore and charcoal in outdoor hearths and furnaces.
Although lead is a common metal, its discovery had relatively little impact in the ancient world. It is too soft to be used for weapons (except possibly as sling projectiles) or for structural elements. However, being easy to cast and shape, it came to be extensively used in the classical world of Ancient Greece and Ancient Rome for piping and storage of water. It was also used as a mortar in stone buildings, and as a writing material. Smeltmills were water-powered mills used to smelt lead or other metals. The Roman lead smelting has led to evidence of global pollution. Greenland ice cores from 500 BCE to 300 CE show measurably elevated lead content in the atmosphere. [8] Researchers studying an ice core from Colle Gnifetti, in the Swiss part of the Monte Rosa massif, have found that higher historical European airborne lead pollution levels are associated with changes in the monetary system from gold to silver from the year 640 CE, with the principal source likely to be the Melle mines in France. Later airborne pollution, between the years 1170 and 1216 CE, correlates even more strongly with contemporaneous records of lead and silver production from mines in the Peak District of England, at levels similar to those seen in the Industrial Revolution. [9] [10] [11]
Georgius Agricola (1494–1555) presented details of lead smelting methods and facilities current in Europe in the first half of the 16th century in Book IX of his treatise on mining and metallurgy, De Re Metallica. Methods ranged from primitive open-hearth arrangements (essentially bonfires on which lead ore was piled) to blast furnaces capable of continuous operation. [12]
In the USA there are 400 forgotten lead smelting firms that operated in the 1930s to 1960s and may have deposited dangerous levels of lead contamination in nearby soil. [13]
Smelting is a process of applying heat and a chemical reducing agent to an ore to extract a desired base metal product. It is a form of extractive metallurgy that is used to obtain many metals such as iron, copper, silver, tin, lead and zinc. Smelting uses heat and a chemical reducing agent to decompose the ore, driving off other elements as gases or slag and leaving the metal behind. The reducing agent is commonly a fossil-fuel source of carbon, such as carbon monoxide from incomplete combustion of coke—or, in earlier times, of charcoal. The oxygen in the ore binds to carbon at high temperatures, as the chemical potential energy of the bonds in carbon dioxide is lower than that of the bonds in the ore.
Chalcopyrite ( KAL-kə-PY-ryte, -koh-) is a copper iron sulfide mineral and the most abundant copper ore mineral. It has the chemical formula CuFeS2 and crystallizes in the tetragonal system. It has a brassy to golden yellow color and a hardness of 3.5 to 4 on the Mohs scale. Its streak is diagnostic as green-tinged black.
In printing, type metal refers to the metal alloys used in traditional typefounding and hot metal typesetting. Historically, type metal was an alloy of lead, tin and antimony in different proportions depending on the application, be it individual character mechanical casting for hand setting, mechanical line casting or individual character mechanical typesetting and stereo plate casting. The proportions used are in the range: lead 50‒86%, antimony 11‒30% and tin 3‒20%. Antimony and tin are added to lead for durability while reducing the difference between the coefficients of expansion of the matrix and the alloy. Apart from durability, the general requirements for type-metal are that it should produce a true and sharp cast, and retain correct dimensions and form after cooling down. It should also be easy to cast, at reasonable low melting temperature, iron should not dissolve in the molten metal, and mould and nozzles should stay clean and easy to maintain. Today, Monotype machines can utilize a wide range of different alloys. Mechanical linecasting equipment uses alloys that are close to eutectic.
The general term slag may be a by-product or co-product of smelting (pyrometallurgical) ores and recycled metals depending on the type of material being produced. Slag is mainly a mixture of metal oxides and silicon dioxide. Broadly, it can be classified as ferrous, ferroalloy or non-ferrous/base metals. Within these general categories, slags can be further categorized by their precursor and processing conditions. Slag generated from the EAF process can contain toxic metals, which can be hazardous to human and environmental health.
A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally pig iron, but also others such as lead or copper. Blast refers to the combustion air being supplied above atmospheric pressure.
Industrial processes are procedures involving chemical, physical, electrical, or mechanical steps to aid in the manufacturing of an item or items, usually carried out on a very large scale. Industrial processes are the key components of heavy industry.
Copper extraction refers to the methods used to obtain copper from its ores. The conversion of copper ores consists of a series of physical, chemical, and electrochemical processes. Methods have evolved and vary with country depending on the ore source, local environmental regulations, and other factors.
The Betterton–Kroll Process is a pyrometallurgical process for refining lead from lead bullion. Developed by William Justin Kroll in 1922, the Betterton–Kroll process is one of the final steps in conventional lead smelting. After gold, copper, and silver are removed from the lead, significant amounts of bismuth and antimony remain. The Betterton–Kroll process is used to remove these impurities. In the process, calcium and magnesium are added to the molten lead at temperatures around 380 °C. The calcium and magnesium react with the bismuth and antimony in the bullion to form alloys with a higher melting point, which then can be skimmed off of the surface. This process leaves behind lead with less than 0.01 percent bismuth by weight. The process is crucial to cheap industrial lead smelting and offers significant advantages over more expensive processes like the Betts Electrolytic process and fractional crystallization.
Pyrometallurgy is a branch of extractive metallurgy. It consists of the thermal treatment of minerals and metallurgical ores and concentrates to bring about physical and chemical transformations in the materials to enable recovery of valuable metals. Pyrometallurgical treatment may produce products able to be sold such as pure metals, or intermediate compounds or alloys, suitable as feed for further processing. Examples of elements extracted by pyrometallurgical processes include the oxides of less reactive elements like iron, copper, zinc, chromium, tin, and manganese.
In metallurgy, refining consists of purifying an impure metal. It is to be distinguished from other processes such as smelting and calcining in that those two involve a chemical change to the raw material, whereas in refining the final material is chemically identical to the raw material. Refining thus increases the purity of the raw material via processing. There are many processes including pyrometallurgical and hydrometallurgical techniques.
Mount Isa Mines Limited ("MIM") operates the Mount Isa copper, lead, zinc and silver mines near Mount Isa, Queensland, Australia as part of the Glencore group of companies. For a brief period in 1980, MIM was Australia's largest company. It has pioneered several significant mining industry innovations, including the Isa Process copper refining technology, the Isasmelt smelting technology, and the IsaMill fine grinding technology, and it also commercialized the Jameson Cell column flotation technology.
Deoxidization is a method used in metallurgy to remove the rest of oxygen content from previously reduced iron ore during steel manufacturing. In contrast, antioxidants are used for stabilization, such as in the storage of food. Deoxidation is important in the steelmaking process as oxygen is often detrimental to the quality of steel produced. Deoxidization is mainly achieved by adding a separate chemical species to neutralize the effects of oxygen or by directly removing the oxygen.
A cupola or cupola furnace is a melting device used in foundries that can be used to melt cast iron, Ni-resist iron and some bronzes. The cupola can be made almost any practical size. The size of a cupola is expressed in diameters and can range from 1.5 to 13 feet. The overall shape is cylindrical and the equipment is arranged vertically, usually supported by four legs. The overall look is similar to a large smokestack.
Zinc smelting is the process of converting zinc concentrates into pure zinc. Zinc smelting has historically been more difficult than the smelting of other metals, e.g. iron, because in contrast, zinc has a low boiling point. At temperatures typically used for smelting metals, zinc is a gas that will escape from a furnace with the flue gas and be lost, unless specific measures are taken to prevent it.
The Chillagoe smelters is a heritage-listed refinery at Chillagoe-Mungana Caves National Park, Mareeba Mining District, Chillagoe, Shire of Mareeba, Queensland, Australia. It operated in the early 1900s. It is also known as Chillagoe State Smelters. It was added to the Queensland Heritage Register on 21 October 1992.
Cobalt extraction refers to the techniques used to extract cobalt from its ores and other compound ores. Several methods exist for the separation of cobalt from copper and nickel. They depend on the concentration of cobalt and the exact composition of the ore used.
The ISASMELT process is an energy-efficient smelting process that was jointly developed from the 1970s to the 1990s by Mount Isa Mines and the Government of Australia's CSIRO. It has relatively low capital and operating costs for a smelting process.
The Bottom-blown Oxygen Converter or BBOC is a smelting furnace developed by the staff at Britannia Refined Metals Limited (“BRM”), a British subsidiary of MIM Holdings Limited. The furnace is currently marketed by Glencore Technology. It is a sealed, flat-bottomed furnace mounted on a tilting frame that is used in the recovery of precious metals. A key feature is the use of a shrouded lance to inject oxygen through the bottom of the furnace, directly into the precious metals contained in the furnace, to oxidize base metals or other impurities as part of their removal as slag.
Agglomerate is a material composed of iron oxides and gangue, roasted and sintered in an agglomeration plant. This product is obtained by burning coal previously mixed with iron ore and oxides. This conditioning of iron ore optimizes its use in the blast furnace.
A water jacket furnace is a type of blast furnace used to smelt non-ferrous metallic ores, most typically ores of copper, lead, or silver-lead. It takes its name from the water jacket arrangement used to cool the lower furnace casing and prolong the life of the furnace hearth. It is sometimes referred to as a water-jacketed blast furnace, copper blast furnace, or lead blast furnace. The water jacket furnace is now virtually an obsolete technology for copper smelting, being nearly entirely replaced, by flash smelting of copper ore concentrates. It remains in use, in a modified form, for lead smelting.
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