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tin processing
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What is tin processing?
Tin processing prepares tin ore for use in various products. The principal tin mineral is cassiterite (SnO_2), which contains about 78.8 percent tin. Tin is a soft, ductile, silvery-white metal.
There are two methods of refining impure tin:
* Fire refining is commonly used and produces tin (up to 99.85 percent) suitable for general commercial use.
* Electrolytic refining is used on the products of complex ores and to produce a very high grade of tin (up to 99.999 percent).Most metallic tin is produced at smelters and refineries located near mining areas.
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Where does tin come from before it is processed?
Before processing, tin primarily comes from cassiterite (SnO_2), a naturally occurring tin oxide that contains approximately 78.8% tin. Though less significant, tin also occurs in complex sulfide minerals like stannite (Cu_2FeSnS_4) and cylindrite (PbSn_4FeSb_2S_14).
Economically viable cassiterite deposits are limited to specific geographic areas, with Southeast Asia, especially China, being the most important. Other major contributors include Myanmar, Thailand, Malaysia, Indonesia, Brazil, Australia, Nigeria, and Congo.
About 80% of the world's tin originates from alluvial or secondary deposits, commonly found on land, but also mined offshore in Indonesia and Thailand. Even in rich tin fields, the concentration of tin is very low; recovering one kilogram of cassiterite may require mining seven or eight tons of ore. Vein deposits, such as those in Bolivia and the United Kingdom, are recovered using underground hard-rock mining techniques.
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How is tin ore separated from other materials?
Tin ore, primarily cassiterite ($SnO_2$), is separated from other materials through various methods based on the properties of the minerals involved.
Alluvial fields, mined by gravel pumping, use high-pressure water jets to dislodge tin-bearing sand. The resulting slurry is then passed through sluice boxes, where the heavier cassiterite settles while lighter waste flows away.
Concentration methods leverage differences in mineral properties, such as density, to achieve separation. Gravity separation is commonly employed, using techniques like heavy-media separation, jigging, spirals, and shaking tables to isolate the heavier tin ore from lighter gangue.
More complex sulfide ores require froth flotation to produce a clean tin concentrate. Additionally, electrostatic methods are used in some plants to process cassiterite concentrates.
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What are the steps to turn tin ore into pure tin metal?
The process of turning tin ore into pure tin metal involves several steps. The primary ore used is cassiterite, which contains tin dioxide ($SnO_2$).
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Mining and Concentration Tin ore is mined using surface or underground techniques, and then concentrated using methods like gravel pumping, dredging, or froth flotation.
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Roasting and Leaching Low-grade concentrates are roasted at temperatures between 550 and 650 °C to remove sulfur and other impurities. The ore is then leached with water or acid solutions.
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Smelting The prepared furnace feed, containing tin oxide, carbon (as anthracite coal or coke), and limestone, is smelted in reverberatory, blast, or electric furnaces. The chemical reduction of tin oxide occurs by heating with carbon, producing tin metal and carbon dioxide gas.
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Refining The impure tin is tapped off and cast into slabs for further refining. The slag, which may still contain some tin, is retreated.
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Why is tin sometimes mixed with other metals?
Tin is often mixed with other metals to enhance its properties for various applications. Pure tin is relatively weak, so it is alloyed to improve its strength and other characteristics. Alloying can also lower the melting point of a metal. For example, adding lead to tin creates a solder with a lower melting point than either metal alone.
Some common tin alloys include bronzes, pewter, and bearing metals. These alloys are used in various applications, such as coatings, solders, and dental fillings. Small amounts of antimony, bismuth, copper, lead, silver, or gold are also added to prevent tin pest, the transformation of white tin to gray tin at low temperatures.
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What products or industries depend on processed tin?
Processed tin is essential to various products and industries because of its softness and ability to improve the properties of other metals. The major commercial applications of tin are in tinplate for packaging, solder alloys for electrical connections, and bearing metals for plain bearings. It is also used in tin and alloy coatings for corrosion protection and decorative finishes, pewter, bronzes, and fusible alloys.
Other uses include:
* The float-glass method of making glass sheet and plate
* Dental fillings
* Aerospace materials
* Cladding material for nuclear reactors1 Britannica SourceCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
tin processing, preparation of the ore for use in various products.
Tin (Sn) is a relatively soft and ductile metal with a silvery white colour. It has a density of 7.29 grams per cubic centimetre, a low melting point of 231.88 °C (449.38 °F), and a high boiling point of 2,625 °C (4,757 °F). Tin is allotropic; that is, it takes on more than one form. The normal form is white tin, or beta tin, which has a body-centred tetragonal crystal structure. The second allotrope, gray or alpha tin, has a face-centred cubic structure. Gray tin is theoretically stable below 13 °C (55 °F), but in practice it is readily formed only at about −40 °C (−40 °F). This transformation is difficult to initiate and is severely retarded by the presence of alloying elements or trace impurities. Nonetheless, it has given rise to the extremely rare laboratory curiosity known as tin pest.
Tin finds industrial application both as a metal and in chemical compounds. As a metal it is used in a very wide variety of industrial applications—but almost always in combination with other elements as an alloy or coating, since its intrinsic softness precludes its use as a structural material. Although tin is usually a minor constituent in alloys, it is an essential one on account of the way in which its special properties confer improvements to the matrix metal.
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The major commercial applications of tin are in tinplate, solder alloys, bearing metals, tin and alloy coatings (both plated and hot-coated), pewter, bronzes, and fusible alloys. In its chemical reactions, tin exists in two valence states (II and IV) and is amphoteric (able to react as both an acid and a base). In addition, it can link directly with carbon to form organometallic compounds. These properties have given rise to many important uses for tin chemicals—for example, in electroplating, agricultural and pharmaceutical products, and plastics and ceramics.
History
There is evidence from both archaeology and literature that tin was one of the earliest metals to be known and used. Its earliest application was as an alloy with copper to form bronze, which was fashioned into tools and weapons. Bronze articles (typically containing about 10 percent tin) have been found in the Middle East dating from about 3500 bce and in Egypt from 3000 bce. Other ancient civilizations also used bronze articles; for example, Chinese bronzes have been dated to about 2250 bce.
Tin was obviously an important item of trade from early times, as it is mentioned in at least three books of the Bible (Numbers, Isaiah, and Ezekiel) dating from as long ago as 700 bce.
Pewter is a tin alloy that also has a long history. Probably the oldest known piece, dating from about 1500 bce, was found in Egypt, but it was the Roman civilization that developed pewter ware for household vessels and ornamental use. These applications have continued to the present day, although the alloy compositions have changed markedly.
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The use of tin as a coating for other metals also has ancient historical roots, with tinned copper vessels for cooking tracing back to Roman times. Most important was the development of tinning iron sheet in order to form tinplate. This began in central Europe in the 14th and 15th centuries and gradually spread throughout the continent. The original uses of tinplate were for household articles, including lanterns, plates, and drinking vessels; however, with the introduction of food canning in 1812, packaging became the major use of tinplate.
An important date from more recent history is 1839, when the American metalsmith Isaac Babbitt first used tin-based alloys in bearings for machinery. Babbitt metal considerably aided the development of the industrial society. Further developments in tin alloys, coatings, and chemicals have contributed to advances in transport, telecommunication, aerospace, packaging, agriculture, and environmental protection.
Ores
The principal tin mineral is cassiterite, or tinstone (SnO2), a naturally occurring oxide of tin containing about 78.8 percent tin. Of less importance are two complex sulfide minerals, stannite (Cu2FeSnS4), a copper-iron-tin sulfide, and cylindrite (PbSn4FeSb2S14), a lead-tin-iron-antimony sulfide. These two minerals occur chiefly in lode deposits in Bolivia, often in association with other metals such as silver.
Unlike most base metals, economically viable deposits of cassiterite are restricted to a few geographic areas. The most important of these is in Southeast Asia and includes the tin-mining areas of China—which accounted for nearly half of all tin production in the early 21st century. Myanmar (Burma), Thailand, Malaysia, Indonesia, Brazil, Australia, Nigeria, and Congo (Kinshasa) are other major tin contributors. Minor producers are Peru, South Africa, the United Kingdom, and Zimbabwe. There is no significant tin deposit in the United States and only relatively small production in Canada.
About 80 percent of the world’s tin comes from alluvial or secondary deposits. Most of these occur on land, but in certain areas, notably in Indonesia and Thailand, the deposits are mined offshore by dredging the seabed.
Even in the richest tin fields, the concentration of tin is very low. This means that up to seven or eight tons of ore may have to be mined in order to recover one kilogram of cassiterite.