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titanium processing
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What is titanium processing?
Titanium processing involves extracting titanium from its ores and preparing titanium alloys or compounds for various applications. The preparation of pure titanium is difficult because of its reactivity. In the Kroll process, titanium tetrachloride (TiCl_4) is derived from ilmenite ((FeTiO_3)) or rutile ((TiO_2)). (TiCl_4) is reduced with either sodium (Na) in the Hunter process, or with magnesium (Mg) in the Kroll process, in sealed steel vessels at approximately 800 to 1,000 °C (1,450 to 1,800 °F) under an inert argon atmosphere. This produces titanium in a porous form called sponge, which is then crushed, and the metal and salts are separated.
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Where does titanium come from?
Titanium is abundant, ranking as the fourth most plentiful structural metal in the Earth's composition. It constitutes about 0.44 percent of the Earth’s crust and is found in nearly all rocks, sand, clay and soils. Deposits of titanium ore are located worldwide, including in Australia, the United States, Canada, and South Africa.
The primary titanium-bearing minerals are rutile, composed of approximately 95% titanium dioxide, and ilmenite, containing 50 to 65% titanium dioxide. These minerals are commonly found in alluvial and volcanic formations, with deposits typically containing between 3% and 12% heavy minerals like ilmenite, rutile, leucoxene, zircon, and monazite.
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How is titanium separated from its ores?
Titanium is extracted from its ores through complex processes due to its high reactivity with elements like oxygen and nitrogen. The process typically involves converting titanium oxide ((TiO_2)) to titanium tetrachloride ((TiCl_4)). This is done by reacting oxide ores with chlorine in a fluidized bed of petroleum coke.
[
TiO_2(s) + 2Cl_2(g) + C(s) \rightarrow TiCl_4(g) + CO_2(g)
]The raw (TiCl_4) is then purified through distillation to remove impurities. To obtain pure titanium metal, (TiCl_4) is reduced using either sodium in the Hunter process or magnesium in the Kroll process, in an inert argon atmosphere at high temperatures (800 to 1,000 °C). This produces titanium in the form of a porous sponge, which is then separated from the resulting salts (like (NaCl) or (MgCl_2)) through acid leaching or vacuum distillation.
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What are the main steps involved in making pure titanium metal?
The production of pure titanium metal involves several steps. The process begins with titanium ore, such as ilmenite or rutile, which is treated with carbon and chlorine at red heat to produce titanium tetrachloride (TiCl_4). The TiCl_4 is purified by fractional distillation to remove impurities like ferric chloride (FeCl_3).
Next, the purified TiCl_4 is reduced with molten magnesium (Kroll process) or sodium (Hunter process) at approximately 800 to 1,000 °C in an inert argon atmosphere. This reaction yields titanium in the form of a porous material called sponge, with salts like NaCl or MgCl_2 trapped within. The titanium sponge is then crushed, and the salts are separated through either a dilute acid leach or high-temperature vacuum distillation. The resulting purified titanium sponge is then consolidated into titanium ingot by consumable-electrode arc-melting in a vacuum or argon environment.
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Why is titanium difficult to process compared to other metals?
Titanium is difficult to process due to its high reactivity with oxygen, nitrogen, and hydrogen at elevated temperatures. This necessitates complex and costly production and fabrication processes. Unlike many metals, titanium cannot be obtained by reducing its oxide with carbon because it readily forms a stable carbide. Moreover, at high temperatures, titanium is very reactive towards oxygen and nitrogen. The Kroll process, used to prepare pure titanium, involves treating ores with carbon and chlorine at red heat to yield titanium tetrachloride, which is then reduced with molten magnesium in an argon atmosphere.
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What are some important uses of titanium that rely on its processing methods?
Titanium's properties, enhanced by specific processing methods, make it invaluable across industries. Its resistance to corrosive environments allows it to be used in chemical processing, where it improves processes and reduces corrosion issues.
In the chlorine industry, coating titanium with platinum-group metals creates anodes that resist corrosion, lowering costs and improving product purity. The aerospace industry relies on titanium alloys for their high strength-to-weight ratio in gas turbines and airframes. Titanium is also used in medical prostheses due to its strength, light weight, and compatibility with body fluids.
The Kroll and Hunter processes are also essential for extracting titanium. These methods involve reducing titanium tetrachloride with magnesium or sodium in an inert atmosphere to produce titanium sponge, which is then processed further.
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titanium processing, the extraction of titanium from its ores and the preparation of titanium alloys or compounds for use in various products.
Titanium (Ti) is a soft, ductile, silvery gray metal with a melting point of 1,675 °C (3,047 °F). Owing to the formation on its surface of an oxide film that is relatively inert chemically, it has excellent corrosion resistance in most natural environments. In addition, it is light in weight, with a density (4.51 grams per cubic centimetre) midway between aluminum and iron. Its combination of low density and high strength gives it the most efficient strength-to-weight ratio of common metals for temperatures up to 600 °C (1,100 °F).
Because its atomic diameter is similar to many common metals such as aluminum, iron, tin, and vanadium, titanium can easily be alloyed to improve its properties. Like iron, the metal can exist in two crystalline forms: hexagonal close-packed (hcp) below 883 °C (1,621 °F) and body-centred cubic (bcc) at higher temperatures up to its melting point. This allotropic behaviour and the capacity to alloy with many elements result in titanium alloys that have a wide range of mechanical and corrosion-resistant properties.
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Although titanium ores are abundant, the high reactivity of the metal with oxygen, nitrogen, and hydrogen in the air at elevated temperatures necessitates complicated and therefore costly production and fabrication processes.
History
Titanium ore was first discovered in 1791 in Cornish beach sands by an English clergyman, William Gregor. The actual identification of the oxide was made a few years later by a German chemist, M.H. Klaproth. Klaproth gave the metal constituent of this oxide the name titanium, after the Titans, the giants of Greek mythology.
Pure metallic titanium was first produced in either 1906 or 1910 by M.A. Hunter at Rensselaer Polytechnic Institute (Troy, New York, U.S.) in cooperation with the General Electric Company. These researchers believed titanium had a melting point of 6,000 °C (10,800 °F) and was therefore a candidate for incandescent-lamp filaments, but, when Hunter produced a metal with a melting point closer to 1,800 °C (3,300 °F), the effort was abandoned. Nevertheless, Hunter did indicate that the metal had some ductility, and his method of producing it by reacting titanium tetrachloride (TiCl4) with sodium under vacuum was later commercialized and is now known as the Hunter process. Metal of significant ductility was produced in 1925 by the Dutch scientists A.E. van Arkel and J.H. de Boer, who dissociated titanium tetraiodide on a hot filament in an evacuated glass bulb.
In 1932 William J. Kroll of Luxembourg produced significant quantities of ductile titanium by combining TiCl4 with calcium. By 1938 Kroll had produced 20 kilograms (50 pounds) of titanium and was convinced that it possessed excellent corrosion and strength properties. At the start of World War II he fled Europe and continued his work in the United States at the Union Carbide Company and later at the U.S. Bureau of Mines. By this time, he had changed the reducing agent from calcium to magnesium metal. Kroll is now recognized as the father of the modern titanium industry, and the Kroll process is the basis for most current titanium production.
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A U.S. Air Force study conducted in 1946 concluded that titanium-based alloys were engineering materials of potentially great importance, since the emerging need for higher strength-to-weight ratios in jet aircraft structures and engines could not be satisfied efficiently by either steel or aluminum. As a result, the Department of Defense provided production incentives to start the titanium industry in 1950. Similar industrial capacity was founded in Japan, the U.S.S.R., and the United Kingdom. After this impetus was provided by the aerospace industry, the ready availability of the metal gave rise to opportunities for new applications in other markets, such as chemical processing, medicine, power generation, and waste treatment.
Ores
Titanium is the fourth most abundant structural metal on Earth, exceeded only by aluminum, iron, and magnesium. Workable mineral deposits are dispersed worldwide and include sites in Australia, the United States, Canada, South Africa, Sierra Leone, Ukraine, Russia, Norway, Malaysia, and several other countries.
The predominate minerals are rutile, which is about 95 percent titanium dioxide (TiO2), and ilmenite (FeTiO3), which contains 50 to 65 percent TiO2. A third mineral, leucoxene, is an alteration of ilmenite from which a portion of the iron has been naturally leached. It has no specific titanium content. Titanium minerals occur in alluvial and volcanic formations. Deposits usually contain between 3 and 12 percent heavy minerals, consisting of ilmenite, rutile, leucoxene, zircon, and monazite.
Mining and concentrating
Although workable known reserves of rutile are diminishing, ilmenite deposits are abundant. Typical mining is by open pit. A suction bucket wheel on a floating dredge supplies a mineral-rich sand to a set of screens called trommels, which remove unwanted materials.
Typically, the minerals are separated from waste material by gravity separation in a wet spiral concentrator. The resulting concentrates are separated by passing them through a complex series of electrostatic, magnetic, and gravity equipment.