Light Metals Paper

Light Metals Extraction 306-457B

Titanium: An Overview of it’s Uses and Production

Geremi Vespa 9929399 December 7th, 2001

Table Of Contents 1. Introduction……………………………………………………..…………Page 3 2. Titanium Dioxide Properties and Uses…………………….…………..Page 4 3. Titanium Metal Properties and Uses……………………….….…….…Page 5 4. Titanium Ores……………………………………………….……..……..Page 6 5. Titanium Ore Processing…………………………………….….………Page 7 6. TiO2 Pigment Production………………………………………..……..Page 10 7. Titanium Metal Production………………………………….…….…...Page 11 8. Advancements in Titanium Metal Production…………….….....……Page 13 9. Conclusion………………………………………………….…….……..Page 14 10. References………………………………………………………………Page 15

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Introduction Titanium was discovered at the end of the eighteenth century. Reverend Wiliam Gregor discovered this previously unknown element while analyzing black magnetic sands in Cornwall, England. A few years later the German chemist M. H. Halproth applied the temporary name “titanium” to the new element. The name is derived from the Titans of Mythology, the first sons of the earth. To this day, the temporary name has remained. Titanium is extremely widely distributed. Small quantities of it can be found just about anywhere. In fact, titanium can even be found in stars, interstellar gas clouds and meteorites. Titanium is the 9th most abundant element in the earth’s crust, representing 0.57% of the total. In addition, titanium is the fourth most abundant structural metal (after aluminum, iron and magnesium). Titanium has many uses, both in its oxide and metal form. Its growth potential as a metal is extremely large if production costs can be improved. This paper’s goal is to inform the reader on the main aspects of titanium and titanium dioxide production, their uses and the advancements in their technology. There is much too much information available to go into great detail for a short paper, so I believe it is more valuable for the reader to be able to understand the basic concepts than to get lost in technicalities.

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Titanium Dioxide Properties and Uses Approximately 93% of the worldwide use of titanium is in its oxide form, titanium dioxide (TiO2). The special properties that make titanium dioxide so important are its high refractive index and good opacity at low particle size. In fact, it is the brightest white pigment with the highest opacity of any commercial product available. The following table compares the refractive index of TiO2 and some other materials: Table 1: Comparison of Refractive Index of Various Materials Refractive Index of TiO2, Fillers, and Binders Material

Refractive Index

Rutile TiO2

2.76

Anatase TiO2 Lithopone Zinc oxide White lead Calcium carbonate "China" clay Talc Silica Acrylics Polyethylene Polystyrene Water Air

2.52 2.13 2.02 2.00 1.57 1.56 1.50 1.48 1.50 1.51-1.54 1.59 1.33 1.00

The index of refraction is a measure of the retardation and redirection of a light wave passing through a medium. It is defined as: n = speed of light in a vacuum speed of light in a medium The decrease in speed is due to the scattering of the light (light has to travel a greater distance since). Therefore, a material with a high index of refraction scatters light very well. If enough light is scattered it appears white. This is due to the fact that light, on its own, is white. A material that absorbs all of incident light appears black, a material absorbs some light appears colored whereas a material that reflects all the incident light appear white. An object is deemed

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opaque if one cannot see through it. Therefore, obviously, opacity is a result of light scattering and absorption. In the western world, about 4 million tons of TiO2 are consumed every year. The main uses of TiO2 are as follows: 51% as a paint pigment, 19% for opacity and color base in plastics, and 17% for whiteness and paper finish in paper products. A pigment is a particulate material used to color and opacify a coating or film and for that reason TiO2 is used. Titanium dioxide is also used as a flux for welding rods, for UV protection in sunscreens, coloring in food and cosmetics, and in jewellery. Titanium Metal Properties and Uses Titanium metal is one of the most fascinating and most promising metal in the modern world. Titanium is an extremely strong, light metal. Titanium is as strong as steel but 45% lighter. It is twice as strong as aluminum and only 60% heavier. In addition, titanium has excellent corrosion resistant because of the formation of a stable oxide layer on the surface. This oxide layer causes the metal to passivate. Because of these properties, titanium metal finds all sorts of uses. It is used in propeller shafts, rigging and other parts of boats that are exposed to seawater. Titanium also finds use in key components of aircraft engines, missiles and rockets where strength, low weight and resistance to high temperatures are important. Titanium is nontoxic and resists human body fluids, making it biocompatible for use in the biomaterials field. It is used to create artificial hips, pins for setting bones and for other biological implants. The table on the nest page shows some mechanical properties of titanium and some titanium alloys.

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Table 1: Mechanical properties of titanium and titanium alloys Tensile Strength (MPa)

0.2 % Yield Strength (MPa)

Unalloyed Grades ASTM grade 1 ASTM grade 4

240 550

170 480

Alpha and Near-Alpha Alloys Ti-5Al-2.5Sn Ti-8Al-1Mo-1V Ti-2.5Al-11Sn-5Zr-1Mo Ti-6Al-2Sn-4Zr-2Mo

790 900 1000 900

760 830 900 830

Alpha-Beta Alloys Ti-6Al-4V Ti-6Al-2Sn-4Zr-6Mo Ti-3Al-2.5V

900 1170 620

830 1100 520

Beta Alloys Ti-3Al-8V-6Cr-4Mo-4Zr Ti-15V-3Cr-3Al-3Sn Ti-10V-2Fe-3Al

900 1000 1170

830 965 1100

Titanium Ores Since Titanium is very widely spread in the earth’s crust, it is present in many different ores. These include: Ilmenite (FeTiO3), Rutile (tetragonal TiO2), Brookite (rhombic TiO2), Perovskite (CaTiO2), Sphene (CaTiSiO5), and Geikielite (MgTiO3). The most common ores are Rutile and Ilmenite. Rutile is found in black sands found along sandy beaches. Ilmenite is even more common than rutile and can be also be found in black sands as well as in hard-rock deposits. The TiO2 content in the two most common ores is displayed on the following page.

Table 2: TiO2 Content in Rutile and Ilmenite

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Titanium Ore

% TiO2

Ilmenite

40 - 60

Rutile

90 - 95

Titanium Ore Processing Rutile ores require very little processing due to the fact that they already contain a high content of titanium. Therefore, the processing of an ilmenite (FeTiO3) ore will be explained. Pure titanium dioxide is needed for both the production of TiO2 pigments and titanium metal. The first step in the mining of an ilmenite ore is to remove the ore from the ground. In the case of black sands this is fairly easy, but for hard rock deposits the ore must be blasted using explosives. The next steps are crushing, screening and gravity separation. The crushing and screening is performed to reduce the particle size of the material and the gravity separation partitions the material because of the large density of the iron in the ilmenite. This gravity separation is done wet and must therefore be dried before further separated by electrostatic and magnetic separation. Electrostatic separation uses a strong electric field to separate substances with different electrical properties. Magnetic separation is similar but uses the difference in magnetic properties. The Iron in the Ilmenite is obviously the element with the good electrical and magnetic properties. After all these separation processes, an Ilmenite concentrate is produced. Since Ilmenite contains significant amounts of iron it, titanium production is often combined with steel production. For example, a flow sheet for Quebec’s QIT (world’s largest Ilmenite concentrate producer) is as follows:

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Figure 1: QIT flow sheet

The enrichment step in the flow diagram consists of oxidizing any sulfur in the concentrate. The reduction step is performed in an electric arc furnace at approximately 60 megawatts and 1700oC. High temperatures make the reaction thermodynamically favorable. Coke is also added in the furnace and the reaction is as follows: Fe2O3.TiO2 + 3C(s)  2Fe(C) + TiO2 + 3CO Molten iron forms on top of a layer of slag. This slag contains about 80% TiO2. This slag can be sent to the chloride of sulfate process (discussed later) or further refined to produce synthetic rutile. Synthetic rutile is produced by leaching the slag with hydrochloric acid. The iron dissolves but titanium dioxide is unaffected by the acid. The product becomes 94.5% TiO2. There are two main methods of further refinining TiO2: the chloride and sulfate process. A flow sheet of the two processes is shown below.

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Figure 2: Sulfate and Chloride Process Comparison

The Sulfate process is used for lower grade feedstocks than the Chloride process. The first step is to leach the ilmenite with sulfuric acid at 150-180oC. The undissolved solids are then removed and the liquid is evaporated and cooled. The precipitated FeSO4.7H2O are filtered off and the filtrate is concentrated to approximately 230 g/l. The Digestion/Crystallization reaction is: 5H2O + FeTiO3 + 2H2SO4  FeSO4.7H2O + TiOSO4 o

A hydrolysis is then performed at 90 C according to the following reaction: TiOSO4 + 2H2O  TiO(OH)2 + H2SO4 The TiO(OH)2 is then washed using water and sulfuric acid, and then calcined at o

1000 C to TiO2. Overall, the Sulfate process consumes about 2500 kWh/t and produces 6 tons of waste per ton of TiO2 manufactured.

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The Chloride process accounts for 60% of the worlds TiO2 production. A highgrade feedstock is needed (>70% TiO2) so usually this method is used to process rutile or synthetic rutile. The main step in this production method is chlorination in a fluidized-bed reactor at 925-1010oC with the addition of coke. The reaction is: TiO2 + 2C +2Cl2  2CO + TiCl4 The purification of the TiCl4 is performed by fractional distillation. The pure TiCl4 is then oxidized at 985oC to produce very pure TiO2 and the chlorine gas is recycled. The Chloride process consumes about 1800 kWh/t and produces around 1 ton of waste per ton of TiO2 manufactured. The lower energy consumption and waste production is directly related to the fact that there are less impurities (e.g. Iron) that must be removed due to the high-grade ore feed. TiO2 Pigment Production After producing pure titanium dioxide by either the sulfate or chloride process the TiO2 must be further milled, classified and surface treated before shipment to customers. The milling and classifying of the TiO2 particles is done in order to increase opacity of the particles. A pure single crystal of TiO2 is colorless and is, in fact, often used for imitation diamond jewelry. The sparkle that is needed in jewelry is obtained because of the high refractive index of TiO2 but because there are only a few scattering surfaces, the crystal is transparent. For use in pigments, the optimum particle size must be around half the wavelength of visible light, or 0.3 microns. The target mean size for pigments is usually between 0.20-0.25 microns. The TiO2 particles are surface treated for many reasons. They include: improved wetting and dispersion in various media, improved compability with the binder (used for agglomeration) and dispersion stability, improved color stability and durability. While the surface treatments vary, they are usually a combination of alumina, silica and/or zirconia which are applied by a wet precipitation process. 10

Lastly, a coating with an organic is then performed to enhance the dispersion of the pigment. Titanium Metal Production There are many different methods of producing titanium metal. Its production needs to be very precise as hot titanium metal easily reacts with oxygen, nitrogen and moisture in the air. These contaminants render the metal so hard and brittle that it is useless. The main methods of producing titanium metal are the Kroll and Hunter processes. In all titanium metal production processes, the metal must be produced under an inert atmosphere due to titanium’s susceptibility to hydrogen and oxygen embrittlement. A brief introduction into the other available methods will be discussed as well. The Kroll process is the most common method of producing titanium. In fact, it is the only process currently used in the United States. The first step is to produce high purity TiCl4. This is achieved by a chlorination step. Magnesium metal is then introduced into a stainless steel retort filled with inert argon gas, heated at 800-900oC and TiCl4 is slowly sprayed into the retort over a couple of days. The reaction is as follows: TiCl4 + 2Mg  Ti + 2MgCl2 To complete the reaction anywhere between 15 and 30 % excess magnesium is needed. The product is called “titanium sponge” and contains some residual magnesium and magnesium chloride. Vacuum distillation or helium sweep leaching removes these.

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The Hunter process is similar to the Kroll process but it uses sodium as a reductant. The process can be a one step reduction reaction: TiCl4 + 4Na  Ti + 4NaCl The process has also been modified into a 2-step process. The first step is to react molten sodium and TiCl4 at 200oC to form TiCl2. Secondly, the TiCl2 is put into a retort containing more sodium metal which completes the reduction reaction. The obtained product is a 4 part NaCl to 1 part Ti mixture. The NaCl is removed by leaching with hydrochloric acid. Kroll predicted that by the late 1960’s, an electrolytic method for the production of titanium would replace the Kroll process. To this date, his prediction has not materialized. However, it is not due to a lack of effort. Many different attempts to produce titanium via an electrolytic method have failed. The most promising method today is the FCC Cambridge process. This process is the reduction of TiO2 in a bath of calcium chloride between 900-1000oC. The cathode consists of pellets of TiO2 pressed together and a graphite anode. The key to this method is the low operation point. Since the melting point of titanium is never achieved, its reactivity with other elements is not a big problem. British Titanium plc (Bti) is in the process of running a pilot plant according to this method. Results, thus far, are promising. A pilot plant capable of producing 1 kg batches of titanium metal has achieved excellent results and a larger plant has been designed to demonstrate the technology on a greater scale. Other attempted methods to producing titanium metal are: a vapor-phase process, molten salt process, plasma process and the AlTi process. The vaporphase process and the molten salt process both have the goal to make the hunter or Kroll process continuous. The plasma and AlTi process are two exotic methods that have failed.

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Advancements in Titanium Metal Production The high cost of titanium metal has been the limiting factor as far as market growth goes. The following graph shows a correlation between price and annual consumption. Figure 2: Consumption/Price of Ti comparison

A potentially large increase in the use of titanium could be for use in the automobile industry. Several components have been identified that could be replaced by titanium or titanium alloys. However, the price of titanium production must be greatly reduced. For use in most automobile applications the cost of titanium must be no more than 4$/lb. The Kroll and Hunter process are both batch processes. The Kroll process is cheaper than the Hunter process due to the reducing agent and the operating temperatures. While some improvements are possible, major changes are improbable. In addition, many of the exotic methods will most likely not lower titanium production prices. The most promising method is the FCC Cambridge process. Should the process prove to be successful the cost of titanium production would drop significantly due to the lower feed and reagent costs.

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Conclusion Titanium is one of the most promising structural light metals. It has the potential for use in many industries and applications. The combination of its strength and weight give it a significant advantage over more commonly employed materials. The main use of titanium is as titanium dioxide. Titanium dioxide is used as a pigment for the paint, plastic and paper industries. It is produced by either the Sulfate or Chloride process. Titanium metal is used in many applications. The main methods of producing titanium are by the Kroll or Hunter process. Low cost titanium would greatly increase its market. Many attempts have been made to lower its production cost and the most promising is the FCC Cambridge process. This process is the direct electrolytic reduction of TiO2. Titanium is a fascinating metal with unique properties that set it aside from many other materials. Titanium will continue to be the object of research and developed for many years to come.

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References Barksdale, Jelks. Titanium: Its Occurrence, Chemistry and Technology. The Ronald Press Company. New York, 1966. Froes, F. H. (1998, September) Titanium and Other Light Metals: Let’s Do Something About Cost. JOM, 15. Andre Gagne. Work Term Report, QIT, Work Term #1 Hartman, A. D., Gerdemann, S. J., Hansen, J. S. (1998, September) Producing Lower-Cost Titanium for Automobile Applications. JOM, 16-19. Kirk-Othmer. Encylopedia of Chemical Technology, 4th ed. 1992. McQuillan, D., McQuillan, M. K. Metallurgy of the Rarer Metals: Titanium. Butterwoths Scientific Publications. London, 1956. http://www.dupont.com/tipure/coatings/index.html http://www.nl-ind.com/kronos/na/titanium2.html http://www.britishtitanium.co.uk/ http://www.consrutile.com.au/ABOUTCRL/dwnstream.htm http://www.austpacresources.com http://www.qit.com http://www.kemira.com http://www.webelements.com http://www.mic-global.com

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