Ilmenite for pigment and metal production

Low-grade ilmenite can be leached with concentrated HCl at atmospheric pressure and at 80°C. After filtration to separate insoluble matter the solution containing TiO2+ and Fe2+ is heated to precipitate titanium hydroxide and recover HCl. The titanium hydroxide is then calcined to synthetic rutile containing 95+%TiO2 while FeCl2 is subjected to oxyhydrolysis or fluidized be to recover HCl and Fe2O3. The process naturally can be applied to high grade ilmenite. It bypasses electric furnace process which applies only to high grade ilmenite and is superior to the sulfuric acid process which is highly pollutant. The product of this process can be used to prepare the white pigment as well as titanium metal. Correspondence to: Fathi Habashi, Department of Mining, Metallurgical, and Materials Engineering Laval University, Quebec City, Canada, Tel: [418] 651 5774, E-mail: Fathi.Habashi@arul.ulaval.ca


Introduction
The major titanium minerals are rutile, TiO 2 and ilmenite, FeTiO 3 (Figure 1 and 2). Rutile is easy to process to titanium metal or TiO 2 pigment by the chlorination method while ilmenite is more complicated because of its high iron content. Since the world reserves of titanium are 90% in the form of ilmenite and only 10% in the form of rutile, the treatment of ilmenite is evidently an important question in metallurgy [1,2].
Ilmenite deposits may be massive as in Province of Quebec ( Figure  3) or as black sands ( Figure 4) associated with magnetite, monazite, and other valuable minerals which are separated by physical methods ( Figure 5). In the first magnetic separation a weak magnet is used to separate magnetite while in the second magnetic separation a highintensity magnet is used to separate ilmenite.  to crystallize FeSO 4 ·7H 2 O which was then centrifuged. Titanium oxide is then precipitated from solution by dilution and seeding resulting in the formation of dilute H 2 SO 4 for disposal (Figures 8 and 9). However, the largest producer of pigment in Salvador, Brazil still uses this technology because it disposes the waste products in the ocean which are removed by the tide.

Separation of iron
Because of the pollution problems associated with the disposal of dilute sulfuric acid and FeSO 4 , iron in the ore is separated at an early stage. This is achieved in two ways: by electric furnace and by hydrometallurgical routes.

Electric furnace process
The electric furnace method was developed in 1950s [5]. The ore was mixed with a certain amount of anthracite which was just enough to reduce the iron oxide component of the ore, then charged in an electric furnace at 1 650°C where iron oxide is reduced to metal while titanium is separated as a slag ( Figure 11). The reactions taking place during reduction are the following: This method is used by the Rio Tinto QIT at its plant in Sorel near Montreal and at Richards Bay in South Africa. It is also used in the Soviet Union at Zaporozhye (Ukraine) and in Japan.
Titanium slag is mainly iron magnesium titanate, (Fe,Mg)Ti 4 O 10 , and a small amount of silicates; typical analyses is 72-85% total TiO 2 . A small amount of TiO 2 is reduced to Ti 2 O 3 . The reduction of the iron oxides is not taken to completion so that some iron oxide is left in the slag to decrease its melting point. Melting point of TiO 2 1840°C and ilmenite 1435°C.
The slag is high in titanium and low in iron ( Figure 12) and is therefore preferable to ilmenite in manufacturing TiO 2 pigment or titanium metal. However, the slag produced in Quebec is not suitable for chlorination because of its high impurity level -about 16.6% as compared to about 6% in other slags [6]. These impurities will not only consume unnecessary amounts of chlorine but also will create a disposal problem. Furthermore, some of these impurities, e.g., calcium and magnesium will interfere with the chlorination process itself which is conducted at 800°C by forming a molten phase (CaCl 2 m.p. 770°C, MgCl 2 m.p. 708°C).
For these reasons, titanium slag was used only for making pigment by the sulfuric acid process [7]. The slag was treated in the same way as ilmenite with the exception that no separation of ferrous sulfate was necessary because the bulk of iron was already separated by reduction in the earlier step ( Figure 13). The sulfuric acid treatment process of the slag, however, still suffered from the disposal problem of the waste acid and as a result it was abandoned in the 1980s and replaced by a new technology based on upgrading the slag to 94.5% TiO 2 by leaching away most of the impurities by HCl under pressure to render it suitable for chlorination.

Hydrometallurgical route
The hydrometallurgical route was developed in 1960s and involved leaching of iron from ilmenite and obtaining a residue rich in titanium (90-95% TiO 2 ) known as "synthetic rutile" [8]. In one case, the Altair     process, a pigment grade TiO 2 was obtained. All these processes use an oxyhydrolysis process for treating ferrous chloride to get HCl for recycle and Fe 2 O 3 as a by-product.

High-pressure method
In this method, high grade ilmenite is decomposed in autoclaves by 20% HCl at 120°C and 200 kPa; iron is solubilized as ferrous chloride leaving a solid containing about 95% TiO 2 which has the chemical analysis to rutile that us why it called synthetic rutile (Figure 14): Low grade ilmenite cannot be treated by this method since all silicates and insoluble matter will contaminate the product. The synthetic rutile is then treated by chlorine to prepare TiCl 4 from which TiO 2 or titanium metal are obtained without pollution problems. The process is used in the USA, England, Japan, Taiwan, and Australia. Oxyhydrolysis could be conducted in a variety of ways as described below.

Atmospheric process
In 2014 it was found by Magpie Incorporation in Canada [9] that low grade ilmenite can be dissolved at 80°C with concentrated HCl at atmospheric pressure. After filtration to remove insoluble matter, the solution is distilled to recover HCl and to hydrolyse titanyl ion to TiO 2 . After filtration, the residue is calcined to produce synthetic rutile ( Figure 16): It is evident that the new leaching technology at ambient pressure is superior to the old electric furnace smelting-autoclave upgrading.

Oxyhydrolysis
Ferrous chloride solution is regenerated to HCl and Fe 2 O 3 by oxyhydrolysis: It is the same technology that is used for treating pickle solution. Two methods are used

Fluidized-bed oxyhydrolysis
In a fluidized-bed reactor the ferrous chloride solution is introduced onto a large bed of hot ferric oxide where heating is provided by the hot fluidizing combustion gases ( Figure 17). As the combustion gas flows through the well agitated bed of oxide it quickly reaches thermal equilibrium with the bed. The solution is fed on top of the bed of oxides. The liquid feed wets the outer layer of the hot oxide particles and is quickly evaporated to form an onion-like layer of new solid oxide on top of the existing oxide, thereby producing dense homogeneous particles.

Spray roaster oxyhydrolysis
In this type of oxyhydrolysis roaster, the ferrous chloride solution is sprayed into an empty cylindrical vessel, while the required energy   is supplied by the up flow of hot gases generated in the bottom burners ( Figure 18). Spray roasters have large diameters to keep the gas velocities low. If the gas velocity is high, too many particles are elutriated with the off-gas, and the product quality and the efficiency of the roaster drop. The off-gas and oxides leave the roaster countercurrently at about 400°C to 500°C. The residence time of the sprayed particles in the high-temperature reaction zone is very short; therefore, very small liquid droplets, which can be quickly heated, should be created by atomization. The fast heat-up results in the formation of a solid oxide crust on the surface of each droplet. As the bulk of the droplet heats, the water content vaporizes and breaks through the oxide shell. Therefore, the spray roasted oxide is composed of very fine "fluffy," hollow spheres.

Production of titanium
Metallic titanium is produced by chlorination of rutile, synthetic rutile, or titanium slag then reduction in a metallothermic reactor of TiCl 4 by magnesium to titanium (Figures 19 and 20 Magnesium chloride is then electrolyzed to get back the magnesium and chlorine for recycle. Figure 21 shows the metallothermic reactor removed from the furnace after reduction from which titanium sponge is recovered (Figure 22).