Materials Transactions, Vol. 54, No. 8 (2013) pp. 1444 to 1453 ©2013 The Mining and Materials Processing Institute of Japan

Removal of Iron from Titanium Ore through Selective Chlorination Using Magnesium Chloride

Jungshin Kang1,+ and Toru H. Okabe2

1Department of Materials Engineering, Graduate School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan 2Institute of Industrial Science, The University of Tokyo, Tokyo 153-8505, Japan

A selective chlorination process using magnesium chloride (MgCl2) as chlorinating agent was investigated with the aim of developing a process for removing iron directly from ilmenite, which is a low-grade titanium ore known as FeTiO3. Two crucibles, one consisting of titanium ore and the other consisting of a mixture of titanium ore and MgCl2, were placed in a gas-tight quartz tube, and then both crucibles were heated to 1000 K. In some experiments, H2O vapor was introduced in the quartz tube. HCl gas produced from the MgCl2/titanium ore mixture reacted with the iron present in the titanium ore placed in the other crucible to produce TiO2. Iron present in the titanium ore of the titanium ore/MgCl2 mixture reacted with MgCl2, and MgTiO3 and MgO were obtained. Iron in the titanium ore present in both crucibles was removed as FeCl2 (l,g). In these experiments, the effects of the particle size of the titanium ore and the atmosphere on selective chlorination were investigated. In addition, titanium ores produced in Vietnam, Australia and China were used as feedstocks. By the chlorination process, 97% TiO2 was obtained directly in one step from the low-grade titanium ore containing 51% TiO2 under certain conditions, thus demonstrating the feasibility of the selective chlorination process for producing high-purity titanium dioxide from low-grade titanium ore. [doi:10.2320/matertrans.M-M2013810]

(Received March 26, 2013; Accepted May 15, 2013; Published July 25, 2013) Keywords: ilmenite, titanium ore, selective chlorination, synthetic rutile, iron removal, titanium smelting

1. Introduction Ilmenite (rock) Ilmenite (sand) Rutile : 30 – 50% TiO2 : 35 – 65% TiO2 : 95% TiO2 Titanium (Ti) is widely used in various fields because of its excellent properties such as high strength to density ratio and Slag process high corrosion resistance; in addition, titanium is the ninth 1) most abundant element on the Earth’s crust. However, 75 – 86% TiO2 (Ti slag) titanium is still used to a much lesser extent than iron (Fe) or aluminum (Al), mainly because of low productivity and UGS process Becher process Benilite process 1) high production costs involved at all processing stages. For 95% TiO2 90 – 93% TiO2 95% TiO2 example, the cost of processing titanium ore is 15 times higher (Upgraded slag) (Synthetic rutile) than that required for processing iron ore.2­5) To reduce the Sulfate process Chloride process Kroll process production costs, it is imperative to improve the early stages of titanium production by developing a simple and effective Titania pigment Titanium processes for processing titanium ore to titanium metal. (5.1Mt TiO2 / year world) (0.1Mt Ti / year world) Ilmenite and rutile are the key minerals used for titanium Fig. 1 Currently used process for titania pigment and titanium produc- production. Chemical formula of ilmenite is FeTiO3 with tion.1,6,8,9) 30­65% TiO2, while that of rutile is TiO2 with 95­100% 1,6,8,9) TiO2. If we consider only the concentration of TiO2, rutile will be the most appropriate feedstock for the to reduce the amount of iron in the TiO2 ore feed for reducing manufacture of titania (TiO2) pigment or titanium metal. the amount of chloride wastes and the chlorine loss during the However, ilmenite is used much more extensively as a chloride process16) or the Kroll process.17) Many companies feedstock. For example, the global production of ilmenite was place a lower limit on the purity of TiO2 feed before placing eight times higher than that of rutile in 2011.7) This is because the feed into the chlorinator. Usually the feeds containing at 18,19) the price of ilmenite is much lesser than that of rutile. Further, least 90% of TiO2 are used. Some countries including ilmenite is much more readily available than rutile, with the Japan have much more strict criteria for a purity of TiO2 feed, 7) share of ilmenite in the world mine reserves being 94%. and a purity of over 95% TiO2 is required in the Kroll process. Therefore, the role of ilmenite as the source for the titanium However, due to the increase in the price of the TiO2 feed by, mineral is expected to become gain more significance. for example, the increase in the consumption of TiO2 feed in As shown in Fig. 1, several processing stages are generally China, recently, some companies in Japan have begun to use 20) required for removing iron from titanium ore for producing 90% TiO2 feed in order to reduce the cost of the feedstock. TiO2 pigment or titanium metal using ilmenite as the In the Becher process, various types of titanium ores are feedstock.1,6,8,9) In many cases, first, ilmenite is upgraded to used as feedstocks.21) However, multiple stages are required 10,11) high purity TiO2 by the Becher process, the Benilite for treating iron, and a huge amount of iron compounds are process,12­14) or the slag production process.15) It is important dumped as wastes. In the Benilite process, processing of iron is simpler than the other processes. However, this process +Graduate Student, The University of Tokyo. Corresponding author, makes use of highly concentrated 18­20% HCl and only E-mail: [email protected] limited types of titanium ore is used as a feedstock.21) In the Removal of Iron from Titanium Ore through Selective Chlorination Using Magnesium Chloride 1445

Chlorinating agents

slag process, iron in the titanium ore is reduced to metal by This study a carbothermic reaction, and TiO2 slag and iron metal are * separated. The scale of the slag process is large, and it is high Ilmenite (FeTiO3) HCl MgCl2 Ilmenite (FeTiO3) H2O speed process. However, TiO2 with a low purity of 75­86% is Selective chlorination Selective chlorination obtained. For obtaining high purity TiO2 slag, it is essential to

employ additional upgrading process such as the upgrade HCl recovery H O TiO FeCl FeCl MgTiO / MgO HCl slag (UGS) process,15) which entails multiple steps for the 2 2 2 2 3 further removal of iron. * Extensive research has been conducted to improve the Ti scrap currently used upgrading processes of titanium ore. Among Titanium metal production Chlorine recovery the various processes, selective chlorination has gained fi signi cant attention. In the selective chlorination process, Ti metal Fe TiCl4 iron is only removed directly from the titanium ore as iron chlorides and high purity TiO is obtained. The selective Fig. 2 Flow diagram of the selective chlorination process investigated in 2 the present study. chlorination processes investigated so far have entailed 22­25) the use of chlorine gas (Cl2) under carbon or CO/Cl2 mixture atmosphere,26­28) or metal chlorides as the chlorine Gas outlet / Not used under vacuum and Ar atmosphere source.29­32) Among these processes, the first two processes Electric furnace Heater require Cl2 gas and installation of the reactor become costly Quartz crucible Mo-lined and it also has environmental issue for operation. quartz crucible Silicone Quartz Quartz The selective chlorination process that uses metal chlorides rubber plug wool [Mo] Ti ore MgCl was recently developed by Okabe et al.29,30) In recent studies, Quartz tube Ti ore 2 the authors investigated further improvement of the selective Vacuum or chlorination using calcium chloride (CaCl2) as the chlorinat- Gas inlet % Water bubbler used ing agent, and 97 TiO2 was successfully obtained directly Gas outlet Ar 31,32) Thermocouple under Ar + H O gas from titanium ore containing 51% TiO2 in a single step. 2 atmosphere only However, because CaCl2 was used as chlorinating agent, it MFC was needed to decrease the activity of CaO by the production Water Empty of complex oxides such as CaTiO for producing HCl gas. 3 Pump Pressure Temp. In addition, high purity TiO2 could not be obtained when the controller experiment was conducted under Ar gas flow atmosphere. gauge Recently, on the basis of thermodynamic analysis,33) it was Fig. 3 Schematic of the experimental apparatus used in the present study. anticipated that extracting chlorine source such as HCl gas from MgCl2 rather than CaCl2 is easier because HCl gas can Table 1 Chemical compositions of titanium ores used in this study. be produced even under standard state condition (aMgO = 1), % *1 and is possible even at lower temperatures. In this study, in Source country Concentration of element i, Ci (mass ) the viewpoint of improvement of HCl gas production and the of titanium ore Ti Fe Al Si Ca Mn Zr Nb Mg verification of feasibility for upgrading titanium ore by Vietnam*2 45.0 49.7 0.33 0.57 0.04 3.47 0.07 0.15 N.D. utilizing MgCl2 for the selective chlorination, the authors Australia*3 48.5 46.7 1.02 1.00 0.07 1.69 0.18 0.18 N.D. used MgCl2 as a chlorinating agent to remove iron directly China*4 47.2 45.4 1.41 1.65 0.21 2.79 0.24 0.27 N.D. from the titanium ore. *1 fl Determined by XRF analysis (excluding oxygen and other gaseous Figure 2 shows the ow diagram of the process used in elements), N.D.: Not Detected. Below the detection limit of the XRF this study. As shown in Fig. 2, the process investigated in this (<0.01%), values are determined by average of analytical results of five study consists of two selective chlorination processes. One samples. *2Natural ilmenite produced in Vietnam. selective chlorination process uses MgCl2 to chlorinate the *3Natural ilmenite produced in Australia. iron in the titanium ore of the titanium ore/MgCl mixture. 2 *4Natural ilmenite produced in China. The other selective chlorination process uses HCl gas produced from the titanium ore/MgCl2 mixture to chlorinate the iron in the titanium ore. The selective chlorination ²97.0%; granular; Wako Pure Chemical Industries, Ltd.) was investigated in this study has the following advantages; (1) it dried in a vacuum dryer (EYELA, VOS-201SD) for more does not involve handling of highly concentrated HCl or Cl2 than 3 days at 473 K before use. In addition, natural ilmenite gas, (2) high purity titanium dioxide is obtained directly from produced in Vietnam, Australia and China were used as the titanium ore in one step by a simple scalable method feedstocks. The compositions of the titanium ores are shown under Ar atmosphere, and (3) various types of titanium ore in Table 1. The particle of titanium ore sample was separated can be used as a feedstock. according to particle diameter using sieve before high temperature experiments. The particle size ranged from 44 2. Experimental to 149 µm was prepared by grinding and sieving the particle size ranged from 149 to 210 µm before the experiments. Figure 3 shows the schematic of the experimental Before the experiments were carried out, a mixture of apparatus used in this study. MgCl2 (anhydrous; purity MgCl2 and titanium ore was placed in the molybdenum-lined 1446 J. Kang and T. H. Okabe

Table 2 Experimental conditions used in the present study. bubbler was controlled by using a mantle heater (Model No.: Atmosphere H O bubbler Particle size HF-200S, As One Co.) and maintained at 303 K. Source Reaction 2 Exp. in the quartz After a preset reaction time, the quartz tube was instantly country time, No.* Flow, Temp., crucible, of Ti ore t A/h Gas Use taken out of the furnace and cooled down at room r f/sccm Tbub/K / dore µm temperature. The residues in the quartz crucible were 121017 Vietnam 5 Vacuum ®®® 44­74 analyzed without subjecting the samples to any leaching 121030 Vietnam 5 Vacuum ®®® 74­149 process. However, the residues in the molybdenum-lined 121031 Vietnam 5 Vacuum ®®® 149­210 quartz crucible were dissolved in deionized water for two 121101 Vietnam 5 Vacuum ®®® 210­297 hours by sonication at room temperature and then leached 121020 Australia 5 Vacuum ®®® 44­74 in 20% HCl aqueous solution for 30 min with stirring at the 121029 China 5 Vacuum ®®® 44­74 rate of 300 rpm at room temperature. 121119 Vietnam 3 Ar 50 ®® 44­74 The compositions of the residues obtained in both fl 121118 Vietnam 5 Ar 50 ®® 44­74 crucibles were analyzed using X-ray uorescence spectrosco- 121117 Vietnam 7 Ar 50 ®® 44­74 py (XRF: JEOL, JSX-3100RII), their microstructures and 121114 Vietnam 9 Ar 50 ®® 44­74 compositions were analyzed using scanning electron mi- / / 121113 Vietnam 11 Ar 50 ®® 44­74 croscopy energy dispersive X-ray spectroscopy (SEM EDS: JEOL, JSM-6510LV), and their crystalline phases were ­ 121216 Vietnam 1 Ar 50 O 303 44 74 identified using X-ray diffraction (XRD: RIGAKU, RINT ­ 121215 Vietnam 3 Ar 50 O 303 44 74 2500, Cu­K¡ radiation) analysis. 121212 Vietnam 5 Ar 50 O 303 44­74 ­ 121211 Vietnam 7 Ar 50 O 303 44 74 3. Mechanism of Selective Chlorination *Experimental conditions; = Weight of titanium ore used in the quartz crucible, wore 0.10 g. To understand the mechanism of the selective chlorination Weight of titanium ore used in the Mo-lined quartz crucible, thermodynamically, FeTiO is assumed as a mixture of FeO wore = 0.25 g. 3 ¼ and TiO . This assumption is acceptable from a thermody- Weight of MgCl2 used in the Mo-lined quartz crucible, wMgCl2 3:00 g. 2 Particle size used in the Mo-lined quartz crucible, dore = 74­149 µm. namic viewpoint and is used in several studies because the Reaction temperature, T = 1000 K. Gibbs energy of formation of FeTiO3 is a small negative value as shown in eq. (1). quartz crucible (quartz crucible: º = 26 mm, I.D.; d = FeOðsÞþTiO ðsÞ¼FeTiO ðsÞ; 24 mm, depth). In addition, the titanium ore was placed in 2 3 ¼ 34Þ ð Þ a quartz crucible (º = 31 mm, I.D.; d = 13 mm, depth). After G r 12 kJ at 1000 K 1 placing the samples in the two crucibles, both crucibles were Figures 4 and 5 show the chemical potential diagrams of placed into the quartz tube (º = 41.5 mm, I.D.; l = 545 mm, the Fe­O­Cl system and the Ti­O­Cl system at 1000 K,

length), and then an appropriate atmosphere was provided respectively, and the abscissa, pCl2 , is the chemical potential

for the samples in each experiment. The quartz tube was of chlorine gas and the ordinate, pO2 , is the chemical then placed in a horizontal furnace that was heated to up to potential of oxygen gas. In addition, the authors provide 1000 K. Fig. 6, which was constructed by overlapping the chemical Table 2 shows the experimental conditions used in the potential diagram of Fe­O­Cl system and that of the Ti­O­Cl present study. When the experiments were conducted under system shown in Figs. 4 and 5, respectively. Any point in the vacuum, the quartz tube was evacuated twice for 10 min each hatched area shown in Fig. 6 belongs to the stability region before the experiments. Ar gas (purity >99.9995%) was of TiO2(s) and FeCl2(l), or TiO2(s) and FeCl3(g). The vapor filled into the quartz tube between the evacuations until the pressure of FeCl2(l) at 1000 K is 0.02 atm, which is high 34) internal pressure was 1 atm. enough to evaporate FeCl2(l). As a result, thermodynami- When the experiments were conducted under Ar gas cally, if the chemical potentials of oxygen and chlorine are atmosphere, after evacuation (carried out as mentioned positioned in the hatched area shown in the Fig. 6, the iron above), Ar gas was filled until the internal pressure of the oxides can be removed as gaseous iron chlorides and solid quartz tube was 1 atm. After the internal pressure of the titanium dioxide can be obtained as a result of the selective quartz tube became 1 atm, the quartz tube was flowed with Ar chlorination process. gas at the rate of 50 sccm via a mass flow controller (MFC), In this study, MgCl2 was used as the chlorinating agent. while maintaining the internal pressure of the quartz tube at Even though MgCl2 was dried in the vacuum oven prior to 1 atm during experiments. use, absorption of H2O from air is expected to occur during When the experiments were conducted under Ar + H2O experimental preparation owing to the hygroscopicity of the gas atmosphere, water in a bubbler was bubbled with Ar gas MgCl2. Therefore, eq. (2) is to be considered in this reaction for 30 min to remove the dissolved oxygen. After pretreatment system. of the water, the quartz tube was filled with Ar gas until the MgCl ðlÞþH OðgÞ¼MgOðsÞþ2 HClðgÞ; internal pressure of the tube reached 1 atm after the evacuation 2 2 ¼ 34Þ ð Þ procedure. Subsequently, Ar gas was injected through the G r 19 kJ at 1000 K 2 water bubbler and the gas flow rate was maintained at 50 sccm As shown in eq. (2), if H2O exists in the system, HCl gas by the MFC, while the internal pressure of the quartz tube was can be produced from MgCl2 at 1000 K in the molybdenum- maintained at 1 atm. The temperature of the water in the lined quartz crucible. In addition, it is easy to obtain HCl gas Removal of Iron from Titanium Ore through Selective Chlorination Using Magnesium Chloride 1447

Fe-O-Cl system, T = 1000 K Ti-O-Cl system, 0 Fe-O-Cl system, T = 1000 K H O(g) / HCl(g) eq.a 2 0 a a Fe O (s) MgO(s) / MgCl (l) eq. H O(g) / HCl(g) eq. 2 3 2 2 e Fe O (s) a H O(g) / HCl(g) eq. 2 3 MgO(s) / MgCl (l) eq. 2 2 d Potential region for e -10 H O(g) / HCl(g) eq. TiO (s) H O(g) / HCl(g) eq. 2 2 selective chlorination 2 TiO (s) / MgTiO (s) -10 H O(g) / HCl(g) eq.d Fe O (s) 2 3 2 3 4 / MgCl (l) eq. TiO (s) / MgTiO (s) 2 Fe O (s) 2 3 3 4 / MgCl (l) eq. c 2 (atm) FeO (s) 2 -20 b CO (g) / CO (g) eq. 2 O c c p (atm) FeO (s) C (s) / CO (g) eq. 2 -20 CO (g) / CO (g) eq. d extrapolated b 2 Fe (s) O c

) eq. extrapolated p (l Fe (s) Ti O (s) C (s) / CO (g) eq. ) eq. 2 4 7 g Ti O (s) d extrapolated -30 3 5 ) / MgCl l) eq. extrapolated ) / HCl( (s g) eq. ( FeCl (l) 2 g 3 2 -30 O( H 2 Ti O (s) ) / HCl( 2 3 g ) / MgCl (s s) / MgTiO O( ( 2 3 -40 2 H TiCl (g) O 4 Ti -40 TiO (s) FeCl (g) ) / MgTiO 3 s FeCl (l) ( 2 2 Oxygen partial pressure, log O Ti -50 Oxygen partial pressure, log FeCl (g) Ti (s) TiCl (s) 3 -50 3

TiCl (s) 2 -60 -20 -15 -10 -5 0 -60 Chlorine partial pressure, log p (atm) -20 -15 -10 -5 0 Cl 2 Chlorine partial pressure, log p (atm) Cl a : b : p / p = 1 2 standrad state H O H 2 2 Ti-O-Cl Fe-O-Cl c : p = 0.1 atm Cl 2 a : b : p / p = 1 standard state H O H d : p / p 2 : Determined by MgCl + H O = 2 HCl + MgO 2 2 H O HCl 2 2 2 c : p = 0.1 atm Cl under a = 0.054 (under TiO (s)/MgTiO (s) eq.) 2 MgO 2 3 d : p / p 2 : Determined by MgCl + H O = 2 HCl + MgO 2 H O HCl 2 2 e : p / p : Determined by MgCl + H O = 2 HCl + MgO under a = 1 2 H O HCl 2 2 MgO 2 under a = 0.054 (under TiO (s)/MgTiO (s) eq.) MgO 2 3 e : p / p 2 : Determined by MgCl + H O = 2 HCl + MgO under a = 1 34) H O HCl 2 2 MgO Fig. 4 Chemical potential diagram of the Fe­O­Cl system at 1000 K. 2 Fig. 6 Combined chemical potential diagram of the Fe­O­Cl system (solid line) and the Ti­O­Cl system (dotted line) at 1000 K.34) Ti-O-Cl system, T = 1000 K 0 H O(g) / HCl(g) eq.a 2 MgO(s) / MgCl (l) eq.a 2 d e The lines corresponding to the H O(g)/HCl(g) eq. and TiO (s) H O(g) / HCl(g) eq. 2 2 2 e -10 H O(g) / HCl(g) eq.d / 2 H2O(g) HCl(g) eq. in Fig. 6 can be derived from eq. (3) by TiO (s) / MgTiO (s) 2 3 considering the reaction shown in eq. (2). If MgO remains as / MgCl (l) eq. 2 d extrapolated . a solid in MgCl2(l) after the experiments, the activity of -20 c (atm) b ) eq CO (g) / CO (g) eq. 2 g 2 / e

O Ti O (s) ( 3 5 c MgO(s)(aMgO) is unity, and then H2O(g) HCl(g) eq. under p Cl C (s) / CO (g) eq. Ti O (s) H a 4 7 ) / l) eq. extrapolated / (g ( MgO(s) MgCl2(l) eq. dominates the reactions in the system. O 2 -30 H 2 Meanwhile, if the solubility of MgO(s) in the MgCl2(l)at ) / MgCl Ti O (s) (s 2 3 3 1000 K is high enough, or if all of MgO(s) reacts with TiO2(s) gTiO M TiCl (g) in titanium ore, the activity of MgO(s) is decreased by TiO (s) ) / 4 -40 (s 2 / TiO forming MgTiO3(s) as shown in eq. (4), and H2O(g) HCl(g) d eq. under TiO2(s)/MgTiO3(s)/MgCl2(l) eq. dominates the Oxygen partial pressure, log Ti (s) TiCl (s) -50 3 reactions in the system. If the activity of the reaction product MgO(s) is decreased in the system, MgCl becomes a TiCl (s) 2 2 stronger chlorinating agent. It is worth noting that both lines -60 / d / -20 -15 -10 -5 0 corresponding to the H2O(g) HCl(g) eq. and H2O(g) HCl(g) e Chlorine partial pressure, log p (atm) Cl eq. in Fig. 6 pass through the stability region of FeCl (l)in 2 2

a : b : p / p = 1 the hatched region. Therefore, iron in the titanium ore can be standrad state H O H 2 2 c : p = 0.1 atm selectively removed from the ore directly as FeCl2(l,g) in the Cl 2 d : p / p 2 : Determined by MgCl + H O = 2 HCl + MgO quartz crucible by the reaction shown in eq. (5). In addition, H O HCl 2 2 2 under a = 0.054 (under TiO (s)/MgTiO (s) eq.) MgO 2 3 the reaction shown in eq. (2) proceeds further by the H2O e : p / p 2 : Determined by MgCl + H O = 2 HCl + MgO under a = 1 H O HCl 2 2 MgO produced according to the reaction shown in eq. (5). Both 2 H2O and HCl gas act as reaction mediators of chlorination Fig. 5 Chemical potential diagram of the Ti­O­Cl system at 1000 K.34) when MgCl2 (+H2O) is used as the chlorinating agent.

log pO ¼ 2 log pCl þ 2 log pH O 4 log pHCl from MgCl when H O is introduced in the reaction system. 2 2 2 2 2 þ 4 log K ðHClÞ2 log K ðH OÞð3Þ On the basis of this reason, a water bubbler was used in this f f 2 ð Þþ ð Þ¼ ð ÞðÞ study for intentionally introducing H2O vapor into the quartz MgO s TiO2 s, FeTiO3 MgTiO3 s 4 tube to accelerate the production of HCl gas according to the ¼ ¼ ¼ 34Þ aMgO 0:054 at 1000 K when aTiO2 1 and aMgTiO3 1 eq. (2). The partial pressure of H O vapor introduced into the 2 FeOðsÞþ2 HClðgÞ¼FeCl ðlÞþH OðgÞ; quartz tube could be fixed at 0.04 atm by using the water 2 2 ¼ 34Þ ð Þ bubbler at 303 K. G r 3:8 kJ at 1000 K 5 1448 J. Kang and T. H. Okabe

MgCl2 by itself can act as the chlorinating agent if it is (a) used in reaction with the titanium ore through physical contact. Both lines corresponding to the MgO(s)/MgCl2(l) a eq. and TiO2(s)/MgTiO3(s)/MgCl2(l) eq. in Fig. 6 also pass through the stability region of FeCl2(l) in the hatched region. a The line corresponding to the MgO(s)/MgCl2(l) eq. considered the standard state, which means that the activity (b) (c) of MgO(s) produced in the molybdenum-lined quartz a crucible is unity. The reaction under MgO(s)/MgCl2(l) eq. is shown in eq. (6). The line corresponding to the TiO2(s)/ MgTiO3(s)/MgCl2(l) eq. considered MgTiO3(s) production during chlorination, and the reaction under TiO2(s)/ MgTiO3(s)/MgCl2(l) eq. is shown in eq. (7). In both cases, iron can be selectively removed from titanium ore directly as FeCl2(l,g) in the molybdenum-lined quartz crucible.

FeOðsÞþMgCl2ðlÞ¼FeCl2ðlÞþMgOðsÞ; 34Þ G r ¼23 kJ at 1000 K ð6Þ

FeOðsÞþTiO2ðsÞþMgCl2ðlÞ¼FeCl2ðlÞþMgTiO3ðsÞ; 34Þ Fig. 7 Photographs of the experimental apparatus after the experiment: G r ¼47 kJ at 1000 K ð7Þ (a) the quartz tube, (b) residue in the quartz crucible, and (c) residue in the molybdenum-lined quartz crucible. 4. Results and Discussion

FeCl (H O) : PDF #01-072-0268 4.1 Observations after the experiments 2 2 2 FeCl : PDF #01-089-3732 Figure 7 shows the representative photographs of the 2 experimental apparatus after the experiments. As shown in The residues condensed inside the low Fig. 7(a), a white deposit was found inside the low temper- temperature part of the quartz tube ature portion of the quartz tube. In addition, the black color of (a.u.) the reactant titanium ore changed to bright grey color in the I product residues, as shown in Fig. 7(b). The results of the Background XRD analysis of the white powder shown in Fig. 8 indicated Intensity, Intensity, that the white deposit was FeCl2 and FeCl2·(H2O)2,as expected from the thermodynamic calculations mentioned before. The vapor pressure of FeCl (l) produced from the 2 10 20 30 40 50 60 70 80 90 quartz crucible and molybdenum-lined quartz crucible is Angle, 2θ (deg.) 0.02 atm at 1000 K, which was sufficient to induce its Fig. 8 Results of the XRD analysis of the white deposit condensed in the evaporation. Therefore, FeCl2(l) evaporated from the both low temperature portion of the quartz tube. crucibles and solidified in the low temperature regions of the quartz tube. The H2O present in the FeCl2 might have originated from the H2O produced in the quartz crucible or iron removed from the titanium ore was greater when the from the air when the silicone rubber plug was removed from experiments were conducted under Ar + H2O gas atmos- the quartz tube during sample preparation for XRD analysis. phere than when the experiments were conducted under Ar atmosphere for equal reaction time. The reduction in the 4.2 Influence of atmosphere on the selective chlorination reaction time can be attributed to the active introduction of Table 3 shows the results of XRF analysis of the residues H2O vapor into the reaction system by using water bubbler, obtained in the quartz crucible and the molybdenum-lined which led to the accelerated production of HCl gas from the quartz crucible. Figures 9 and 10 show the XRD patterns MgCl2 in the molybdenum-lined quartz crucible. of the residues obtained in the quartz crucible and the Among the impurities present in the titanium ore, MnO(s) molybdenum-lined quartz crucible when the experiments can be removed by HCl gas by the reaction shown in the were conducted under Ar gas or Ar + H2O gas atmosphere, eq. (8). Table 3 shows that the concentration of Mn in the respectively. residues obtained in the quartz crucible decreased as the As shown in Table 3, Fig. 9(a) and Fig. 10(a), a purity of reaction time increased when the experiments were con- about 97% TiO2 was obtained in the quartz crucible when the ducted under Ar gas or Ar + H2O gas atmosphere. In experiments were conducted under Ar gas or Ar + H2O gas addition, the concentration of Mg in the residues obtained atmosphere for 11 or 7 h, as expected from the thermody- in the quartz crucible could not be assessed for all cases. namic calculation. A purity of TiO2 was calculated by Although the vapor pressure of MgCl2 at 1000 K is as low converting all elements in Table 3 to its nominal simple as 0.0003 atm, MgCl2 can evaporate depending on the oxides. In addition, when the water bubbler was used in the atmosphere, such as in vacuum. Based on the results of the experiments, the reaction time required for obtaining high concentration of Mg listed in Table 3, the authors inferred purity TiO2 decreased. As shown in Table 3, the amount of that there was no reaction through gas phase or negligible Removal of Iron from Titanium Ore through Selective Chlorination Using Magnesium Chloride 1449

Table 3 Analytical results of the residues obtained in the quartz crucible and the molybdenum-lined quartz crucible: Influence of atmosphere on selective chlorination at 1000 K.

Quartz crucible Mo-lined quartz crucible H2O bubbler Reaction time, Concentration of Concentration of Exp. No.*2 A/ % *1 % *1 Temp., tr h element i, Ci (mass ) element i, Ci (mass ) Use / Tbub K Ti Fe Mn Mg Ti Fe Mn Mg 121119 ®® 3 73.0 23.4 2.30 N.D. 61.3 18.0 1.25 18.3 121118 ®® 5 83.2 13.9 1.47 N.D. 58.5 19.3 1.14 19.8 121117 ®® 7 92.1 5.88 0.70 N.D. 58.4 19.8 0.98 19.3 121114 ®® 9 94.4 3.67 0.44 N.D. 62.5 19.1 1.96 15.3 121113 ®® 11 96.7 1.77 0.14 N.D. 63.4 18.1 1.12 15.5 121216 O 303 1 61.0 35.1 2.94 N.D. 57.8 26.6 1.61 12.7 121215 O 303 3 77.7 19.6 1.94 N.D. 55.9 23.4 1.24 18.0 121212 O 303 5 90.9 7.23 0.98 N.D. 56.6 20.7 1.23 19.9 121211 O 303 7 97.2 1.24 0.13 N.D. 57.1 19.4 1.25 20.5 *1Determined by XRF analysis (excluding oxygen and other gaseous elements), N.D.: Not Detected. Below the detection limit of the XRF (<0.01%), values are determined by average of analytical results of five samples. *2Experimental conditions; Weight of titanium ore used in the quartz crucible, wore = 0.10 g. Weight of titanium ore used in the Mo-lined quartz crucible, wore = 0.25 g. ¼ Weight of MgCl2 used in the Mo-lined quartz crucible, wMgCl2 3:00 g. Particle size used in the quartz crucible, dore = 44­74 µm. Particle size used in the Mo-lined quartz crucible, dore = 74­149 µm. Reaction temperature, T = 1000 K. Source country of titanium ore: Vietnam. Ar gas was flowed through the quartz tube at a rate of 50 sccm via mass flow controller while the internal pressure of the quartz tube was maintained at 1 atm during the experiments.

MgTiO3 : PDF #00-006-0494

TiO2 : PDF #00-021-1276 TiO : PDF #03-065-0191 FeTiO : PDF #01-089-2811 2 3 (a) FeTiO3 : PDF #01-075-1208 (b) MgO : PDF #01-087-0651

(1) (1) Residue in the quartz crucible Residue in the Mo-lined crucible (Exp. No. : 121113) t ' = 11 h (Exp. No. : 121113) t ' = 11 h r r

(2) (2) Residue in the quartz crucible Residue in the Mo-lined crucible (Exp. No. : 121114) t ' = 9 h (Exp. No. : 121114) t ' = 9 h r r

(3) (3) Residue in the quartz crucible Residue in the Mo-lined crucible t ' = 7 h r (Exp. No. : 121117)

(a.u.) (Exp. No. : 121117) (a.u.) I

t ' = 7 h I r Intensity, Intensity, Intensity, Intensity, (4) Residue in the quartz crucible (4) Residue in the Mo-lined crucible (Exp. No. : 121118) (Exp. No. : 121118) t ' = 5 h t ' = 5 h r r

(5) Residue in the quartz crucible (5) Residue in the Mo-lined crucible (Exp. No. : 121119) (Exp. No. : 121119) t ' = 3 h t ' = 3 h r r

10 20 30 40 50 60 70 80 90 10 20 30 40 50 60 70 80 90 Angle, 2θ (deg.) Angle, 2θ (deg.)

Fig. 9 (a) XRD patterns of the residues obtained in the quartz crucible when the experiments were conducted under Ar gas atmosphere: (1) 11 h, (2) 9 h, (3) 7 h, (4) 5 h and (5) 3 h. (b) XRD patterns of the residues obtained in the molybdenum-lined quartz crucible when the experiments were conducted under Ar gas atmosphere: (1) 11 h, (2) 9 h, (3) 7 h, (4) 5 h and (5) 3 h. 1450 J. Kang and T. H. Okabe

MgTiO3 : PDF #01-079-0831 MgO : PDF #01-075-0447

TiO2 : PDF #01-073-1232 FeTiO3 : PDF #01-071-1140

(a) FeTiO3 : PDF #01-075-1203 (b) TiO2 : PDF #01-076-0649

(1) Residue in the quartz crucible (1) Residue in the Mo-lined crucible (Exp. No. : 121211) (Exp. No. : 121211) t ' = 7 h t ' = 7 h r r

(2) Residue in the quartz crucible (2) Residue in the Mo-lined crucible (Exp. No. : 121212) (Exp. No. : 121212) t ' = 5 h t ' = 5 h r r (a.u.) (a.u.) I I (3) Residue in the quartz crucible (3) Residue in the Mo-lined crucible (Exp. No. : 121215) (Exp. No. : 121215)

t ' = 3 h Intensity, t ' = 3 h

Intensity, Intensity, r r

(4) Residue in the quartz crucible (4) Residue in the Mo-lined crucible (Exp. No. : 121216) (Exp. No. : 121216) t ' = 1 h t ' = 1 h r r

10 20 30 40 50 60 70 80 90 10 20 30 40 50 60 70 80 90 Angle, 2θ (deg.) Angle, 2θ (deg.)

Fig. 10 (a) XRD patterns of the residues obtained in the quartz crucible when the experiments were conducted under Ar + H2O gas atmosphere: (1) 7 h, (2) 5 h, (3) 3 h and (4) 1 h. (b) XRD patterns of the residues obtained in the molybdenum-lined quartz crucible when the experiments were conducted under Ar + H2O gas atmosphere: (1) 7 h, (2) 5 h, (3) 3 h and (4) 1 h.

reaction between MgCl2 in the molybdenum-lined quartz (a) crucible and the titanium ore in the quartz crucible.

1=2 MnOðsÞþHClðgÞ¼1=2 MnCl2ðlÞþ1=2H2OðgÞ; 34Þ G r ¼17 kJ at 1000 K ð8Þ Figure 11 shows the SEM images of the Vietnamese titanium ore before experiment and the residue obtained in the quartz crucible when the experiment was conducted under Ar gas atmosphere for 11 h. As shown in Fig. 11, pores were generated on the surface of the residue after the experiment. These results show that iron was selectively removed from 5μm titanium ore as FeCl2(l,g) leaving pores on the surface of the residues in the quartz crucible because of the high vapor (b) pressure of FeCl2 at 1000 K. As a result, it can be expected that the HCl gas produced from the MgCl2 could react with iron in the central portion of the titanium ore particle through the generated pores. As shown in Figs. 9(b) and 10(b), the crystalline phases of the residues obtained in the molybdenum-lined quartz crucible were MgTiO3 and MgO. Despite the presence of crystalline phase of MgTiO3 in the residues revealed by the XRD analysis, the crystalline phase of MgO was also found in the residues present in the molybdenum-lined quartz 5μm crucible after the experiments. The most intense peak corresponded to MgO in most cases. These results show Fig. 11 SEM images of the microstructure: (a) the Vietnamese titanium ore e before experiment, and (b) the residue in the quartz crucible when the that the lines corresponding to the H2O(g)/HCl(g) eq. and a experiment was conducted under Ar gas atmosphere (Exp No.: 121113). MgO(s)/MgCl2(l)eq. dominated the reactions that occurred in the quartz crucible and molybdenum-lined quartz crucible, respectively, when the experiments were conducted under Ar molybdenum-lined quartz crucible when the experiments gas or Ar + H2O gas atmosphere. were conducted under Ar gas or Ar + H2O gas atmosphere Even though the iron was sufficiently removed leaving 1.2 for 11 or 7 h, respectively. Figure 12 shows the SEM image or 1.8% in the titanium ore in the quartz crucible, about 18 or and results of the EDS of a cross section of the residue 19% of iron remained in the titanium ore present in the obtained from the molybdenum-lined quartz crucible. As Removal of Iron from Titanium Ore through Selective Chlorination Using Magnesium Chloride 1451

(a) Table 4 Analytical results of residues obtained in the quartz crucible and the molybdenum-lined quartz crucible: Influence of the particle size of the Position No. 1 Position No. 12 titanium ore on selective chlorination at 1000 K.

Quartz crucible Mo-lined quartz crucible Concentration of Concentration of Exp. Particle Particle *2 element i, element i, No. size, 1 size, 1 Ci (mass%)* Ci (mass%)* dore/µm dore/µm Ti Fe Mn Mg Ti Fe Mn Mg 121017 44­74 96.8 0.60 0.06 1.12 74­149 54.1 21.9 1.15 21.0 121030 74­149 96.9 0.53 0.07 1.11 74­149 53.9 24.6 1.56 18.6 50 μm 121031 149­210 96.9 0.61 0.08 1.16 74­149 50.2 24.2 1.49 22.6 (b) 50 121101 210­297 96.6 0.59 0.06 1.28 74­149 53.2 23.0 1.47 20.7 Mg *1Determined by XRF analysis (excluding oxygen and other gaseous Ti fi 40 elements), values are determined by average of analytical results of ve Fe samples. *2Experimental conditions; 30 Weight of titanium ore used in the quartz crucible, wore = 0.10 g. (mass %) i Weight of titanium ore used in the Mo-lined quartz crucible, , C i wore = 0.25 g. 20 ¼ Weight of MgCl2 used in the Mo-lined quartz crucible, wMgCl2 3:00 g. Reaction time, trA = 5h. Reaction temperature, T = 1000 K. 10 Composition Source country of titanium ore: Vietnam. Experiments were conducted under vacuum. 0 1357911 Position No. concentration of Mg in the residues obtained in the quartz crucible could not be detected when the experiments were Fig. 12 (a) SEM image of the cross section of the residue obtained from the molybdenum-lined quartz crucible (Exp. No.: 121117). (b) Corre- conducted under Ar gas atmosphere. In addition, a weak sponding EDS results of the cross section of the residue obtained from the intensity peak of MgTiO3 was identified, as shown in molybdenum-lined quartz crucible (Exp. No.: 121117). Fig. 13(a). These results show that even though the vapor pressure of the MgCl2 is low as 0.0003 atm at 1000 K, a shown in Fig. 12, the reaction between MgCl2 and the central portion of MgCl2 evaporated from the molybdenum-lined portion of the titanium ore particle was hindered because of quartz crucible reacted with the titanium ore in the quartz the production of MgTiO3 at the outer portion of the titanium crucible under vacuum. ore particle. Therefore, iron was partially removed from the As shown in Table 4 and Fig. 13(b), about 22­25% of iron titanium ore in the molybdenum-lined quartz crucible. remained and MgO and MgTiO3 were produced in the molybdenum-lined quartz crucible. It is expected that iron in 4.3 Influence of the particle size of the titanium ore on the center of the titanium ore particle does not react with the selective chlorination MgCl2 due to the formation of MgTiO3 at the outer part of Table 4 shows the results of analyzing the residues the titanium ore particle, similar to the case shown in the obtained in the quartz crucible and the molybdenum-lined Fig. 12. In addition, MgO(s) found in the molybdenum-lined quartz crucible, and Figs. 13(a) and 13(b) show the XRD quartz crucible also shows that the lines corresponding to the e a patterns of the residues obtained in the quartz crucible and H2O(g)/HCl(g) eq. and MgO(s)/MgCl2(l) eq. dominated the molybdenum-lined quartz crucible, respectively, when the reactions that occurred in the quartz crucible and various sizes of Vietnamese titanium ore were used as a molybdenum-lined quartz crucible, respectively. feedstock under vacuum. As shown in Table 4 and Fig. 13(a), a purity of about 97% 4.4 Various kinds of the titanium ores produced in TiO2 was obtained in the quartz crucible when the particle several countries size ranged from 44 to 297 µm. It is certain that the HCl gas Table 5 shows the results of analyzing the residues produced from the molybdenum-lined quartz crucible could obtained in the quartz crucible and the molybdenum-lined react with the entire volume of the titanium ore particle quartz crucible, and Figs. 14(a) and 14(b) show the XRD through the pores generated by the reaction between HCl gas patterns of the residues obtained in the quartz crucible and and iron. Therefore, according to these results, the selective the molybdenum-lined quartz crucible when the Australian chlorination reaction that occurred in the quartz crucible did titanium ore and the Chinese titanium ore were used as a not depend on the particle size of the titanium ore. feedstock, respectively. It was also reconfirmed that the concentration of Mn in the As shown in Table 5 and Fig. 14(a), a purity of about 92% residues obtained in the quartz crucible decreased because of TiO2 was obtained in the quartz crucible. The purity of TiO2 the reaction shown in the eq. (8) for all the particle size obtained was lower than that obtained when the Vietnamese ranges. However, the concentration of 1.1­1.2% Mg in the titanium ore was used as the feedstock. As shown in eq. (8), residues obtained in the quartz crucible was analyzed when Mn in the titanium ore can be removed by HCl gas produced the experiments were conducted under vacuum, while the from the molybdenum-lined quartz crucible. However, it is 1452 J. Kang and T. H. Okabe

MgTiO3 : PDF #01-079-0831 MgO : PDF #01-074-1225

TiO2(rutile) : PDF #03-065-0191 FeTiO3 : PDF #01-075-1211

(a) MgTiO3 : PDF #01-079-0831 (b) TiO2 : PDF #03-065-1118

(1) (1) Residue in the quartz crucible Residue in the Mo-lined crucible d = (Exp. No. : 121017) d = (Exp. No. : 121017) ore ore 44 - 74 μm 44 - 74 μm

(2) Residue in the quartz crucible (2) (Exp. No. : 121030) Residue in the Mo-lined crucible d = d = ore ore (Exp. No. : 121030) 74 - 149 μm 74 - 149 μm (a.u.) (a.u.) I I (3) (3) Residue in the quartz crucible Residue in the Mo-lined crucible d = (Exp. No. : 121031) d = (Exp. No. : 121031) ore ore Intensity, Intensity, Intensity, Intensity, 149 - 210 μm 149 - 210 μm

(4) (4) Residue in the Mo-lined crucible Residue in the quartz crucible (Exp. No. : 121101) d = d = ore (Exp. No. : 121101) ore 210 - 297 μm 210 - 297 μm

10 20 30 40 50 60 70 80 90 10 20 30 40 50 60 70 80 90 Angle, 2θ (deg.) Angle, 2θ (deg.)

Fig. 13 (a) XRD patterns of the residues obtained in the quartz crucible when the ore particle size was in the range: (1) 44­74 µm, (2) 74­ 149 µm, (3) 149­210 µm and (4) 210­297 µm. (b) XRD patterns of the residues obtained in the molybdenum-lined quartz crucible when the ore particle size was in the range: (1) 44­74 µm, (2) 74­149 µm, (3) 149­210 µm and (4) 210­297 µm.

Table 5 Analytical results of residues obtained in the quartz crucible and Vietnamese titanium ore (97% TiO2). In practice, this the molybdenum-lined quartz crucible: Various types of the titanium ores difference is unimportant because a purity of 92% TiO2 is produced in several countries at 1000 K. sufficient for application of the Kroll process. Mo-lined quartz ð Þþ ð Þ¼ ð Þþ ð Þ Quartz crucible 1=6Al2O3 s HCl g 1=3 AlCl3 l 1=2H2O g ; crucible ¼ 34Þ ð Þ Source G r 62 kJ at 1000 K 9 Exp. Concentration of Concentration of country No.*2 element i, element i, 1=4 SiO2ðsÞþHClðgÞ¼1=4 SiCl4ðgÞþ1=2H2OðgÞ; of Ti ore % *1 % *1 34Þ Ci (mass ) Ci (mass ) G r ¼ 54 kJ at 1000 K ð10Þ Ti Fe Mn Mg Al Si Ti Fe Mn Mg 121020 Australia 92.2 2.27 0.14 1.80 0.74 1.17 62.8 21.1 0.54 13.2 5. Conclusions 121029 China 91.7 2.62 0.10 1.47 0.93 1.21 50.9 19.1 0.72 25.5 The authors have considered the use of MgCl as the *1Determined by XRF analysis (excluding oxygen and other gaseous 2 elements), values are determined by average of analytical results of five chlorinating agent to develop a selective chlorination process samples. for producing high purity titanium dioxide by upgrading low- *2 Experimental conditions; grade titanium ore containing 51% TiO2. Iron was removed Weight of titanium ore used in the quartz crucible, w = 0.10 g. ore from the titanium ore as FeCl2(l,g) by the HCl gas produced Weight of titanium ore used in the Mo-lined quartz crucible, / = from the MgCl2 titanium ore mixture at 1000 K in the quartz wore 0.25 g. % Weight of MgCl used in the Mo-lined quartz crucible, w ¼ 3:00 g. crucible and TiO2 with purity of 97 was obtained when the 2 MgCl2 + Particle size used in the quartz crucible, dore = 44­74 µm. experiments were conducted under Ar gas or Ar H2O gas = ­ Particle size used in the Mo-lined quartz crucible, dore 74 149 µm. atmosphere. The time required for the completion of the Reaction temperature, T = 1000 K. reaction was decreased when the experiments were con- A = Reaction time, tr 5h. ducted under Ar + H O gas atmosphere because of the Experiments were conducted under vacuum. 2 accelerated production of HCl gas. The authors also demonstrated the direct production of difficult to remove other impurities such as Al, Si, Zr and Nb 97% TiO2 from the Vietnamese titanium ore that contained in the titanium ore by HCl gas, as shown in eqs. (9) and (10). particles of sizes ranging from 44 to 297 µm by using the HCl The amount of these impurities in the Australian titanium ore gas produced from MgCl2/titanium ore mixture. In addition, and the Chinese titanium ore are larger than the amount of the when the Australian or the Chinese titanium ores were used impurities in the Vietnamese titanium ore as shown in as the feedstock, 92% TiO2 was obtained. This was attributed Table 1. When comparing the purity of residues obtained in to the presence of impurities like Al or Si in the titanium ore the quartz crucible, the purity of the residue obtained from that were difficult to remove by HCl gas. the Australian and the Chinese titanium ores (92 and 92% The iron present in the titanium ore was also removed as TiO2) was lower than that of the residue obtained from the FeCl2(l,g) by the direct reaction between MgCl2 and the Removal of Iron from Titanium Ore through Selective Chlorination Using Magnesium Chloride 1453

TiO (rutile) : PDF #01-072-1148 2 of their preliminary studies. This research was partly funded MgTiO : PDF #01-079-0831 3 by a Grant-in-Aid for the Next Generation of World-Leading FeTiO3 : PDF #01-075-0519 Fe O : PDF #01-089-0951 Researchers (NEXT Program). Jungshin Kang is grateful for 3 4 fi SiO2 : PDF #01-085-0865 the nancial support provided by the MEM (Mechanical, TiO (anatase) : PDF #01-073-1764 (a) 2 Electrical and Materials Engineering) International Graduate

(1) Residue in the quartz crucible Program from the Ministry of Education, Culture, Sports, (Exp. No. : 121020, Australia) Science and Technology, Japan (MEXT).

REFERENCES (a.u.) I (2) Residue in the quartz crucible (Exp. No. : 121029, China) 1) F. Habashi (ed.): Handbook of Extractive Metallurgy, (VCH Verlagsgesellschaft mbH, Weinheim, Germany, 1997) Vol. 2, Intensity, Intensity, pp. 1129­1180. 2) A. Moriya and A. Kanai: Shigen-to-Sozai 109 (1993) 1164­1169. 3) T. Fukuyama, M. Koizumi, M. Hanaki and S. Kosemura: Shigen-to- 10 20 30 40 50 60 70 80 90 Sozai 109 (1993) 1157­1163. Angle, 2θ (deg.) 4) K. Faller and F. H. Froes: JOM 53 (2001) 27­28. MgTiO : PDF #01-079-0831 5) F. H. Froes, H. Friedrich, J. Kiese and D. Bergoint: JOM 56 (2004) 3 40­44. TiO2 (rutile) : PDF #03-065-0190 FeTiO : PDF #01-071-1140 6) J. E. Kogel, N. C. Trivedi, J. M. Barker and S. T. Krukowski: Industrial 3 Minerals & Rocks Commodities, Markets, and Uses, 7th ed., (Society (b) MgO : PDF #00-045-0946 for Mining, Metallurgy, and Exploration, Inc. (SME), Littleton, (1) Residue in the Mo-lined crucible Colorado, USA, 2006) pp. 987­1013. (Exp. No. : 121020, Australia) 7) G. M. Bedinger: Mineral Commodity Summaries: Titanium Mineral Concentrates, U.S. Geological Survey, Washington, DC, January,

(a.u.) ­ I (2013) pp. 174 175, http://minerals.usgs.gov/minerals/pubs/commodity/ titanium/mcs-2013-timin.pdf. (2) Residue in the Mo-lined crucible 8) D. Filippou and G. Hudon: JOM 61 (2009) 36­42.

Intensity, Intensity, (Exp. No. : 121029, China) 9) T. S. Mackey: JOM 46 (1994) 59­64. 10) R. G. Becher, R. G. Canning, B. A. Goodheart and S. Uusna: Proc. Aust. Inst. Min. Metall. 21 (1965) 21­44. 11) W. Hoecker: European Patent EP0612854, (1994). 10 20 30 40 50 60 70 80 90 12) J. H. Chen and L. W. Huntoon: United States Patent 4019898, (1977). Angle, 2θ (deg.) 13) J. H. Chen: United States Patent 3967954, (1976). 14) J. H. Chen: United States Patent 3825419, (1974). Fig. 14 (a) XRD patterns of the residues obtained in the quartz crucible 15) M. Guéguin and F. Cardarelli: Miner. Process. Extr. Metall. Rev. 28 when various types of titanium ore were used as feedstock: (1) Australian (2007) 1­58. ilmenite and (2) Chinese ilmenite. (b) XRD patterns of the residues 16) M. K. Akhtar, S. Vemury and S. E. Pratsinis: AIChE J. 40 (1994) 1183­ obtained in the molybdenum-lined quartz crucible when various types 1192. of titanium ore were used as feedstock: (1) Australian ilmenite and 17) W. Kroll: Trans. Electrochem. Soc. 78 (1940) 35­47. (2) Chinese ilmenite. 18) T. Iida: Kinzoku 82 (2012) 218­221. 19) Y. Ito: Titan 60 (2012) 212­218. 20) The Japan Titanium Society: Titan 61 (2013) 84. 21) W. Zhang, Z. Zhu and C. Y. Cheng: Hydrometallurgy 108 (2011) 177­ titanium ore. However, when the MgCl2 directly reacted with 188. the titanium ore, 18­25% of iron remained in the titanium ore 22) K. I. Rhee and H. Y. Sohn: Metall. Mater. Trans. B 21 (1990) 341­347. ­ because of the formation of MgTiO3 at the outer part of the 23) S. Fukushima and E. Kimura: Titanium · Zirconium 23 (1975) 67 74. 24) E. Kimura, A. Fuwa and S. Fukushima: Nippon Kogyo Kaishi 95 titanium ore, which hindered further reaction between MgCl2 (1979) 821­827. and iron present at the central portion of the titanium ore 25) A. Fuwa, E. Kimura and S. Fukushima: Metall. Mater. Trans. B 9 particle, physically. (1978) 643­652. 26) K. I. Rhee and H. Y. Sohn: Metall. Mater. Trans. B 21 (1990) 331­340. Acknowledgements 27) K. I. Rhee and H. Y. Sohn: Metall. Mater. Trans. B 21 (1990) 321­330. 28) L. K. Doraiswamy, H. C. Bijawat and M. V. Kunte: Chem. Eng. Prog. 55 (1959) 80­88. The authors are grateful to Professor Tetsuya Uda, Kyoto 29) H. Zheng and T. H. Okabe: Proc. 16th Iketani Conf., Masuko University; Professors Kazuki Morita and Takeshi Yoshikawa, Symposium, ed. by S. Yamaguchi, (The 16th Iketani Conference The University of Tokyo; Professor Ryosuke O. Suzuki, Organizing Committee, 2006, Japan) pp. 1005­1010. Hokkaido University; and Messrs. Susumu Kosemura, 30) R. Matsuoka and T. H. Okabe: Proc. Symp. on Metallurgical Masanori Yamaguchi and Yuichi Ono, Toho Titanium Co., Technology for Waste Minimization, (134th TMS Annual Meeting, 2005, San Francisco, United States) http://www.okabe.iis.u-tokyo.ac.jp/ Ltd., for their valuable suggestions and for supplying samples japanese/for_students/parts/pdf/050218_TMS_proceedings_matsuoka.pdf. that were used throughout this research. Furthermore, the 31) J. Kang and T. H. Okabe: Proc. 4th Asian Conf. on Molten Salt authors thank Dr. Katsuhiro Nose, Dr. Yuki Taninouchi, Dr. Chemistry and Technology, and 44th Symposium on Molten Salt Hideaki Sasaki and Mr. Hisao Kimura for their valuable Chemistry, (Molten Salt Committee, the Electrochemical Society of ­ suggestions and technical assistance. The authors would like Japan, Japan, 2012) pp. 176 182. 32) J. Kang and T. H. Okabe: Metall. Mater. Trans. B 44 (2013) 516­527. to specially thank Professor Haiyan Zheng of Northeastern 33) T. H. Okabe and J. Kang: Molten Salts 56 (2013) 15­26. University and Mr. Ryosuke Matsuoka of Global Advanced 34) I. Barin: Thermochemical Data of Pure Substances, 3rd ed., (VCH Metals Pty., Ltd., for providing useful information and results Verlagsgesellschaft mbH, Weinheim, Germany, 1995).