Iron Removal from Titanium Ore by Electrochemical Method

Transcription

1 Iron Removal from Titanium Ore by Electrochemical Method Isao Obana 1 and Toru H. Okabe 2 1 Graduate School of Engineering, The University of Tokyo 2 International Research Center for Sustainable Materials, Institute of Industrial Science, The University of Tokyo 1

2 Introduction Features of titanium Lightweight and high strength Corrosion resistant Biocompatible Some titanium alloys: shape memory effect superelasticity Applications Aircraft Spacecraft Chemical plants Implants Artificial bones, etc. The Kroll process: Currently employed Ti production process Mg & TiCl 4 Feed port Reaction Container Sponge Titanium MgCl 2 Chlorination Ti ore + C + 2 Cl 2 TiCl 4 (+ FeCl x ) + CO 2 Reduction TiCl Mg MgCl 2 Electrolysis Ti + 2 MgCl 2 Mg + Cl 2 2

3 Upgrading Ti ore Others FeO x Others Upgrade Chloride wastes FeO x TiO x TiO x Discarded Ti ore (Ilmenite, FeTiO x ) Low grade Ti ore Ti metal (FeTiOX) Upgraded Ti ore (TiO2) Ti smelting MCl x Selective chlorination FeCl x (CaCl2) (+AlCl3) Upgraded Ilmenite (UGI) Ti scrap Chlorine recovery Fe TiCl 4 Advantages: 1. Material cost can be reduced by using low-grade ore. 2. Chlorine circulation in the Kroll process can be improved. 3. This process can also be applied to the new Ti production processes, e.g., the direct electrochemical reduction of TiO 2. 3

4 Previous study Vacuum pump Pyrometallurgical de-fe process FeO x (s, in Ti ore) + MgCl 2 (s, l) FeCl x (l, g) + MgO (s) Condenser Deposit (FeCl x ) Susceptor Mixture of Ti ore and MCl x RF coil Quartz Tube CaCl 2 (s, l) + H 2 O (g) HCl (g) + CaO (s) FeO x (s, in Ti ore) + HCl (g) FeCl x (l, g) + H 2 O (g) T = 973~1373 K The selective chlorination of Ti ore by MgCl 2 or CaCl 2 is found to be feasible. N 2 or N 2 +H 2 O gas Ref. R. Matsuoka and T. H. Okabe: Symposium on Metallurgical Technology for Waste Minimization at the 2005 TMS Annual Meeting, San Francisco, California ( ). 4

5 Study objectives Low-grade Ti ore (FeTiO x ) Fe removal by selective chlorination TiO 2 + flux Direct reduction of TiO 2 obtained after Fe removal Application of electrochemical method using molten salt Ti powder 1. Thermodynamic analysis of selective chlorination 2. Fundamental experiments of selective chlorination by electrochemical methods 3. Reduction experiment for the sample obtained by selective chlorination 5

6 Thermodynamic analysis (Ti ore chlorination) Fe-Cl-O and Ti-Cl-O system, T = 1100 K Oxygen partial pressure, log p O2 (atm) TiO 2 (s) TiO (s) Ti (s) Fe 2 O 3 (s) Fe 3 O 4 (s) FeO (s) Fe (s) FeCl 2 (l) FeCl 3 (g) Chlorine partial pressure, log p Cl2 (atm) Potential region for selective chlorination of iron from titanium ore CO/CO 2 eq. C/CO eq. H 2 O(g)/HCl (g) eq. MgO (g)/mgcl 2 (l) eq. CaO (s)/cacl 2 (l) eq. a CaO = 0.1 Potential region for chlorination of titanium TiCl 4 (g) TiCl 3 (s) TiCl 2 (s) Fig. Chemical potential diagram for Fe-Cl-O and Ti-Cl-O systems at 1100 K TiO 2 FeO x Stable FeCl x (g) Ti ore : FeTi x O y For simplicity, it is assumed to be a mixture of TiO x and FeO x The selective chlorination of Ti ore by controlling chlorine partial pressure may be possible using an electrochemical technique. 6

7 Chlorination by increasing Cl 2 potential Electrolysis Cathode: Fe n+ + n e Fe Ca e Ca Anode: 2 Cl (in CaCl 2 ) Cl e FeCl 3, AlCl 3, O 2, CO 2 gas DC power source e FeO x + Cl 2 FeCl x + O 2 Molten salt (CaCl 2, MgCl 2, etc.) Upgraded or low-grade Ti ore (e.g., FeTiO x ) Chlorine chemical potential in molten CaCl 2 at anode can be increased electrochemically. 7

8 Theoretical decomposition voltage Table Standard Gibbs energy of decomposition and theoretical voltage of that in several chemical species at 1100 K. Reactions G o /kj mol -1a E o /V a CaCl 2 (l) = Ca (l) + Cl 2 (g) FeO (s) = Fe (s) + 1/2 O 2 (g) FeO (s) + 1/2 C (s) = Fe (s) + 1/2 CO 2 (g) FeO (s) + CaCl 2 (l) + C (s) = FeCl 2 (l) + CO (g) + Ca (l) FeTiO 3 (s) + CaCl 2 (l) + 1/2 C (s) = TiO 2 (s) + FeCl 2 (l) + Ca (l) + 1/2 CO 2 (g) a: I. Barin: Thermochemical Data of Pure Substances, 3rd ed. (Weinheim, Federal Republic of Germany, VCH Verlagsgesellschaft mbh, 1997) Under a certain condition, the selective chlorination of Fe in Ti ore may proceed below the theoretical decomposition voltage of CaCl 2. 8

9 Low-grade Ti ore TiO 2 + flux (FeTiO x ) Fe removal by selective chlorination Direct reduction of TiO 2 obtained after Fe removal Iron removal by selective chlorination using an electrochemical method Ti powder 9

10 Experimental apparatus (a) Reaction chamber (b) Reaction cell V A Potential lead (Nickel wire) Stainless steel tube (Electrode) Ar inlet Rubber plug (a) O.D. 19 mm I.D. 17 mm (b) Support rod (Stainless steel tube) Wheel flange Air hole Thermocouple Heater Mild steel crucible (Cathode) Screw (Stainless steel) Surface of molten salt Graphite crucible (Anode) Sample Holes for molten salt diffusion Molten salt (CaCl 2 ) Ceramic insulator Graphite crucible Sample (Ti ore, CaCl 2, etc.) Height 40 mm 10

11 Selective chlorination experiments Experimental conditions: Temperature: Atmosphere: Molten salt: Cathode: Anode: Exp. No. A B C D E Mass of sample i, w i /g Ti ore Carbon CaCl 2 Ilmenite UGI powder 4.00 ーーー K Ar CaCl 2 (800 g) Mild steel crucible (I.D. 96 mm) Graphite crucible (I.D. 17 mm) ー ー ー 0.18 Voltage, E/V ー ー 1.5 ー ー 2.0 Low initial Fe content Time, t /h e Sample Mild steel crucible (Cathode) Voltage monitor /controller Molten CaCl 2 Graphite crucible containing Ti ore (Anode) 11

12 Results of the selective chlorination experiments XRF analysis Table Analytical results of the samples obtained after electrochemical selective chlorination Sample Concentration of element i, C i (mass%) Ti Fe Ca Si Ilmenite Exp. A Exp. B Exp. C Exp. X UGI Exp. D Exp. E a: Average values of the samples obtained from the upper and lower parts of the graphite crucible V Fe/Ti ratio, R Fe/Ti (%) Fe/Ti ratio decreased from 114% to 7.2% (ilmenite) and from 2.00% to 0.18% (UGI). 94% of Fe in ilmenite and 92% of Fe in UGI were successfully removed. 12

13 Result of a selective chlorination experiment XRD analysis Intensity, I(a. u.) Ilmenite FeTiO 3 :CaTiO 3 :TiO 2 Discussion FeTiO 3 (s) + CaCl 2 (l) CaTiO 3 (s) + FeCl x (l, g) FeTiO 3 (s) + CaCl 2 (l) + C (s) TiO 2 (s) + FeCl x (l, g) + CO x (g) + Ca (s) Angle, 2θ (degree) Fig. XRD pattern of the start sample and the sample obtained after Fe removal (Exp. B) A mixture of CaTiO 3 and TiO 2 was obtained after Fe removal. CaTiO 3 can be utilized as a feed material of direct TiO 2 reduction processes (e.g., FFC, OS, EMR-MSE processes). 13

14 Low-grade Ti ore TiO 2 + flux (FeTiO x ) Fe removal by selective chlorination Direct reduction of TiO 2 obtained after Fe removal Ti powder Direct reduction of TiO 2 after Fe removal by electrochemical method 14

15 Reduction experiment apparatus Direct reduction by electrochemical method was applied. Carbon anode Electrolysis Cathode: TiO e Ti + 2 O 2 CaCl 2 molten salt Anode: C + x O 2 CO x + 2x e Ti crucible TiO 2 feed Fig. Schematic illustration of the experimental apparatus in this study. 15

16 Reduction experiments Experimental conditions: Temperature: 1100 K Atmosphere: Ar Molten salt: CaCl 2 (800 g) Cathode: Ti crucible (I.D. 18 mm) Anode: Graphite rod (O.D. 3 mm) Table Analytical results of the sample obtained after electrochemical selective chlorination Sample Concentration of element i, C i (mass%) Ti Fe Ca Si UGI Exp. D Exp. E Mass of element i, w i / g Voltage, Time, Exp. Ti ore CaTiO 3 CaCl 2 E/V t /h R-1 ー R-2 R-3 ー ー R ー V Fe/Ti ratio, R Fe / Ti (%) 16

17 Result of the reduction experiments Intensity, I(a. u.) XRD analysis Angle, 2θ (degree) Fig. XRD pattern of the sample obtained after the reduction experiment (Exp. R-2) CaTiO 3 was changed into Ti 2 O during this reduction experiment. A complete reduction was not achieved in this study. :Ti 2 O :CaTiO 3 Intensity, I (a.u.) Current monitor e - 10 Ti reduction by EMR : Ti JCPDS # Angle, 2θ (degree) Fig. XRD pattern (Cu-Kα) of the obtained powder sample after reduction at 1173 K using the EMR process. e - Carbon anode CaCl 2 molten salt 2500 ppm O In a previous study, low oxygen titanium powder was obtained. TiO 2 preform (Cathode) Ca-X alloy Ref. T. Abiko, I. Park, and T.H. Okabe, Proceedings of 10th World Conference on Titanium, Ti-2003, (Hamburg, Germany, July 2003),

18 Summary The selective chlorination of Ti ore by using an electrochemical method was investigated, and 94% of Fe was successfully removed directly from low-grade Ti ore. The feasibility of Ti smelting process for directly producing metallic Ti from low-grade Ti ore was demonstrated. Low-grade Ti ore TiO 2 + flux Reduction by electrochemical method Ti powder (FeTiO x ) Iron removal by selective chlorination Development of an industrial scale process for producing low-cost titanium 18

19 Question and Answer 19

20 History of Titanium 1791 First discovered by William Gregor, a clergyman and amateur geologist in Cornwall, England Klaproth, a German chemist, gave the name titanium to an element re-discovered in Rutile ore Nilson and Pettersson produced metallic titanium containing large amounts of impurities M. A. Hunter produced titanium with 99.9% purity by the sodiothermic reduction of TiCl 4 in a steel vessel. (119 years after the discovery of the element) 1946 W. Kroll developed a commercial process for the production of titanium: Magnesiothermic reduction of TiCl 4... Titanium was not purified until 1910, and was not produced commercially until the early 1950s. 20

21 Titanium Production (a) Production of titanium sponge in the world (2003). China 4 kt Kazakhstan 9 kt Russia 26 kt Total 65.5 kt USA 8 kt Japan 18.5 kt (28% share) (b) Transition of production volume of titanium mill products in Japan. Amount of titanium mill products [kt] kt (2004) Year Fig. Current status of titanium production, (a) production of titanium sponge in the world (2003), (b) transition of production volume of titanium mill products in Japan. 21

22 Symbol Table Comparison between common metals and titanium. Melting point (K) Density (g / K) Specific strength ((kgf / mm 2 ) / (g / cc)) Price (Yen / kg) Production volume (10 6 ton / year world) Titanium Ti ~ 10 Clarke number a 0.46 (rank 10) 7.56 (rank 3) 4.7 (rank 4) a: Values in parentheses are the existence rank in the earth s crust. ~ 0.1 Aluminum Al ~ 6 20 Iron Fe ~

23 Flowchart of the titanium production Ti feed (TiO 2 ) Reductant (C) Chlorine (Cl 2 ) Chlorination CO 2, FeCl x,alcl 3 etc. Crude TiCl 4 H 2 S etc. Distillation Other compounds Pure TiCl 4 Reductant, Mg Reduction Sponge Ti + MgCl 2 + Mg Vacuum distillation MgCl 2 + Mg Electrolysis MgCl 2 Sponge Ti Crushing / Melting Ti ingot Fig. Flowchart of the titanium production based on the Kroll process. 23

24 Composition of titanium ore (a) Low grade titanium ore (ilmenite) (b) Up-graded titanium ore (UGI) Others 10% FeO x 2% Others 3% FeO x 45% TiO x 45% TiO x 95% Fig. (a) Composition of low grade titanium ore (ilmenite), and (b) that of up-graded titanium ore (up-graded ilmenite, UGI). 24

25 Upgrading Ti ore for minimizing chloride wastes Others FeO x Others Upgrade Chloride wastes FeO x TiO x TiO x Discarded Ti ore (Ilmenite, FeTiO x ) 1. A large amount of chloride wastes (e.g., FeCl x ) are produced in the Kroll process. 2. Chloride waste treatment is costly, and it causes chlorine loss in the Kroll process. Importance Upgraded Ilmenite (UGI) 1. Reduction of disposal cost of chloride wastes 2. Minimizing chlorine loss in the Kroll process 3. Improvement of environmental burden 4. Reduction of material cost using low grade ore 25

26 Refining process using FeCl x This study Low-grade Ti ore (FeTiO X ) Upgraded Ti ore (TiO 2 ) Carbo-chlorination MCl X Selective chlorination (Cl 2 ) FeCl x (+AlCl 3 ) TiCl 4 feed CO x FeCl x (+AlCl 3 ) Ti metal or TiO 2 production FeCl x Ti scrap Chlorine recovery Fe TiCl 4 Advantages: 1. Utilizing chloride wastes from the Kroll process 2. Low cost Ti chlorination 3. Minimizing chlorine loss in the Kroll process caused by generation of chloride wastes Effective utilization of chloride wastes Development of a new environmentally sound chloride metallurgy 26

27 The Benilite process Ilmenite Reductant (Heavy oil etc.) Reduction (in kiln) Fe 2+ / TiFe = 80~95% Reduced ore HCl aq. HCl vapor (18~20% HCl) Leaching (in digestor) 145C (2.5 kg/cm 2 ) *4 hr *2 step Leached ilmenite Water Spray acid Fuel Filtration Roasting TiO 2 Sol. Iron oxide (90% purity) HCl Calcination Absorber TiO 2 (Synthetic rutile) 95% TiO 2 1% TiFe HCl aq. Fig. Flowsheet of the Benilite process. 27

28 The Beacher process (WLS) Ilmenite Coal (low ash) Reduction (in kiln) Air Reduced ore Gas + particle Particle Screen +1 mm -1 mm Cyclone Gas Mag. separator Waste (Non. mag.) Reduced ilmenite NH 4 Cl Leaching Air TiO 2 H 2 SO 4 aq. Iron oxide + Sol. Acid Leaching Thickener TiO 2 Iron oxide Sol. Filtering / Drying TiO 2 (Synthetic rutile) TiO 2 92~93% TiFe 2.0~3.5% Fig. Flowchart of the Beacher process. 28

29 Thermocouple Cathode (stainless steel) Ceramic tube Alumina tube TiO 2 (CaCl 2 ) + 4 e - Ti + 2 O 2- (CaCl 2 ) or TiO 2 (CaCl 2 ) + 2 Ca Ti + 2 CaO Anode lead wire (W) Fused CaCl 2 bath Alumina crucible TiO 2 powder Electric furnace Graphite crucible (anode) Fig. Electrochemical reduction of TiO 2 in CaCl 2. (Ref. Mem. Fac. Eng., Nagoya Univ., 19, (1967) ) 29

30 Carbon anode Ti cathode O (in Ti) + 2 e - O 2- (in CaCl 2 ) Cl 2 Cl - Cl - Ca 2+ e - C CO X Ca2+ O 2- O 2- Ca 2+ O 2- Ca Ca [O] in Ti Ti e - [O] O 2- Ca Ti Ca 2+ Ca 2+ Cl - CaCl 2 molten salt Fig. The principle of electrochemical deoxidization of titanium. (Ref. Met. Trans. B, 24B, June, (1993) ) 30

31 Titanium ore Chlorination or sulfate method Titanium reduction by FFCprocess TiO 2 C CO x Titanium oxide TiO 2 Molten salt Mixing with Binder Cathode Anode Recovery of titanium electrode TiO e - Ti + 2 O 2 (in CaCl 2 ) Cathode formation Crushing and leaching Calcination (TiO 2 electrode) FFC titanium Fig. Schematic illustration of the procedure of the FFC process. (Ref. Nature, 407, 21, Sep. (2000) 361.) 31

32 Production process under investigation FFC Process (Fray et al., 2000) OS Process (Ono & Suzuki, 2002) e - TiO 2 powder Carbon anode e - Carbon anode Ca TiO 2 preform CaCl 2 molten salt CaCl 2 molten salt Electrolysis Cathode: TiO Ca Ti + 2 O 2- + Ca 2+ Electrolysis Cathode: (b1) TiO e - Ti + 2 O 2- Anode: (a1) Ca e - Ca Anode: (b2) C + x O 2- CO x + 2x e - (a2) C + x O 2- CO x + 2x e - (b3) 32

33 Production process under investigation EMR / MSE Process (Electronically Mediated Reaction / Molten Salt Electrolysis) Current monitor / controller e - TiO 2 e - CaCl 2 -CaO molten salt (a) TiO 2 reduction Carbon anode Ca-X alloy (X = Ag, Ni, Cu, ) e - e - (b) Reductant production Cathode: TiO e - Ti + 2 O 2- Anode: Ca Ca e - Electrolysis Cathode: Ca e - Ca Anode: C + x O 2- CO x + 2x e - Over all reaction TiO 2 + C Ti + CO 2 (c1) (c2) (c3) (c4) (d) 33

34 (a) FFC Process (Fray et al., 2000) e - Carbon anode (b) OS Process (Ono & Suzuki, 2002) TiO 2 powder e - Carbon anode (C) EMR / MSE Process (Okabe et al., 2002) e - e - e - Current monitor / controller Carbon anode CaCl 2 molten salt Ca CaCl 2 molten salt TiO 2 preform Electrolysis Cathode: TiO e - Ti + 2 O 2- (a1) TiO Ca Ti + 2 O 2- + Ca 2+ Electrolysis Cathode: Ca e - Ca (b1) (b2) TiO 2 feed EMR CaCl 2 MSE molten salt Ca-X alloy Cathode: TiO e - Ti + 2 O 2- Anode: Ca Ca e - (c1) (c2) Anode: Anode: Electrolysis C + x O 2- CO x + 2x e - (a2) C + x O 2- CO x + 2x e - (b3) Cathode: Ca e - Ca (c3) Fig. Schematic illustration of experimental apparatus for titanium smelting in the future. Anode: C + x O 2- CO x + 2x e - (c4) Over all reaction TiO 2 + C Ti + CO 2 (d) 34

35 Features of several titanium production process Advantages Disadvantages Kroll Process High purity titanium available Complicated process Easy metal / salt separation Slow production speed Established chlorine circulation Batch type process Utilizes efficient Mg electrolysis Reduction and electrolysis operation can be carried out independently FFC Process Simple process Difficult metal / salt separation Semi-continuous process Reduction and electrolysis have to be carried out simultaneously Sensitive to carbon and iron contamination Low current efficiency OS Process Simple process Difficult metal / salt separation Semi-continuous process Sensitive to carbon and iron contamination PRP (Preform Effective control of purity Low current efficiency Reduction and morphology Difficult recovery of reductant Process) Flexible scalability Resistant to contamination Small amount of fluxes necessary EMR / MSE Resistant to iron and carbon Environmental burden by leaching Process contamination Difficult metal / salt separation when oxide Semi-continuous process system Reduction and electrolysis operation Complicated cell structure can be carried out independently Complicated process 35

36 Product Ti pellets Ti (+ CaO + CaCl 2 ) Carbon anode Feed preform (TiO 2 + CaCl 2 ) Current monitor / controller A e - V n A e - V e - CO x gas CaCl 2 -CaO e - Ca CaCl 2 -CaO molten salt TiO e - = Ti + 2 O 2- Ca (Ca-X alloy) = Ca e - Daytime reduction O 2-, Ca 2+ Ca-X reductant alloy Ca (Ca-X alloy) C + x O 2- = CO x + 2x e - Ca e - = Ca (Ca-X alloy) Nighttime electrolysis Fig. Conceptual image of the new titanium reduction process currently under investigation (EMR / MSE process, Oxide system). 36

37 Preform Reduction Process (PRP) TIG weld Stainless steel cover Stainless steel reaction vessel Feed preform (MO x + flux) Stainless steel plate R reductant Ti sponge getter MO x + R M + RO M = Nb, Ta, Ti R = Mg, Ca Fig. Schematic illustration of the experimental apparatus for producing titanium powder by means of the preform reduction process (PRP). 1. Amount of flux (molten salt) is small. 2. Easy to prevent contamination from reaction vessel and reductant. 3. Highly scalable. 37

38 (a) Conventional Metallothermic Reduction Feed powder (b) Preform Reduction Process (PRP) Feed preform Reductant vapor Reductant vapor Reductant (R = Ca, Mg) Reductant (R = Ca, Mg) Fig. Metal powder production process: (a) conventional metallothermic reduction, (b) preform reduction process (PRP). 38

39 Selective chlorination using MgCl 2 Vacuum pump Chlorides Condenser Glass flange Glass beads Stainless steel net Deposit (FeCl x...) FeO x (s) + MgCl 2 (l) = FeCl x (l) + MgO (s) Chlorination Reactor N 2 or N 2 +H 2 O gas Stainless steel susceptor Carbon crucible Mixture of Ti ore and MgCl 2 RF coil Quartz flange Ceramic tube (Fe-free Ti ore) Experimental condition T = 1100 K, t = 1 h, Atmosphere : N 2, Ti ore (UGI) : 4 g, MgCl 2 : 2 g Fig. Experimental apparatus for selective-chlorination of titanium ore using MgCl 2 as a chlorine source. 39

40 Results of previous study FeO x (s) + MgCl 2 (l) = FeCl x (l, g) + MgO (s) XRD analysis XRF analysis Intensity, I (a. u.) Deposit obtained after selective -chlorination. FeCl 2 was generated Angle, 2θ (deg.) : FeCl 2 Fig. XRD pattern of the deposit at chlorides condenser. The sample powder was sealed in Kapton film before analysis Residue after selective-chlorination. Fe was selective chlorinated. Table Analytical results of titanium ore, the residue after selective chlorination, and the sample after reduction. These values are determined by XRF analysis. Ti ore (UGI from Ind.) After heating sample After reduction sample Concentration of element i, C i (mass %) Ti Fe Si Al V

41 Chlorination of Ti using FeCl 2 Quartz tube Sample mixture: (e.g., FeCl 2 +Ti powder) Ti (s) + 2 FeCl 2 (s) = TiCl 4 (g) + 2 Fe (s) Sample deposits Heater (on Si rubber, NaOH gas trap and quartz tube) Carbon crucible Fig. Experimental apparatus for chlorination of titanium using FeCl 2 as a chlorine source. XRF analysis Table Analytical results of the samples before and after heating and the sample deposited on quartz tube and Si rubber. These values are determined by XRF analysis. Concentration of element i, C i (mass %) Residue before heating Residue after heating Dep. on quartz tube after heating Dep. on Si rubber after heating Ti Fe Cl

42 This study Low-grade Ti ore (FeTiO x ) MCl x (CaCl2) Selective chlorination by electrochemical method FeCl x Ti scrap Chlorine recovery Upgraded Ti ore (TiO 2 ) FeCl x (+ AlCl 3 ) Fe TiCl 4 Ti smelting by electrochemical method Ti metal Fig. Flowchart of new titanium smelting process from titanium ore discussed in this study. 42

43 Iron removal process by electrochemical method Selective chlorination Iron removal process Cathode: Fe n+ + n e - Fe Ca e - Ca Anode : 2 Cl - Cl e - FeO x + Cl 2 FeCl x (l, g) + O e - A V TiFeO X Ti ore(tio 2 + FeO x ) Reference electrode Mild steel crucible(cathode) Molten CaCl 2 Carbon crucible(anode) Establishment of a new up-grading process of Ti ore by electrochemical method. Direct reduction process from Ti ore to Ti metal can be achieved. e - 2. TiO 2 reduction process (e.g. EMR-MSE process) Cathode: Anode : A TiO 2 Ti e - e - O 2- Ti reduction TiO e - Ti + O 2- Ca(or Ca-X) Production of reductant Ca e - Carbon electrode Ti crucible(cathode) Molten CaCl 2 -CaO Ca-X alloy 43

44 (a) Iron removal process e - Carbon crucible containing Ti ore + CaCl 2 mixture (Anode) (b) FFC process (Fray et al., 2000) e - Carbon anode CaCl 2 molten salt Molten CaCl 2 Sample Mild steel crucible (Cathode) TiO 2 preform Electrolysis Electrolysis Cathode: Ca e - Ca (a1) Cathode: TiO e - Ti + 2 O 2- (b1) Anode: 2 Cl - Cl e - (a2) Anode: C + x O 2- CO x + 2x e - (b2) FeO x + Cl 2 + C FeCl x + CO x (a3) Fig. Schematic illustrations of the processes investigated in this study. 44

45 Potential of several reaction 2CaCl 2 + O 2 2CaO + 2Cl 2 2MgCl 2 + O 2 2MgO + 2Cl 2 4HCl + O 2 2H 2 O + 2Cl 2 2CO + O 2 2CO 2 2C + O 2 K log p Cl22 / p O2 = log p Cl22 / p O2 = 0.48 log p Cl22 / p O2 = 1.49 log p O2 = log p O2 = e.g. FeO + MgCl 2 FeCl 2 + MgO ΔG= kj < 0 45

46 Table Gibbs energy change of formation in the Fe-Ti-O system. Reactions Gibbs energy change, G ο f (kj/mol) Ref. a 900 K 1100 K 1300 K Fe (s ) + Cl 2 (g ) = FeCl 2 (s ) [1] Fe (s ) + Cl 2 (g ) = FeCl 2 (l ) [1] Fe (s ) Cl 2 (g ) = FeCl 2 (g ) [1] Fe (s ) Cl 2 (g ) = FeCl 3 (g ) [1] Fe (s ) O 2 (g ) = FeO (s ) [1] 2 Fe (s ) O 2 (g ) = Fe 2 O 3 (s ) [1] 3 Fe (s ) + 2 O 2 (g ) = Fe 3 O 4 (s ) [1] Ti (s ) + Cl 2 (g ) = TiCl 2 (s ) [1] Ti (s ) + Cl 2 (g ) = TiCl 2 (g ) [1] Ti (s ) Cl 2 (g ) = TiCl 3 (s ) [1] Ti (s ) Cl 2 (g ) = TiCl 3 (g ) [1] Ti (s ) + 2 Cl 2 (g ) = TiCl 4 (g ) [1] Ti (s ) O 2 (g ) = TiO (s ) [1] Ti (s ) O 2 (g ) = TiO (g ) [1] Ti (s ) + O 2 (g ) = TiO 2 (s ) [1] 2 Ti (s ) O 2 (g ) = Ti 2 O 3 (s ) [1] 3 Ti (s ) O 2 (g ) = Ti 3 O 5 (s ) [1] 4 Ti (s ) O 2 (g ) = Ti 4 O 7 (s ) [1] a: References [1] I. Barin, Thermochemical Data of Pure Substances, 3rd ed., (Weinheim, Federal Republic of Germany, VCH Verlagsgesellschaft mbh, 1997). 46

47 Temperature, T / K TiCl 4 (l) -2 Region suitable for vaporization of chlorides Vapor pressure, log p i (atm) CaCl 2 (s, l) TiCl 2 (s) TiCl 3 (s) FeCl 3 (s,l) -10 Ti (s,l) Fe (s,l) MgCl 2 (s, l) FeCl 2 (s,l) Reciprocal temperature, 1000 T -1 / K -1 Fig. Vapor pressure of iron, calcium, magnesium and titanium chlorides as a function of reciprocal temperature. 47

48 Thermodynamic analysis (FeO x chlorination) Fe-Cl-O system, T = 1100 K Oxygen partial pressure, log p O2 (atm) Fe 2 O 3 (s) Fe 3 O 4 (s) FeO (s) Fe (s) FeCl 2 (l) FeCl 3 (g) Chlorine partial pressure, log p Cl2 (atm) CaO (s) / CaCl 2 (l) a CaO = 0.1 H 2 O(g) / HCl (g) CO / CO 2 eq. C / CO eq. MgO (g) / MgCl 2 (l) eq. e.g. Fig. Chemical potential diagram for Fe-Cl-O system at 1100 K. Ti ore : mixture of TiO x and FeO x. FeO X (s) + MgCl 2 (l) FeCl X (l, g) + MgO (s, l) FeO x can be chlorinated by controlling oxygen and chlorine partial pressure. 48

49 Thermodynamic analysis (TiO x chlorination) Ti-Cl-O system, T = 1100 K Oxygen partial pressure, log p O2 (atm) TiO 2 (s) Ti 3 O 5 (s) Ti 2 O 3 (s) TiO (s) Ti (s) Fe / FeCl 2 eq. Ti 4 O 7 (s) TiCl 3 (s) TiCl 2 (s) TiCl 4 (g) Chlorine partial pressure, log p Cl2 (atm) CaO (s) / CaCl 2 (l) a CaO = 0.1 H 2 O(g) / HCl (g) CO / CO 2 eq. C / CO eq. MgO (g) / MgCl 2 (l) eq. Fig. Chemical potential diagram for Ti-Cl-O system at 1100 K. Ti ore : mixture of TiO x and FeO x. Since TiCl 4 is highly volatile species, chlorine partial pressure must be kept in the oxide stable region. 49

50 50

51 This chapter Low-grade Ti ore (FeTiO x ) MCl x (CaCl 2 ) Selective chlorination by electrochemical method FeCl x Ti scrap Chlorine recovery Upgraded Ti ore (TiO 2 ) FeCl x (+ AlCl 3 ) Fe TiCl 4 Ti smelting by electrochemical method Ti metal Fig. Flowchart of the new titanium smelting process discussed in this study. 51

52 Ti ore Flux Binder Mixing Slurry Flux : CaCl 2, MgCl 2 Binder: Collodion Preform fabrication Feed preform Calcination / Iron removal FeCl x Sintered feed preform Fig. Flowchart of the procedure of preform fablication supplied for Fe removal experiment. 52

53 Table Composition of titanium ore (ilmenite) and up-graded ilmenite (UGI) used this study. Sample name Composition (mass%) a Total Fe TiO 2 Fe 2 O 3 FeO MnO Al 2 O 3 SiO 2 MgO Nb 2 O 5 P 2 O 5 Moisture ilmenaite b c UGI d < UGI e a: Nominal value. b: Natural ilmenite ore produced in Australia. c: This is value as Mn. d: Up-graded ilmenite by the Beacher process (see Fig. 1-7). The ore was produced in Australia. e: Up-graded ilmenite by the Benilite process (see Fig. 1-6). The ore was produced in India. 53

54 Table Starting materials used in this study. Materials Form Purity or conc. (%) Supplier Collodion a Liquid 5.0 Wako Pure Chemical., Inc. CaCl 2 Powder 95.0up Kanto Chemicals, Inc. Ca Ti CH 3 COOH HCl 2-Propanol Chip 98.0up Osaka Tokusyu Goukin Co., Ltd. Sponge 98.0up Toho Titanium Co., Ltd. Liquid 99.7 Kanto Chemicals, Inc. Liquid 35 Kanto Chemicals, Inc. Liquid 99.5up Kanto Chemicals, Inc. Aceton Liquid 99.0up Kanto Chemicals, Inc. Graphite Crucible Kanto Chemicals, Inc. a : 5 mass% nitro cellulose, mass% ethanol, mass% diethylether. 54

55 Experimental apparatus Electrochemical interface Sample Voltage monitor / controller e - Furnace Molten CaCl 2 Holes on crucible 10 A power source Mild steel crucible (Cathode) Electrochemical control unit Graphite crucible containing Ti ore (Anode) 55

56 V 1 V 2 A 1 A 2 Potential lead (Nickel wire) Stainless steel tube Ar inlet Rubber plug Wheel flange Reaction chamber Thermocouple Heater Mild steel crucible Graphite crucible Ti ore, sample Preform containing Ti ore Molten salt (CaCl 2 ) Ceramic insulator Fig. Schematic illustration of the experimental apparatus in a voltage measurement. 56

57 (a) O.D. 19 mm I.D. 17 mm (b) Support rod (Stainless steel tube) Air hole Screw (Stainless steel) 40 mm Surface of molten salt Inlet of molten salt Graphite crucible Sample (Ti ore, CaCl 2 etc.) Fig. Schematic illustration of the graphite crucible used in this experiment, (a) appearance, (b) inner content. 57

58 i e - A 8 CaCl 2 molten salt Immersion current, i / ma TiO 2 preform (Cathode) Carbon crucible containing Ti ore (Anode) Immersion time, t / s Fig. Variation of the external current from the dipped preform to the graphite crucible. 58

59 V CaCl 2 molten salt TiO 2 preform (Cathode) Carbon crucible containing Ti ore (Anode) Immersion voltage, V / mv Immersion time, t / s Fig. Electromotive force between the dipped preform and the graphite crucible. 59

60 Table Analytical results of various samples a. Sample # Concentration of element i, C i (mass%) b Ti Fe Ca Cl Si Al Cr Fe / Ti ratio c, R Fe / Ti (%) A B C D E a : Ilmenite (FeTiOx) produced in China. b : Determined by X-ray fluorescence analysis. This value excludes carbon and gaseous elements. c : Indicator of iron removal from titanium ore. 60

61 Temperature, T / Liquid CaCl 2 FeCl 2 content, x (mol%) FeCl FeCl 2 2 Fig. Phase diagram for the CaCl 2 -FeCl 2 system [2]. 61

62 V 1 V 2 A Potential lead (Nickel wire) Stainless steel tube Ar inlet Rubber plug Wheel flange Reaction chamber Thermocouple Heater Mild steel crucible (working) Nickel quasi-reference electrode Graphite crucible (counter) Ti ore Molten salt (CaCl 2 ) Ceramic insulator Fig. Schematic illustration of the experimental apparatus for cyclic voltammetry in molten CaCl 2. 62

63 2 (a) 1 0 Current, i / A (b) Ca e - = Ca (on Fe) V 2 Cl - = Cl e - (on C) Potential (vs Ni quasi-ref.), E / V 2 Fig. Cyclic voltammograms for molten CaCl 2 at 1100 K (a) before pre-electrolysis, (b) after pre-electrolysis, cathode sweep; working: Fe rod; counter: C rod, anode sweep; working: C rod; counter: Fe rod, scan rate: 100 mv / s, immersion length: 4 cm. 63

64 Table Standard Gibbs energy of formation and theoretical voltage for reactions in this study. Reactions Gibbs energy change, G ο f / kj Theoretical voltage for reactions, E o f / V Temperature, T / K Ref. a Fe (s ) + Cl 2 (g ) = FeCl 2 (l ) [1] Fe (s ) Cl 2 (g ) = FeCl 2 (g ) [1] Fe (s ) Cl 2 (g ) = FeCl 3 (g ) [1] Fe (s ) O 2 (g ) = FeO (s ) [1] 2 Fe (s ) O 2 (g ) = Fe 2 O 3 (s ) [1] 3 Fe (s ) + 2 O 2 (g ) = Fe 3 O 4 (s ) [1] Ti (s ) O 2 (g ) = TiO (s ) [1] Ti (s ) O 2 (g ) = TiO (g ) [1] Ti (s ) + O 2 (g ) = TiO 2 (s ) [1] 2 Ti (s ) O 2 (g ) = Ti 2 O 3 (s ) [1] 3 Ti (s ) O 2 (g ) = Ti 3 O 5 (s ) [1] 4 Ti (s ) O 2 (g ) = Ti 4 O 7 (s ) [1] Ca (s ) + Cl 2 (g ) = CaCl 2 (l ) [1] Ca (s ) O 2 (g ) = CaO (s ) [1] CaO (s ) + C (s ) = Ca (s ) + CO (g ) [1] CaO (s ) C (s ) = Ca (s ) CO [1] C (s ) O 2 (g ) = CO (g ) [1] C (s ) + O 2 (g ) = CO 2 (g ) [1] Fe (s ) + Ti (s ) O 2 (g ) = FeTiO [1] 2 Fe (s ) + Ti (s ) + 2 O 2 (g ) = Fe 2 TiO [1] a: References b: E o = - G o / nf, where n is electron transfer number, and F is Faraday constant. [1] I. Barin, Thermochemical Data of Pure Substances, 3rd ed., (Weinheim, Federal Republic of Germany, VCH Verlagsgesellschaft mbh, 1997). 64

65 2 1 (a) Ca e - = Ca (on Fe) V 2 Cl - = Cl e - (on C) 2 (b) Ca e - = Ca (on Fe) Current, i / A V C + x O 2- = CO x + 2x e - (on C) 2 (c) Ca e - = Ca (on Fe) V C + x O 2- = CO x + 2x e - (on C) Potential (vs Ca / Ca 2+ ref.), E / V 3 Fig. Cyclic voltammograms for molten CaCl 2 at 1100 K after Ca deposition using various carbon electrode, (a) C rod, scan rate: 100 mv / s, (b) C crucible, scan rate: 100 mv / s, (c) Ti ore holding C crucible, scan rate: 20 mv / s, cathode sweep; working: Fe rod; counter: Carbon, anode sweep; working: Carbon; counter: Fe rod, immersion length: 2 cm. 65

66 Temperature, T / C Liq. Two liquids CaCl 2 Ca content, x Ca (mol%) Ca Fig. Phase diagram for the CaCl 2 Ca system [3]. 66

67 e - Mild steel crucible (Cathode) Carbon crucible containing Ti ore + CaCl 2 mixture (Anode) Sample Molten CaCl 2 Fig. Schematic illustration of experimental apparatus for iron removal by electrochemical method. 67

68 V A Potential lead (Nickel wire) Stainless steel tube Ar inlet Rubber plug Wheel flange Stainless steel reaction chamber Thermocouple Heating element Mild steel crucible (Cathode) Graphite crucible (Anode) Ti ore Molten salt (CaCl 2 ) Ceramic insulator Fig. Schematic illustration of the experimental apparatus for iron removal by electrochemical method. 68

69 Ti ore ( + Fe 2 O 3 etc) CaCl 2 Electrochemical iron removal TiO 2 + CaCl 2 Distilled water Separation CaCl 2 CH 3 COOH aq., HCl aq., Distilled water, Isopropanol, Acetone TiO 2 Leaching S L Vacuum drying TiO 2 powder Waste solution Fig. Flowchart of the procedure for iron removal experiment by electrochemical method. 69

70 Experiment 1 Experimental condition: Temperature: 1100 K Atmosphere: Ar Molten salt: CaCl 2 (800 g) Cathode: Mild steel crucible (I.D 96 mm) Anode: Graphite crucible (I.D 17 mm) e - Sample Voltage monitor / controller Exp. No. Mass of Ti ore (Ilmenite), w / g A 4.00 B 4.00 C 4.00 Voltage, E / V Time, t / h Mild steel crucible (Cathode) Molten CaCl 2 Graphite crucible containing Ti ore (Anode) 70

71 Result 1 XRF analysis Table Analytical results of the sample obtained after the electrochemical selective chlorination. Disscussion Ti ore (Ilmenite, FeTiO x ) Sample Concentration of element i, C i (mass %) Fe / Ti ratio, e - Ti Fe Ca Si V R Fe / Ti (%) Ti ore Exp. A After the electrochemical treatment, Fe in the Ti ore was selectively chlorinated and removed Exp. B Exp. C a: Average of the samples obtained from the upper part and lower part of the graphite crucible. Unreacted part Molten CaCl 2 Graphite crucible (Anode) Unreacted part was remained at the bottom of the graphite crucible. 71

72 Table Experimental condition for iron removal from Ti ore by electrochemical method c. Exp. Mass of feed materials i, w i / g Voltage, V / volts Reaction time, t / hr Exp. Mass of feed materials i, w i / g Voltage, V / volts Reaction time, t / hr UGI a Ilmenite b UGI a Ilmenite b A B C D E F G H I J K L M N O P ー a: Upgrade ilmenite by the Benilite process (see Fig.1-6 ). The ore was produced in India (see Table 3-1). b: Ilmenite (FeTiO x ) produced in China. c: Temperature: 1100 K, Ar atmosphere. 72

73 10 A Power Source 20 cm Fig. Schematic illustration of electrochemical interface in this experiment. 73

74 Exp. K Current, I / A Exp. L Exp. M Exp. N Time, t / second Fig. Current generated by imposed each voltage. 74

75 Table Analytical results of the samples obtained after iron removal by electrochemical method. Exp. Composition i, C a i / mass % Fe / Ti Note b # Al Si S Cl Ca Sc Ti V Mn Fe Ni / % UGI c nd nd UGIAUS UGI c nd _UGI A nd _UGI_P04_1 B nd nd nd nd nd nd nd nd nd nd nd nd _UGI_P02 C nd _UGI_P05_2 D nd _UGI_P06_1 E _UGI_P07_2 F nd nd _UGI_P10_1 G nd nd nd _UGI_P01_1 H nd _UGI_P03_1b Ilmenite d nd _ilmenite Ilmenite d nd _ilmenite Ilmenite d nd _ilmenite Ilmenite d nd nd _ilmenite I _ilmenite_P33_2 J nd _ilmenite_P38_1 K nd _ilmenite_P15_1 L nd _ilmenite_P14_1 M nd _ilmenite_P13_3 N _ilmenite_P12_2 O nd _ilmenite_P46_2 P nd _ilmenite_P45_1 Q nd _ilmenite_B_1 a: Determined by XRF analysis. b: Experimental date. c: Upgraded ilmenite produced in Australia. d: Ilmenite (FeTiO x ) produced in China. nd: not detected. Below detection limit of XRF (< 0.01%) 75

76 100 mm V 1 V 2 A 1 A 2 Potential lead (Ni wire) Stainless steel tube (Electrode) Ar inlet Rubber plug Wheel flange Thermocouple Heater Mild steel crucible (Cathode) Graphite crucible (Anode) Ti ore + CaCl 2 mixture Molten salt (CaCl 2 ) Ceramic insulator Fig. Schematic illustration of experimental apparatus in this experiment. 76

77 12 3 Current / A Current Voltage Voltage / V Time / s 0 Fig. Current value passed by imposed certain voltage, and voltage in this experiment, Exp. F. 77

78 Intensity, I (a. u.) : CaTiO 3 (JCPDS # ) : TiO 2 (JCPDS # ) Angle, 2θ (degree) Fig. XRD pattern of the obtained sample after selective chlorination experiment. 78

79 Table Experimental condition and analytical results of the chlorination experiment using ilmenite. Mass of feed material i, w i / g CaCl 2 / FeO x Imposed Reaction Average Fe / Ti Obtained Exp. Ilmemite Carbon CaCl 2 ratio, voltage, time, current, ratio a, sample, M Ca / Ti / - V / volts. t / hr I / A R Fe / Ti / % w / g Note b - Ilmenite c _ilmenite A _P48 1 B _P49 C _P50 Use bath # 2 D _P53 E _P55 F c c _P56 3 (Old) 4 G _P57 H _P58 I _P59 J _P60 K _P61 L _P62 M P63 N _P64 O _P66 P _P67 Q _P69 R _P70 S _P72 T _P73 U d d _P74 V e e _P75 a: Indicator of iron removal from titanium ore. b: Experiment number c: Ilmenite (FeTiO x ) produced in China. d: 2.0 volts 20 minutes, and 1.5 volts 3hours e: 1.8 volts 6 hours, and 3.0 volts 3 hours f: 2.0 volts, 1.5 volts, 1.8 volts, and 2.0 volts, 1 hour respectively 79

80 Table Experimental conditions and analytical results of the chlorination experiment using UGI. Mass of feed material i, w i / g CaCl 2 / FeO x Imposed Reaction Fe / Ti Obtained Mass decrease of ratio, voltage, time, ratio b, sample, carbon crucible, Exp. UGI a CaCl 2 M Note c Ca / Ti / - V / volts t / hour R Fe / Ti / % w 1 / g w 2 / g d _UGIAUS A _P77 A _P89 B _P79 B _P87 C _P82 Use bath # 5 C _P86 D _P81 E _P78 F _P84 F _P85 G _P80 H 2.08 e _P88 4 I f f _P76 5 J _P83 K 1.59 g _P90 a: Up-graded ilmenite by the Beacher process (see Fig. 1-6). The ore was produced in Australia. b: Indicator of iron removal from titanium ore. c: Experiment date and number d: Reference e: Mixture 2.08 g of Ti ore and 0.08 g of carbon powder f: 2 volts 2 hours, and 2 volts 2hours g: Up-graded ilmenite by the Benilite process (see Fig. 1-5). The ore was produced in India. 80

81 Low-grade Ti ore (FeTiO x ) MCl x (CaCl 2 ) Selective chlorination by electrochemical method FeCl x Ti scrap Chlorine recovery Upgraded Ti ore (TiO 2 ) FeCl x (+ AlCl 3 ) Fe TiCl 4 Ti smelting by electrochemical method Ti metal This chapter Fig. Flowchart of new titanium smelting process from titanium ore discussed in this chapter. 81

82 V A Potential lead (Nickel wire) Stainless steel tube Ar inlet Rubber plug Wheel flange Reaction chamber Thermocouple Heater Mild steel crucible Ti crucible (Cathode) Graphite rod (Anode) Mixture of Ti ore after Fe removal and CaCl 2 Molten salt (CaCl 2 ) Ceramic insulator Fig. Schematic illustration of the experimental apparatus for electrochemical reduction of Ti ore after Fe removal. 82

83 Ti ore (+Fe 2 O 3 etc) CaCl 2 Mixing Mixture CaCl 2 Electrochemical reduction CH 3 COOH aq., HCl aq., Distilled water, Isopropanol, Acetone Ti + CaCl 2 Leaching S L Vacuum drying Ti powder Waste solution Fig. Flowchart of the experimental procedure for electrochemical reduction of Ti ore after Fe removal. 83

84 Table Experimental conditions for electrochemical reduction of Ti ore after Fe removal. Exp. No. Mass of feed material i, C i / g Ti ore CaTiO 3 CaCl 2 Voltage, E / V Time, t / h R1 ー R2 ー R a ー R b ー a: The sample obtained by selective chlorination exp. A. b: The sample obtained by selective chlorination exp. D. 84

85 Temperature, T / C K CaO content, x CaO (mol%) CaCl CaO Fig. Phase diagram for the CaCl 2 CaO system. 85