Direct Production of Titanium Powder from Titanium Ore by Preform Reduction Process

Haiyan Zheng 1 and Toru H. Okabe 1

1 Institute of Industrial Science, University of Tokyo, Graduate Student

Current status of industrial production of Ti

Metal Iron Aluminum TitaniumSymbol Fe Al TiMelting point (K) 1809 933 1939Density (g/cm3 at 298 K)

7.9 2.7 4.5

Specific strength((kgf/mm2)/(g/cm3))

4~7 3~6 8~10

Clarke no. 4 3 9Price (\/kg) 50 600 3000Production volume (t/world in 2003)

9.6 x 108 2.2 x 107 6.6 x 104

1/150001/300

Comparison with common metals

World production of Ti sponge (2003)

China4 kt

USA8 kt

Russia26 ktTotal

65.5 ktKazakhstan9 kt

Japan18.5 kt (28% share)

Introduction

Chlorination Ti ore + C + 2 Cl2 → TiCl4 (+ MClx) + CO2

Reduction TiCl4 + 2 Mg → Ti + 2 MgCl2

Electrolysis MgCl2 → Mg + Cl2

The Kroll process Current commercial Ti production process

Features of the Kroll process:◎High-purity Ti can be obtained.◎Metal/salt separation is simple.○Chlorine circulation is established.○Efficient Mg electrolysis can be utilized.○Reduction and electrolysis can be carried out independently.×Process is complicated.×Reduction process is batch type.×Production speed is low.×Chloride wastes are produced.

Mg & TiCl4 feed port

Mg & MgCl2 recovery port

Ti sponge

Ti/Mg/MgCl2 mixture

Furnace

Metallic reaction vessel

Production cost of Ti is high and its application is limited.

Direct reduction of TiO2

e–

CaCl2 molten salt

TiO2 preform

Carbon anode

(a) FFC process (Fray et al.)

TiO2 powder

Carbon anode

e–

CaCl2 molten salt

Ca

(b) OS process (Ono & Suzuki)

CaCl2-CaO molten salt

Current monitor/controller

e–

Carbon anode

TiO2

e–

Ca-X alloy

(c) EMR/MSE process (Okabe et al.)

(d) PRP

Reductant vaporReductant(R = Ca or Ca-X alloy)

Feed preform(TiO2 feed + flux)

Common features:

○Simple process○Semi-continuous process

×Difficult to control the purity×Large amount of molten salt

Preform reduction process (PRP)

Features: → Simple and low-cost process◎Suitable for uniform reduction◎Flexible scalability○Possible to control the morphology of the powder by varying the flux content in the preform○Possible to prevent the contamination from the reaction container and control purity ○Amount of waste solution is minimized○Molten salt as a flux can be reduced in comparison with the other direct reduction process△Leaching is required×Difficult to produce calcium and control its vapor

TiO2(s) + Ca(g) → Ti(s) + CaO(s)

Purpose of this study:Development of a new smelting process for producing Ti with high purity and productivity and low cost

Reductant vapor

Feed preform(TiO2 feed + flux)

Reductant(R = Ca or Ca-X alloy)

Flowchart of the PRP

Powder

Feed preform

Reduced preform

Mixing

Vacuum drying

Ca vapor

Acid Waste solution

Slurry

Preform fabrication

Ti ore Flux Binder

FeClx

Reduction

Ti ore: Rutile Flux: CaCl2Binder: Collodion

Sintered feed preform

Leaching

Calcination/iron removal

(1)

(2)

(3)

(4)

Research work

Exp.No. a

Cationicmolar ratio

Calcination Reduction

Temp. Time Temp. Time

RCat./Ti b Tcal./K t'cal./h Tred./K t'red./h

A 0.2 1273 1 1273 6

B 0.3 1273 1 1273 6

C c 0.2 1273 2 1273 9

D c 0.3 1273 2 1273 9

Experimental conditions

a: Natural rutile ore produced in South Africa after pulverization.b: Cationic molar ratio, RCat./Ti = NCat./NTi, where NCat. and NTi are the mole amounts of the cations in the flux and Ti, respectively.c: C powder was added to the preform during the fabrication step in experiments C and D.

Table Experimental conditions in this study.

Stainless steel net

Reductant (Ca)

Stainless steel reaction vessel

Ti sponge getter

Feed preformafter Fe removal

TIG welding

Stainless steel cover

Stainless steel holder

Experimental results 1Exp. A, RCat./Ti = 0.2

Photographs(1)

(2)

(3)

(4)

Inte

nsity

, I

(a.u

.)

: TiO2

: CaCl2: CaCl2 (H2O)4

JCPDS # 21-1276JCPDS # 74-0522JCPDS # 01-0989

JCPDS # 44-1294: Ti

Angle, 2 (deg.)10080604020

(1)

(2)

(3)

(4)

XRD patterns: TiO2

: CaCl2: CaCl2 (H2O)4

JCPDS # 21-1276JCPDS # 74-0522JCPDS # 01-0989

: Ti: Ca: CaO

JCPDS # 44-1294JCPDS # 23-0430JCPDS # 48-1467

Metallic Ti was successfully obtained after the experiment.

Feed preform

TiO2 + CaCl2 + Binder

Preform after calcination

TiO2 + CaCl2

Preform after reduction

TiO2 + CaO +Ca

Sample obtainedafter leaching

Ti powder

Experimental results 2Exp. B, RCat./Ti = 0.3

・ Metallic Ti exhibiting a coral-like structure was obtained.・ Purity of Ti was greater than 99 mass %.

Table Analytical results of the obtained sample.

a: Determined by X-ray fluorescence analysis, and the value excludes carbon and gaseous elements.

5 m

(1)

(3)

(2)

(4)

SEM images

5 m

5 m5 m

StepConcentration of element i, Ci

a (mass %)

Ti Fe Al Ca Cl

(1) 68.00 1.07 0.44 11.66 18.83

(2) 60.68 0.42 0.33 14.88 23.70

(3) 17.74 0.07 (0.00) 67.42 14.76

(4) 99.10 0.03 0.30 0.58 (0.00)

Feed preform

TiO2 + CaCl2 + Binder

Preform after calcination

TiO2 + CaCl2

Preform after reduction

TiO2 + CaO + Ca

Sample obtainedafter leaching

Ti powder

Experimental results 3

SEM image

Exp. C, RCat./Ti = 0.2, C powder: 0.2 g

5 m

Table Analytical results of the obtained sample.

a: Determined by X-ray fluorescence analysis, and the value excludes carbon and gaseous elements.

Iron removal efficiency was improved when C powder was added to the preform.

StepConcentration of element i, Ci

a (mass %)

Ti Fe Al Ca Cl

(1) 67.64 1.36 0.50 10.20 20.29

(2) 65.99 0.13 0.08 11.65 22.15

(3) 18.79 0.10 (0.00) 67.98 13.09

(4) 98.23 0.23 0.56 0.98 (0.00)

XRD pattern(4)

20 40 60 80 100

JCPDS # 44-1294: Ti(4)

Experimental results 4

・ High-purity metallic Ti powder was obtained directly from natural Ti ore.

・ Iron removal ratio was enhanced when C powder was added to the preform.

・ Ti powder with a yield of 88% was obtained.

Exp. No.

Cationic molar ratio

RCat./Ti a

Concentration of Ti and Fe in

the obtained Ti powderC b (mass %)

Iron removal ratio c

(%)

Yield(%)

Ti Fe others

A 0.2 98.16 0.88 1.76 59 -

B 0.3 99.10 0.03 0.87 56 -

C 0.2 98.23 0.23 1.54 90 79

D 0.3 98.44 0.14 1.42 65 88

Table Composition of the samples obtained after leaching and yield of Ti powder

a: Cationic molar ratio, RCat./Ti = NCat./NTi, where NCat. and NTi are the mole amounts of the cations in the flux and Ti, respectively.b: Determined by X-ray fluorescence analysis, and the value excludes carbon and gaseous elements.c: Iron removal ratio: (CFe/CTi (Before) – CFe/CTi (After))/(CFe/CTi (Before))

Discussion

FeOx (FeTiOx,s) + HCl(g) → FeClx(g)↑ + H2O(g)FeOx (FeTiOx,s) + CaCl2(l) → FeClx(g)↑ + CaO (CaTiOx,s) aCaO << 1

・ FeOx can be chlorinated using CaCl2 + H2O.

・ TiOx cannot be chlorinated using CaCl2 or CaCl2 + H2O.

Mechanism of iron removal (Ti ore chlorination)

Fig. Combined chemical potential diagram of the Fe-Cl-O (dotted line) and Ti-Cl-O (solid line) systems at 1300 K.

TiCl4(g)TiCl3(g)

–40

–10

–30

–20

–50

–60–40 –10–30 –20 0

CaO(s)/CaCl2(l) eq.

H2O(g)/HCl(g) eq.MgO(g)/MgCl2(g) eq.

log pCl2 (atm)

FeCl3(g)Ti3O5(s)Ti4O7(s)

FeCl2(g)

Fe2O3(s)

Fe3O4(s)FeO(s)TiO2(s)Fe(s)

Ti2O3(s)

TiO(s)

Ti(s)

Region for Selective chlorination of iron

log

p O2 (

atm

)

The feasibility of the preform reduction process (PRP), based on the calciothermic reduction of natural Ti ore, was demonstrated.

・ 90% of iron was successfully removed by selective chlorination during the calcination step.

・ When C powder was added to the preform, iron was removed more efficiently, and Ti powder with a purity of 98% and yield of 88% was obtained.

・ It was experimentally demonstrated that high-purity metallic Ti powder (greater than 99 mass %) was obtained directly from natural Ti ore (rutile ore) by the PRP.

Currently, the development of a more effective method for the direct removal of iron from Ti ore, analysis of the detailed mechanism of selective chlorination, and development of an efficient recycling system of CaCl2 flux and the residual Ca reductant are under investigation.

Conclusion

Ti powder obtained after leaching

Typical experimental apparatusfor the reduction process

0

1 cm

C(s)/CO(g) eq.CO(g)/CO2(g) eq.