Titanium Extraction by Molten Oxide Electrolysis

Naomi A. Fried and Donald R. Sadoway

Department of Materials Science & EngineeringMassachusetts Institute of Technology

Cambridge, Massachusetts

Sadoway, MIT TMS Meeting, Charlotte, NC March 15, 2004

the need for new technology

many unit operations

problems with Ti extraction today:

high capital costshigh operating costs

environmental liabilities

C & Cl in presence of Odioxins? furans?

Sadoway, MIT TMS Meeting, Charlotte, NC March 15, 2004

Titanium extraction: the front end

O2O2

TiCl4

O2

TiCl4

Sadoway, MIT TMS Meeting, Charlotte, NC March 15, 2004

Titanium extraction: Kroll reduction

Cl2

MgCl2

TiCl4TiCl4

MgCl2

Cl2

Sadoway, MIT TMS Meeting, Charlotte, NC March 15, 2004

a technological response?

extreme form of molten salt electrolysis

molten oxide electrolysis:

where pure oxygen gas is by-product

most metals are found in nature as oxides

“like dissolves like”

Sadoway, MIT TMS Meeting, Charlotte, NC March 15, 2004

schematic of prototype cell

TiO2 Ti + O2

Green metallurgy: processes emitting

only products

Sadoway, MIT TMS Meeting, Charlotte, NC March 15, 2004

Molten oxide electrolysis: the front end

TiO2

O2

TiCl4

TiO2

O2

“Bayer-like”

Sadoway, MIT TMS Meeting, Charlotte, NC March 15, 2004

Molten oxide electrolysis:

O2 by-product high purity TiO2

Molten Oxide Electrolysis

Sadoway, MIT TMS Meeting, Charlotte, NC March 15, 2004

feasibility assessment: issues

molten titanates reportedly exhibit electronic conduction

inert anode operable at 1700ºC

Sadoway, MIT TMS Meeting, Charlotte, NC March 15, 2004

feasibility assessment: current study

electrical conductivity measurements

transference number measurements

modeling electrical properties

applicability to titanium production

Sadoway, MIT TMS Meeting, Charlotte, NC March 15, 2004

conductivity measurements

inventing two new techniques for aggressive melts at high temperatures:

moveable coaxial cylinders

4-point crucible

Sadoway, MIT TMS Meeting, Charlotte, NC March 15, 2004

experimental apparatus

conductivity measurements:- impedance spectroscopy- varying immersions or

varying interelectrode gapisolate melt resistance

Sadoway, MIT TMS Meeting, Charlotte, NC March 15, 2004

all-metal, coaxial-cylinder electrode

(does not contact liquid)enabling high-accuracy conductivity measurements in the most chemically aggressive melts

Mo

Sadoway, MIT TMS Meeting, Charlotte, NC March 15, 2004

moveable coaxial cylinders

Sadoway, MIT TMS Meeting, Charlotte, NC March 15, 2004

TiO2 – BaO phase diagram

Sadoway, MIT TMS Meeting, Charlotte, NC March 15, 2004

tailoring electrical properties

73% TiO2

67% TiO2

67% TiO2

73% TiO2

73% TiO2solid phase present

73% TiO2solid phase present

tran

sfer

ence

num

ber

telectronic

tionic

4.00

3.98

3.96

3.94

3.92

3.90

67% TiO2

73% TiO2

elec

tric

al c

ondu

ctiv

ity (

S/cm

)

ln(σ•T) = 9.867 - 1778/T

ln(σ•T) = 9.896 - 1836/T73% TiO2

67% TiO2

67% TiO2

73% TiO2

73% TiO2solid phase present

73% TiO2solid phase present

tran

sfer

ence

num

ber

telectronic

tionic

4.00

3.98

3.96

3.94

3.92

3.90

67% TiO2

73% TiO2

elec

tric

al c

ondu

ctiv

ity (

S/cm

)

ln(σ•T) = 9.867 - 1778/T

ln(σ•T) = 9.896 - 1836/T

Sadoway, MIT TMS Meeting, Charlotte, NC March 15, 2004

transference number measurements

- stepped-potential chronoamperometry with impedance correction

isolate electronic and ionic components of conductivity

Sadoway, MIT TMS Meeting, Charlotte, NC March 15, 2004

stepped-potential chronoamperometry

potential step = 80 mVinitial current peak of 1.62 A

decaying to 1.27 Ainitial relaxation peak of −0.30 A

decaying to −0.02 A

TiO2–BaO (73 mol% TiO2) T=1400°C

potential step = 80 mVinitial current peak of 1.62 A

decaying to 1.27 Ainitial relaxation peak of −0.30 A

decaying to −0.02 A

TiO2–BaO (73 mol% TiO2) T=1400°C

potential step = 80 mVinitial current peak of 1.62 A

decaying to 1.27 Ainitial relaxation peak of −0.30 A

decaying to −0.02 A

TiO2–BaO (73 mol% TiO2) T=1400°C

Sadoway, MIT TMS Meeting, Charlotte, NC March 15, 2004

tailoring electrical properties

73% TiO2

67% TiO2

67% TiO2

73% TiO2

73% TiO2solid phase present

73% TiO2solid phase present

tran

sfer

ence

num

ber

telectronic

tionic

73% TiO2

67% TiO2

67% TiO2

73% TiO2

73% TiO2solid phase present

73% TiO2solid phase present

tran

sfer

ence

num

ber

telectronic

tionic

73% TiO2

67% TiO2

67% TiO2

73% TiO2

73% TiO2solid phase present

73% TiO2solid phase present

tran

sfer

ence

num

ber

telectronic

tionic

Sadoway, MIT TMS Meeting, Charlotte, NC March 15, 2004

electrowinning experiments

galvanostatic electrolysis at 1450°C

(-) Cu( ) | TiO2 – BaO – MgO | Pt (+)

electrolytic generation of oxygen gas confirmed

Sadoway, MIT TMS Meeting, Charlotte, NC March 15, 2004

next steps

electrolysis in a fully idealized cell:

(-) C | TiO2 – BaO | Pt (+)

electrolysis in a cell w/ idealized anode:

(-) M( ) | TiO2 – BaO | Pt (+)

selection and testing of anode materials

Sadoway, MIT TMS Meeting, Charlotte, NC March 15, 2004

lunar colonization: NASA

oxygen for human life support and rocket propellant

lunar regolith is a multicomponent silicate rich in iron and titanium.

Sadoway, MIT TMS Meeting, Charlotte, NC March 15, 2004

… in closing

high-accuracy electrical conductivity and transference number measurements in molten oxides at extreme temperatures

electrolytic production of liquid titanium not unviable

implications for fluxes and slags,e.g., welding, refining, &

metallothermic reduction

Sadoway, MIT TMS Meeting, Charlotte, NC March 15, 2004

acknowledgment