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1 PRODUCTION OF MAGNESIUM AND ALUMINUM-MAGNESIUM ALLOYS FROM RECYCLED SECONDARY ALUMINUM SCRAP MELTS A.J. Gesing 1 , S.K. Das 1 , R. Lutfe 2 1. Phinix L.L.C., 2. MER Corp.

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1

PRODUCTION OF MAGNESIUM

AND ALUMINUM-MAGNESIUM

ALLOYS FROM RECYCLED

SECONDARY ALUMINUM SCRAP

MELTS

A.J. Gesing1, S.K. Das1, R. Lutfe2

1. Phinix L.L.C., 2. MER Corp.

2

Outline

• Need for Mg recovery for recycling

• Mg recovery process concept

• Theoretical considerations and experimental

program

• Experimental results

• Markets and economics

• Proof-of-concept

3

Need for recovery and recycling of Mg scrap

• Mg is formed by HP diecasting

• In-house diecasting scrap is recycled

• Post-consumer Mg scrap is not recycled

• Mg scrap shred is usually left in Al fraction

• Most Mg is recycled as alloying element of Al

• Excess Mg is chlorinated out of Al alloy melt

>30,000 tonnes of Mg/year in NA• This chlorination is equivalent to burning

US$60 million/year in NA

4

Expensive prime dilution• 300,000 tonnes/y of energy intensive prime Al is used in

NA to dilute ~0.5wt% excess Mg in the UBC melt

destined for 3X04 can body alloy at a premium of

~US$950/tonne.

• 100,000 tonnes/y of expensive and energy intensive

prime Al is used in NA to dilute ~1 wt% excess Mg in the

mixed 3754-6111 new stamping plant scrap melt

destined for 6111 auto closure sheet at a premium of

~US$600/tonne

• Electrorefining of Mg for recycling from these sheet alloy

melts in NA would:

• recover 7,000 tonnes/y of Mg valued at:

$14 million/y

• avoid 400,000 tonnes/y of prime Al, with premiums of:

US$345 million/y

5

Mg recycling process concept

Replace chlorination

system with an

electrorefining cell in Al

remelt facility

+

Al melter

Electrolyte

Anode + Al-Si-Cu-Mn-Fe melt

Al-Mg-Si-Cu-Mn-Fe scrap

Prime purityMg-Al melt

Specification purityAl-Si-Cu-Mn-Fe

-

Cathode – Mg-Al

Al-Si-Cu-Mn-Fe melt

6

Mg recycling process concept

Replace chlorination

system with an

electrorefining cell in Al

remelt facility

7

Mg electrorefining cell

Mg-Al (r=1.6)

Electrolyte(r=2.0)

Al-Mg(r=2.3)

Mg2+ + 2 e- Mg

Mg Mg2+ + 2 e-

?

DE = 0DE = -RT/2F × ln( )

[Mg]Mg

[Mg]Al

Open circuit potential

8

Preferred Fluoride Electrolyte

Only one viable composition range for fluorides for 2.05 density

system:

84+/-3 LiF + 16+/-3 MgF2

Advantages:

• Very high ionic electrical conductivity low power consumption

• Very low electronic conductivity high current efficiency

• Low viscosity good circulation

• No complexing between Li+ and Mg2+ high mobility of Mg2+ in

the electrolyte.

• Not very hygroscopic

• Superheat in the right range for liquid containment in electrolyte

freeze

Disadvantages:

• Experimentally 0.2 wt% Li in MgAl cathode metal

9

Electrorefining experiments

Anode +

Cathode -

Mg collection

Al impeller

Ar purge

Electrolyte

Al

C felt filter

Mg feed

Mg out

Vacuum

Electrolyte impeller

Lid

Alumina insulator

30 cm

10

Laboratory cell parameters

Electrolyte 84 LiF + 16 MgF2

Inter-electrode distance (cm) 8

Nominal cathode electrode area (cm2) 50–300

Cathode material graphite or steel

Anode crucible material graphite

High temperature electrical insulator >99.5% alpha alumina

Current density (A/cm2) 0.5–3.5

Cell current (A) 50–300

Cell voltage (V) 0.5–3

11

Electrorefining Results

Cell voltage and energy consumption

• Low cell voltage: 1 V @ 0.9 A/cm2, 2.1 V @ 3.5 A/cm2

• Stable operation: +/- 0.1 V up to CD of 3.5 A/cm2

• Energy consumption: 2.5 kWh/kg of Mg @ 0.9 A/cm2

0

0.5

1

1.5

2

2.5

0 1 2 3 4

Ce

ll vo

ltag

e (

V)

Current density (A/cm2)

12

Mg extraction from the anode alloy

• Mg added to anode at intervals to keep Mg in Al melt at ~1.5 wt%

• Al cathode sampled at intervals and analyzed for Mg content. Measured

concentration compared with calculations based on assumed current efficiency.

• Efficiency of Mg extraction from Al anode: ~ 100% (best fit of prediction to data)

10

15

20

25

30

35

40

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 1 2 3 4 5 Mg

AZ6

1 a

dd

itio

n t

o A

l me

lt (

g)

Mg

in A

l an

od

e a

lloy

(wt%

)

Electrorefining time (hours)

predicted

average

Mg AZ61 addition

13

Electrolyte stability

• Electrolyte sampled at intervals and analyzed by EDX-XRF.

• Stable XRF intensity ratio IMg / IF indicates no change in the LiF:

MgF2 ratio during electrolysis

0.1

0.2

0.3

0.4

0.5

0 1 2 3 4 5 6 7

EDX

X-r

ay in

ten

sity

rat

io I

Mg/I

F

Elapsed time (h)

Electrorefining at current density of 0.88 A/cm2

14

Mg recovery at the

cathode

Mg weight

recovered > 62 g

Mg content of

cathode>99%

Mg recovery by

weight>87%

Mg recovery by

acid dissolution

- H2 evolution97%

14

Mg

Mg

electrolyte

Steel

Steel tube

+ Al

-

15

Cathode Mg product elemental composition Sample

Comments#1 wt% #2 wt%

Mg 98.60…. 99.66…. High selectivity for Mg

Al 0.86…. 0.0630 Variable between Mg droplets:

different current density

different Mg% in Al

Li 0.5400 0.2200

Na 0.0055 0.0075

Fe 0.0106 0.0021 (Si + Fe) 0.02~0.04% << 0.3% target

(Si+Fe+Cu+Zn+Mn+Co) 0.025~0.046%

NO electrolytic transfer to cathode

PRIME PURITY product

Si 0.0077 0.0395

Mn <0.0010 0.0011

Zn 0.0015 0.0016

Co 0.0035 0.0015

Cu <0.0010

• Cathode product used for ICP was recovered from the cathode surface during cell post-mortem

• Contaminants are diluted by a factor of 20-100 when Mg product is used as alloying additive to Al

• Na + Li can be refined out of the molten Al alloy

• Mg product composition is suitable for alloying prime Al alloys

16

Anode Al product ICP elemental composition

• Anode product was sampled during electrorefining run with power on.• Mg and alkali metals are extracted from the anode pool during electrorefining• Transition metals remain in the anode and are not transferred to the

cathode product

• Mg in the Al product can be reduced to 0.14 wt%, OK for foundry alloys

Start EndComment

wt% wt.%

Al 95.560

0

98.800

0

Al concentrates as Mg moves to cathode

Mg 3.3500 0.1400 20X reduction, 95% Mg removed

Li 0.1020 0.0090 << 0.05%, 90% Li removed

10X reduction during electrorefining

Na 0.0019 0.0014 No change

Fe 0.2220 0.2920

No change

No undesirable electrolytic transfer to the

cathode product

Si 0.0620 0.0550

Mn 0.5470 0.5430

Zn 0.1500 0.1530

Cu 0.3450

Co 0.0070 0.0060

17

Selected Markets• 38x and 319 foundry alloy: ( US market 1.0 ×106 t/y)

– 380.X scrap melter feed with 1-2 wt% Mg; product 0.1% Mg

– Drivers: eliminate chlorination, recover Mg, improve Al recovery

• 3004 can body sheet: (US market 1.5 × 106 t/y)

– 100% UBC melter feed (83% 3004 + 17% 5182, ~1.5 wt% Mg melt)

– product with ~1% Mg

– Drivers: reduce feed costs (no prime Al), recover Mg

• 6111 auto closure sheet: (US market 0.3 × 106 t/y)

– New, mixed 5754 (3% Mg) and 6111 (1% Mg) stamping plant sheet scrap

melter feed with 1.5%~2% Mg; product with ~0.75% Mg

– Drivers: reduce feed costs (no prime Al or scrap sorting ), recover Mg

• Mg hardener for alloying prime Al alloys

– Prime quality Mg electrorefined from each of the three markets above.

– Drivers: Low cost prime purity Mg (same production cost and

environmental impact as secondary Al alloy products <<< prime Mg

production cost and environmental impact)

18

Conclusions• Experimental results exceeded almost all project targets.

– Low energy consumption

– Low GHG emissions

– High current efficiency

– High Mg recovery

– Product compositions suitable for selected markets

• Techno-economic results

– Production costs competitive with Al secondary alloy production for

the selected markets

• Conceptual process and equipment design combined with positive

experimental results and profitable tecno-economic analysis give a

proof-of-concept for the RE12 electrorefining process of Mg

recovery from Al alloy melts.

19

AcknowledgementsFinancial and technical assistance:

US DOE ARPA-e, Contract Number DE-AR0000413.

James Klausner (Program Director), Bahman Abbasi,

Thomas Bucher and Daniel Matuszak.

Industrial and commercialization:

Ray Peterson of Real Alloy

Experiments at MER Corporation

Raouf Loutfy, Kevin Loutfy, David Thweatt, Y. Kim,

Jay DeSilva, Charles Ibrahim and Mr. Robert Hoffman

Mark Gesing of Gesing Consultants Inc.

Al alloy scrap samples

Real Alloy and Alcoa

FactSage training and support

Prof. Arthur Pelton, Christian Robelin, Aimen Gheribi, Patrice Chartrand