Design of a Hydrometallurgical Treatment System for Aluminium Waste

Thomas J. Robshaw, Keith Bonser, Glyn Coxhill, Dr Robert Dawson & Dr Mark D. Ogden

1

The SNUCER Group

Dr Mark D. Ogden

2

SHEFFIELD

Ion-Exchange: What We Do

R­ A+ B+ R­ B+ A+Polymermatrix

R+X­ Y­ R+Y­ X­

Cation­exchange

Anion­exchange

Gold refiningPharmaceutical 

purification

Juice processing

Water softening

Metal separation

Sugar decolourisation3

Hall­Héroult electrolytic cellFor aluminium production

REDOX reactions:

2Al2O3 + 3C 4Al + 3CO2

Al2O3 + 3C 2Al + 3CO

Spent Potlining (SPL)

4

Al2O3, Na3AlF6,

AlF3

~50% carbon10% fluoride1% cyanide

1st­cut

2nd­cutGraphite­based

Cement­based

TOXIC EXPLOSIVE

ENORMOUS SAFE STORAGE CHALLENGE

Characteristics of SPL

5

Fluorspar (CaF2)Global reserves: 310 MT“CRITICAL MINERAL”

2nd­cut

GraphiteGlobal reserves: 800 MT

Graphite and Fluorspar

6

050

100150200250300350400450

Eur

o to

nne­

1

Hydrometallurgical SPL Treatment

Proposed new system for maximum fluoride recovery

7

Grinding and screening

Caustic leach

Solid/liquid separation Acid leach

Leachate mixing

Solid/liquid separation

Inert carbon/cement 

product

Solid/liquid separation

Ion­exchange circuit

NaOH

Mixed­cut SPL

H2SO4

Input

Process

Output

Solid waste­stream

Liquid waste­stream

SPL Characterisation and Leaching

10 20 30 40 50 60 70 800

50100150200250300350PXRD 

spectra

10 20 30 40 50 60 70 800

1000

2000

3000

4000

Inte

nsity

 (a.u

.)

2 theta

Sample A Sample B

NaOH (1M) / H2O2 (3%), 3 hrsH2SO4 (0.5M), 2 hrsCombine leachates F­ NO3

­ Fe Al Ca Si0

500

1000

1500

2000

Con

cent

ratio

n in

 leac

hate

 (mg 

L­1)

0.5 M Na0.25 M SO4

2­

pH ~310 30 50 70

0

500

1000

1500

2000

2500

10 30 50 700

5000

10000

15000

Sample A Sample B

Inte

nsity

 (a.u

.)

2 theta

La-MTS9501 Resincitrate > sulfate > oxalate > iodide > nitrate > cromate

> bromide > thiocyanide > chloride > formate > acetate >

fluoride

FFM. Kanesato et al., Chem. Letters, 1988, 207. 9

Puromet MTS9501

Bead diameter = 300 µm

*Full coordinate spheres not shown for clarity

Change of recovery strategy (Na3AlF6) ?

Uptake Mechanisms

T.J. Robshaw et al., Chem. Eng. J., 2019, 367, 149.

F

FF

F

OFH

H

+F

OH

H

2+OH

HAl Al Al

CaF2

€370 per Tonne

Na3AlF6

€750 per Tonne

Proposed Ion-Exchange Circuit

SPL leachate streams Carousel

Lead column

Breakthrough column

Fluoride­loaded column

Pump

NaOH(aq)

Fluoride-selective electrode

Pump

pH electrode

Pump

pH adjust

Na3AlF6(aq)

Defluoridated leachate

To precipitation 

stage

Fluoride­selective electrode

11T.J. Robshaw et al., J. Hazard. Mater., 2019, 361, 200.

La­MTS9501

La­MTS9501

La­MTS9501

100 150 200 250 300 350 400 450 5000

0,5

1

1,5

ExperimentalDose­Response model

Effluent volume (mL)

Bre

akth

roug

h (a

.u.)

20 30 40 50 60 70 80 90 100 110 1200

0,20,40,60,8

11,2

Bre

akth

roug

h (a

.u.)

0 50 100 150 200 250 300 350 400 450 5000

50

100

150

200

250

300

350

400

450

500

Effluent volume (mL)

Fluo

ride 

efflu

ent c

once

ntra

tion 

(mg 

L­1)

q0 = 37 mg g­1

SPL leachate

Pump

Fluoride­selective electrode

12

Dynamic Resin Performance

Contaminants

Recovery

0 100 200 300 400 500 600 7000

200

400

600

800

1000

1200

1400

1600

1800

Fluoride AluminiummL eluent

Con

c. in

 elu

ent (

mg 

L­1)

Elution with water 1M NaOH

€

€€

€

€

€

€€€

13

Conclusions

La­MTS9501 resin is highly suitable for purpose

Al in SPL leachate produces synergistic uptake mechanism

Recovery of synthetic cryolite may be possible

14

AcknowledgementsDr Mark Ogden & the SNUCER groupDr Robert Dawson & research groupPolymer Centre CDTEngineering & Physical Sciences Research CouncilBawtry Carbon InternationalTrimet AluminiumRoyal Society of Chemistry (Environment Sustainability & Energy Division)You for listening

15

See poster 123 for more fluoride work!Tjrobshaw1@Sheffield.ac.uk

Supporting Information

16

Al Metal Productio

n

Pyrometallurgical SPL Treatment

D.G. Brooks et al., Light Metals, 1992, 283-287.

✦ Produces 2.5 T waste per T SPL processed✦ In operation today

17

Proposed Leaching Treatment

Caustic leachate

To IX circuit

Solid/liquid separation

Na3AlF6 and Al2O3 solublised

Solid/liquid separation

CaF2 and NaAl4O17 solublised

Purifiedgraphite

Leachate mixing?

Slurry

Impellor

CN- destruction

H2O2

NaOH(aq)

Ground & screened

SPL

HNO3(aq)

Acidic leachate

18

Cryolite PrecipitationPXRD spectrum of cryolite precipitated from leachate before IX treatment

19

10 20 30 40 50 60 70 800

100

200

300

400

500

600

700

800

900

1000

10 20 30 40 50 60 70 800

100

200

300

400

500

600

700

2 theta

Inte

nsity

 (a.u

.)

Literature spectrum for comparison

XPS Analysis of Resin Beads

La environmentsAl environments O environments

6567697173757779818385100

200

300

400

500

Binding energy (eV)

Cou

nts 

(s­1

)

5225275325375421000200030004000500060007000

Binding energy (eV)

Cou

nts 

(s­1

)

8208308408508608701800200022002400260028003000

Binding energy (eV)

Cou

nts 

(s­1

)

52252753253754215002000250030003500400045005000

Cou

nts 

(s­1

)

8208308408508608702000

2500

3000

3500

4000

4500

5000

Cou

nts 

(s­1

)(none)

NaF

 sol

utio

nLe

acha

te

C. Stosiek et al., Chem. Mater., 2010, 22, 2347. S. Selvasekarapandian et al., Physica B., 2003, 337, 52.

Aluminium hydroxyfluoride 

(AHF)

20

Resin Regeneration Study

Equilibrium fluoride uptake of La­MTS9501 over 5 adsorption/desorption cycles

21

0

10

20

30

40

50

60

70

qe (m

g g­

1)