RECOVERY OF PRECIOUS METALS FROM DISCARDED

CELLPHONESE. de la Torre , S. Espinoza, A. Guevara

ESCUELA POLITÉCNICA NACIONALQuito - Ecuador

Faculty of Chemical Engineering and Agroindustry

Department of Extractive Metallurgy

• Pb• C

o• Ni• C

d• Cr

Au, Ag, Pd, Nb, Rh

• Epoxy Resins• Glass fiber• Cu, Pb, Co, Ni, Fe, Cd, Cr• Flame RetardantPVC/PC/ABS

ceramics

• Low cost and effectiveness to dissolve noble metals.

4Au + 8(CN)- → 4Au(CN)2-

• Au > Ag > Pd > Rh

• [CN]-, dp, t

• Cyanicide (Cu)

Cyanidation

• The elements from the group of Platinum (Pd, Rh) are soluble in mineral acids

Pd + 2HNO3 → Pd(NO3)2 + 2H-

Pd + H2SO4 → Pd(SO4) + 2H-

• With HNO3 and H2SO4 the dissolution is slow.

• Nd y Rh are dissolved with difficulty

• Presence of Cl- ion benefits the dissolution ofPd

Acid Leaching

1000 ºC1h

0,5 g30 ml Aqua Regia

Ta – 850ºC 3 h

0,72 atm 21% O2

960 ºC 1h

Samples Characterization

Electronic Microscope MEB-EDX

Metal Concentration Average

Au 244 - 857 g/t 421 g/t

Ag 520 - 2901 g/t 1355 g/t

Pd 68 - 80 g/t 74 g/t

Rh 44 - 54 g/t 49 g/t

Nb 5 – 40 g/t 15 g/t

Cu 10 - 43 % 29%

Chemical Characterization

 

 

muestra 72Fecha:7/27/2010 6:21:10 PMTamaño de imagen:384 x 384Aum:500xHV:20.0kV

1 2 3 4 5 6 7 8 9keV

0

2

4

6

8

10

12

14

cps/eV

Ag Ag Ag Au Au Au Au

Nb Nb

Nb

dore 1 Fecha:7/27/2010 6:10:37 PM HV:20.0kV D. imp.:8.17kcps El AN Series unn. C norm. C Atom. C Error [wt.%] [wt.%] [at.%] [wt.%] -------------------------------------------- Ag 47 L-series 57.74 67.14 77.49 1.8 Au 79 M-series 26.14 30.40 19.21 1.0 Nb 41 L-series 2.11 2.46 3.30 0.1 -------------------------------------------- Total: 85.99 100.00 100.00

Cyanidation

• Preliminary Treatments

• Parameter Definition ([NaCN], t)

• Size reduction• Roasting

• Leaching NH3 / HNO3

Acid Leaching

• Preliminary Treatments

• Parameter Definition (Concentration, t)

• Size reduction

• Roasting

[NaCN] 2 g/LTime 24 hpH 10,5% Solids 2,5-5%Stirring 500 rpm

4x4 cm1x1 cm7x7 mm5x5 mm

1000 m

136 m

Size reduction, roasting and cyanidation

Influence of roasting and size reduction in the gold and silver cyanidation

[NaCN] 2 g/L; solids 2,5-5%, time24 hours

0

20

40

60

80

100

100 1 000 10 000 100 000

Rec

over

y of

met

als i

n so

lutio

n (%

)

Particle size (µm)

Au Roasted Sample Ag Roasted Sample

Au Not Roasted Sample Ag Not Roasted Sample

0 1 2 3 4 5 6 7 8 90

20

40

60

80

100

Au Ag

Concentration of NaCN (g/L)

Met

al R

ecov

ery

in s

olut

ion

(%)

Influence of the concentration of cyanide in gold and silver recovery

Roasted sample; d80 136 m; solids 2,5-5%, time 24 hours

Influence of cyanidation time in the gold and silver recovery

0 5 10 15 20 25 30 35 40 45 500

20

40

60

80

100

Au AgCyanidation time(h)

Met

al R

ecov

ery

in s

olut

ion

(%

)

Roasted sample; d80 136 m; solids 2,5-5%, [NaCN] 4 g/L

NH3 (v/v) HNO3 (v/v)

9,7 % 19,5 %16,7 % 33,3 %

14 % Solids

2 h

500 rpm

Preliminary treantments: Leaching NH3 / HNO3

Influence of pretreatments with NH3 and HNO3

NH3 (16,7%) HNO3 (33,3%)0

20

40

60

80

100

Cu Disuelto (%)Au Recuperado por cianuración (%)Ag Recuperada por cianuración (%)

Roasted sample d80 136 m; Pretreatment time 2h

Concentration HNO3

35 g/L

ConcentrationH2SO4

35 g/L

Time 1 a 6 h% Solids 2,5 - 5

Stirring speed. 500 rpm

Acid Leaching

Concentration NaCl 0,1 M

Concentration H2SO4

60% w/w

Time 1 a 6 h% Solids 8

Stirring speed 500 rpm

Kinetics of paladium leaching

0 1 2 3 4 5 6 70

20

40

60

80

100

Pd con H2SO4 Pd con HNO3

Time (h)Met

al R

ecov

ery

in s

olut

ion

(%)

Roasted sample; d80 136 m; solids 2,5-5%, [acid] 50 g/L

Effects of chloride ions in the leaching of paladium with sulfuric acid

0 1 2 3 4 5 6 70

20

40

60

80

100

H2SO4 (60% v/v) y NaCl (0,1M)H2SO4 50[g/L]

Time (h)Rec

over

y of

Pd

in s

olut

ion

(%)

Roasted sample; d80 136 m

Leaching HNO3

Filtering ElectrowinningElectrowinning

Elution

Scrubber

Dismantling

Roasting Milling

Leachinf NH3

Filtering

Cyanidation

CIP

Filering

Discarded Cellphones

Printed circuit board

Solid Waste

Gases to atmosphere

Ammonia liquor

Cyanide liquor

Cases, keyboards, Screens

Charged Carbon

Au, Ag Ag, Pd

Acid liquor

Gases

• It is factible to recover 85% Au , 80% Ag, 80% Pd y 80% Cu by installing a treatment plant of 195 kg/month for the printed circuit boards of discarted cellphones

• Nb y Rh couldn`t be recovered

Conclusions

Economic criteriaCapacity 195 kg/month

Investment USD 63400VAN USD 12 679TIR 18%

Investment recovery 5 years

C/B 1.5

RECOVERY OF PRECIOUS METALS FROM DESCARTED

CELLPHONESE. de la Torre , S. Espinosa, A. Guevara

ESCUELA POLITÉCNICA NACIONALQuito - Ecuador

Faculty of Chemical Engineering and Agroindustry

Department of Extractive Metallurgy