perumin 31: upgrading of a tetrahedrite-rich copper concentrate through hydro and...

UPGRADING OF A TETRAHEDRITE-RICH COPPER CONCENTRATE

THROUGH HYDRO- AND ELECTROMETALLURGICAL TREATMENT

Åke Sandström

Minerals and Metals Research Laboratory, MiMeR,

Division of Sustainable Process Engineering,

Luleå University of Technology

Sweden

PERUMIN - 31st Mining Convention, Arequipa 2013

Short on Luleå University of Technology

Background

Aim of the study

Leaching of antimony

Electrowinning of antimony

Acknowledgments

Outline

LTU’s metal chain

Discovering, exploring and

verifying mineralizations and

orebodies

Building, operating and

maintaining mining and

mineral-industry facilities

Concentrating ore,

processing minerals and

producing metals and

other products

Closure and remediation of

mines and other mineral-

industrial facilities

APPLIED GEOPHYSICS

ORE GEOLOGY

GEOMETALLURGY

ROCK MECHANICS

AND ROCK

ENGINEERING

APPLIED GEOLOGY

SOIL MECHANICS

MINERAL

PROCESSING

PROCESS

METALLURGY

CHEMISTRY

GEOMETALLURGY

Background

Source: Marquest Asset Management, 2013


Background cont.

• Tetrahedrite, tennantite, enargite are common impurity

minerals associated with copper ores

• Economically attractive minerals but unsuitable as feedstock

in copper smelters (impurity)

• Nearly 80% of world’s Cu is produced via the smelting route

and the preferable Sb/As level should be < 0.2%

• To utilize complex impure mineral deposits upgrading of the

concentrates will be important for future copper resource

processing


Source: European commission, June 2010


Background cont.

Antimony


Background cont.

Antimony usage Antimony price

Aim of the study

• To upgrade a copper concentrate by selective removal of impurity elements through alkaline sulphide leaching.

• To recover antimony as a saleable product through electrowinning.


Alkaline sulphide leaching

As2S3(s) + 3S2-(aq) → 2AsS33-(aq) Orpiment

Sb2S3(s) + 3S2-(aq) → 2SbS33-(aq) Stibnite

HgS(s) + S2-(aq) → HgS22-(aq) Cinnabar

SnS2(s) + S2-(aq) → SnS32-(aq) Berndtite

Leaching

Arsenic in arsenopyrite (FeAsS) is not soluble

Cu12Sb4S13(s) + 6S2-(aq) → 5Cu2S(s) + 2CuS(s) + 4SbS33-(aq) Tetrahedrite

2Cu3AsS4(s) + 3S2-(aq) → 3Cu2S(s) + 2AsS43-(aq) Enargite


Cu12As4S13(s) + 6S2-(aq) → 5Cu2S(s) + 2CuS(s) + 4AsS33-(aq) Tennantite

Material Chemical analysis:

Size fraction Cu

%

Fe

%

Zn

%

Sb

%

As

%

-106+75 µm 15.6 11.1 16.1 5.8 1.9

-75+53 µm 15.2 14.2 16.8 5.4 1.9

-53+38 µm 15.7 13.3 16.9 5.7 1.8

Leaching

From the Casapalca Mine, Peru

Mineralogy:

Tetrahedrite, chalcopyrite, pyrite,

sphalerite, galena


Leaching conditions

Na2S concentration: 59, 89 and 148 g/L

NaOH concentration: 30 and 60 g/L

Particle size = -53+38, -75+53 and -106+75 µm

Temperature: 84, 91, 98 and 105º C

Time: 6 h

Solid concentration: 0.5% (w/v)

Leaching


Sulphide Concentration Effect

Conditions: NaOH = 60 g/L, size = -75+53 µm, T = 105º C

Leaching


Particle Size Effect

0 1 2 3 4 5 60

10

20

30

40

50

60

70

Leaching time, h

An

tim

on

y r

em

ov

al, %

-53+38 microns

-75+53 microns

-106+75 microns

Conditions: Na2S = 89 g/L, NaOH = 60 g/L, T = 105º C

Leaching


Temperature Effect

0 1 2 3 4 5 60

10

20

30

40

50

60

Leaching time, h

An

tim

on

y r

em

ov

al,

%

84 oC

91 oC

98 oC

105 oC

Conditions: Na2S = 89 g/L, NaOH = 60 g/L, size = -75+53 µm

Leaching


Chemical controlled model,

0

0.05

0.1

0.15

0.2

0.25

0.3

0 50 100 150 200 250 300 350 400

Leaching time, min

1-

(1-X

) 1

/3

84 oC

91 oC

98 oC

105 oC

Leaching


Arrhenius Plot

2.6 2.65 2.7 2.75 2.8 2.85 2.9

x 10-3

-10

-9.5

-9

-8.5

-8

-7.5

-7

-6.5

1/T, 1/K

ln k

, 1

/min

ln k = - 9753*(1/T) + 18.5

Ea = 81 kJ/mol

Diffusion controlled process: 4<Ea<12 (kJ/mol)

Chemical controlled process: Ea>42 kJ/mol

Leaching


Cu (%) Zn (%) Pb (%) Sb (%) As (%)

Copper concentrate 15.74 13.91 17.02 5.73 2.24

Upgraded concentrate 15.59 17.28 19.08 0.21 0.08

Concentrate and Upgraded Concentrate

Leaching


Conclusions on leaching

• Tetrahedrite leaching is strongly dependent on S2- and OH-

concentration, temperature and particle size

• The process is chemically reaction controlled

• The lixiviant selectively removes impurities

• Tetrahedrite decomposes and forms insoluble copper

sulphides and soluble Sb sulphide complexes

• The concentrate is up-graded with an Sb content acceptable

for most copper smelters


Electrowinning (EW) Background

EW of antimony in non-diaphragm cells with an original electrolyte consisting of: S2-, OH-,

SbS33- with Na+ as counter-ion

Possible anode reaction products:

Unwanted: S22-, S2O3

2- (can oxidise deposited Sb at cathode to Sb3+ or Sb5+)

Preferred: SO32-, SO4

2-

S2- → Sº + 2e- Eo = -476 mV

S2- + Sº → S22-

4OH- → O2 + 2H2O + 4e- Eo = +401 mV

S2- + 2O2 → SO42-

How to avoid unwanted reaction products?

High OH--concentration in electrolyte should be maintained

Anodic current density (potential) should be high


EW conditions

Anode wire

Anode to cathode area: 1/10

Anode: Nickel wire (=0.38 mm)

Cathode: Stainless steel plate

Cathodic C.D.: 50, 100, 150, 200, 250 (A/m2)

Anodic C.D: 500 - 2500 (A/m2)

NaOH conc.: 100, 200, 250, 300, 350, 400 (g/L)

Temperature: 45, 60, 75, 90 (ºC)

Na2S conc.: 60, 100, 150 (g/L)

Sb conc. (initial): 35 (g/L)

Time: 9 (h)


Effect of NaOH concentration on anode reactions

Conditions: Sb 35 g/L, Na2S 100 g/L, Anode C.D. 2000 A/m2, Temp. 75º C, 9 h

Antimony EW results


NaOH conc.

g/L

Molar ratio

(OH-:S2-)

S2O32-

formed,

g/L

SO32-

formed,

g/L

SO42-

formed,

g/L

Anode

efficiency,

%

100 2.9:1 3.88 0.52 0.99 12

200 5.9:1 2.13 1.14 2.09 26

250 7.3:1 1.84 1.25 2.95 36

300 8.8:1 0.97 0.52 4.80 59

350 10.3:1 0.00 0.43 6.81 84

400 11.8:1 0.00 0.00 7.20 89

Dependence of sulphide ion concentration

Conditions: Sb 35 g/L, NaOH 350 g/L, Cathode C.D. 200 A/m2, Temp. 75º C

Antimony EW results


Dependence of cathode current density

Conditions: Sb 35 g/L, NaOH 350 g/L, Na2S 100 g/L, Temp. 75º C

Antimony EW results


Dependence of NaOH concentration

Conditions: Sb 35 g/L, Cathode C.D. 200 A/m2, Na2S 100 g/L, Temp. 75º C

Antimony EW results


Dependence of electrolyte temperature

Conditions: Sb 35 g/L, NaOH 350 g/L NaOH, Na2S 100 g/L, Cathode C. D. 200 A/m2

Antimony EW results


Effect of polysulphide

Conditions: Sb 35 g/L, NaOH 350 g/L, Na2S 100 g/L, Cathode C.D. 200 A/m2

Antimony EW results


Conditions: Sb 25 g/L, NaOH 350 g/L, Na2S 100 g/L, Cathode C. D. 200 A/m2, 75ºC, 6 h

Effect of thiosulphate

Antimony EW results


Conditions: Sb 25 g/L, NaOH 350 g/L, Na2S 100 g/L, Cathode C. D. 200 A/m2, 75ºC, 6 h

Conclusions on EW

• Current efficiency of Sb deposition is highly dependent on

NaOH concentration and current density

• Excess free S2- ions should be avoided

• Increase in temperature and NaOH concentration decreases

the specific energy of the process

• Polysulphide and thiosulphate lowers current efficiency

considerably

• Current efficiency improved by almost 50% compared to

conventional non-diaphragm electrolytic cells

• Saleable antimony can be produced in non-diaphragm

electrolytic cells


Acknowledgements

Dr. Samuel A. Awe for performing the experimental work

Financial contributions from these organizations are greatly appreciated:

•Swedish Governmental Agency for Innovation Systems, VINNOVA

•Boliden Mineral AB

•LKAB

•Adolf H. Lundin Charitable Foundation


Thank you for the attention!


perumin 31: upgrading of a tetrahedrite-rich copper concentrate through hydro and...

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