UPGRADING OF A TETRAHEDRITE-RICH COPPER CONCENTRATE THROUGH HYDRO- AND ELECTROMETALLURGICAL TREATMENT. Åke Sandström

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1 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

2 Outline Short on Luleå University of Technology Background Aim of the study Leaching of antimony Electrowinning of antimony Acknowledgments

LTU s metal chain Discovering, exploring and verifying

maintaining mining and mineral-industry facilities

and other products Closure and remediation of mines and

GEOLOGY GEOMETALLURGY ROCK MECHANICS AND ROCK ENGINEERING

4 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 mineralindustrial facilities APPLIED GEOPHYSICS ORE GEOLOGY GEOMETALLURGY ROCK MECHANICS AND ROCK ENGINEERING MINERAL PROCESSING PROCESS METALLURGY CHEMISTRY GEOMETALLURGY APPLIED GEOLOGY SOIL MECHANICS

5 Background Source: Marquest Asset Management, 2013

6 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

7 Background cont. Antimony Source: European commission, June 2010

8 Background cont. Antimony usage Antimony price

9 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.

10 Alkaline sulphide leaching Leaching As 2 S 3 (s) + 3S 2- (aq) 2AsS 3-3 (aq) Sb 2 S 3 (s) + 3S 2- (aq) 2SbS 3-3 (aq) HgS(s) + S 2- (aq) HgS 2-2 (aq) SnS 2 (s) + S 2- (aq) SnS 2-3 (aq) Orpiment Stibnite Cinnabar Berndtite 2Cu 3 AsS 4 (s) + 3S 2- (aq) 3Cu 2 S(s) + 2AsS 4 3- (aq) Cu 12 Sb 4 S 13 (s) + 6S 2- (aq) 5Cu 2 S(s) + 2CuS(s) + 4SbS 3 3- (aq) Cu 12 As 4 S 13 (s) + 6S 2- (aq) 5Cu 2 S(s) + 2CuS(s) + 4AsS 3 3- (aq) Enargite Tetrahedrite Tennantite Arsenic in arsenopyrite (FeAsS) is not soluble

$Leaching Material Chemical analysis: Size fraction Cu % Fe % Zn % Sb % As % -106+75 µm 15.6 11.1 16.1 5.8 1.9-75+53 µm 15.2 14.2 16.$

11 Leaching Material Chemical analysis: Size fraction Cu % Fe % Zn % Sb % As % µm µm µm Mineralogy: Tetrahedrite, chalcopyrite, pyrite, sphalerite, galena From the Casapalca Mine, Peru

12 Leaching Leaching conditions Na 2 S concentration: 59, 89 and 148 g/l NaOH concentration: 30 and 60 g/l Particle size = , and µm Temperature: 84, 91, 98 and 105º C Time: 6 h Solid concentration: 0.5% (w/v)

13 Leaching Sulphide Concentration Effect Conditions: NaOH = 60 g/l, size = µm, T = 105º C

14 Antimony removal, % 70 Particle Size Effect Leaching microns microns microns Leaching time, h Conditions: Na 2 S = 89 g/l, NaOH = 60 g/l, T = 105º C

15 Antimony removal, % Leaching 60 Temperature Effect oc 91 oc 98 oc 105 oc Leaching time, h Conditions: Na 2 S = 89 g/l, NaOH = 60 g/l, size = µm

16 Leaching Chemical controlled model, oc 91 oc 98 oc 105 oc 1- (1-X) 1/ Leaching time, min

17 ln k, 1/min Leaching -6.5 Arrhenius Plot ln k = *(1/T) Ea = 81 kj/mol /T, 1/K x 10-3 Diffusion controlled process: 4<E a <12 (kj/mol) Chemical controlled process: E a >42 kj/mol

18 Leaching Concentrate and Upgraded Concentrate Cu (%) Zn (%) Pb (%) Sb (%) As (%) Copper concentrate Upgraded concentrate

19 Conclusions on leaching Tetrahedrite leaching is strongly dependent on S 2- 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

20 Background Electrowinning (EW) EW of antimony in non-diaphragm cells with an original electrolyte consisting of: S 2-, OH -, SbS 3-3 with Na + as counter-ion Possible anode reaction products: Unwanted: S 2-2, S 2 O 2-3 (can oxidise deposited Sb at cathode to Sb 3+ or Sb 5+ ) Preferred: SO 2-3, SO 2-4 S 2- Sº + 2e - E o = -476 mv S 2- + Sº S 2 2-4OH - O 2 + 2H 2 O + 4e - E o = +401 mv S O 2 SO 2-4 How to avoid unwanted reaction products? High OH - -concentration in electrolyte should be maintained Anodic current density (potential) should be high

21 EW conditions 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/m 2 ) Anodic C.D: (A/m 2 ) Anode wire NaOH conc.: 100, 200, 250, 300, 350, 400 (g/l) Temperature: 45, 60, 75, 90 (ºC) Na 2 S conc.: 60, 100, 150 (g/l) Sb conc. (initial): 35 (g/l) Time: 9 (h)

22 Antimony EW results Effect of NaOH concentration on anode reactions NaOH conc. g/l Molar ratio (OH - :S 2- ) S 2 O 2-3 formed, g/l SO 2-3 formed, g/l Conditions: Sb 35 g/l, Na 2 S 100 g/l, Anode C.D A/m 2, Temp. 75º C, 9 h SO 2-4 formed, g/l Anode efficiency, % : : : : : :

23 Antimony EW results Dependence of sulphide ion concentration Conditions: Sb 35 g/l, NaOH 350 g/l, Cathode C.D. 200 A/m 2, Temp. 75º C

24 Antimony EW results Dependence of cathode current density Conditions: Sb 35 g/l, NaOH 350 g/l, Na 2 S 100 g/l, Temp. 75º C

25 Antimony EW results Dependence of NaOH concentration Conditions: Sb 35 g/l, Cathode C.D. 200 A/m 2, Na 2 S 100 g/l, Temp. 75º C

26 Antimony EW results Dependence of electrolyte temperature Conditions: Sb 35 g/l, NaOH 350 g/l NaOH, Na 2 S 100 g/l, Cathode C. D. 200 A/m 2

27 Antimony EW results Effect of polysulphide Conditions: Sb 35 g/l, NaOH 350 g/l, Na 2 S 100 g/l, Cathode C.D. 200 A/m 2 Conditions: Sb 25 g/l, NaOH 350 g/l, Na 2 S 100 g/l, Cathode C. D. 200 A/m 2, 75ºC, 6 h

28 Antimony EW results Effect of thiosulphate Conditions: Sb 25 g/l, NaOH 350 g/l, Na 2 S 100 g/l, Cathode C. D. 200 A/m 2, 75ºC, 6 h

29 Conclusions on EW Current efficiency of Sb deposition is highly dependent on NaOH concentration and current density Excess free S 2- 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

30 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

31 Thank you for the attention!

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