Bioleaching Low Grade Primary Sulfides at Collahusi

8/12/2019 Bioleaching Low Grade Primary Sulfides at Collahusi

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Bioleaching study for low grade primary sulfides at Collahuasi

C. LorcaCollahuasiBaquedano 902, Iquique, [email protected]

ABSTRACT

Collahuasi performed a preliminary study to measure the response of lowgrade primary ores of the Rosario deposit to bioleaching. The study

includes the chemical and mineralogical characterization of the ores, thesearch for native bacteria and their isolation and ore adaptation, shakertests with mesophilic and thermophilic bacteria, preparation of differentcultures, and one meter height inoculated column tests with 1 sizesamples at 60, 77 and 113 F.

Results indicate that Rosario ores contained mesophilic and moderatethermophilic bacteria and all the ores under study showed to be compatibleand amenable for bioleaching. The highest extraction rate is reached at ahigher temperature and acid consumptions are moderate to high.
mailto:[email protected]:[email protected]


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INTRODUCTION

Collahuasi began to study potential leachable resources in 2001 in order tosustain or increase the production capacity of the Oxide Plant, programmedto operate until 2008 with the original reserves.The main potential resources are low grade primary sulfides that will begenerated from Rosario mine operation from 2004 until 2032. Theseresources are estimated at 1.1 billion ton with an average grade of 0.36 %CuT at a 0.2 %CuT cut off grade.

TESTWORK

Program planning and execution

The study was conducted at CIMM T&S laboratories in Antofagasta,assisted by the Laboratorio de Tecnologa Minera from UniversidadCatolica del Norte - Antofagasta. The program test and protocols were

prepared with the support of Mr. Randolph Scheffel, internationalconsultant, and Mr. Francisco Arriagada, IDESOL consultant. Themineralogical study was performed by MAM Ltd., and the sequential copperanalysis was performed by CIMM T&S La Serena.

Ore samples and characterization

Rosario sulfides were classified into 27 geological units (GU) using ascriteria rock type, alteration and mineralization. Rock types includeandesites, sediments, three different porphyries and rhyolite. Alterationfacies include potassic-propilitic, sericitic, biotitic or argilic. Mineralization ismainly chalcopyrite followed by chalcosite and bornite. The GU

classification and estimated contributions are shown in Figure 1.To conduct the test work, eight samples representing the main GU wereprepared from 4 drill cores. Those samples represent 82 % of theresources. See Figure 2.

Sample preparation

To prepare the sample composites, each sample was crushed andscreened into four size fractions -1 + , - + , - + 10 # and 10#. Each fraction was accurately sampled to be characterized and alsostored in separated drums.


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Geological Number of Total meters Average Total Unit

Unit drills included in grade sample contribution

the composite (% CuT) (Kg) (%)

1 5 98 0.40 218 27.5

2 2 10 0.51 22 15.2

3 6 181 0.46 342 5.7

4 23 675 0.48 1567 5.2

6 15 303 0.42 621 14.17 1 4 0.55 9 4.2

12 4 34 0.41 70 6.2

14 2 8 0.43 16 4.6

1,313 0.46 2863 82.6

Figure 2. Sample origin

Total

Chemical characterization

A sequential copper analysis was implemented, associating the sulphuricacid soluble fraction with the easy soluble copper (oxides), the cyanidesoluble fraction with the moderately soluble copper (secondary sulphides)and the refractory fraction with the insoluble copper (mainly chalcopyrite).

In addition, total sulphur and sulphate sulphur were analyzed to calculatesulphide mineral distribution. Total iron and manganese were analyzed asthey represent the main impurities related with the leaching process. SeeFigure 3.

Contrib

CuT FeT Mn S (T) S (Sulf.) S (SO4) CO3 CuSCit CuSS CuSCN CuR UG

(%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%)

1 0.410 3.980 0.160 1.430 1.430 < 0.001 1.200 0.016 0.020 0.054 0.337 27.50

2 0.480 3.150 0.046 0.820 0.820 < 0.001 0.110 0.02 0.023 0.135 0.322 15.16

3 0.510 1.970 0.005 1.940 1.940 < 0.001 0.100 0.012 0.017 0.089 0.405 5.67

4 0.545 2.290 0.039 1.750 1.750 < 0.001 0.220 0.013 0.015 0.047 0.484 5.16

6 0.450 5.070 0.150 2.410 2.410 < 0.001 0.490 0.02 0.026 0.079 0.345 14.09

7 0.520 1.550 0.029 0.870 0.870 < 0.001 0.140 0.011 0.012 0.020 0.488 4.23

12 0.425 8.080 1.360 1.950 1.950 < 0.001 6.550 0.015 0.016 0.037 0.372 6.22

14 0.380 6.900 0.660 3.520 3.520 < 0.001 2.140 0.028 0.031 0.044 0.305 4.60

Average 0.450 4.117 0.231 1.667 1.667 0.000 1.143 0.017 0.021 0.071 0.358 82.63

CuSS = Soluble Cu in sulphuric acid CuSCN = soluble copper in Sodium cyanide CuR = Refrac tory copper

Figure 3. Chemical analysis

UG

Mineralogical characterization

Mineralogical characterization was performed with optical microscope andsupported with X-ray diffraction, to identify copper and gangue species.See Figure 4.


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GU 1 GU 2 GU 3 GU 4 GU 6 GU 7 GU 12 GU 14

(%) (%) (%) (%) (%) (%) (%) (%)

Calcopirita CuFeS2 0.97 1.11 1.26 1.48 0.99 1.46 1.03 0.96

Calcosina Cu2S 0.06 0.06 0.03 0.02 0.09 0.01 0.02 0.02

Covelina CuS 0.01 0.05 0.00 0.01 0.02 0.00 0.00 0.00

Copper Bornita Cu5FeS4 0.00 0.00 0.04 0.01 0.01 0.00 0.07 0.01

ores Enargita Cu3AsS4 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00Atacamita Cu2Cl(OH)3 0.00 0.00 0.02 0.00 0.00 0.02 0.00 0.00

Brochantita Cu4SO4(OH)6 0.00 0.02 0.00 0.00 0.00 0.00 0.00 0.00

Crisocola CuSiO3-2H2O 0.03 0.01 0.01 0.00 0.03 0.00 0.02 0.02

Pseudomalaquita Cu2SO4(OH)6 0.02 0.02 0.02 0.04 0.02 0.00 0.00 0.04

Pirita FeS2 1.99 0.68 2.75 2.23 3.80 0.66 2.91 5.90

Molibdenita MoS2 0.04 0.06 0.02 0.07 0.01 0.02 0.00 0.03

Magnetita Fe3O4 0.28 0.21 0.03 0.03 0.15 0.02 0.05 0.03

Hematita Fe2O3 0.08 0.04 0.21 0.10 0.01 0.16 0.00 0.00

Limonita FeOOH 0.20 0.04 0.00 0.00 0.03 0.00 0.00 0.00

Rutilo TiO2 0.03 0.11 0.07 0.30 0.07 0.22 0.06 0.00

Subtotal 3.71 2.41 4.47 4.29 5.23 2.57 4.16 7.01

Calcita 5.07 2.63 1.29 1.24 2.59 0.00 2.09 2.39

Clorita 2.40 2.49 0.12 0.06 2.09 0.50 5.44 3.51

Biotita 2.76 1.36 0.01 0.07 2.41 0.68 5.61 3.70

Illita 4.87 3.80 2.48 3.59 3.74 7.60 3.01 4.60

Sericita 19.01 10.52 15.51 18.65 15.55 15.81 12.52 11.94

Gangue Caolinita 6.82 9.43 6.95 4.46 4.65 11.81 5.61 6.42

Montmorillonita 4.46 3.47 4.55 5.47 4.56 5.79 2.75 3.68Anfibola 5.60 2.90 2.85 1.37 1.43 2.90 0.00 3.95

Apatito 0.10 0.15 0.00 0.13 0.14 0.15 0.12 0.26

Hidrobiotita 1.31 1.36 0.13 1.89 0.67 0.68 1.08 1.24

Granate 0.00 0.00 0.00 0.00 0.97 0.00 4.66 1.78

Cuarzo 17.70 24.49 30.09 28.94 30.15 24.53 24.28 22.22

Epidota 1.48 4.63 0.02 0.14 1.52 0.08 1.23 1.40

Titanita 0.00 0.00 0.00 0.77 0.00 0.00 1.28 1.46

Jarosita 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Plagioclasa 17.70 24.49 24.06 23.15 18.09 18.40 24.28 22.22

Piroxeno 0.00 0.00 0.00 0.00 1.52 0.13 0.00 0.00

Pirofilita 2.49 0.00 2.53 2.43 0.00 0.00 0.00 0.00

Feld. Potsico 4.55 5.90 4.64 3.34 4.65 8.26 1.87 2.14

Turmalina 0.00 0.00 0.28 0.00 0.00 0.00 0.00 0.00

Yeso 0.00 0.00 0.01 0.00 0.05 0.11 0.04 0.09

Subtotal 96.30 97.59 95.52 95.70 94.76 97.43 95.85 92.99

Total 100.01 100.00 99.99 99.99 99.99 100.00 100.01 100.00

Figure 4. Mineralogical characterization

A comparison exercise was done between the sequential chemical assayand the mineralogical study, related with chalcopyrite content. See Figures5 and 6.


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Average

GU 1 GU 2 GU 3 GU 4 GU 6 GU 7 GU 12 GU 14 contribution

Calcopirita 82.24 78.82 85.09 92.11 75.84 96.27 84.14 88.41 82.54

Calcosina 11.73 9.83 4.67 2.87 15.90 1.52 3.77 4.25 9.52

Covelina 1.63 6.81 0.00 1.19 2.94 0.00 0.00 0.00 2.37

Bornita 0.00 0.00 4.94 1.14 1.40 0.00 10.46 1.68 1.53

Enargita 0.00 0.00 0.94 0.00 0.00 0.00 0.00 0.00 0.06

Atacamita 0.00 0.00 2.22 0.00 0.00 2.21 0.00 0.00 0.27

Brochantita 0.00 2.25 0.00 0.00 0.00 0.00 0.00 0.00 0.41

Crisocola 2.56 0.72 0.67 0.00 2.28 0.00 1.64 1.79 1.64

Pseudomalaquita 1.84 1.57 1.46 2.69 1.64 0.00 0.00 3.87 1.66

GU contribution 27.50 15.16 5.67 5.16 14.09 4.23 6.22 4.60 100.00

Figure 5. Fine copper contribution according mineralogy (%)

Mineralogical characterizationChemical characterization

GU

Average147 1264321

10

20

30

40

5060

70

80

90

100

0

Figure 6. Fine copper contained in chalcopyrite (%)

Preliminary studies

Bottle roll tests

This test measures copper extraction and sulphuric acid consumption using1 Kg of sample at size 10 # Tyler under constant acidity. Three pHlevels were used 1.0, 1.5 and 2.0. Sampling, pH control and acid additionwas made at 1, 2, 4, 8, 24, 48, 72 and 96 hours. Figure 7 shows asummary from 45 tests.


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CuT extraction

(Kg/t) (Kg/Kg Cu) (%)

1.0 59.0 110.6 13.0

1 1.5 52.8 106.6 12.3

2.0 26.5 85.9 8.1

1.0 32.3 44.0 16.2

2 1.5 18.2 27.6 13.8

2.0 12.0 32.0 9.3

1.0 17.7 25.4 14.0

3 1.5 11.4 18.1 12.4

2.0 6.2 13.9 9.5

1.0 28.7 53.1 10.2

4 1.5 14.6 29.0 9.8

2.0 8.5 20.1 8.3

1.0 49.8 56.7 20.3

6 1.5 33.2 40.3 18.6

2.0 17.2 33.2 12.3

1.0 24.8 91.5 5.5

7 1.5 15.7 59.9 5.1

2.0 12.2 48.9 5.0

1.0 104.7 221.7 11.3

12 1.5 62.2 158.2 9.2

2.0 34.0 127.9 6.3

1.0 50.3 83.4 16.0

14 1.5 20.7 37.3 14.8

2.0 26.6 72.0 9.6

GU pHNet acid consumption

Figure 7. Bottle roll tests summary

Bioleaching laboratory studies

Liquid and solids samples were taken at the mine site in sterile flasks, atotal of 56 bacterial growth tests were done at 25 C and 45 C during 6

days in a media culture for ferroxidans microorganisms.The strongest five populations were selected to conduct a second test toadapt them to a mineral media. A composite prepared with GU 1, 3, 4, 6and 12 was used in this stage. The best cultures, mesophilic and moderatethermophilic, were selected to prepare inocules for column campaigns. Themesophilic culture presented thiobacillus ferroxidans, leptospirillumferroxidans and sulfobacillus. Moderate thermophilic culture presentedmainly leptospirillum.A third bioleaching flask campaign was run using both the mesophilic andthe thermophilic cultures and individual UG samples 1, 3, 4, 6 and 12. Seefigures 8 and 9.


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Max. Population Max. Population

(%) dia pH Eh (mV) (mo/ml) (%) dia pH Eh (mV) (mo/ml)

UMET 1 38.1 26 2.9 592 8.42E+09 UMET 1 72.0 43 1.7 629 6.40E+09

UMET 3 43.5 26 2.2 656 6.20E+09 UMET 3 55.0 43 1.5 657 4.56E+09

UMET 4 33.8 26 2.3 643 4.90E+09 UMET 4 61.1 43 1.5 643 4.92E+09

UMET 6 60.0 26 2.6 605 5.15E+09 UMET 6 72.5 43 1.7 625 5.50E+09

UMET 12 37.7 8 3.4 560 8.50E+09 UMET 12 44.0 43 2.1 596 6.10E+09

Mesophilic bioleaching (25 C) Thermophilic bioleaching (45 C)

CuT extraction CuT extractionOre Ore

Fig. 8 Extraction with mesophilic culture

0

10

20

30

40

50

60

70

80

90

100

1 8 19 26

Dias de cultivo

Extrac

cin(%C

uT)

UMET 1 UMET 3 UMET 4 UMET 6 UMET 12

Fig. 9 Extrac tion with thermophilic culture

0

10

20

30

40

50

60

70

80

90

100

1 8 14 22 27 35 43

Dias de cultivo

Extrac

cin(%C

uT)

UMET 1 UMET 3 UMET 4 UMET 6 UMET 12

Bioleaching in columns

The tests were performed in 6 diameter 1 meter height columns with about30 Kg of sample prepared with a defined size distribution. To keep carefultemperature control, three isolated small rooms were kept at constanttemperature. Irrigation was intermittent applying solution at a rate of 10l/h/m2, with one day rinse and a two or three days rest period, previous tothe inoculation an acid preconditioning was applied. Total operation timewas 217 days. Tests at 15 C and 25 C were inoculated with mesophiliccultures and tests at 45 C were inoculated with moderate thermophilic

cultures.All the irrigation solution was prepared diluting the industrial plant raffinateto 8 gpl acid, 0.3 gpl Cu and 2 gpl total iron.The drainage was sampled and composited in a sequence that coversincreasing periods of time. Both On and Off samples were analyzed for Cu,FeT, Fe+2, Mn, Mg, Ca, Na, K, SiO2, As, total sulphur and sulphates.Additionally, pH, redox potential and bacterial counting wereinstantaneously measured. Copper extraction, acid consumption, bacterialbehavior and impurities behavior were measured. Summary results areshown in Figure 9, 10 and 11.


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Column Ore Temp. Irrig /rest

(C) CuT CuS(S+CN) CuR

1B GU 1 15 1/3 22.89 57.39 13.47

2B 45 1/2 40.43 68.47 35.29

3B 45 1/3 42.59 66.03 42.47

4B 45 1/3 42.20 70.30 38.38

5B GU 3 15 1/3 17.59 34.71 7.22

6B 45 1/3 35.34 52.78 23.38

7B GU 4 15 1/3 12.21 42.25 4.58

8B 45 1/3 29.82 59.02 21.21

9B GU 6 15 1/3 26.06 62.68 11.48

10B 15 1/3 27.65 64.56 16.65

11B 25 1/2 30.25 63.08 9.95

12B 25 1/3 29.04 66.37 15.68

13B 25 1/3 28.64 62.26 16.94

14B 45 1/2 46.59 67.88 35.04

Extraction (%)

Figure 9. Columns

(Kg/t) (Kg/Kg C

35.60 35.57

62.18 36.43

52.44 30.99

53.69 31.39

3.08 3.75

8.14 4.76

8.64 13.91

15.92 10.28

24.20 20.79

24.10 20.28

33.29 22.76

30.77 24.01

27.98 22.23

54.59 25.30

15B 45 1/3 43.68 69.58 35.63 42.28 22.37

16B 45 1/2 47.74 72.43 38.00 55.87 26.34

Net acid consumptio

tests results


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GU 3 GU 4

Col 15 Col 14 Col 16 Col 2 Col 3 Col 4 Col 6 Col 8

(XG) Ln(XG) (%) (%) (%) (%) (%) (%) (%) (%)

-1 1/2" + 3/4" 3.29 33.17 26.15 32.20 20.58 35.59 28.57 20.23 19.30

-3/4" + 1/4" 2.40 45.11 46.00 52.89 44.96 49.88 48.24 44.00 33.33

-1/4" + 10 # 1.19 67.27 65.45 67.27 63.46 65.38 65.38 52.08 47.27

- 10 # 69.42 72.02 69.42 70.23 70.69 69.54 35.94 38.47

GU 6 GU

Figure 10. Copper extraction at 45 C

Rec. CuT (%) = -18.534Ln(Xg)+ 88.38

R2= 0.9917

0

10

20

30

40

50

60

70

80

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Ln (XG) (mm)

Rec.

(%C

uT)

Col 14 Col 15 Col 16

Col 2 Col 3 Col 4

Col 6 Col 8 Linear (Col 14)

Fig. 11. Extraction vs % Refractory copper

0

10

20

30

40

50

60

70

80

70 75 80 85 90 95 100

% Cu R

ExtractionCuT(%)

Bottle - pH 1.5 flask with mesophilic c ultureflask with thermophilic culture Bottle - pH 1.0Columns with mesophilic culture Columns with thermophilic culture


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CONCLUSIONS

1 Ore characterization shows that there is a good correlation betweenthe refractory copper fraction estimated from the copper sequentialanalysis and the chalcopyrite content from the mineralogical study.

2 From the bottle roll tests, the highest recovery obtained by GU 6 isrelated with the lowest chalcopyrite content. The lowest recoveryobtained by GU 7 is related with the highest chalcopyrite content too.The highest acid consumptions registered by GU 1 and 12 isassociated with the rock type, andesite or volcanic sediment, with apotassic-propilitic or argilic alteration. The lowest acid consumers areGU 2, 3, 4 and 6, whose lithology is porphyry or rhyolite with sericiticalteration.

3 The bioleaching laboratory flask studies, suggest the ore samplesfrom the mine site were able to generate native bacterial populations.

For the mesophiles tests (25 C) final extractions were 34 to 60 % in26 days and for moderate thermophiles tests (45 C) were 44 to 72 %in 43 days. GU 6 reached the highest Cu extraction both in thebioleach flask test and the chemical leach test in bottles due to hishigher solubility ratio.

4 The columns tests suggest that the temperature and particle size(Figures 10 and 11) are the variables with highest impact on copperrecovery. Soluble fractions and refractory fractions showed growingextraction with temperature and smaller particle sizes. Morecompetent rock, porphyries, are less amenable to leaching and showthe lowest recoveries. The intermittent irrigation seems to have no

influence, or is within the experimental error.Chalcopyrite extraction, related to the refractory fraction, was clearlyenhanced with temperature as can see in Figure 11. Flask testsreached better results due to their finer particle sizes. As an average,copper columns extractions at 45 C were 20 extraction units higherthan extractions at 15 C.The acid consumption showed two different behaviors : the firstincreased with time and is related with rock type Andesite volcanicsediment; the second one, related with the porphyric rock and highestpyrite content, changed from an acid consumer to an acid generator.


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Acknowledgements

My gratitude to Mr. Ricardo Palma, Collahuasi Development VP, for givingme the opportunity to prepare this paper, and to all who contributed to thedevelopment of the metallurgical testwork program.

Bioleaching Low Grade Primary Sulfides at Collahusi

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