1. Integrated piloting of a thermophilic nickel-copper bioleaching process
Presented at the
SAIMM Hydrometallurgy Conference 2009
held in Muldersdrift, Gauteng
24-26 February 2009
by John Neale
Biotechnology Division, Mintek

2. The BioMinE project Biotechnology for the Minerals Industry in Europe
Integrated Research and Technology Development project
November 2004 – October 2008
37 participating partners
Overall budget: €17.9-million
EC contribution: €11.6-million

3. Mintek’s contribution to BioMinE
Coordinator of the largest ‘Work Package’ – Bioleaching
Development of integrated bioleach-based processes for the recovery of base metals from complex, low-grade sulphide concentrates
Target resource: Aguablanca nickel-copper concentrate
Extensive bench-scale bioleach testing
Integrated bioleaching and metals recovery pilot-plant campaign
Most of Mintek’s R&D effort was aimed at the bioleaching of chalcopyrite
Chalcopyrite “passivates” in sulphate medium at 35°C
Higher operating temperatures
Finer grinding
Addition of catalysts
Redox control

4. Bioleaching of base metal concentrates
Early 1990s:
BioNIC integrated piloting and feasibility study (BHP Billiton)
Mesophiles, moderate thermophiles (35-45 °C)
Late 1990s:
Kasese commercial bioleach plant for cobalt extraction from pyrite (BRGM)
Mesophiles (35-40 °C); 1,000 t/a of cobalt cathode
2001:
Demonstration plant and feasibility study for chalcopyritic copper, zinc and lead concentrate (Mintek/BacTech)
Moderate thermophiles (45 °C); 1 t/d of copper
2003:
Commercial demonstration plant for chalcopyrite concentrate containing arsenic (Alliance Copper)
Thermophiles (70-78 °C); 20,000 t/a of copper

5. Demonstration and commercial plants
Kasese, Uganda
BioCOP, Chuquicamata, Chile
Mintek-BacTech, Mexico

6. Aguablanca Mine, southern Spain
Open-pit nickel-copper sulphide mine
Located 80 km north of Seville, in southern Spain
Owned by Lundin Mining Corporation
Treatment plant commissioned in 2005
1.7 million tonnes of ore per annum
Bulk concentrate: 7.3 % Ni, 6.9 % Cu
Concentrate shipped to a smelter
Underground expansion being evaluated based on increased resource base

7. Objectives and scope of work
Proposition is to extend Aguablanca treatment plant with addition of a bioleaching and metals-refining facility
On-site metal production
Increase realized metal value
Phase 1 test work:
Concentrate characterization
Bioleach amenability testing
Phase 2 test work:
Open circuit bioleach miniplant operation
Bench-scale solution purification and metals recovery tests
Phase 3 test work:
Integrated pilot plant testing
Additional bioleach optimization tests
Conceptual engineering study
Preliminary economic evaluation

8. Conceptual process flowsheet
Bioleaching
Solid-liquid
separation
& washing
Neutralisation
& iron
precipitation
Copper
electro-
winning
cathode
solvent
extraction
Nickel
Wash
water
Bioresidue
Lime-
stone
Gypsum
Magnesia
Lime
hydroxide
precipitate Mg

9. Concentrate description
Reground to a d90 of µm
28.9 % Fe
24.4 % S2-
6.29 % Cu
5.24 % Ni
6.28 % Si
23.7 % pyrite (FeS2)
20.7 % pyrrhotite (Fe(1-x)S)
18.5 % chalcopyrite (CuFeS2)
14.5 % pentlandite ((Fe,Ni)9S8)
21.6 % silicates

10. Bioleach amenability tests
Effect of temperature
Three-stage continuously operated reactor system
6-day residence time
10 % feed solids concentration
Particle size of d90 = 10 µm
Microbial culture
Metal extraction
(%) Cu Ni
Mesophiles (35 °C)*
Moderate thermophiles (45 °C)
Thermophiles (70 °C) 30 65 95 76 99
* Single-stage reactor at 3-day residence time
Thermophiles at 70 °C required for chalcopyrite bioleaching

11. Bioleach amenability tests
Effect of grind size
Operating conditions
Cu extraction (%)
Ni extraction (%) R1 R2 R3
3-stage, 70 °C, 10 µm, 6 days
3-stage, 70 °C, 20 µm, 6 days
1-stage, 70 °C, 35 µm, 3 days
Batch, 70 °C, 35 µm, 6 days
83.5
72.4
52.9
72.8
92.0
82.0 -
95.1
90.7
98.7
96.3
87.7
98.1
99.3
97.4
99.4
R1/2/3 = Reactor 1/2/3
Regrinding to ~10 µm a prerequisite for high copper extractions

12. Preliminary specifications for downstream plant
Range of batch bench-scale tests performed
Primary iron precipitation
Solvent extraction
Secondary iron precipitation
Nickel hydroxide precipitation
Magnesium removal
Results used to set initial operating parameters for integrated pilot plant

13. Integrated pilot plant

14. Integrated bioleach plant performance
Bioleach plant operated for 220 days
Recycle loops closed
Very stable operation
Steady redox potential
Stable oxygen uptake rates
Swift recovery from process upsets
No impact of recycle on process performance
Sulphide oxidation 99.4 %
Iron extraction 95.8 %
Nickel extraction 99.3 %
Copper extraction 95.0 %
Bioliquor tenors:
5.8 g/L nickel
5.6 g/L copper
17.9 g/L iron

15. Effect of redox control
Feed R1 R2 R3
Microbial culture
Temperature (°C)
pH level
Redox (mV, Ag|AgCl))
Cumulative residence time (d)
Feed solids concentration (%)
Grind – d90 (µm)
Thermophiles
9.8 10 70
1.6
430
3.0
1.3
550
4.5
1.25
580
6.0
[Fe] (g/L)
[Cu] (g/L)
[Ni] (g/L)
14.5
7.1
6.7
17.4
7.0
6.9
18.0
Fe extraction (%)
Cu extraction (%)
Ni extraction (%)
S2- extraction (%)
48.4
96.2
93.8
67.3
68.6
97.8
98.4
94.2
75.6
98.1
98.7
98.8
Redox control reduces the residence time from 6 to ~4 days

16. With redox control, a coarser grind can be tolerated
Effect of grind size
Feed R1 R2 R3
Microbial culture
Temperature (°C)
pH level
Redox (mV, Ag|AgCl))
Cumulative residence time (d)
Feed solids concentration (%)
Grind – d90 (µm)
Thermophiles
9.4 20 70
1.7
430
3.0
1.4
550
4.5
1.3
570
6.0
[Fe] (g/L)
[Cu] (g/L)
[Ni] (g/L)
13.6
7.3
6.7
16.0
7.4
7.0
19.2
7.6
7.5
Fe extraction (%)
Cu extraction (%)
Ni extraction (%)
S2- extraction (%)
40.7
92.7
85.1
63.7
63.1
95.8
96.9
84.7
70.1
96.0
97.9
94.2
With redox control, a coarser grind can be tolerated

17. Primary iron precipitation
Five reactors
Operating temperature of 60 °C
Residence time of 5 hours
Product recycle for seeding
Difficult to settle/filter product
Extent of copper loss depends on pH level
Iron removal of 99.5 % at a pH level of 3.0

18. Copper SX-EW Standard reagent suite
2 extraction stages, 1 scrubbing, 2 stripping
98-99 % copper extraction
LME A-grade copper cathode produced

19. Secondary iron precipitation
Five reactors
Operating temperature of 60 °C
Residence time of 5 hours
Product recycle for seeding
Target pH level of 5.0
Gypsum/iron product easy to settle
Effective copper and nickel scavenging from product using a cyclone
75 % copper, 80 % nickel recovery in 18 % of mass
Recycle to bioleach

20. Nickel hydroxide precipitation
Various options considered
Single-stage process chosen
Five reactors
Operating temperature of 60 °C
Residence time of 5 hours
Product recycle for seeding
Target pH level of 7.8
Nickel removal of 99.5 %
Product nickel content between 31.6 and 47.5 %
Precipitate difficult to dewater by filtration (60 % moisture retained)

21. Magnesium hydroxide precipitation
Five reactors
Operating temperature of 60 °C
Residence time of 5 hours
Product recycle for seeding
Target pH level of 9.5
Complete magnesium removal
Product relatively easy to filter
Liquor recycled to bioleach process

22. Conceptual engineering study
96,000 t/a of concentrate
5,400 t/a of copper cathode
4,857 t/a of nickel as nickel hydroxide intermediate
Concentrate regrinding in a bead mill (Deswik/IsaMill): 14.3 kW.h/t
Bioleach reactors: 12 × 1,620 m3 vessels
Three nickel recovery options considered:
Nickel hydroxide precipitation
Nickel sulphide precipitation
Nickel SX-EW

23. Preliminary economic evaluation
Biohydrometallurgical process with production of metal and/or metal intermediates is cost-competitive

24. Impact of low redox process
Decreased residence time (6  4 days)
Individual bioleach reactor volume reduced to 920 m3
Bioleach capital cost reduced by 40 %
Overall plant cost reduced by 12 %
Overall operating cost reduced by 4 %
IRR increased from 29.9 % to 31.7 %

25. Overall conclusions
Long-term demonstration of thermophile-based bioleach process achieved
Integrated pilot-plant operation attained
Economic viability of biohydrometallurgical processes established
Controlled low redox process for chalcopyrite bioleaching shows potential to reduce bioleach capital costs significantly
This process has been developed to the point where it can be offered commercially

26. Thank you