Integrated piloting of a thermophilic nickel-copper bioleaching process Presented at the SAIMM Hydrometallurgy Conferenc

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

9. Concentrate description • Reground to a d90 of 10-12 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 * Single-stage reactor at 3-day residence time Thermophiles at 70 °C required for chalcopyrite bioleaching

11. Bioleach amenability tests Effect of grind size 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 Redox control reduces the residence time from 6 to ~4 days

16. Effect of grind size 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 www.mintek.co.za