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

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

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

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

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

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

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

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

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

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

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

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

Integrated pilot plant

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

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

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

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

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

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

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)

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

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

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

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 %

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

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