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High Pressure Acid Leaching of Nickel Laterite Ores: Chemistry and MOC Challenges

High Pressure Acid Leaching of Nickel Laterite Ores: Chemistry and MOC Challenges. Mohamed Buarzaiga IAPWS Workshop May 12, 2009. Presentation Outline. Overview of laterite ores processing Brief overview of HPAL chemistry Few examples of MOC challenges. Background.

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High Pressure Acid Leaching of Nickel Laterite Ores: Chemistry and MOC Challenges

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  1. High Pressure Acid Leaching of Nickel Laterite Ores: Chemistry and MOC Challenges Mohamed Buarzaiga IAPWS Workshop May 12, 2009

  2. Presentation Outline • Overview of laterite ores processing • Brief overview of HPAL chemistry • Few examples of MOC challenges

  3. Background • Ni sources: sulfide and oxide ores • Ni oxide (laterite) ores found mainly in tropical and subtropical regions (70% of Ni) • Depleting Ni sulfide ores • Four HPAL plants were built in the last 15 years and others are under construction • Vale Inco is building a large plant in New Caledonia (Goro)

  4. Typical HPAL Flowsheet Conc. Sulfuric Acid Feed 240-270 C 250-500 kg acid/t ore Autoclave Leaching CaCO3 Primary Neutralization Lime Air SO2 U/F Tailings S/L Separation Tailing Neutralization CaCO3 Secondary Neutralization Air S/L Separation Solids to PN PLS MHP or MSP Barren Solution S/L Separation Intermediate Product

  5. Goro AutoclaveCircuit 67°C Ore slurry 92°C Recycling hot water 200°C Feed Slurry Steam Leached slurry 200°C 270°C 150°C 92°C H2SO4

  6. Goro HPAL Autoclave

  7. Goro HPAL Heat Recovery

  8. Simplified Autoclave Chemistry • MeO + 2 H2SO4 Me2+ + 2 HSO4- + H2O • H2SO4 = H+ + HSO4- • Goethite  Hematite Conversion • 2 FeOOH + 6 H+ 2 Fe3+ + 4 H2O • 2 Fe3+ + 3 H2O  Fe2O3 + 6 H+ • Net: 2 FeOOH  Fe2O3 + H2O • Alunite Formation • 6 AlOOH + 9 H2SO4 3 Al2(SO4)3 + 12 H2O • 3 Al2(SO4)3 + 14 H2O  2 (H3O)Al3(SO4)2(OH)6 + 5 H2SO4 • Net: 6 AlOOH + 4 H2SO4 + 2 H2O  2 (H3O)Al3(SO4)2(OH)6 • Cr(VI) Formation • 3 MnO2 + 2 Cr3+ + 2 H2O  3 Mn2+ + 2 HCrO4- + 2 H+

  9. Sulfate Distribution % Feed Comp 2.0 Ni 0.15 Co 2.1 Al 1.9 Cr 0.99 Mn 39.8 Fe 11.9 SiO2 2.8 MgO

  10. MOC Challenges • Harsh service environment • High temperature and pressure • Jets of high-pressure acidic slurry • Abrasive particles • Hot acidic slurry for downstream circuits • Solution may contain chloride anions

  11. MOC Challenges: Autoclave Circuit • Ti clad steel for pressure vessels using explosion cladding • Base steel: ASTM A516 Gr 70 • Cladding Ti material: Gr 1, Gr 11, Gr 17 • 100-mm steel thickness with 8-mm Ti clad • Acid injection into autoclave: Teflon or tantalum lining on titanium dip tubes • Block vales

  12. Autoclave Valve Erosion M. King JOM, July 2005

  13. MOC Challenges: Autoclave Feed Pumps • Diaphragm pumps to handle abrasive slurry • Temperature limitation on pump  200 C • “Drop leg” design for diaphragm protection • Specialty elastomers seats for check valves • Pulp dilution and implication for downstream circuits

  14. Concluding Remarks • An overview of a challenging high T process in the mining industry • Proper selection of MOC is critical • Interactions with universities and other R&D centers have been valuable

  15. Thank you!

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