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

Explore the chemistry and challenges of High Pressure Acid Leaching (HPAL) in processing nickel laterite ores, with a focus on autoclave circuitry and materials of construction. Learn about HPAL chemistry, MOC challenges, and typical HPAL flowsheets. Discover the complexities and solutions in the harsh service environment of HPAL processes.

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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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