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

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

• Mohamed Buarzaiga
• IAPWS Workshop
• May 12, 2009

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Presentation Outline

• Overview of laterite ores processing
• Brief overview of HPAL chemistry
• Few examples of MOC challenges

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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)

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Typical HPAL Flowsheet
Feed
Conc. Sulfuric Acid
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
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Goro Autoclave Circuit
67C
Ore slurry
92C
Recycling hot water
200C
Feed Slurry
Steam
Leached slurry
200C
270C
150C
92C
H2SO4
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Goro HPAL Autoclave
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Goro HPAL Heat Recovery
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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

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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
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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

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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

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Autoclave Valve Erosion
M. King JOM, July 2005
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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

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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 RD
  centers have been valuable

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Thank you!