High Pressure Acid Leaching of Nickel Laterite Ores: Chemistry and MOC Challenges Mohamed Buarzaiga...
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Transcript of High Pressure Acid Leaching of Nickel Laterite Ores: Chemistry and MOC Challenges Mohamed Buarzaiga...
High Pressure Acid Leaching of Nickel Laterite Ores: Chemistry
and MOC Challenges
Mohamed BuarzaigaIAPWS Workshop
May 12, 2009
Presentation Outline
• Overview of laterite ores processing
• Brief overview of HPAL chemistry
• Few examples of MOC challenges
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)
Autoclave Leaching
Primary Neutralization
S/L Separation Tailing Neutralization
Secondary Neutralization
S/L Separation
MHP or MSP
S/L Separation
Lime
PLS
Barren Solution
U/F
Intermediate Product
CaCO3
Air
Solids to PN
Tailings
Feed
CaCO3
SO2
Air
Conc. Sulfuric Acid Typical HPAL Flowsheet
240-270 C250-500 kg acid/t ore
Goro Autoclave Circuit
H2SO4
92°C150°C
200°C
92°C
67°C
Steam
200°C270°C
Ore slurry
Leached slurry
Feed Slurry
Recycling
hot water
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+
Sulfate Distribution
Residue19%
Free Acid31%
Mg11%
Ni + Co13%
Mn4%
Fe + Al + Cr22%
% Feed Comp2.0 Ni0.15 Co2.1 Al1.9 Cr0.99 Mn39.8 Fe11.9 SiO2
2.8 MgO
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
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
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
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