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 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 SeparationTailing Neutralization Secondary Neutralization S/L Separation MHP or MSP S/L Separation Lime PLS Barren Solution U/F Intermediate Product CaCO 3 Air Solids to PN Tailings Feed CaCO 3 SO 2 Air Conc. Sulfuric Acid Typical HPAL Flowsheet  C kg acid/t ore

Goro Autoclave Circuit H 2 SO 4 92°C 150°C 200°C 92°C 67°C Steam 200°C 270°C Ore slurry Leached slurry Feed Slurry Recycling hot water

Goro HPAL Autoclave

Goro HPAL Heat Recovery

Simplified Autoclave Chemistry MeO + 2 H 2 SO 4  Me HSO H 2 O H 2 SO 4 = H + + HSO 4 - Goethite  Hematite Conversion 2 FeOOH + 6 H +  2 Fe H 2 O 2 Fe H 2 O  Fe 2 O 3  + 6 H + Net: 2 FeOOH  Fe 2 O 3  + H 2 O Alunite Formation 6 AlOOH + 9 H 2 SO 4  3 Al 2 (SO 4 ) H 2 O 3 Al 2 (SO 4 ) H 2 O  2 (H 3 O)Al 3 (SO 4 ) 2 (OH) 6  + 5 H 2 SO 4 Net: 6 AlOOH + 4 H 2 SO H 2 O  2 (H 3 O)Al 3 (SO 4 ) 2 (OH) 6  Cr(VI) Formation 3 MnO Cr H 2 O  3 Mn HCrO H +

Sulfate Distribution % Feed Comp 2.0 Ni 0.15 Co 2.1 Al 1.9 Cr 0.99 Mn 39.8 Fe 11.9 SiO 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 mm steel thickness with 8-mm Ti clad Acid injection into autoclave: Teflon or tantalum lining on titanium dip tubes Block vales

Autoclave Valve Erosion M. King JOM, July 2005

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

Thank you!