High Pressure Acid Leaching of Nickel Laterite Ores

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)

Conc. Sulfuric Acid Typical HPAL Flowsheet Feed Autoclave Leaching 240 -270 C 250 -500 kg acid/t ore Ca. CO 3 Primary Neutralization Air SO 2 S/L Separation U/F Tailing Neutralization Ca. CO 3 Air Secondary Neutralization S/L Separation Solids to PN PLS MHP or MSP S/L Separation Intermediate Product Lime Barren Solution Tailings

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

Goro HPAL Autoclave

Goro HPAL Heat Recovery

Simplified Autoclave Chemistry • • • Me. O + 2 H 2 SO 4 Me 2+ + 2 HSO 4 - + H 2 O H 2 SO 4 = H+ + HSO 4 Goethite Hematite Conversion • • Alunite Formation • • 2 Fe. OOH + 6 H+ 2 Fe 3+ + 4 H 2 O 2 Fe 3+ + 3 H 2 O Fe 2 O 3 + 6 H+ Net: 2 Fe. OOH Fe 2 O 3 + H 2 O 6 Al. OOH + 9 H 2 SO 4 3 Al 2(SO 4)3 + 12 H 2 O 3 Al 2(SO 4)3 + 14 H 2 O 2 (H 3 O)Al 3(SO 4)2(OH)6 + 5 H 2 SO 4 Net: 6 Al. OOH + 4 H 2 SO 4 + 2 H 2 O 2 (H 3 O)Al 3(SO 4)2(OH)6 Cr(VI) Formation • 3 Mn. O 2 + 2 Cr 3+ + 2 H 2 O 3 Mn 2+ + 2 HCr. O 4 - + 2 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 Si. O 2 2. 8 Mg. O

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 A 516 Gr 70 • Cladding Ti material: Gr 1, 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

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!