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

Goro HPAL Autoclave

Goro HPAL Heat Recovery

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

Autoclave Valve Erosion

M. KingJOM, 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!