A Cobalt Solvent Extraction Investigation in Africa’s Copper Belt

Tanja Könighofer

Premium-Grade Co-Metal Specification

Premium Grade Co Metal = $34/lb (August 2008)

CoEW Electrolyte Composition

A Co-Circuit Flowsheet

Copper Circuit

Fe/Al Removal

Co Upgrade

Cu Ion

Exchange

Impurity Solvent

Extraction

Zn Ion

Exchange

Co Solvent

Extraction

Co ElectrowinningImpurities to

TailingTreatment

Impurity Bleed

Cu Recovery

Ore

Tails

Cu Metal

Bleed stream

Precipitate to Tails

Co Metal

Testwork Objectives

• Produce a raffinate stream containing <10mg/L cobalt

in order to minimise cobalt losses.

• Limit the amount of magnesium, reporting to the cobalt

electrowinning circuit to less than 5% of that contained

in the feed to the cobalt solvent-extraction circuit.

• Test pre-neutralisation with 10M NaOH.

• Determine the zinc build-up within the cobalt solvent

extraction strip circuit.

Theory

2AH+ + M2+ A2Mn2+ + 2H+

A represents R2P(O)O-

Overbar represents a species in the organic phase..R2P(O)OH(org)+NaOH(aq) R2P(O)ONa(org)+H2O(aq)

Order of Metal Extraction of Cyanex 272 vs pH

• Fe3+>Zn2+>Al3+>Cu2+>Mn2+>

Co2+>Mg2+>Ca2+>Ni2+.

Extraction Isotherm with McCabe-Thiele Plot

1

2

3

4

Stripping Isotherm versus McCabe-Thiele Plot

1

2

3

CoSX Circuit

E3 E2 E1 Sc1 Sc2 Sc3E4E5 S1 S2 S3

Strip Liquor

Loaded Strip

Liquor

Scrub Liquor

Aqueous Feed

Raffinate

Stripped Organic

Aqueous Organic

Co & Mg Extraction efficiencies & pH in final extraction stage

Co Slippage

100% Co Extraction

[Mg] in aqueous phase in extraction circuit

[Mg] in the organic phase

Extraction Scrub Strip

Mg scrubbing efficiency

• < 5% Mg reporting to strip circuit achievable in 3 stages• < 5% Mg reporting to strip circuit achievable in 1 stage, if

Mg loading in extraction is limited

[Co] in organic phase of E1 & final scrub stage

3 Scrub stages

1 Scrub stage

[Zn] in S1

pH = 3.5

[Zn] in S3

[H2SO4] = 8 to 9g/L

Conclusions & Recommendations

• Extraction

– 18% (v/v) Cyanex 272 in aliphatic diluent

– 4 Stages using 40g/L NaOH for pH control

– 1 pre-neutralisation stage using 10M NaOH

– Increase pH profile in extraction using pre-neutralisation

– [Co] < 10mg/L in Raffinate

– 99% Co extraction efficiency

– pH profile of 4.9 in E1 and 5.7 in E4

– Phase ratio = 1.0

– Mg scrubbing enhanced by decreased pH profile from E4 to E1

Conclusions and Recommendations

• Scrubbing

– Scrub liquor = advance electrolyte (55g/L Co)

– O:A = 40

– < 5% Mg from feed reports to loaded strip liquor using 3 stages

– < 5% Mg from feed reports to loaded strip liquor using 1 stage if co-

extraction limited in extraction

– 68% and 39% scrubbing achieved in 3 and 1 stages respectively

– Recommend 2 stages be employed and optimised on full-scale plat

Conclusions and Recommendations

• Stripping

– Strip liquor = spent electrolyte (55g/L Co, 8-9g/L H2SO4)

– O:A = 0.67

– 100% Co stripping achieved in 3 stages when pH in S1 between

3.5 and 4.0

– pH control in S1 by addition of 30g/L H2SO4

– Zn accumulation, possible contamination of Co metal

– Slip in pH

– Recommend controlled periodic stripping of organic at low pH –

strip liquor recycled to upstream unit operations

Thank you

TWP MATOMO PROCESS PLANT (PTY) LTD