a cobalt solvent extraction investigation in africa s copper belt l.
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A Cobalt Solvent Extraction Investigation in Africa’s Copper Belt

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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. Testwork Objectives.

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premium grade co metal specification
Premium-Grade Co-Metal Specification

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

testwork objectives
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.
slide6

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
Order of Metal Extraction of Cyanex 272 vs pH
  • Fe3+>Zn2+>Al3+>Cu2+>Mn2+>Co2+>Mg2+>Ca2+>Ni2+.
mg in the organic phase
[Mg] in the organic phase

Strip

Scrub

Extraction

mg scrubbing efficiency
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
zn in s1
[Zn] in S1

pH = 3.5

zn in s3
[Zn] in S3

[H2SO4] = 8 to 9g/L

conclusions recommendations
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
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 recommendations20
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