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A Cobalt Solvent Extraction Investigation in Africa’s Copper Belt

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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A Cobalt Solvent Extraction Investigation in Africa’s Copper Belt

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  1. A Cobalt Solvent Extraction Investigation in Africa’s Copper Belt Tanja Könighofer

  2. Premium-Grade Co-Metal Specification Premium Grade Co Metal = $34/lb (August 2008)

  3. CoEW Electrolyte Composition

  4. A Co-Circuit Flowsheet

  5. 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.

  6. 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)

  7. Order of Metal Extraction of Cyanex 272 vs pH • Fe3+>Zn2+>Al3+>Cu2+>Mn2+>Co2+>Mg2+>Ca2+>Ni2+.

  8. Extraction Isotherm with McCabe-Thiele Plot 1 2 3 4

  9. Stripping Isotherm versus McCabe-Thiele Plot 1 2 3

  10. CoSX Circuit

  11. Co & Mg Extraction efficiencies & pH in final extraction stage 100% Co Extraction Co Slippage

  12. [Mg] in aqueous phase in extraction circuit

  13. [Mg] in the organic phase Strip Scrub Extraction

  14. 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

  15. [Co] in organic phase of E1 & final scrub stage 1 Scrub stage 3 Scrub stages

  16. [Zn] in S1 pH = 3.5

  17. [Zn] in S3 [H2SO4] = 8 to 9g/L

  18. 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

  19. 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

  20. 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

  21. Thank you

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