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 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 + + M 2+  A 2 Mn H + A represents R 2 P(O)O - Overbar represents a species in the organic phase.. R 2 P(O)OH (org) +NaOH (aq)  R 2 P(O)ONa (org) +H 2 O (aq)

Order of Metal Extraction of Cyanex 272 vs pH Fe 3+ >Zn 2+ >Al 3+ >Cu 2+ >Mn 2+ >Co 2+ >Mg 2+ >Ca 2+ >Ni 2+.

Extraction Isotherm with McCabe-Thiele Plot

Stripping Isotherm versus McCabe-Thiele Plot 1 2 3

CoSX Circuit

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 [H 2 SO 4 ] = 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 H 2 SO 4 ) –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 H 2 SO 4 –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