Recovery of Cobalt, Gold and Bismuth from the Nico Deposit, NWT, Canada - Part 111: Recovery of Cobalt

A process has been developed to recover cobalt, gold and bismuth from the NICO deposit in Canada. The process consists of a bulk rougher flotation followed by an optional separation by flotation to produce a bismuth concentrate and a cobalt concentrate, grading on average 12.8 % Bi and 1.8% Co, respectively. Cobalt is leached by pressure oxidation at 97% efficiency, producing a pregnant solution suitable for further processing. Before optimization, about 38% of the bismuth is recovered in the selective concentrate, wherefrom it is recovered by ferric chloride leaching followed by cementation, at overall efficiencies exceeding 98%. The gold is recovered from the cobalt and bismuth leach residues by cyanidation, at 95% efficiency. Previous work described the results of the leaching of the concentrates, recovery of gold (Part I) and the recovery of bismuth (Part 11). This work describes the results of the cobalt recovery testwork and the resulting conceptual flowsheet. The sulfur dioxide-oxygen system was the most efficient for the oxidationlprecipitation of iron and arsenic from cobalt bearing pregnant leach solutions, producing purified solutions assaying <1 mg/L As and <8 mg/L Fe. The efficiency of cobalt solvent extraction (from the resulting purified PLS containing about 1 g/L Co) ranged from 9 1 to 98%; the co-extractions ranged from 88 to 100% for copper, from 28 to 33% for magnesium, from 6 to 7% for calcium and from 96 to 98% for zinc. Sulphide precipitation processes (using either sulfur dioxidelelemental sulfur or sodium sulfide) produced residual copper concentrations in the cobalt strip solution ranging from 0.1 to 2 mg/L Cu. About 90% of the calcium and magnesium were separated by scrubbing the organic with cobalt sulfate, producing residual concentrations of 12 mg/L Ca and from 180 to 330 mg/L Mg in typical feed solutions directed to cobalt carbonate precipitation tests. Cobalt carbonate precipitation efficiencies ranged from 75 to 78% when calcium and magnesium co- precipitations were restricted from 8 to 17% and 0.3 to 0.4%, respectively. The limits required by most stringent specifications on commercial grade cobalt carbonate products were met or exceeded.