Pilot-plant tests of the metallurgical design for the NorthMet copper-nickel project in northern Minnesota have met the expectations of owner PolyMet Mining (POM-V, POMGF-O).
The tests, by metallurgical consulting firm SGS Lakefield Research, assessed the project’s proposed combination of standard flotation with autoclaving and precipitation.
Tests of three composite samples of NorthMet mineralization showed average recoveries of 94% of copper and 72% of nickel, to produce a concentrate with 11.1% copper and 2.5% nickel. Precious metal recoveries averaged 83% for palladium, 68% for platinum and 58% for gold.
Autoclaving recovered 98% of the copper, 97% of the nickel, and 98% of the cobalt in the flotation concentrate. The autoclave circuit recovered highly variable fractions of the precious metals, probably because of losses to metal samples placed in the circuit to test their corrosion resistance in operating conditions. Late-stage recoveries of palladium increased to 90%, those of platinum to 94%, and those of gold to 76%, and more than 99% of the precious metal extracted in autoclaving was recovered in the final precipitation stage of the process.
The results will be incorporated into a final feasibility study for NorthMet.
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