Semi-industrial scale testing of biologically-induced copper heap leaching at Imperial Metals Corporation - Mount Polley Mine

Copper-oxide ties up 47% of the 0.3% grade copper ore at Mount Polley Mine this copper is not easily extracted by conventional milling technologies. This study evaluated the effectiveness of biologically-induced copper heap leaching at a semi-industrial scale as an alternative process. The heap was amended with elemental sulphur and Acidithiobacillus thiooxidans to generate sulphuric acid. Compositional changes in leachate and solid phase were monitored. Geochemical modeling (MINTEQA2) of leachate parameters predicted speciation and mineral precipitation. Only 1% of the potentially extractable copper was removed over one year. Solid phase copper increased at 0.5 m depth from 1666 ppm to 3854 ppm, likely due to redistribution of copper within the heap during leachate recycling. X-ray diffraction and geochemical modeling indicated that covellite was forming on ore surfaces. To improve future copper yields, oxygen supply and distribution should be increased and physical parameters of sulphur and ore particles should be addressed. --P.ii.