Heap leaching represents an attractive processing route for such ores because of its low capital intensity and reduced energy consumption relative to conventional mineral processing routes (Ghorbani et al., 2016). In current industrial practice, copper heap leaching is applied primarily to oxide minerals and secondary sulfides such as chalcocite and covellite, which dissolve readily in acidic ferric sulfate environments (Watling, 2006). Primary sulfides present a significantly greater challenge. Chalcopyrite dissolution rates under typical heap leaching conditions are extremely slow, particularly at temperatures below approximately 60 °C. This behaviour is widely attributed to passivation phenomena that inhibit electron transfer between the mineral surface and oxidizing species in solution (Watling, 2013). An example of Cu extraction from predominantly CuFeS2 ore is shown in Figure 1 (previously unpublished UBC data). In Figure 1, Cu extractions under standard sulfide bio-leach conditions do not exceed 32% after 30 months. Figure 1 – Cu extraction from sulfide ores in uncatalyzed 30 cm high laboratory columns with ore grades varying from 0.2 to 0.7% Cu and ores containing more than 75% Cu as CuFeS2. Results are for sulfuric acid bioleaching of agglomerated ore, conditions: pH ~ 1.8, T ≅ 20 ± 2°C To improve leach extents and kinetics, significant industrial and academic effort has been directed toward enabling the direct heap leaching of chalcopyrite-bearing ores since ca. 2000. If successful, such technologies could allow the production of cathode copper from low-grade sulfide ores using existing SX–EW infrastructure. 2. ELECTROCHEMICAL BASIS OF CHALCOPYRITE LEACHING Sulfide leaching in sulfate solutions is known to be an electrochemical process (Woodcock, 1961; Peters & Majima, 1968; Bailey & Peters, 1976). Chalcopyrite dissolution in acidic sulfate media is fundamentally an electrochemical process involving coupled anodic and cathodic reactions.
RkJQdWJsaXNoZXIy MTM0Mzk2