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Galvanic interaction between chalcopyrite and pyrite during atmospheric leaching Mayne, Darren Douglas

Abstract

Chalcopyrite is the most abundant copper minerals, yet one of most difficult to leach due to a passive layer which forms under a variety of oxidative leaching conditions. For this reason, chalcopyrite has traditionally been processed by pyrometallurgical routes. However, due to a host of environmental and economic issues there has been increased interest in developing a hydrometallurgical process to treat primary copper sulfides. A novel process was developed at UBC in which pyrite was added intentionally to chalcopyrite to provide a galvanically-assisted leach. The ground minerals were subjected to an acidified ferric sulfate solution at atmospheric pressure, and excellent copper recovery was achieved. The present study continued this work, applying the technology to several chalcopyrite concentrates in order to determine optimal conditions for the leach. Leaching experiments were conducted in a sealed 3-liter jacketed glass stirred-tank reactor. Initial work with a concentrate from Zambia was conducted using pyrite from the Huanzala region of Peru. It was determined that a pyrite-to-chalcopyrite ratio of 2.7 was optimal. The solution potential should be controlled above 455 mV vs Ag/AgCI, although it is difficult to comment on the optimal range due to gas liquid mixing limitations at higher potentials. Initial acid content of 1.8 kg per kg concentrate and a leach temperature of 80°C were also selected for best results. Pyrite remained an effective catalyst when recycled wet as very little was oxidized during the leach. A second chalcopyrite concentrate from Mongolia was obtained, along with a pyrite concentrate from the same mine. The optimal conditions from the previous study were used. Initial experiments showed a significant induction period, but the induction period deceased substantially when a second charge of concentrate was used with the wet-recycled residue. It was believed that reagents used in the flotation circuit may have fouled the surface of the pyrite, thus reducing its effectiveness as a galvanic catalyst. Attempts were made to 'activate' the pyrite concentrate prior to use, but these proved unsuccessful. It remains unclear why the pyrite becomes more reactive when recycled.

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