Biomining

Our access to easily extractable copper is gradually diminishing as demands for copper continues to grow worldwide. To meet these demands, non-traditional, metallurgically challenging deposits are expected to become more prevalent, thereby forcing us to deal with more complex, and lower-grade ores containing higher levels of impurities. Arsenic-challenged deposits is a concern for the copper mining industry as arsenic produces hazardous fumes and oxide dusts during the smelting process. Smelting with arsenic therefore poses a significant risk to the health of the workers and to the environment. Safe removal and disposal of stabilized arsenic is often difficult and costly. The mining industry has developed several methods for dealing with arsenic impurities, which includes precipitation with scorodite and pressure hydrometallurgical procedures (150C and 1380kPa) for processing high concentration of arsenic while extracting copper in parallel. However, many procedures requires an enormous amount of energy or additional acidic chemicals to help selectively separate arensic-containing minerals in the ore mixtures. With stricter legislation in place, the mining industry is facing increasing pressure to progressively reduce the amount of allowable arsenic concentrations for smelters. Consequently, fines and penalties are set for arsenic concentrations exceeding 0.2%, while ores past 0.5% arsenic concentrations are rejected by smelters. It would be more economically and environmentally beneficial to remove the minerals containing arsenic at an earlier stage such as during flotation. Their separation is nevertheless difficult as they generally have similar flotation behaviour to the valuable minerals with which they are associated. This is the case in separating arsenopyrite (FeAsS) from pyrite, or removing enargite (Cu3AsS4) and tennantite (Cu12As4S13) from covellite (CuS), chalcocite (Cu2S) and chalcopyrite (CuFeS2). Apart from arsenopyrite, the amount of literature dealing with the separation of arsenic minerals is scarce. One of the potential separation methods relies on the selective oxidation of sulfide minerals due to differences in their electrochemical properties (e.g., Tolley et al., 1996, Byrne et al., 1995, Kydros et al., 1993, Wang et al., 1992, Beattie and Poling, 1988, Guongming and Hongen, 1989 and Chander, 1985). Oxidation can promote the adsorption of collectors, such as xanthate, at low to moderate levels of oxidation, or prevent their adsorption at high levels of oxidation by creating a physical barrier of oxidation products for their diffusion to the mineral surface.

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