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Continuous biological leaching of copper from a chalcocite ore and concentrate in a saline environment Weston, Jacqueline May


Biological leaching of a chalcocite ore and its concentrate was studied in both batch and continuous tests in a 3 g/L chloride environment. The feed material was obtained from the Zaldivar mine in Chile. The total copper contents of the ore and concentrate were 1.56% and 17.3% respectively, and the particle sizes were P₈₀ 108 µm and P₈₀ 53 µm respectively. The mineralogy consisted mainly of chalcocite (Cu₂S), pyrite (FeS₂) and brochantite (Cu₄(SO₄)(OH)₆). A mixed bacterial culture dominated by Thiobacillus ferrooxidans was obtained from the mine site for use in this study. Shake flask and batch stirred reactor tests were carried out to determine the amenability of both the ore and the concentrate to biological leaching. The effects of several variables on the rate and extent of copper extraction were investigated. In the shake flask tests and the batch reactor tests, it was determined that the bacterial culture was capable of oxidizing both the ore and the concentrate with average copper extractions of 90% and 97% obtained respectively. Continuous biological leaching was carried out in a series of three stirred tank reactors (4 L, 2 L and 2 L) for a period of four months. The bacteria were able to adapt to progressively lower system residence times and higher pulp densities. At the lowest residence time achieved of 2⅔ days with a pulp density of 10%, the steady state copper extraction was 82% for the ore and 83% for the concentrate. The copper bioleach rate achieved in the first bioleach stage was 16 mg/L/h for the ore and 250 mg/L/h for the concentrate. This study demonstrated the feasibility of the continuous biological leaching of either a chalcocite ore or a chalcocite concentrate in a 3 g/L chloride environment. The bacteria-rich leach residue from the process would be an excellent source of inoculum for biological heap leaching.

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