Abstract
Leaching behavior of a chalcopyrite concentrate by Thiobacillus ferrooxidansstrain, isolated from an acid mine water, was considered on the basis of the results of batch shake flask experiments. Then, its leaching mechanism and rate controlling factors were also considered.It was found that under the same pulp density, there was a linear relation between the initial specific surface area and the upper limit of copper concentration attainable with a high leaching rate (Fig. 3).Leaching proceeded in two stages (Fig. 6-9). The first stage was characterized by a high growth rate, a high demand of hydrogen ion and a high leaching rate of copper. The second stage was characterized by a generation of hydrogen ion, a low leaching rate of copper and a low growth rate. It was observed that the second stage of leaching was followed by a leaching behavior similar to the first stage, then by another second stage behavior.The leaching mechanism of the first stage is mainly indirect (Eq. 6 and Eq. 9), and the reactions proceed by depositing elemental sulphur on the mineral surface (Eq. 11-15) until reaching a particular thickness. In the second stage, the deposited elemental sulfur is dissolved by bacterial catalytic action and sulfuric acid is produced.The main factor affecting the rate in the leaching of a chalcopyrite concentrate by Thiobacillus ferrooxidans is the oxidation of sulfide to sulfate. Accordingly, for improvement of the leaching rate, it is necessary to accelerate this oxidation reaction.
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