In the previous report, the authors considered the leaching mechanism of chalcopyrite concentrate by Thiobacillus ferrooxidans, and pointed out that leaching rate was mainly controlled by the deposition of elemental sulphur on the mineral surface. In this report, the effect of the coexistence of Thiobacillus thiooxidans, whose energy source is elemental sulphur, with Thiobacillus ferrooxidans on the leaching of a chalcopyrite concentrate was investigated. During the culture of both species the relation between the surface tension of the culture medium and cell number was examined, and the phospholipid which is one of the extracellular substances in the culture of both microorganisms were qualitatively analyzed by thin layer chromatography. The leaching efficiency of a chalcopyrite was conspicuously improved by the coexistence of Thiobacillus thiooxidans with Thiobacillus ferrooxidans. The results indicated that in order to make efficient the leaching of chalcopyrite concentrate, it is necessary that the reactions of equations (1) to (3) or (4) mentioned in the text must consecutively proceed. However, the initially high leaching rate of chalcopyrite did not continue to the complete dissolution of chalcopyrite. The reason is that the growth of Thiobacillus thiooxidans was depressed by the increase of ferrous ion concentration, and that it became impossible to keep the sequence in the above mentioned reactions. Accordingly it is indicated that in order to improve further the efficiency of leaching it is necessary to artificially control the chemical constituents of the leaching solution. As the cell number increased, the surface tension of the culture medium decreased. Phosphatidylethanolamine and phosphatidylglycerol were detected as phospholipid. The phospholipid is polar-nonpolar substance, accordingly these extracellular substances would affect the leaching rate.
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