Abstract: The bioleaching of chalcopyrite by moderate thermophiles from Dexing Copper Mine was researched at 45 ℃.The experiment results showed that proper amount of Fe²⁺(4 g/L)was helpful for the growth of bacteria and the bioleaching of chalcopyrite.The high bacterial activity could accelerate the bioleaching of chalcopyrite.In the acidity range of test，the bacterial activity is highest in pH 1.50.Furthermore，the lower the pulp density was and the smaller the particle size was，the more favorable the bioleaching rate was.In the best condition，the leaching rate of chalcopyrite in 45 ℃ was 73.32% in 49.2 d.The residue of bioleaching was studied by X-ray diffraction(XRD)，and the results demonstrated that sulfur and jarosite may be the passivation layer of chalcopyrite.

Key words: Chalcopyrite, Bioleaching, Moderate thermophiles, Passivation