Bioleaching of marmatite flotation concentrate by the adapted strains of Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans in mixed cultures was carried out at initial pH of 2.0, temperature of 35 degrees C, particle size of -42 mu m (over 90%), pulp density of 15% and air flow of 500 L min(-1) in a 10-L air-lift reactor. Experimental results showed that the addition of Fe(2+)ion was favorable to improving the growth and activity of leaching bacteria and increasing the dissolution rate of marmatite. In the leaching system with Fe 21 ions added, the weight loss of the concentrate was over 70%, the leaching ratio of zinc was over. 80% and the concentration of zinc ions in the leach liquor was about 50 g L-1 after 10 days of bioleaching. The technological feasibility of a microbiological process using the adapted strains of Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans in mixed cultures for extracting zinc from a marmatite flotation concentrate has been demonstrated. (c) 2004 Published by Elsevier B.V.