Bioleaching of a marmatite flotation concentrate with a moderately thermoacidophilic iron-oxidizing bacterial strain (MLY) was investigated in batch experiments. Experimental results showed that the dissolution rate of marmatite was influenced markedly by pH, temperature, pulp density and particle size of ore. The bioleaching of the concentrate by the moderate thermophile was more effective when carried out under the higher acidity and temperature compared with Acidithiobacillus ferrooxidans. The adapted strain of the moderate thermophile could provide more rapid and complete oxidation of marmatite than its original strain and in the sterile control. (c) 2005 Elsevier Ltd. All rights reserved.