Acidophilic iron-oxidizing microorganisms are important for both, the environment and for biotechnological applications. Biogeneration of ferric from ferrous iron was studied using an iron-oxidizing consortium developed during polymetallic concentrate bioleaching. A promising iron oxidizing consortium was developed by adaptation and selection, which resulted in bacterial iron oxidation activity under the extreme conditions of 250 g/L ferrous sulphate as initial substrate and 500 g/L ferric sulphate. The development of iron oxidizers improved the iron oxidation rate from 0.019 to as high as 0.6 g/L/h in the shake flask studies with 25 % initial ferrous sulphate in the medium. The consortium showed dominance of Leptospirillum ferrooxidans and Acidithiobacillus ferrooxidans. A fixed film bioreactor was further developed to improve rates of iron oxidation. The developed fixed film bioreactor operated successfully for 200 batches without external addition of inoculum with the highest iron oxidation rate of 1.89 g/L/h. The biological ferric iron generation process provides continuous leaching agent in the form of ferric sulphate, which would be a promising eco-friendly biotechnological process for the indirect extraction of precious metals from sulphidic mineral concentrates.