During coal combustion various toxic compounds are generated from its sulphur content. Their environmental impacts are considered to be very important. While there are various conventional preparation methods to remove the sulphur in the fuel, recent work reveals that newly-isolated micro-organisms, naturally present in coal, have the ability to reduce its sulphur content. The removal of sulphur using biological leaching involving acidophilic iron oxidising bacteria like Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans are examined and a computational technique based on computational fluid dynamics is developed to model the biological leaching of sulphur from coal. The model was validated against a pack-column experiment carried out for iron separation during 60 days. The mathematical model predicted iron separation over time is similar to experimental measurements, with an average difference of 5.5%. According to the experimental results, there was an overall reduction of 33% of pyrite, whereas the model prediction was 32%. The model results shows overall good agreement with pack-column experimental data. (c) 2007 Elsevier Ltd. All rights reserved.