Oxidation of Ferrous Sulfate by Growing Cultures of Thiobacillus Ferrooxidans

Oxidation of ferrous iron in acid solutions is an important reaction producing soluble ferric iron. The oxidizing property makes the ferric ion one of the most useful reagents in hydrometallurgy. The ferrous iron oxidation kinetics of Thiobacillus ferrooxidans growing in batch culture was examined. T. ferrooxidans oxidized ferrous iron at pH 1.5 in the presence of oxygen and utilized carbon dioxide as a sole carbon source for growth. The total amount of biomass produced was 1.6 10-3 M of bacterial carbon (Cbact) and was estimated from the amount of CO2 absorbed from air. Specific growth rate, m reached the value of 0.1 h-1. The culture achieved maximum specific iron oxidation rate qFe of approx. 8 moles Fe/mole Cbact/h and corresponding specific oxygen consumption rate qO2 of approx. 2 mole O2/mole Cbact/h. The standard redox potential of the Fe3+/Fe2+ couple measured in the cultivation medium with ferrous iron was 675 mV (the theoretical value is 771 mV) and the slope (RT/zF) was 28.26 (calculated theoretical value at 30°C is 26.12 mV). The Nernst equation can be regarded as a calibration line for the redox electrode, which can be used as a means of studying the kinetics of biological oxidation of ferrous iron.